Significance of Tilt angle of Panels

How to calculate the Solar Panel Angle of your solar system? 

The solar panel angle of your solar system is different depending on which part of the world you are. 

Solar panels give the highest energy output when they are directly facing the sun at right angles.


The sun moves across the sky and will be low or high depending on the time of the day and the season. For that reason the ideal angle is never fixed.

To get the most sun reaching the panel throughout the day, you need to determine what direction the panels should face and calculate an optimal tilt angle. This will depend on:

  •     Where you live
  •         What time of the year you need the most solar energy

 The direction of solar panels is decided depending on whether the installation is in the northern or southern hemisphere of the globe. In case of northern hemisphere, which is the case for India, the panels are fixed south facing. In case of southern hemisphere, the panels are placed north facing.

Keeping the module perpendicular to the incoming sunlight means that the module intercepts the maximum amount of sunlight. The problem is that the Sun constantly moves in relation to the stationary PV module. Actually, the apparent motion of the Sun is due to the Earth’s motion. Even if we place a module so that it is perpendicular to the Sun at noon, it is not even close to perpendicular in the morning and evening. This daily east to west solar motion is called solar azimuth. Also consider that the Sun’s apparent height in the sky changes from winter to summer. This yearly north to south solar motion is called solar declination.

 

 

 

Actually you can face a PV module south, tilt it so the included angle between its face and the ground is your latitude, and you’re done. It will work and it will work well. What we are talking about here is squeezing anywhere from 10% to 40% more power from PV modules by keeping them as perpendicular as possible to the incoming sunlight. 

If the module is to be kept perpendicular to the sun’s daily east to west motion (azimuth), then a device called a tracker is used. A tracker follows the sun’s daily motion and provides anywhere from 25% to 35% more power from the PV modules. If you keep up with the sun’s seasonal north to south migration, then manual adjustment boosts PV power production by up to 10%.

 

Calculation of Panel Angle

The calculation of the panel angle (A) is based on the supposition that the panel will be perpendicular to the sun’s rays at noon. Noon is the time when the sun is highest in the sky. This is when the angle between the plane of the horizon and a line drawn from the site to the sun is greatest.

This calculation involves two parameters, These are the latitude of the site (L) and the declination of the sun (D). The declination of the sun is the latitude at which the sun is directly overhead at solar noon. This varies from 23.5° north latitude on the summer solstice (June 21) to 23.5° south latitude on the winter solstice (December 21). These latitudes are known as the Tropic of Cancer and the Tropic of Capricorn. On the equinoxes (March 21 and September 21) the declination of the sun is 0°, so that it is directly over the equator at solar noon. The equation for calculating the declination(D) for any day is:

 

                                                                           D = 23.5sin((T/365.25)*360)

 

where T is the number of days to the day in question as measured  from the spring equinox (March 21)

For any particular day of the year, the panel angle (A) i.e. the angle between the panel and the horizontal plane, is then calculated from the equation:

                                                                                 A = L - D

 

The graphical representation of tilt angle of panels for each day is as shown below in the image.

  

 

Calculating the Optimal solar panel Angle 

As a rule of thumb, solar panels should be more tilted during winter to gain most of the low winter sun, and less  tilted during summer to gather energy from the overhead sun. 

If your installation has dual axis trackers, then for each day, the tracker will calculate the Azimuth and the Declination angle which is pre- programmed and move accordingly in order to gather maximum energy. The angle for each day can be calculated as mentioned in above formula. 

If your installation has single axis tracker, then it will track the azimuth of the sun everyday, to gather most out of the tilt which is programmed. 

In case of adjustable tilt, usually most users tend to use this facility and change their tilt angle seasonally to assure maximum benefit from the solar panels. According to above image, the latitude of the site can be calculated and the relative tilt angles for the same are displayed for each month. 

For fixed tilt, the angle is finalized based on energy requirement of the consumer. If the consumer requires more energy during summer, then accordingly from the above image, the latitude can be co-related with the months of maximum usage and the tilt angle can be set. 

For example, if where you stay is at a latitude of 10o  , and the maximum usage is during the winter months, then 15o can be added to your latitude to get the tilt angle.

 

Information on Battery Rating (Amp hours)

The Amp Hour (AH) specification provides a measurement of battery capacity.  In other words, it is an indication of how much energy can be stored by the battery.

A typical Amp Hour specification might read, “100 AH @ 20HR”.

The specification is saying that the battery will provide 5 amps of current at a useable voltage continuously for 20 hours.  The “5 amps” was calculated by dividing 100 by 20.

Similarly, a battery with a specification that reads “150 AH @ 15 hours” will provide 10 amps of current at a useable voltage continuously for 15 hours.

It should be noted that a useable voltage is considered to about 10.5 volts and above on a battery that is under load (or has devices connected).

 

A Common Misunderstanding Associated with Amp Hours

Consider the 100 Amp Hour battery. As indicated above, it will provide 5 amps of current for twenty hours while maintaining a voltage above 10.5 volts.

A common mistake is made when it is assumed that the 100 AH battery will also provide 100 amps for 1 Hour.  It won’t.  In fact, a battery of this type may only provide about 40 minutes of continuous 100 amp service at best.

This is due to a well known characteristic associated with lead acid batteries. Specifically the capacity will decrease as the rate of discharge increases.

In other words the relationship between battery capacity (how much energy is available) and the rate of discharge is not a linear one.

 

“C” Rating of a Battery

A “C” rating is simply a battery’s capacity (or AH/amp hour rating) when discharged over a specific period of time.

This rating is acquired by adding a specific size load to a battery to make it completely dead in a 3, 5, 8, 10, 20 or 100 hour period.

For each test the battery is discharged until the battery reaches a voltage of 1.75 volts per cell. Discharging a battery to 1.75 volts per cell is considered to be fully discharged. For example: a 6 volt battery is discharged until the voltage reaches 5.25 volts.

 

Battery Voltage (Nominal)

Ending Battery Voltage

2 VOLT

1.75 VOLTS

4 VOLT

3.50 VOLTS

6 VOLT

5.25 VOLTS

8 VOLT

7.00 VOLTS

12 VOLT

10.50 VOLTS

24 VOLT

21.00 VOLTS

 

 

 

 

 

 

 

 

 

 

 

 

If the specific load discharges the battery in 5 hours, the manufacturer adds up the AHs the battery produced (in that 5 hour period) and calls it a C5 rating.

If another smaller load discharges the battery in 20 hours, the manufacturer adds up the AHs the battery produced (in that 20 hour period) and calls it a C20 rating.

·         A C3 rating means the battery has been completely discharged over a period of 3 hours. SUPER FAST DISCHARGE

·         A C5 rating means the battery has been completely discharged over a period of 5 hours. VERY FAST DISCHARGE

·         A C8 rating means the battery has been completely discharged over a period of 8 hours. FAST DISCHARGE

·         A C10 rating means the battery has been completely discharged over a period of 10 hours. FAST DISCHARGE

·         A C20 rating means the battery has been completely discharged over a period of 20 hours. MEDIUM DISCHARGE

·         A C100 rating means the battery has been completely discharged over a period of 100 hours. SLOWER DISCHARGE

Importance of DC & AC fuse

What is a fuse?

A fuse is a type of over-current protective device that is designed to be a sacrificial element in an electrical power system. Fuses are designed to open circuits when excessive currents are present due to over-currents, and in this manner, are designed to prevent further damage to the system that might result if the fuse were not present. Fuses are sacrificial in that they are generally good for one time use and are destroyed in the process of operating. The use of fuses in a circuit provides cheap insurance should there be an accidental or unintentional fault in the system wiring or components.

According to the fuse standard IEC 60269-1, a fuse is “a device that by fusing of one or more of its specially designed and proportioned components opens the circuit in which it is inserted by breaking the current when this exceeds a given value for a sufficient time. The fuse comprises all the parts that form the complete device”.

Why use a fuse?

Fuses have many unique performance characteristics, such as:

Optimum Component Protection 
Fuses reduce short circuit (fault) currents that flow to a low value by "current limitation". There is no need for complex short circuit calculations and no concerns about costly future upgrades due to system expansion with increased fault currents. Their compact size offers low cost over-current protection for the highest short circuit levels.

 

Safety 
Fuses do not produce gas, flames, arcs or other materials when clearing any value of over-current up to the highest level of short circuit. In addition, the speed of operation on high short circuit currents limits significantly the flash hazard at the fault location.

 

Reliability 
No moving parts to wear out or become contaminated by dust, oil or corrosion and no nuisance tripping. If a fault occurs, the fuse immediately operates in its predetermined manner or co-ordinates with other circuit components. The cause of the fault is then ascertained, corrected and a new fuse fitted. Fuse replacement ensures protection is restored to its original state of integrity. It should be stressed that the time taken for the replacement is very small in relation to the fault correction.

 

Simple co-ordination 
Standardised fuse characteristics and a high degree of current limitation ensure that there is simple and effective co-ordination between fuses and with other devices. 
 

  

Are AC and DC fuses the same? 

Direct currents are very difficult to stop or interrupt when compared to alternating currents. Alternating current sources reverse the flow of current many times a second (in some locations 100 times a second on 50 Hz systems). Each time the current reverses, it goes to zero in magnitude. A zero current is very easy for a melting fuse to stop or interrupt—it is already stopped, and there is no force trying to sustain an arc across the fuse element.

DC currents, as the name implies, are currents that travel in one direction only. They do not reverse. Fuses bear the entire burden (with no help from the current) of acting to stop these currents. The internal elements of a fuse must react to an over-current condition (usually by melting) and as they react, they must do so with enough capability to interrupt the current from flowing while extinguishing any arc that might form. DC fuses are relatively sophisticated devices that have many different internal elements that must work together. The complexity of DC fuses sometimes results in a higher cost than AC fuses that may contain only a single element. There are fuses with equal AC and DC voltage ratings, but the DC interrupt rating is significantly less than the AC interrupt rating.

Difference between DC wiring & AC Wiring

 AC and DC

AC and DC describe the types of current flow in a circuit. In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically. The voltage in AC circuits also periodically reverses because the current changes direction.

Home and office outlets are almost always AC. This is because generating and transporting AC across long distances is relatively easy. At high voltages, less energy is lost in electrical power transmission. Higher voltages mean lower currents, and lower currents mean less heat generated in the power line due to resistance. AC can be converted to and from high voltages easily using transformers. AC is also capable of powering electric motors. It is useful for many large appliances like dishwashers, refrigerators, and so on, which run on AC.

 

 

Everything that runs off of a battery, plugs in to the wall with an AC Adapter, or uses a USB cable for power relies on DC. Examples of DC electronics include:

  • Cell phones
  • Laptop
  • Flat-screen TVs (AC goes into the TV, which is converted to DC)
  • Flashlights
  • Hybrid and electric vehicles 

Consider the following scenario:

·      A power plant is feeding a house located over 1000 feet away.

·      The house demands 100Amps current at 480V.

·      The plant generates 100Amp at 480V

·      Assume a DC system and an AC system with the AC system employing a transformer rated 480/4800V near the generating station and a 4800/480V transformer near the house. See figure below.

 

 

DC System

AC System

To carry 100Amps over the line, a larger cable (in diameter) will be required for the DC system.

 

After transformation, the current on the power line will be 10Amps. A smaller cable will be required.

 Larger cable means lower conductor resistance. Typically, 0.15 ohms per 1000feet can be used for a 100Amp conductor. In which case,

Voltage Drop (VD) across the line = 0.15*100 = 15V.

Smaller cable (in diameter) means higher resistance. Typically, a 1.5 ohms per 1000feet can be used for a 10Amp conductor. In which case,

Voltage Drop (VD) = 1.5*10 = 15V.

Same as a DC system.

 

 

Losses in transmission system = VD*Current (in watts) = 15*100 = 1500 watts

Losses in transmission system (in watts) = 15*10 = 150 watts.

Ten times less than DC transmission.

 

 Transformers cannot operate with DC supply wired to it. The only way to step down voltage for distribution is through a motor-generator set or a rotary converter – an inefficient process.

Transformers operate at 99% efficiency at full load. Used through out the AC system.

 

As for the sizes of the cables used in AC and DC systems, It is common knowledge that liquids flow through large-diameter pipes easier than they do through small-diameter pipes. The same general principle holds for the flow of electrons through conductors: the broader the cross-sectional area (thickness) of the conductor, the more room for electrons to flow, and consequently, the easier it is for flow to occur (less resistance). So, higher the amperage, greater will be the thickness of the cable.

As seen in the scenario presented above, AC is capable of reducing the amperage, and still providing the same wattage by increasing the voltage, which allows us to reduce the thickness of the cable and transmission losses, thereby saving a much energy and cost. DC Cables on the other hand tend to have greater transmission losses over short distances.

In a Solar PV Project, we try to reduce the DC cables length starting from the Solar panels till the inverter in order to minimize losses and cost (depending on the site). Once the DC cables are introduced to the inverter, we can convert it to AC and then, spread the wires all across the loads in a systematic manner.

Should we use Copper wires or Aluminium wires?

There are obviously materials property differences, such as, capacity, weight, and cost between aluminum (Al) and copper (Cu) to consider for an electrical application.  Al was more prevalent in the past for products such as bus bars, fuses, and breakers. Overtime, some designers have changed components from Al to Cu. Today, due to cost stability and coating some designers are switching back. 

The main material property in deciding between using Al or Cu in an electrical application is its capacity. Cu offers a better electrical capacity per volume. However, Al has better capacity per weight. As a raw material, Al is approximately 70% lighter than Cu. For wires, Al can be up to 60% lighter than comparable current carrying copper wires.

The weight is not a direct relation as more Al is necessary to match the capacity of Cu. Al carries about half the capacity of Cu. The difference in the weight to electrical capacity ratio means generally, one pound of Al has the electrical conductivity equal to 1.85 lb. of Cu. For example, a Cu busbar could weight around 550 lb., whereas the same busbar in Al would be about 300 lb. Reducing weight may help shipping or even labor cost.

Cable sizing formula used during installations

For DC side (includes cables from PV module to AJB, from AJB to Inverter),

Area of Cross Section= (2*L*I*ρ)/(%drop*V)     

 

L = Length of cable (metres)       

I = Current estimated through the cable (Amps)

ρ = Resistivity of the material of the cable. For eg. : Copper, Aluminium

%drop = Drop in voltage allowed during transmission

V = Voltage estimated through the cable (Volts)

 

For AC side (includes cables from Inverter to ACDB)

Area of Cross Section=(2*L*I*ρ*φ)/(%drop*V)

Where ,

L = Length of cable (metres)      

I = Current estimated through the cable (Amps)

ρ = Resistivity of the material of the cable. For eg. : Copper, Aluminium

%drop = Drop in voltage allowed during transmission

V = Voltage estimated through the cable (Volts)

φ = Power factor

 

What is resistivity?

Resistivity is one of the terms used while calculating cable thickness, especially since it varies according to the material of the wire used. It is a measure of how strongly a material opposes the flow of electric current. A definition of resistivity is the electrical resistance per unit length and per unit of cross-sectional area. This is for a particular material at a specified temperature. a low resistivity indicates a material that readily allows the movement of electrons. Conversely a high resistivity material will have a high electrical resistance and will impede the flow of electrons. Elements such as copper and aluminium are known for their low levels of resistivity. Silver and in particular, gold have a very low resistivity, but for obvious cost reasons their use is restricted. It is denoted by the symbol ρ and its dimensions are ohm-metre.

 

What is Power Factor?

Power Factor is simply the measure of the efficiency of the power being used, so, a power factor of 1 would mean 100% of the supply is being used efficiently. A power factor of 0.5 means the use of the power is very inefficient or wasteful. It is the ratio between the kW and the kVA drawn by an electrical load where the kW is the actual load power and the kVA is the apparent load power.

Simply, it is a measure of how efficiently the load current is being converted into useful work output and more particularly is a good indicator of the effect of the load current on the efficiency of the supply system.

So what causes Power Factor to change? In the real world, a power factor of 1 is not obtainable because equipment such as electric motors, welding sets, fluorescent and high bay lighting create what is called an “inductive load” which in turn causes the current  in the supply to lag the volts. The resulting lag is called Power Factor.

Generally for household applications, the value is taken anywhere between 0.8 – 0.9.

What is Islanding and how to deal with it?

Islanding: what is it and how to protect from it?

Islanding is a critical and unsafe condition in which a distributed generator, such as a solar system, continues to supply power to the grid while the electric utility is down. 

Islanding and distributed power generation

Islanding is a critical and unsafe condition, which may occur in a power system. This condition is caused due to an excessive use of distributed generators in the electrical grid.

Before going into more detail, it is important to understand distributed generation:

Solar power generators, wind generators, gas turbines and micro generators such as fuel cells, micro turbines, etc. are all examples of distributed generators.

 

What is islanding?

The fact that anyone could supply electricity back to the grid causes the problem of islanding. It is a condition in which a distributed generator like solar panel or wind turbine continues to generate power and feed the grid, even though the electricity power from the electrical utility is no longer present.

Also it exposes utility workers to life critical dangers of shocks and burns, who may think that there is no power once the utility power is shut down, but the grid may still be powered due to the distributed generators.

Anti-islanding or islanding protection

To avoid this problem, it is recommended that all distributed generators shall be equipped which devices to prevent islanding. The act of preventing islanding from happening is also called anti-islanding.

 

Problems caused by islanding 

Islanding causes many problems, some of which are listed below:

Safety Concern: Safety is the main concern, as the grid may still be powered in the event of a power outage due to electricity supplied by distributed generators, as explained earlier. This may confuse the utility workers and expose them to hazards such as shocks.

Damage to customer’s appliances: Due to islanding and distributed generation, there may a bi-directional flow of electricity. This may cause severe damage to electrical equipment, appliances and devices.

Some devices are more sensitive to voltage fluctuations than others and should always be equipped with surge protectors.

Inverter damage: In the case of large solar systems, several inverters are installed with the distributed generators.

islanding could cause problems in proper functioning of the inverters.

 

Ways to detects and resolve islanding

There are many ways to detect islanding. We can categorize those as active- and passive detection methods:

Active islanding detection

Active detection methods involve the technique of constantly sending a signal back and forth between the distributed generator and the grid to ensure the status of electrical supply, which is available in the inverter technology today. 

Passive islanding detection

Passive detection methods, on the other hand, make use of transients in the electricity (such as voltage, current, frequency, etc.) for detection.

The quickest and easy way to prevent any problems is to shut off the distributed generator when requested by the utility.

Working principle of MCB

Working principle of MCB ( Miniature Circuit Breaker)

There are two arrangement of operation of miniature circuit breaker.

·        Due to thermal effect of over current

The thermal operation of miniature circuit breaker is achieved with a bimetallic strip whenever continuous over current flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts.

 

·        Due to electromagnetic effect of over current.

During short circuit condition, sudden rising of current, causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts.

  

Operating Mechanism of Miniature Circuit Breaker 

The operating mechanism of miniature circuit breaker provides the means of manual opening and closing operation of miniature circuit breaker. It has three-positions "ON," "OFF," and "TRIPPED". The external switching latch can be in the "TRIPPED" position, if the MCB is tripped due to over-current. When manually switch off the MCB, the switching latch will be in "OFF" position. In close condition of MCB, the switch is positioned at "ON". By observing the positions of the switching latch one can determine the condition of MCB whether it is closed, tripped or manually switched off. 

 

Based on the number of poles, the breakers are classified as- 

·        SP – Single Pole : switching & protection is affected in only one phase.

§  Application : Single Phase Supply to break the Phase only. 

·        DP – Double pole: switching & protection is affected in phases and the neutral.

§  Application: Single Phase Supply to break the Phase and Neutral. 

·        TP – Triple Pole : switching & protection is affected in only three phases and the neutral is not part of the MCB.

§  Application : connection of three wires for three phase system (R-Y-B Phase). 

·        TPN – Triple Pole and Neutral : Same as TP but  has additional neutral which is only switched but has no protective element incorporated.

§  Application: Three Phase Supply with Neutral. 

·        4P – Four Pole : Same as TPN but the neutral pole is also having protective release as in the phase poles.

§  Application: Three Phase Supply with Neutral. 

 

MCB Ratings :

Normally there are ratings 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCBs.

Any rating above 100A, MCCB (Moulded Case Circuit Breaker) is used which comes in the range of 100 – 1000A.

Rain water harvesting in India

India receives the highest rainfall among countries comparable to its size. Its landmass has gorgeous and perennial rivers criss-crossing it – particularly through the northern part. But the other side of the story is this: one part or another of India has continued to experience drought conditions with an alarming regularity. The rivers have been drying up and getting polluted. The underground water tables are shrinking rapidly.

    If water management is not accorded the importance it deserves, the country can very much expect to find itself in troubled waters as the years roll by. Estimates of the Central Ground Water Board are that the reservoir of underground water will dry up entirely by 2025 in as many as fifteen States in India – if the present level of exploitation and misuse of underground water continues. By 2050, when more than 50 per cent of the Indian population is expected to shift to the cities, fresh drinking water is expected to get very scarce. A new category of refugees is expected to emerge around that time: the water migrants. Future wars, between or within nations will be fought on the issue of water.

Scenario

    India –which has 16 per cent of the world’s population, 2.45 per cent of the world’s land area and 4 per cent of the world’s water resources already has a grave drinking water crisis .

    The reservoir of underground water ,estimated presently at 432 billion cubic meters (BCMs) has been declining at a rapid rate of 20 cms annually in as many as fifteen States with major metropolitan centers including Delhi, being estimated to go dry as early as 2015 on account of over-exploitation and misuse.

    According to a study done by the New Delhi-based Central Ground Water Board, it will take just 2,600 additional tubewells running at an average of ten hours per day to exhaust the entire reserve of underground water in Delhi. Punjab, Haryana, Bihar, Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh, Maharashtra and Orissa have also been categorized by the Ground Water Board as the potentially ‘gray areas’.

Problem

    The annual inter-State feuds over water are becoming more and more common in India . Per capita water availability in the country which was 5,000 cubic metres earlier , has dropped to 2,200 cubic metres. This is against the world figure of 8,500 cubic metres. As a result, India is fast approaching a phase of stressed water availability conditions.

Several perennial flows like the Ganga-Brahmaputra-Barak are becoming seasonal. Rivers are dying or declining and aquifers are getting over-pumped. Thus, people have to depend on limited municipal water supply. Consequently, they are forced to rely on their own resources. This scarcity has led to the birth of water markets with private entrepreneurs doing business in supplying water tankers. This, once again, is putting pressure on surface and groundwater sources which are fast depleting all over the country.

    Eighty-five per cent of India’s urban population has access to drinking water but only 20 per cent of the available drinking water meets the health and safety standards.

    Furthermore, there are serious inequities in the distribution of water. Consumption of water ranges from 16 litres per day to 3 litres per day depending on the city and the economic strata of the Indian consumer.

    The water in rivers is wasted as it flows into the sea and is not properly harnessed. The debate on dams as a means of harnessing water continues to make this issue politically and environmentally sensitive. No clear ecologically stable and financially viable solution has emerged.The poor state of local and municipal authorities renders them unable to provide basic water to the cities. Strengthening of local bodies could lead to another means of addressing this issue.

Policy

    India’s national water policy gives overriding priority to drinking water. The policy requirements of urban development projects include a drinking water component. India is developing both its ground and surface water resources. Current policies prioritize the utilization of static reserves to prevent ground water mining but development of ground water mining is very intensive in Punjab, Haryana, Uttar Pradesh and some other parts of India.

    India’s rainfall is temporal (with as much as 70 per cent rainfall occurring in four months) and the rain is also unevenly distributed. With the glacier or snow-fed surface or river water, there is the multiplying problem of pollution.

    There are vast stretches of Indian rivers that are unable to support fish on account of the levels of pollution caused by the unwillingness or reluctance on the part of small and big industrialists to adhere to effluent treatment norms. While pollution is a problem, an equally important issue is to prevent the groundwater levels from declining any further. And it is here that the concept of rainwater harvesting comes into place.

Rainwater Harvesting

    On account of inadequate awareness or planning, excess rainfall water has been getting discharged into the oceans after coursing its way through the drains and rivers. In effect, it is possible to prevent this wastage of water by storing it during the rainy season — for use as drinking water during the dry seasons. Or for allowing it to seep underground in the dry areas as a measure of maintaining adequate levels of ground water. This water can subsequently be ‘recharged’ or pumped up for irrigational or drinking water purposes. And this is what rainwater harvesting is all about.

    There are different ways in which rainwater can be harvested. There is a method of what is known as ‘rooftop harvesting’ in which the rainwater is allowed to get collected in built-up tanks. This water can be used for direct consumption as also for recharging groundwater through simple filtration devices. Water can also be collected in tanks that have cement slabs built at their base to prevent the water from seeping underground. This method is usually employed in the desert areas of Rajasthan which often face drinking water problem.

Ancient Traditions

    Historically, Indians have been the world’s greatest water harvesters. Proof of this is found in a variety of archaeological material which speak of the functional classification of rainfall regimes, soil types, crop mixes, and irrigation techniques of the ancient Indians. This evidence translates to a proliferation of types of harvesting systems — rain fed, stream or river fed, and groundwater-based. Each of India’s 15 ecological zones had systems adapted to local needs and micro-ecological peculiarities- such as artificial wells like khadins, typical to Rajasthan but which can be made and used to store rainwater elsewhere too. Or the intricate networks of bamboo pipelines that carry water over inhospitable terrain in southern Meghalaya and are technologically adequate to function as a drip irrigation system for betel leaf plantations. Or the Mughal groundwater-based water supply system in Burhanpur town in Madhya Pradesh, so well-engineered that people use it even today.

    Evidently, the art and science of collecting water where it falls is then the ancient, ‘dying wisdom’ that needs to be revived to meet our contemporary fresh water needs adequately, equitably and sustainably. 

Governmental Initiatives

    The Government of India is well aware of this. Plans for adopting an inter-ministerial approach for tackling the water situation are being worked out while several state governments are enacting legislations to make rainwater harvesting compulsory in all housing societies, residential, commercial, industrial and other complexes. The Delhi Development Authority and the Municipal Corporation of Delhi have amended their existing building bye-laws, making it compulsory for every house or hotel, 200 yards or more in area, to undertake rainwater harvesting.

Roof Load Analysis

Evaluating the ability of a roof to support solar modules requires assessing the condition and construction of the roof, calculating the weight impact of the solar modules and support structures, and taking into account the potential impact of snow and wind.  Typical solar modules weigh 20 to 50 pounds each and are distributed evenly across a roof along with the racking systems that support them.  By dividing the weight of the modules and underlying racking by the area of the modules, we generally find that the combined weight of solar modules and the racking that supports them puts about 3-4 pounds of weight per square foot on a roof.  Most structures built after 1980 are designed to support loads far greater than this.  Local permitting rules must be consulted, but generally such loads are acceptable.

 

However, this assumption of a distributed load is generally not valid.  The weight of the modules is actually distributed to a limited number of mounting points and installers generally try to minimize this number and as a result the number of roof penetrations, thus reducing the potential for roof leaks. This strategy has a downside that it can create large point loads on the trusses that support the racking. Assessing the extent of these point loads involves adding up the contributions of the roofing materials themselves as well as the solar equipment.

 

An even greater concern is wind loading caused by uplift accumulated through the solar array and acting on the attachment points that support the solar modules. In some cases, solar modules can act as a sail and the wind from under the modules can create very high uplift loads. With enough upward force, solar modules can come loose from the roof and it is even possible that the roof itself can be pulled off along with the solar modules.  Calculating wind uplift forces (Fw) is similar to other load calculations (it is a product of the local wind force multiplied by the module length multiplied by the rail spacing) but is complicated by the fact that these forces vary significantly depending upon where the modules and rails are located on the roof.

What is SPD and ELCB?

SPD (Surge Protection Device)

A surge protector is an appliance or device designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. This device is connected in parallel on the power supply circuit of the loads that it has to protect. SPD connected in parallel has a high impedance. Once the overvoltage appears in the system, the impedance of the device decreases so surge current is driven through the SPD, bypassing the loads which are meant to be protected. It is the most commonly used and most efficient type of overvoltage protection.

SPD eliminates overvoltages

·        in common mode,

§  between phase and neutral or earth;

§  Conducts the energy to earth.

·        in differential mode,

§   between phase and neutral.

§  distributes the energy to the other live conductors.

 

3 types of SPD’s are considered by the IEC standards:

 

1.     10/350 µs wave: to characterize the current waves from a direct lightning stroke. Here 10 µs represents rise time and 350 µs is the voltage surge duration.

 

 

2.     8/20 µs wave: to characterize the current waves from an indirect lightning stroke. Here 8 µs represents rise time and 20 µs is the voltage surge duration.

 

 

3.     The overvoltages created by lightning strokes are characterized by a 1.2/50 µs voltage wave. This type of voltage wave is used to verify equipment's withstand to overvoltages of atmospheric origin.

 

 

ELCB (Earth Leakage Circuit Breaker)

If any current leaks from the electrical installation, there must be an insulation failure in the electrical circuit which must be properly detected and prevented otherwise, there may be a high chance of electrical shock if anyone touches the installation. An earth leakage circuit breaker does it efficiently. Basically it detects the earth leakage current and makes the power supply off by opening the associated circuit breaker.

 

Working principle

The working principle of voltage ELCB is quite simple. One terminal of the relay coil is connected to the metal body of the equipment to be protected against earth leakage and other terminal is connected to the earth directly. If any insulation failure occurs or live phase wire touches the metal body, of the equipment, there must be a voltage difference appears across the terminal of the coil connected to the equipment body and earth. This voltage difference produces a current to flow the relay coil. If the voltage difference crosses, a predetermined limit, the current through the relay becomes sufficient to actuate the relay for tripping the associated circuit breaker to disconnect the power supply to the equipment.

Significance of Solar tracking

 

How does a solar tracker work?

Trackers direct solar panels or modules toward the sun. These devices change their orientation throughout the day to follow the sun’s path to maximize energy capture.

 

In photovoltaic systems, trackers help minimize the angle of incidence (the angle that a ray of light makes with a line perpendicular to the surface) between the incoming light and the panel, which increases the amount of energy the installation produces. Concentrated solar photovoltaics and concentrated solar thermal have optics that directly accept sunlight, so solar trackers must be angled correctly to collect energy. All concentrated solar systems have trackers because the systems do not produce energy unless directed correctly toward the sun.

 

Single-axis solar trackers rotate on one axis moving back and forth in a single direction. Different types of single-axis trackers include horizontal, vertical, tilted, and polar aligned, which rotate as the names imply.

 

 

Dual-axis trackers continually face the sun because they can move in two different directions. Types include tip-tilt and azimuth-altitude. Dual-axis tracking is typically used to orient a mirror and redirect sunlight along a fixed axis towards a stationary receiver. Because these trackers follow the sun vertically and horizontally they help obtain maximum solar energy generation.

 

 

 

 

 

Advantages:

§  Trackers generate more electricity than their stationary counterparts due to increased direct exposure to solar rays. This increase can be as much as 10 to 25% depending on the geographic location of the tracking system.

§  There are many different kinds of solar trackers, such as single-axis and dual-axis trackers, all of which can be the perfect fit for a unique jobsite. Installation size, local weather, degree of latitude and electrical requirements are all important considerations that can influence the type of solar tracker best suited for a specific solar installation.

§  Solar trackers generate more electricity in roughly the same amount of space needed for fixed tilt systems, making them ideal for optimizing land usage.

§  In certain states some utilities offer Feed in Tariff (FiT) rate plans for solar power, which means the utility will purchase the power generated during the peak time of the day at a higher rate. In this case, it is beneficial to generate a greater amount of electricity during these peak times of day. Using a tracking system helps maximize the energy gains during these peak time periods.

§  Advancements in technology and reliability in electronics and mechanics have drastically reduced long-term maintenance concerns for tracking systems.

 

Unlike many other components of a solar power system, selecting a tracker is more challenging because of the following reasons:

·         It is the only component in a solar pv system that has moving parts so selection needs to focus on a trouble-free, low maintenence system

·         Use of trackers in Indian solar power plants has been a recent phenomenon, and hence little information is available from real life installations

·         There are both Indian and international tracker brands available, and each has its own set of features and unique selling points, making comparison and selection quite intricate.

Why is Grounding/Earthing required?

What is Earthing System?

The connection between electrical appliances and devices with the earth plate or electrode through a thick wire of low resistance to provide safety is known as Earthing or Grounding.

Earthing System or Grounding System in Electrical network is for safety purpose. The Main objective of earthing system is to provide an alternative path for dangerous current to flow so that the problem of electric shock and damaging of equipment’s can be cured.

Metallic part of an equipment are grounded and if the equipment’s insulation fails than there will be no dangerous voltages present in equipment box.

The circuit gets sorted and fuse will blow immediately, in case the live wire touches the earthed case.

Particularly, it can affect the magnitude and distribution of current in short circuits through the system and the effects of the system are on equipment and people who will near to the circuit.

Why you should have an Earthing System?

This question generally arises, when you have all the right equipment’s, wires, socket and well maintained electrical devices, Yet, why is there need of an Earthing system.

The Answer is very simple..

Earthing system makes your building electrically shock free and gives you a safe place.

Below are some of the points which can easily make you think about earthing system.

·         Safety for Human Life, Electrical Devices and Building

It saves the human life from danger of electrical shock which can cause death, by blowing a fuse.

Protects your electric equipment’s or devices.

It provides a safe path for lighting and short circuit currents.

·         2Voltage Stabilization

You know that electricity has many sources. As Every transformer considered to be a separate source. And if there is not a point which will act as common point, then it becomes more difficult to make a calculation between these sources.

In the Electrical distribution systems, Earth is the omnipresent conductive surface, which makes it a universal standard for all electric system.

·         Over Voltage Protection

Earthing System provides an alternative path in the electrical system to minimize the dangerous effect in the electrical system which happens at the time of lighting and unintentional contact with high voltage lines.

 

Scientific Perspective

Grounding is one of the most important safety factors of any electrical system and solar PV is no different than the other electrical system, So it is also important to ground the PV modules.

There is an electrical voltage between the PV cell and the frame and it can cause electrons come loose from the material used in the PV module and discharge through grounded frame. This causes a polarization that can adversely alter the characteristic curve of the PV cells. It leads to deterioration of the cells which is called as Bar Corrosion (It looks like bar codes).

 

Most of the PV panels are made of P-type cells which lead to polarization and negative potential is generated which are neutralized through the grounding negative array pole. If the array cannot be grounded because of the inverter used or if the modules are already polarized then the neutralization is done through specially manufactured devices such as SMA has recently developed a PVO box which neutralizes the reverse voltage.

 

 

When a PV module generates electricity its surface area becomes charged and acts like a capacitor. This capacitance has an undesirable effect and known as parasitic capacitance. During the operation of the PV module it is also connected to the inverter where the fluctuating voltage constantly changes the state of charge of parasitic capacitor and causes a displacement current proportional to the capacitance and to the voltage amplitude. This leads to a leakage current. This leakage current is not dangerous, however, it superimposes possible residual current that could occur through touching a live line through a damaged insulation and can seriously hinder its detection.  Hence, grounding of SPV modules and inverter becomes very important. Most of the inverter manufactures provide negative and positive grounding option depending upon PV module connecting to an inverter. For example, A Sun power module requires a positive grounding. While a CdTe or Amorphous Silicon module requires a negative grounding. The positive and negative grounding depends that how modules top surface is charged.

How do Solar panels work?

Solar Panels

How we get our Power?

Energy comes in different forms. Light is a form of energy. So is heat. So is electricity. Often, one form of energy can be turned into another. This fact is very important because it explains how we get electricity, which we use in so many ways. Electricity is used to light streets and buildings, to run computers and TVs, and to run many other machines and appliances at home, at school, and at work. One way to get electricity is to burn a fuel like oil or coal. This makes heat. The heat then makes water boil and turn into steam. The steam runs a machine called a turbine that produces electricity. Often, this electricity then goes into a public power system that sends it out, through wires, to homes, schools, and businesses over a wide area. This method for making electricity is popular. But it has some problems. Our planet has only a limited supply of oil and coal. They are not renewable fuels. Once they are used, they are gone forever. Also, they give off gases when they are burned. These gases may make the air dirty, or polluted, and some of them may change Earth’s climate.

 

Free and clean energy

Another way to make electricity uses sunlight. Sunshine is free and never gets used up. Also, there is a lot of it.  The sunlight that hits the Earth in an hour has more energy than the people of the world use in a year. A little device called a solar cell can make electricity right from sunlight. A solar cell doesn’t give off any gases. It doesn’t even make any noise. A solar panel is a group of solar cells that work together.

Solar cells and solar panels have lots of uses. They are in everyday things like calculators, watches, and flashlights. There are solar-powered toys, radios, and MP3 players. There are solar-powered cell phones and pagers. Using solar power with devices like these means you never have to worry about batteries. Solar panels are sometimes used to make the electricity to light up road signs and bus stops. They may make the electricity that makes roadside emergency phones or parking meters work. Even some ATMs (machines that let you get money from or put money into your bank account) have solar panels.

The ceiling lights and all kinds of machines and appliances used at home, school, and work get their electricity from the wires running through the building. Usually, this electricity comes to the building from the public power system, or grid. But solar panels can also be used along with power from the grid. People sometimes put solar panels on their homes. Large buildings may have them as well. They make it possible to use less of the grid’s costly electricity. In addition, they are a backup in case of a power failure, or blackout. In some areas the grid itself gets some power from solar panels.

 

 

How Solar Cells Use Light

Only part of the energy sent toward Earth by the Sun actually makes it to Earth’s surface. Some solar energy gets bounced back into space. Some gets absorbed by the air. Most of the solar energy that does make it to Earth’s surface is in the form of visible light. Solar cells can use the energy of this light to make electricity. But they don’t work equally well with all forms of light. Different types of solar cells use different wavelengths. This means a cell can use only some of the solar energy that it receives.


 

Solar cells come in various sizes.Some are tinier than a stamp. Some are 5 inches (12 centimeters) across. The cells are made of a type of material known as a semiconductor. Often, they are made of silicon. Semiconductors can conduct, or carry, electricity. They don’t do this as well as metals, however. That is why they are called “semi.” Because they only “semi” conduct electricity, they can be used to control electric current. On their top and bottom they typically have metal contacts through which current can flow. A typical simple cell has two layers of silicon. One is known as n-type. The other is p-type. The layers are different from each other.

 

How Solar Cells Make Electricity

 


The process of making electricity begins when the silicon atoms absorb some light. The light’s energy knocks some electrons out of the atoms. The electrons fl ow between the two layers. The flow makes an electric current. The current can leave the cell through the metal contacts and be used. When light hits a solar cell, much of its energy is wasted. Some light bounces off or passes through the cell. Some is turned into heat. Only light with the right wavelengths, or colors, is absorbed and then turned into electricity.


 

A single simple solar cell makes only a little electricity. For most purposes more is needed. For this reason, cells are often linked together in groups known as solar modules. A solar module  as a frame that holds the cells. Some modules are several feet long and wide. They usually can produce up to a few hundred watts of electricity. If more power is needed, modules can be joined together to form a large solar array. Modules are sometimes called solar panels. Arrays are also sometimes called solar panels. Whatever you call a group of solar cells, the fact remains: the more cells you link together, the more electricity you make. With enough   modules, huge amounts of power are possible.

Replacing DG Sets with Solar Rooftop Installations

Diesel generators

All over India, Diesel Generators (DG sets) are used by factories, commercial establishments, residential societies and individual households for power backup. DG sets have become a go-to option for backup due to:

·         Easy availability in the market.

·         Small installation space requirement.

·         Low cost of diesel.

According to a survey by CERC (Central Electricity Regulatory Commission) in 2014, over 90,000 MW of power is supplied by DG sets, and is estimated to grow by 5000 – 8000 MW every year. Although grid based supply has considerably increased over the last decade, it is still in inadequate considering the growing demand of consumers and weak financial condition of distribution companies (discom).

Today, DG sets are functioning as mini-grids for societies, providing a mix of diesel based and grid based electricity to its residents. However, diesel based generation is not only expensive but also damages the environment significantly, contributing to noise pollution as well as air pollution. In 2012, a part of WHO declared that the exhaust of diesel engines as carcinogenic to humans.

Financially, the approximate cost of generation from a DG set is about Rs.16 to 17 per unit, excluding the capital cost. Including the capital expenditure, the cost per unit rises to Rs.27 to 33. This is around 4 times the cost of the grid supply.

Over the years, the energy deficit in india has been steadily reducing which has resulted in lower rate of power outages. Currently the average power cuts are less than 1 hour/day in many of Indian Cities. Accordingly the usage of DG sets has also reduced, thereby declining their benefits also.

Therefore a combination of reducing power shortages, high cost of DG sets and worsening air quality means that time has come for residential societies to consider alternatives to DG for backup needs.

Solar Rooftop

Earlier, societies and individual households did not consider solar rooftop for backup power due to its high cost of generation. Lack of awareness and operational history made people skeptical about its reliability and life. But with the prices of the solar panels, which account for 50 – 55% of total cost of installation, sharply falling in the last few years, solar rooftop has emerged as a viable solution for back up needs. The cost per unit from a solar installation is about Rs. 7 – 8 which is half the cost of the supply from DG sets.

 

Additionally, the monthly bill is also reduced due to various schemes the state government has initiated which makes the consumer eligible for remuneration for every unit fed back into the grid. This has been primarily done in order to promote more residents to go for solar option for their power needs. DG sets provide no such benefit. In fact the governments plan to achieve 100 GW of total solar capacity rests on 40 GW of solar rooftop capacity.

Incentives for the Capital investment as well as the power generated by solar rooftops have encouraged a growth to the entire solar eco-system which includes :

·         Panel manufacturers

·         Suppliers

·         Installation companies

·         RESCO’s (Renewable energy service companies)

·         And finally, the consumer.

But despite, the various efforts being made through all channels, rooftop installations in residential sector has not yet picked up.

Lets hope that the ambitious plan of the government comes through even though the target for 2015-16 of 200 MW was backed by only 166 MW of rooftop installations.

 

What is holding back growth?

1.       Lack of Awareness

Most people do not know about the capital incentives for rooftop solar or generation benefits such as net and gross metering systems. Therefore, aggressive marketing of rooftop solar is essential to its growth.

 

2.       Lengthy approval process

Surprisingly, discom officials lack understanding of the connections and the approval process which leads to delays as long as six months in the power generation scheme to commence.

 

 

 

3.       Frequent policy changes

Repeated revision leads to confusion amongst the developers and project delays. The efficiency and impact of the policy have to be observed for some time  for the programme to succeed.

 

4.       Discom issues

It is possible that in the near future, the consumers will partly or wholly offset their electricity needs through solar rooftop installations, which is a great concern for discoms as it will lead to loss of their profitable consumer base.

 

 

                               

Solar Potential on rooftops

Over the next decade, growing urbanization will lead to greater incomes which will lead to an exponential growth in housing most which will be met by multi-storied residential housing.

Assuming,

·         an average flat to be of 750 sq ft.

·         1 million flats added every year.

·         5kW load per household

Given, the recent policy by Ministry of Environment, Forest and Climate requires 1% of demand load to be met through renewable sources, average size of rooftop solar per household will be about 250 – 300 Watts.

This translates to a potential of 3 GW atleast in only residential high rises in coming years.

 

Solar rooftop feasibility assessment

The steps to assess the feasibility of replacing DG sets with solar rooftops and whether they can match the requirement :

1.       Size of solar PV is based on usable rooftop area available.

2.       Inverter size is based on connected load. The two possibilities are

a.       Inverter size equals PV size.

b.       Inverter is based on minimum load needed per flat.

3.       Battery size is based on energy required during outage.

a.       Battery aligned with inverter size.

b.       Battery is based on minimum load needed per flat.

4.       Energy generated by DG set is calculated considering 60% loading of diesel generator during operational hours.

 

Savings from solar rooftop

The payback period for a residential society is around 6 – 7 years which means around 18 years, the residents will get electricity at no cost due to minimal operating expenses of the solar rooftop system. However they will have to replace inverters and batteries every 5 -10 years, the cost of which can be easily supported by the savings.

 

 

Wind and Solar Integration

Off Grid wind/solar

In many parts of the India, Wind and Solar energy are abundantly available which pay way for their optimal integration.

With the latest inverter technology, it is possible to integrate wind and solar energy even for daily household power requirement. The inverters and power conditioning units by Studer are capable of handling both wind and solar equipment in order to convert the natural energies to usable AC power for the household.

 

 

The integration primarily involves usage of both the wind and sunlight available in the location. Estimations regarding the sum total energy that both sources can potentially provide can be calculated using the insolation data available in the MNRE website, and the wind speed data available in the NIWE website <http://niwe.res.in:8080/NIWE_WRA_DATA/#>.

The major advantage of an off-grid solar/wind hybrid system is that when solar and wind power production are used together, the reliability of the system is enhanced. In addition, the size of battery storage can be reduced slightly as there is less reliance on one method of power production.

Wind speed is low in summer whereas the solar radiation is brightest and longest. The wind is strong in monsoon months whereas less sunlight is available owing to cloud cover. Because the peak operating times of wind and solar systems occur at different times of the day and year, hybrid systems are more likely to produce , dependable power to our demands. When neither the wind nor the solar systems are producing, most hybrid systems provide power through the energy stored in batteries. Even during the same day there are different and opposite wind and solar resource patterns. Those different patterns can make the off-grid hybrid systems the best option for electricity production especially if there’s cut offs from the electrical grid. When one or both of these resources is available, the electricity produced can directly feed the load and charge the batteries that will be used when both of these resources are no longer sufficiently available.

Lets take a look into a case study for Mustigiri in Bagalkati district in Karnataka in order to get a perspective.

Mustigeri is located in Bagalkati district having plain terrain; the ownership of land is private land which is easily accessible and located Near Mustigeri village. The nearest substation is Badamai substation near 12kms has GPS details of Lat 15o58'39.3''N & Long 75o33'39.0''E with elevation 616m.

 

 

 

 

Above figures show trends of solar and wind hybrid average monthly power generation from January to December at Mustigeri. On an annual span, it is observed that there's slight decrease in Wind Power Generation from January up to March and an increase of solar generation within the same duration. The seasonal variations in this region aids hybrid average power generation. Though wind trend decreases after March for a small duration and rises with advancing south west monsoon. During April and July, wind trend is maximum depicting maximum wind power generation. The solar trend on the other hand decreases during the months of March to July and gradually increases from end of August until November. Post September, it's end of monsoon at most of the places, due to which wind trends together shows a simultaneous decrease and increase until the month of December and solar trend to increases simultaneously. After which they slightly rise and contribute to the Annual trend. 

 

 

The Table below gives details of expected annual energy production from 1MW solar PV plant and 1 MW wind turbine . Wind Turbine can generate at this particular area about 1.85 MU and Solar PV plant can generate 1.54 MU of electricity and cumulatively can generate 3.40 MU of electricity.

 

How to clean the Solar Panels

Tips for cleaning the solar panels

Solar panels generally get covered in dust especially in particularly dry areas or where panel tilt is minimal. Dust and other substances such as bird droppings can build up over time and impact on the amount electricity generated by a module.

Safety first – follow the procedure in your manual for shutting down the system before commencing cleaning.

Clean your solar panels on an overcast day, early in the morning or in the evening. If the sun is beating down on the panels, any water used can quickly evaporate and dirt will become smeared.

Early morning can be a particularly good time for cleaning as dew that has settled on the panels overnight will likely have softened the hard dirt; meaning you’ll need to use less water and less energy to clean your solar panels.

If the panels are dry, before tackling the modules with water, brush off any loose materials first – this will make cleaning easier and faster.

Don’t use metal objects or harsh abrasive products for removing caked on materials – scratching the glass on a solar panel can affect its performance as scratches will cast shadows. Avoid using detergents if possible as these may streak the glass of the panel. Use of abrasive powders also risks scratching the panels.


Given the nature of good quality solar panel glass, clean water and a little scrubbing with a coarse cloth covered sponge or soft brush should remove the most stubborn grime.

 

If your mains-supplied water is hard (mineral-rich) and rainwater is available; use that as a final rinse; then squeegee dry. If hard water is all you have, just be sure to squeegee well as mineral-ladened water can form deposits on glass as it dries.

Oily stains can occur in some installation scenarios, such as if you live near an airport and are under a flight path or if you live adjacent to and downwind of a major roadway frequented by trucks. If oily stains start appearing on your panels; isopropyl alcohol can be used as a spot-cleaning substance..

 

In most residential installation scenarios, solar panel cleaning just isn’t worth the bother due to the potential danger of accessing your rooftop. Unless dirt is clearly visible or performance is noticeably impacted; simply let nature do the job for you – just as it does in creating solar power.

What is Insolation and how it plays a role while harnessing solar energy?

Insolation

Solar radiation which we receive as heat and light can be converted to useful thermal energy or for production of electricity either through solar photovoltaic route or through solar thermal route.  Availability of reliable solar radiation data is vital for the success of solar energy installations in different sites of the country. For solar collectors which are flat in nature, solar radiation data in the form of Global Horizontal Irradiance (GHI) is useful whereas for solar collectors which are concentrating in nature Direct Normal Irradiance (DNI) data is required. 

The solar insolation data is available on various websites, one of them being the MNRE portal : http://mnre.gov.in/sec/solar-assmnt.htm

Solar insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter (W/m2) or kilowatt-hours per square meter per day (kWh/m2/day) In the case of photovoltaics it is commonly measured as kWh/year/kWp (kilowatt hours per year per kilowatt peak rating). Some of the solar radiation will be absorbed, while the remainder will be reflected. Usually the absorbed solar radiation is converted to thermal energy, causing an increasing in the object’s temperature. Some systems, however, may store or convert a portion of the solar energy into another form of energy, as in the case of photovoltaics or plants.

The amount of insolation received at the surface of the Earth is controlled by the angle of the sun, the state of the atmosphere, altitude, and geographic location.

The insolation into a surface is largest when the surface directly faces the Sun. As the angle increases between the direction at a right angle to the surface and the direction of the rays of sunlight, the insolation is reduced in proportion to the cosine of the angle.

Solar insolation levels are used to determine what size solar collector is needed to efficiently provide adequate levels of hot water. Geographic locations with low insolation levels require larger collectors than locations with higher insolation levels.

 

Generally, during estimations of the energy available to any household, monthly insolation data is extracted from the official websites based on the location of installation to calculate the yearly benefit to the customer. The number of panels increase in number to meet the demand in a location where the insolation is lesser as compared to a higher irradiation region.

Impact of shadows on solar panels

Effect of shadows on solar panels.

When deciding to install a solar photovoltaic system, the positioning of the solar panels is vital. It is pretty obvious that the solar panels should be orientated such that they face the sun at the time of day when the sun is highest in the sky; but a secondary important consideration is shading. If even a small section of a photovoltaic panel is shaded – for example by the branch of a tree – there is a very significant drop in power output from the panel. This is because a PV solar panel is made up of a string of individual solar cells connected in series with one another. The current output from the whole panel is limited to that passing through the weakest link cell. If even one cell is completely shaded, the power output from the panel will fall to zero. If one cell is 50% shaded, then the power output from the whole panel will fall by 50% – a very significant drop for such a small area of shading.

 

Solution

The obvious solution is to locate the solar array somewhere that shade is not an issue during the peak sunlight hours, but this is not always possible. Therefore, Bypass diodes are connected between panels in a system, and also between groups of cells in a panel so that the only power loss is from the shaded portion.

When a panel is partially shaded, the current from the un-shaded part of the panel passes through a diode which bypasses the shaded group(s) of cells. While some power is lost as heat in the diode due to the voltage drop, the overall power generation of the partially shaded panel is better than it would be without the diodes, and the diodes also protect the panel from damage.

 Nowadays, almost all panels come with inbuilt Bypass Diodes which are present in the junction box at the backside of the panel, thereby reducing the concern of the user regarding the shading issue.

 

The use of bypass diodes allows a series of connected cells or panels to continue supplying power at a reduced voltage rather than no power at all. Bypass diodes are connected in reverse bias between a solar cells (or panel) positive and negative output terminals and has no effect on its output. Ideally there would be one bypass diode for each solar cell, but this can be rather expensive so generally one diode is used for each panel.

Future of Small Scale Rooftop Solar Installations

GROWING POPULARITY OF SMALL-SCALE SOLAR POWER

The interest in renewable technologies has risen dramatically over the past decade. The growth in the industry has been driven by a number of factors, one of which is consumer behavior. In order to meet an ever-growing consumer demand for efficiency, today's brands are positioning their products as "green" or highly efficient.

What this tells us is that consumers are taking steps toward becoming more environmentally conscious and looking for new ways to reduce their carbon footprints. While this is just scratching at the surface, the growing demand of energy-efficient products demonstrates where the market is trending and where our future is headed.

Solar energy today, is becoming more affordable. As the price of solar continues to decline, the number of investments continues to grow. This decline in the cost of photovoltaic technology will drive huge surge in investment in solar, both large-scale and small-scale, majority of which will go on rooftop and other local PV systems, giving consumers and businesses the ability to generate their own electricity and to store it using batteries.

Prime Minister Narendra Modi's push for India joining the International Solar Alliance has put the spotlight on the country's nascent solar industry. Entrepreneurs are already working on several projects, large and small, both in the commercial space and the consumer one. Many startups have also sprung up in the last five years. Rural areas are the biggest market in solar power, because many villages are still not covered by the power grid. Of the state's 200-odd million people, 30 million still do not have any access to electricity.

One of the biggest challenges start-ups face is the lack of finance or capital. Many people who are willing to install solar panels do not have access to ready capital. The government needs to ensure finance is easily available, especially to rural folk.

In January 2015, the Indian government expanded its solar plans, targeting US$100 billion of investment and 100 GW of solar capacity, including 40 GW's directly from rooftop solar, by 2022. The rapid growth in deployment of solar power is recorded and updated monthly on the Indian Government's Ministry of New and Renewable Energy website.

In 2015, only 55% of all rural households had access to electricity, and 85% of rural households depended on solid fuel for cooking. Solar products have increasingly helped to meet rural needs, and by the end of 2015, a cumulative total of just under 1 million solar lanterns had been sold in the country, reducing the need for expensive kerosene. In addition, a cumulative total of 30,256 solar powered water pumps for agriculture and drinking water had been installed. During 2015 alone, 118,700 solar home lighting systems were installed, and 46,655 solar street lighting installations were provided under a national program. The same year saw just over 1.4 million solar cookers distributed or sold in India.

India is ranked number one in solar electricity production per watt installed, with an insolation of 1700 to 1900 kilowatt hours per kilowatt peak. With growing awareness, reducing rates, financial subsidies, quick returns and the government plans for the small scale solar programs, we can only expect to see a majority of consumers opting for energy through the solar medium.

In Karnataka alone, the installation scale was 77 MW as of 31st March, 2015 which went up to 146 MW by 31st March, 2016 and had reached 327 MW by 31st December,2016. The growth is already evident and it is only a matter of time before we will be seeing solar energy being used in every other household.

According to a report in December 2016, the cost of solar power in India, China, Brazil and 55 other emerging market economies dropped to about one third of its price in 2010, making solar the cheapest form of renewable energy and also cheaper than power generated from fossil fuels such as coal and gas. The report also cited a $64 per megawatt-hour solar power contract signed in India in early 2016, as proof of remarkable falls in the price of electricity from solar sources.

 

As of the end of July 2015, the following are the five most prominent incentives:

 

1. Accelerated Depreciation: For profit making enterprises installing rooftop solar systems, 40% of the total investment can be claimed as depreciation in the first year. This will significantly decrease tax to be paid in Year 1 for profit making companies.

 

2. Capital Subsidies: Capital subsidies are applicable to rooftop solar power plants, up to a maximum of 500 kW. While the original capital subsidy was 30%, it has recently been reduced to 15%.

 

3. Renewable Energy Certificates: Renewable Energy Certificates (RECs) are tradeable certificates that provide an incentive to those who generate green power by providing financial incentives for every unit of power they generate.

 

4. Net Metering Incentives: Net metering incentives depend on two aspects: a) whether the net meter is installed; and b) the incentive policy of the utility company. If there is a net metering incentive policy in our state and if there is a net meter on our rooftop, then we can get financial incentives for the power generated.

 

5. Assured Power Purchase Agreement (PPA): The power distribution and purchase companies owned by state and central governments guarantee the purchase of solar power as and when it is produced. The PPAs offer a high price equal to that of the peaking power on demand for the solar power which is secondary power or negative load and an intermittent energy source on daily basis.