Power plant technology could cut the cost of solar power
UK researchers are helping design a power plant that could make generating heat and electricity using solar thermal energy cheaper.
Engineers from Cranfield University are involved in an EU-funded project to build a €22m (£19m) facility in Egypt that will provide electricity, heat and desalinated water to a new university campus.
The technology planned for the site could help to cut the cost of concentrated solar power (CSP) — which generates electricity from steam turbines using heat from the sun — by around five per cent for construction and five to 10 per cent for operation.
’If you need heating and cooling, or if you need to store energy for later use, solar thermal has distinct advantages’
Dr Chris Sansom, Cranfield University
Research from the project could also help provide a clearer price comparison between CSP and photovoltaics (PV), at a time when plans for the world’s largest solar farm have recently been altered in favour of more PV for economic reasons.
The new system operates at much higher temperatures than existing models of CSP generation, using a single tank of molten salts to store the sun’s heat and use it to create steam, instead of two.
Cranfield’s engineers, led by Dr Chris Sansom (pictured above), will also help to design parabolic optical reflectors that require less glass than conventional designs and nano-devices for harvesting waste heat energy from the plant.
In conventional CSP plants, the hot salts would be stored in a storage tank and then pumped through a system to create steam for the turbines before reaching a second cold-storage tank. The new facility will instead feature a single tank with a steam-generating chamber inside it.
‘The advantage of the single tank is one of reduced construction costs (saving one tank in comparison with the previous two-tank designs) and reduced operating costs (lower maintenance costs and only 30–40 per cent of the molten salts costs),’ said Sansom.
‘The reason that two-tank systems have been used thus far in large-scale solar plants is because they have typically operated at lower temperatures with oil as the storage medium.’
The site, part of the University of Science and Technology in Borg-el-Arab, will feature 10,000m2 of parabolic troughs, each around 12 by 5m in area, to capture the sun’s energy and heat up a pipeline of molten sodium nitrate and potassium nitrate to a temperature of around 550°C.
Part of the project will involve testing troughs made with glass less than 3mm thick, which is cheaper to manufacture and requires less structural support than traditional 5mm-thick glass reflectors but may deform more under desert conditions.
The Cranfield team is also developing nano-scale thermoelectric converters (TECs) to harvest waste heat from surfaces in the power plant. These devices create a voltage from two adjoining materials with different temperatures.
The problem with TECs is that increasing their electrical conductivity increases their thermal conductivity and so their electrical resistance, making it very difficult to improve their efficiency, said Sansom.
‘However, using nano-scale techniques we can decouple the two properties. We can change the structure of the material to decrease the thermal conductivity without affecting the electrical conductivity.’
CSP has been in commercial use since the 1980s but has recently begun a rapid expansion, with more than 18.5GW of generation capacity currently under development, according to GM Research.
However, the technology is facing competition from the falling price of PV. Solar Millennium recently altered its plans to build a 1GW solar farm — the world’s largest — in California, replacing the first 500MW of CSP capacity with PV.
Dr Christoph Wolff, the firm’s chief executive officer, said in a statement: ‘Whereas the electricity from solar-thermal power plants was more economic only less than two years ago, this relation has changed completely due to the sharp drop in PV module prices, particularly from Asia.’
But he stressed there was still a future for CSP in the energy mix, a view backed by the Cranfield team.
‘If you want to generate electricity and supply the grid, PV looks good,’ said Sansom. ‘If you need heating and cooling, or if you need to store energy for later use, solar thermal has distinct advantages. It is much easier to store heat.’