Turn your rooftop into PV solar plant


Solar energy is a hot topic today. Some of the factors to consider before installing a solar power plant on the rooftop of your building include electrical load, current rate, roof size, load capacity and geographic location of the building. The subsidy given by the government, local regulations and incentives are also key determinants in evaluation.

Rooftop solar arrays are best installed on a large, flat roof where direct sunlight is available without shadows from the surrounding structures. If there is shadow on a part of the terrace during the day, photovoltaic (PV) solar panels will not be able to harvest the sun’s energy for that period.

By PS Deodhar

Sunday, January 09, 2011:Need for rooftop installations


In the US, the total number of grid tied rooftop solar power projects grew by 81 per cent in 2008 (to 196 MW) and an additional 93 per cent in 2009 (to 385 MW). Non-residential rooftop and backyard installation was the fastest growing solar market that grew at 109 per cent. This segment includes rooftop PV solar installations for commercial and government buildings, factories, warehouses, schools, colleges and universities. In fact, solar power projects have been growing by over 62 per cent a year for the past five years in the US.

You may ask why is solar power growing worldwide. Are factors beyond climate change concerns driving the growth? Many of us believe that this will happen in India, too. There are great merits in promoting installation of solar plants especially on rooftops and backyards lying unused. In fact, India should promote them in preference to megawatt plants.

Let us consider how many thousand square kilometres of rooftops and backyards in India are currently lying unused. Like in the US, India too has commercial and government buildings, factories, warehouses, schools, colleges and universities with very large unused terraces and backyards. We can have at least a gigawatt of solar power pushed into the grid to augment shortages. With small rooftop solar power plants feeding into the copper grid at fag end of the grid, quality of the power to every customer in the vicinity will improve during the productive hours in daytime. Terminal points of the grid suffer from high source impedance and solar power injection will help to lower it and consequently stabilise the line voltage.

Say, 5MW solar energy from a hundred 50kW rooftop or backyard solar power plants is fed into a small city grid like Miraj, Ratnagiri or Ratlam. All consumers in that area will get cleaner uninterrupted power from the local copper grid. The high impedance of the local grid helps power to remain local and thus, instantly helps improve local power quality. That’s why all other countries in the world allow solar plant owners to feed power into the local grid at low voltage end.

Many would not know that total investment in these 100 x 50kW power plants will be the same if not less than in a large 5MW plant. The answer is, therefore, to go for small grid fed plants owned by small privately owned utilities. Rs 17 or 18 per unit of buying rate from such plants will attract thousands of small investors like a magnet. In most of the areas in India, solar power can then be a fiscally sound investment that reduces electricity payments immediately, as well as hedges the small solar plant owners against local utility price increases.

Solar Mission’s priority, in fact, must be to improve power quality in smaller towns and remote areas. When solar power is fed at 33kV low impedance point of copper grid, this will not happen! There is also a sociocultural impact of this. Use of PV solar power is a green initiative on your part, making you eligible for a ‘carbon credit’. Carbon credits are a representation of the carbon that would have been emitted if the energy had been generated by a typical fossil fuel power plant instead of a renewable power plant.

Govt’s role in encouraging small producers

Change in government policies will help rapid solar power growth in our country via rooftop and other low power solar plants. Jawaharlal Nehru, a democrat, would have been happy with a faster move to mission targets steered by these new small manufacturers of electricity. I hope the micro, small and medium enterprises (MSME) secretary is reading this. Dr Farooq Abdullah’s Ministry of New and Renewable Energy (MNRE) may please quickly clarify when will the power utilities be instructed to buy solar power from 5kW to 100kW solar plants at the same rate as +1MW plants. As more and more rooftop solar power plants feed power into the grid, local power utility companies should be happy to buy power at higher price since this will enable them to own the carbon credits.

MNRE needs to remove all the remaining roadblocks to encourage rooftop and backyard solar power plants of 5 to 500kW capacity to feed their solar power into the grid and augment shortage of supply from utility companies. Every other country in the world pays a high rate for such solar power fed into the grid and this makes such investment well rewarding. USA, Canada, Germany, France, Spain and Portugal not only pay but encourage every citizen to do so. Proven and secure technology to compute the amount of energy in kWh fed into the grid is well developed and widely available even in India. The available metering technology is secure enough for the government not to worry about misuse. Actually, the government need not pay as high as Rs 18. Farookh Saheb can still look generous even with much less!

If a villager to whom the government has failed to provide access to the electricity generates his own power, say, one unit a day (1 kWh), how can the government not give him Rs 18 for his unit of power if it pays to other city investors in solar generation? He will be well within his rights to demand it than be happy with a few thousand rupees of subsidy given as a favour by an all powerful government. The government (MNRE) knows well that the investment needed per kilowatt of PV solar power is almost the same for a kW plant installed by the farmer and 10MW plant installed by institutional investors.

Let us remember big plants need big land—about 3 acres or more per megawatt. That one factor indeed makes such a plant high in cost. It will be a wrong use of such land unless the land is non-arable, or commercially and strategically unsuitable. It would be unwise not to use currently unused millions of rooftops for generating solar power and feeding into the grid and encourage large plants only?

What’s in a PV solar power system?

Very soon, the government will be buying power generated from rooftop and backyard solar power plants. Notwithstanding what it decides, let us look at the key considerations in evaluating solar option.

Size and physical load capacity of your roof: Geographic location of your rooftop or backyard and continuous availability of the sunlight

Your own electrical load and current rate: State government, local utility and local community regulations and incentives

Before you go further, it is important to have a basic understanding of the components of a solar power system and how it generates electricity. PV solar power systems are very simple electric power generating plants comprising the following basic component systems:

  • A set of PV panels that transform sunlight (photons) into DC electricity
  • A racking system that firmly holds the panels to the roof and exposes the panels to the sun at an advantageous angle
  • Inverters that transform DC electricity into AC electricity
  • Wiring that connects everything
  • Storage battery (in the case of grid fed power plant, big size battery is not necessary to store and use that power after sunset.)

Of all the components, solar module accounts for the biggest cost, which can be 70 per cent of the total project cost. Cost per watt is currently about Rs 130 to Rs 150 ex-factory. As a result, a variety of solar module types have proliferated. There are a variety of means to tilt the panels toward the sun to generate more electricity.

Currently, commercially available silicon based solar panels (called PV solar panels) are made from solar cells encased in a special type of toughened glass. Silicon solar modules have been in the field for more than 50 years and perform quite predictably. These are guaranteed for 25 years of field life but the power yield drops about 0.6 per cent per year. One can use monocrystalline (made from a single crystal) or polycrystalline (made from multiple crystals) panels. Monocrystalline panels are a little more efficient but the cost per watt is almost the same.

Copper indium gallium diselenide (CIGS) panels may become a preferred type for commercial rooftop projects in another five years. These have the potential to deliver reasonable efficiencies at a lower cost than traditional crystalline panels. However, the cost per watt may not necessarily go down, only the panel size per watt will drop. Today solar panels (depending on the brand) are bankable, that is, banks will extend loan capital for their purchase.

How solar panels are installed on rooftop

Many solar system installers and owners have had good experiences with penetrating anchoring of panel structures if done scientifically and with care. Non-anchored installation systems are also possible but need careful design to withstand heavy winds. Such systems are designed to connect the solar power system to a roof using weights, rather than fasteners that must be anchored in the roof. Solar installation companies, often called integrators, can complete a small rooftop project in several weeks.

Before signing a contract with an integrator to install a solar system, consider the following issues:

Roof condition: If you have an old roof that needs significant maintenance or replacement, you may want to do that before installing the solar array.

Space availability: Solar power projects work best on flat roofs without obstructions.

Weight load: Some roofs are not designed to hold much additional weight. Ascertain the acceptable weight you can add to your roof before signing a contract.

Go solar!

When you have a rooftop PV solar plant, you will become a power manufacturer. In the long run, the cost of traditional fossil fuel electricity will increase, while the cost of solar electricity will decrease. It is still murky to determine as to when solar power will cost less than fossil fuel electricity but it may happen soon since fossil fuels are becoming more and more expensive and depleting at a fast pace. Based on the current prices and assuming that one takes advantage of the 80 per cent depreciation permitted on such investment in the first year, the cost of power per unit, kWh, from a well maintained solar plant will be less than Rs 8 per watt for plant of any capacity between 5 kW and 1 MW. (I will be able to further elaborate this for those who want to know.)

As the price of coal increases and the cost of building new coal and oil and nuclear power plants continues to climb, renewable energy alternatives like solar will become much more attractive to everyone. In any case, if the government and successive governments honour their commitment to pay for your solar energy fed into the grid at Rs 17, you have a profitable deal!

The author is ex-chairman, Electronics Commission, Government of India, and a former advisor to late Rajiv Gandhi

Electronics Bazaar, South Asia’s No.1 Electronics B2B magazine



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