Here comes the sun

 
Last Updated: Sunday 28 June 2015

Here comes the sun

India has had mixed results with its solar programme. The government is now gearing up to launch several mega schemes to harness this abundant source. The solar mission aims to do exactly that. Industry has also shown interest in tapping this energy source of the future. Technology and financing, though, remain question marks. How can India realize its solar dream?

Picture thousands of solar reflectors, spread over parts of the Great Indian Thar Desert, glistening under the sun, quietly and efficiently generating emission-free, green electricity, at competitive costs. Solar thermal power plants, also called concentrating solar power (csp) generating systems, can make this a reality.

Details near the dark central region of a planet-sized sunspot on the surface of the Sun
Down to Earth
Photo SST, ROYAL SWEDISH ACADEMY OF SCIENCES
The potential is unlimited. Covering just one per cent of the world's deserts with csp systems would generate more energy than the current global energy demands.For India the potential stands at six million terawatt hours (tWh) per year. In 2006-07 India generated 662.5 tWh.

A square piece of land, 55 kilometres each side, in the empty desert, is enough to meet India's current energy demand.

With more than 300 sunny days each year, large parts of Rajasthan and Gujarat can produce 6-6.4 kilowatts per square metre. Sparsely populated, these areas are ideal for renewable energy. This potential is yet to be realized.

No commercial csp system operates in the country. To induce projects, the Union Ministry of New and Renewable Energy (mnre) announced in January 2008 a generation-based incentive scheme for solar thermal and solar photovoltaic (pv) ventures. The incentive for generating one unit of electricity from solar thermal is fixed at Rs 10. By June 2008, the government had received applications to set up 500 megawatts (mw) of solar thermal plants. "Companies are coming up with offers of huge capacity of 50 mw and more, but we cannot sanction them without verifying if they would be able to deliver," said an mnre official.

The scheme has a number of limitations. The total installed capacity under the scheme (combined for solar thermal and solar pv) is limited to 50 mw for the duration of the 11th five-year plan (2007-2012). Each project developer is limited to a maximum of 5 mw and each state is limited to a maximum of 10 mw. "The cap of 50 mw is because of unstable grids and solar systems deficient in producing peaking power, which is generally needed during the evening hours," said B Bhargava, senior director (photovoltaics) mnre.

This may change. Industry sources revealed the government was considering increasing the overall cap to 1,000 mw. Till now, only one 2- mw plant has been sanctioned under the scheme in West Bengal; construction is yet to start.

Mirror mirror on the wall...
In a solar thermal power plant, mirrors are made to concentrate sunlight trapped in a pipeline to heat oil, molten salts or other chemicals which can trap heat for a longer duration of time. This heat is used to generate steam in a boiler that runs a turbine to produce electricity. csp technologies vary in how they concentrate sunlight. For example, in parabolic trough systems, parabolic trough-shaped mirror reflectors concentrate sunlight on thermally efficient receiver tubes placed in the trough's focal line.A heat transfer fluid is circulated through the receiver tubes and heated to temperatures up to 400C. The fluid passes its heat to other working fluid, typically water or steam, through a series of heat exchangers, which is further used to drive a conventional turbine generator. Other systems include the power tower system and the parabolic dish system.

csp has higher operating efficiency and lower cost compared to pv. While even the most efficient solar pv can generate about 20 mw per sq km (km2), for solar thermal generation it is about 35 mw/km2. csp also has major advantages in energy storage, a critical component of technologies harnessing intermittent energy sources like wind and solar. The storage allows for higher plant capacity factors, compensation for vagaries in solar radiation, increased ability of the plant to provide firm capacity and consequently greater carbon dioxide (co2) emissions reductions.

These assume greater importance in India, given its weak inadequate grid and generation capacity, translating to limited grid back-up capability. csp systems can be easily integrated into conventional power plants as they utilize the same generator as most other fossil fuel based thermal power plants.

The exact cost of csp systems is currently a grey area, primarily because of a lack of standardization as the technology is still developing. Apart from technology, the plants vary greatly in specifications like storage capacity, efficiency of solar field, and generation capacity of the plant. However, qualified cost forecasts put down the capital costs of a parabolic trough plant--with 12 hours of storage capacity, no fossil fuel back-up and a nearly 55 per cent capacity factor--at us $ 4,816 per kW (total plant capacity of 100 mw) in 2004, and us $ 3,220 per kW (total plant capacity 400 mw) in 2020. The respective costs of electricity are us 10.37 cents and us 6.21 cents per unit. These costs are far lower than even the most efficient solar pv systems on per watt basis. csp plants present the possibility of a high local content during construction and operation and maintenance, unlike solar pv where silicon--the major cost component--has to be imported. Additionally, carbon credits can serve as an income stream to reduce the cost.

Over the past two years, rising oil prices have brought csp systems into sharp relief. Countries such as the us and Spain have taken the lead; Australia, Israel, Morocco and even the oil-rich countries of Iran and Algeria have shown progress. In Spain, construction of the world's biggest solar thermal power stations--Andasol 1 and 2--are almost complete.

By early 2008, as much as 4,000 mw of solar thermal was in the pipeline in Spain and five more plants are underway. The German company Solar Millennium AG and the Spanish plant builder Cobra is building Andasol. They are working on liquid salt, which can be heated to 500oC--oil can be heated to only 400oC. The plants would use liquid salt to store heat during the day to generate electricity at night.

India stumbles
Though India was one of the first industrializing countries to show interest in csp technology, it failed to keep up the momentum. As early as 1988, a 50-kW parabolic trough technology pilot project provided by the German company man Technolgie GmbH and Co, was established at the government-run Solar Energy Centre campus in Gwalpahri near Delhi. Within two years the glass casing that maintains the vacuum around the pipelines that trap the heat started cracking due to excess heat rendering the plant inefficient. "Being imported, damaged parts could not be replaced," said Prakash, caretaker of the facility.

In 1994 a feasibility report was prepared for a fossil fuel-solar hybrid project in Mathania, near Jodhpur in Rajasthan. India was the first of the four countries to be given the Global Environment Facility (gef) grant for this project of us $ 49 million.

Despite arranging for complete finance for the project, it was abandoned due to rising prices of naphtha (the primary fuel), limited guarantees by private contractors for working and spare parts, and lack of commitment to lay down a gas pipeline to substitute naphtha with natural gas as primary fuel.

In 1995, a Solar Energy Enterprise Zone (seez) was also envisioned in Rajasthan and three power purchase agreements were signed with aesdp, Sun Source Ltd and Energen International Ltd for a total solar generation capacity of 300 mw. None of projects of the seez ever took off, owing to lack of finances.

The mnre scheme has led to renewed interest in csp. The Rajasthan Electricity Regulatory Commission had invited expressions of interest (eoi) for solar pv and thermal power plants in February 2008. eoi to setup 900 mw has been received so far.

"Companies such as India Bulls and Essar have responded with an eoi. Applicants were required to pay Rs 25,000 per mw for registration," said A K Patni, in charge of the solar cell at the Rajasthan Renewable Energy Corporation Ltd.

mnre recently proposed another scheme for installing 20,000 mw of electricity from solar thermal and pv by 2020. But the incentive pattern it proposed is so high that the cost to the exchequer would be about Rs 20,000 crore per year in subsidy alone.

Many in the government believe it is not viable at this stage and that the ministry will find it impossible to fund such a scheme.

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