New Renewable Energy Technologies: Status and Prospects - Part 3 - Solar Power
The current worldwide installed solar capacity is about 40,000 MW of photovoltaic power and about 1,170 MW of concentrated solar power.
Solar power in the form of photo voltaic cells has been around for many years. Over the last few years, the cost of the cells themselves has dropped rapidly until it is now around $1000/kW. At this price, many manufacturers of solar cells have gone bankrupt. Solyndra defaulted on $500 million loan from US taxpayers. The Chinese company Suntech, the largest manufacturer in the world, went bankrupt with debts of $1.6 billion.
One disincentive to solar power is the large land area required. A 1000 MW Concentrated Solar Power facility requires 6000 acres of land, enough for about ten coal-fired plants with the same rated output. Producing 1000 MW from photovoltaics requires over 12,000 acres of land.
Since the costs are significantly higher than from conventional sources the development of solar power is driven entirely by subsidies. For residential installations the subsidies are often provided by "net metering" that offers the same price for imported and exported electricity. If the import and export are equal over a year, the consumer pays nothing. Yet the consumer exports electricity to the grid when it has little value - such as summer afternoons. In return, the consumer takes expensive electricity from the grid every night and, in particular on cold, cloudy winter days and nights. The consumer makes no contribution to the cost of the transmission and distribution system and the cost of the generation and fuel to provide his electricity when the sun is not shining.
Net metering finishes up being a subsidy from poor consumers who cannot afford solar panels to rich consumers who can. If everybody had solar panels and net metering the power industry would go broke, the power system would collapse and anarchy would prevail.
As a result of the subsidies, solar power is being developed in northern latitudes where there is less sunshine and where the skies are often cloudy. Typical capacity factors in desert areas are about 21% but in high latitudes they can be 10% or less. This leads to the absurd situation where Germany is the world's leading market for photovoltaic systems, with a total installed capacity of 17GW and a capacity factor of 10% in 2010. The German government is now reducing the very generous feed-in tariffs to slow the boom in the industry and reduce the 13bn paid out annually in incentives.
A major disadvantage of solar power in high latitudes is that system peak demands nearly always occur in winter evenings. This is when solar power output is very low or, more often, zero. As a result, solar power generates most energy when it is not needed and virtually none when it is needed. The only way of mitigating this problem would be to come up with a technology that can provide low-cost, efficient long-term storage for electricity. No such technology exists and none is on the horizon.
In Germany during 2010 the total amount of power generated by photovoltaics was just 12TWh, or 2% of the total output of 603TWh. If we assume an average PV system capacity of 13GW over the whole year, the theoretical output would have been 114TWh, giving a capacity factor of just 10.5%. A less efficient use of money would be hard to find.
In the UK, the government introduced the following feed-in tariffs in April 2010:
- - Less than 4kW - 43.3p/kWh in first year, declining to 18.8p over 10 years
- 4-10kW - 37.8p/kWh, reducing to 16.4p
- 10-50kW - 32.9p/kWh, reducing to 14.3p
- 50-100kW - 32.9p/kWh, reducing to 8.5p
- Greater than 100kW - 30.7p/kWh, reducing to 8.5p (but with different rates of decline depending on size and when installed)
Many householders are putting their money into such schemes, which offer payback periods of less than ten years and a considerably higher rate of return than offered by bank savings accounts.
In the UK, the capacity factor would not be above 9%, and could be significantly less. A 1000 MW nuclear station with a capacity factor of 90% would generate the same amount of energy as 10,000 MW of solar power. Based on these figures, the equivalent installation cost of a 1000 MW solar farm PV is about $20,000/kW. This is more than three times the cost of nuclear power-and even more when an allowance is made for backup generation! In reality the price is even higher then calculated above: home installers typically offer to install a 2.5 kW unit for £12,500. This works out at $8000/kW of nominal capacity. The equivalent price to nuclear is then more than $50,000/kW.
Solar power suffers from all the problems of wind because it generates no power at all in the night-time and a cloud going over the sun can drop the output by 60% in a very short period. So it too needs backup, system support and even more transmission capacity per unit of energy generated than wind power.
Future Developments in Solar Power
It is difficult to see how there can be any major improvements in the overall economics of solar power. It costs more than 3 times the cost of alternative methods of generation and even if the solar cells cost nothing, the cost of mounting, installation, cabling, inverters, transformers, grid connection and system support would still make the power too expensive to contemplate. However, as with wind, there is a niche market in isolated areas where the only power comes from small diesel generators.
 According to http://re.jrc.ec.europa.eu/pvgis/download/download.htm the capacity factor of UK solar cells at an optimum angle is 9.5%. Cells in Cyprus would have a capacity factor of 16.3%
 But even then, it is not equivalent because the solar units generate no power at night and during winter evenings when the system load is highest. At the very least, 1000 MW of backup generation is needed. This will be inefficient open cycle gas turbines as they are the only ones that are able to react sufficiently rapidly.