Thermal solar – pros and cons
Unfortunately in winter when heat is most needed, there is little solar energy available. Vacuum and flat collector panels, including associated infrastructure (e.g. new hot water tanks) and installation, all mean that costs are high, although are reducing, like solar PV, as the technologies become more widespread. Evacuated tube systems are even more costly, but are commonly thought to be more suited to climates with lower levels of sunshine such as the UK. That said, varying grants, loans and incentives are available through UK government sources to encourage uptake.
It should be remembered that the primary objective of solar thermal systems is essentially to produce hot water, although the heated water can also be used in central heating systems (Woodford 2014).
Solar combi-boiler systems are available and these are designed to contribute to space heating systems. They are estimated to replace 15%-25% of the total energy used for all heating in the home (YouGen 2013). Considering and applying passive solar building design techniques can also assist the overall heating of domestic dwellings. Although there is little accurate information available, the payback time in Scotland is thought to be 10—15 years for solar thermal systems.
As with other renewables, storage to extend the generating period when the sun is not shining is one of the ‘cutting edge’ areas of research.
…heat is a great way to store energy, and solar thermal is a great way to produce it...The energy captured in a solar thermal system just hangs around as heat until it is released to finish its trip to the turbine and generator.”
(Janardhan and Fesmire 2011: 26)
The challenge is to store the heat in a substance that takes time to cool off. Salt is one of these substances and when heated to a molten state can retain its heat long after the sundown. In CSP systems this heat can be used to continue to generate steam to power turbines during the evening. The costs of such systems are very high at present and so research is on-going.