By Prabhu Deodhar, Life Fellow IEEE (USA) - 6 luglio 2011
Today, a large number of multi-MW solar photovoltaic (PV) power plants are being planned or installed in several countries all over the world. For several valid reasons stated below, many experts are convinced that installing such large centralized plants to utilize solar power is unnecessary, a wasteful investment and technologically inappropriate.
Given that solar energy is omnipresent, it can be harvested for power at any location. However in case of conventional power plants (hydro or thermal) they need to be developed adjacent to the energy source. This makes it necessary to transport power at great cost to places where it is required. On the contrary, with solar energy, we have a potential solution to generate power where it can be used; i.e. from mountain tops to the deep sea. Solar energy is therefore ideal for distributed power generation, thus saving line losses in transporting power at hazardously high voltages.
PV has the advantage of being truly modular. It can reach cost efficiencies with installations that are just a few kilowatts to 20 MW or even 200 MW. The cost per watt of solar power is the same as a 10 kW plant or 150 MW plant. In fact, the land cost and other soft costs make big plants more expensive.
In reality, all multi-MW plants are basically clusters of several 500-kW plants since solar inverter capacities are limited to about 500 kW and no more. Why not have one hundred 500 kW plants instead of one giant 50 MW plant?
The biggest problem with the multi-MW solar PV plant is that it loses 12-15 percent of expensive power as it passes through a series of power transformers. PV solar inverters generate power at 400V three-phase. In large plants, this power is first boosted to 66kV or more with several power transformers and then stepped down to 400V with another string of transformers to suit consumer requirements. In addition, there is a further transmission loss of 5-7 percent in the power grid. Why suffer an avoidable 20 percent loss of expensive solar power? In sharp contrast, smaller solar plants with close proximity to their users incur no energy loss during transmission.
A major limitation of solar PV is the large space occupied per kW. Land could be used more profitably rather than being covered with solar modules. Large solar plants, often built in remote areas, can create environmental issues or conflict with agricultural land. Issues related to security and maintenance of large centralized power plants also loom large.
Finally, the last problem relates to the way power flows in the power grid and its network analysis. Huge amounts of power is always circulating at a 66kV or 132kV level in the grid. Injecting even 200 MW of power is just a tiny fraction of that. So this small addition does not bring much relief to problems like blackouts and wide fluctuations at the “high impedance” end of the grid. Feeding power at 400V will actually alleviate grid-congestion more than monster plants that, more often than not, add to the already congested transmission and distribution system. Voltage swings occur due to high impedance of the grid. Feeding solar power locally at 400V will immediately reduce network impedance and deliver stable, clean power.
In countries like India, promoting local PV solar power generation is an ideal solution due to its common blackouts and voltage swings. This is a meaningful and technically sound alternative to a large-sized solar PV power plant. It is the most effective and profitable way to redress power problems like blackouts and voltage fluctuations at the consumer end.
Governments should encourage small solar plants below 500 kW by installing solar modules on unused terraces and roofs. This will inject 400V three-phase output directly into a substation at the local end of the grid. Injecting high quality solar power in this way will immediately improve the quality of local power during day time hours, avoiding blackouts and voltage fluctuations. Loss of power during the day is the most common problem faced by farmers and industrial consumers. In fact, this is when the substation transformers tend to fail due to overheating. Injecting solar power will allow these transformers to run without heating up, thereby extending their life.
Distributed solar power would actually create new opportunities for Small and Medium Enterprise (SME) investment in solar power generation. Besides generating solar power, this also generates local employment. SMEs then ensure that the plants are maintained with great care. The most important benefit is that of productivity gain wherein the community gets clean stable power during working hours for at least 300 days each year. Forty percent of Indians do not get electrical supply at all. Imagine what would happen to the quality of life of these 400 million people if we extend off-grid solar electricity in their towns and villages. The resultant productivity gain would change the face of Indian economy. The same holds true for every other region in the world.
The sun produces its own energy by the process of nuclear fusion. But all hazards connected with nuclear energy are taken care of by the sun and 'clean energy', free from all conceivable hazards and risks. It is showered on us free of cost. Since the energy input is free, the cost of solar PV is basically the capital appropriation cost. As new technologies emerge, the cost of solar PV is dropping fast. In the near future, it will match the ever-rising cost of power from fossil fuels. Many of us believe that solar energy will ultimately prevail as the world’s prime source of energy.
The information and views expressed in this article are those of the author and not necessarily those of RenewableEnergyWorld.com or the companies that advertise on its Web site and other publications.