Solar generation systems can now produce electricity and store it for hours, using solar tower power without any need for batteries.
The massive expansion of solar panels on rooftops and solar farms across the world has captured the headlines, but the other established way of generating electricity from sunlight – concentrated solar power (CSP), or solar tower power – is also making great strides.
For a long time, using mirrors to concentrate the sun’s rays to heat molten salt and produce superheated steam to drive a generator’s turbines was thought to be a more promising technology than photovoltaic panels (PV), because it was originally cheaper.
But as the price of the panels has dropped dramatically in the last five years, CSP fell out of favour, although some countries continued to support its development.
Now the cost of CSP is also falling. But it has another major advantage: unlike the panels, it can go on producing power long after the sun has set, and can store it for up to 15 hours, for use when it’s needed.
Dubai, the largest city in the United Arab Emirates, where sunshine is almost guaranteed, is a fan of both solar technologies. It has just announced that electricity from a proposed 200 megawatt CSP project, to be completed in 2021, will be priced at 9.45 cents per kilowatt hour – 40% below the previous world record.
The cost is well above the 3 cents per kilowatt hour of the cheapest solar PV, but has the advantage of running for 15 hours at full power during the night, doing away with the need for any fossil fuels for back-up generation.
CSP has many variations, all ways of concentrating solar power onto liquid to heat it and so create steam for driving turbines. The two main types use parabolic troughs or mirrors to aim the sunlight at a central tower. Troughs have been more widely used so far, but towers are gaining fast – the latest scheme, Dubai’s, uses a tower.
Current technology for storage uses sodium nitrate and potassium nitrate together heated to 566°C to store the heat in a large tank until it is needed. It is then fed gradually through a heat exchanger to produce superheated steam for the turbines.
“The UAE’s focus on renewable energy generation has led to a drop in prices worldwide and has lowered the price of solar and wind power bids in Europe and the Middle East”
Dubai Electricity and Water Authority (Dewa) has ambitious plans to reach 1000 megawatts of CSP as part of plans to boost capacity for its solar park from 1000 MW by 2020 to 5,000 MW by 2030. The first 13 MW of PV came on line in 2013. The city aims to have 7% of clean energy by 2020, 25% by 2030 and 75% by 2050.
There were a number of bids for Dubai’s CSP projects. Consortiums included Saudi Arabia’s Acwa Power and China’s Shanghai Electric, followed by the Abu Dhabi clean energy company Masdar, with partners EDF of France and Abengoa of Spain.
.Saeed Al Tayer, the managing director and chief executive of Dewa, claimed: “The UAE’s focus on renewable energy generation has led to a drop in prices worldwide and has lowered the price of solar and wind power bids in Europe and the Middle East.”
Paddy Padmanathan, chief executive of Acwa Power, said it was exciting to see CSP technology with storage “offering dispatchable solar energy – day and night, competing with fossil fuel-based alternatives.” Several of the companies involved said they would continue to compete for future projects.
The United States was one of the pioneers of CSP, and many sunny countries in the Middle East and Africa are now developing projects, including South Africa, but, as with many other renewable projects, China is hoping to take a lead.
China plans to build 1.3 GW of CSP capacity by 2018 in a first batch of 20 CSP projects which includes nine solar towers, seven parabolic trough plants and four linear Fresnel plants (using a form of lens which also concentrates solar power).
So far the Chinese have yet to decide which is the most promising technology.