For many people solar energy means PV solar electricity. But, although that is expanding, it’s still only around 50GW of grid linked capacity globally and, by contrast, the perhaps less glamorous but at present far cheaper technology of solar thermal heat collection is well ahead. In fact, globally, there is now more solar heat capacity in place than wind power capacity, and its still expanding. It could account for around one-sixth of the world’s total low-temperature heating and cooling needs by 2050, according to a roadmap by the International Energy Agency (IEA). This would eliminate some 800 megatonnes of carbon dioxide (CO2) emissions per year, or more than Germany’s total CO2 emissions in 2009. By 2010 there was 195GW (th) installed global (118GW of it in China), rising to 245 GW by 2011.

Paolo Frankl, Head of IEA’s Renewable Energy Division, commented: ‘Given that global energy demand for heat represents almost half of the world’s final energy use – more than the combined global demand for electricity and transport – solar heat can make a significant contribution in both tackling climate change and strengthening energy security, The IEA’s Solar Heating and Cooling Roadmap outlines how best to advance the global uptake of solar heating and cooling (SHC) technologies, which, it notes, involve very low levels of greenhouse-gas emissions. Some SHC technologies, such as domestic hot water heaters, are already widely in use in some countries, but others, like large scale solar fired district heating, are just entering the wider deployment phase, while solar powered cooling is still at the development stage.

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Although SHC only makes a modest contribution to world energy demand at present, the roadmap envisages that, if governments and industry took concerted action, solar energy could annually produce more than 16% of total final energy use for low-temperature heat and nearly 17% for cooling by around 2050. This would correspond to a 25-fold increase in absolute terms of SHC technology deployment in the next four decades.

In addition to replacing fossil fuels that are directly burned to produce heat, solar heating technologies can also replace electricity used for heating water as well as individual rooms and buildings. This would be especially welcome in countries without gas infrastructure and lacking alternative heating fuels. South Africa is cited as an example of a country that would benefit, as electric water heating currently accounts for a third of average household (coal-based) power consumption there.

On top of this, the report notes that solar thermal cooling technology – in which the sun’s heat is used to power thermally driven absorption chillers or evaporation devices to cool air – can reduce the burden on electric grids at times of peak cooling demand by fully or partially replacing conventional electrically powered air conditioners in buildings. As climate change impacts, cooling is going to become a major issue around the world, not just in currently hot climates, and direct solar cooling has obvious attractions.

The roadmap also stresses the scope for expanding use of these technologies in industry. Often overlooked is several industry sectors’ significant energy demand for low- and medium-temperature heat in such processes as washing, drying agricultural products, pasteurisation and cooking. Those industrial processes offer enormous potential for solar heating technologies, which could supply up to 20% of total global industrial demand for low temperature heat by 2050.

However, the IEA say dedicated policy support is needed for these technologies to be used effectively, with a stable, long-term policy framework. http://www.iea.org/publications/freepublications/publication/name,28277,en.html

Given the variable availability of solar energy, a key area for development and support is storage. As I’ve mentioned before, there are many solar heat collector projects around the EU linked to district heating networks backed up by large heat stores, some of them being interseasonal stores, with Marstal’s 13.5MW solar array and linked heat store in Denmark being the largest so far. Some involve well insulated large tanks, or engineered thermal masses: for example for one of the first (at Burgdorf in Switzerland) see www.jenni.ch/ However Underground Thermal Energy Storage (UTES), with excess heat stored in the ground in the summer, to be extracted in the winter, may be cheaper. Some systems use deep vertical boreholes: for example see the Drake project in Canada www.dlsc.ca.

In the UK, the Centre for Alternative Technology pioneered solar heat storage , but in terms of UTES, much of the running is now being made by ICAX via their Interseasonal Heat Transfer system, which they aim to deploy in a wide range of construction projects, with ground storage of heating and cooling energy using insulated Thermal Banks for interseasonal thermal storage. For example ICAX worked together with REHAU on a pilot project for the Highways Agency at Toddington in which Interseasonal Heat Transfer was used to successfully capture solar heat energy from the road during the summer, store it in Thermal Banks in the ground and release it back to the road during the following winter to keep the road free of ice. REHAU pipework used for the solar capture, storage and heat distribution performed well during the trial, and REHAU has now formed an alliance with ICAX which will see it supply pipework for future IHT projects, typically in schools, prisons and commercial buildings where there is appropriate outside space for solar capture. www.icax.co.uk/

DECC seem to have woken up to the possibility of solar inputs to district heating networks, backed up by large heat stores, although at present the main focus in the heat storage field seems to be on its potential role in evening out demand on the electricity grid. DECC has launched a £3m competition in a drive to push heat storage technologies into commercial production. The Energy Technologies Institute is also investing £14m in Isentropic’s gravel tank heat storage tech, to see if it can reduce strain on electricity sub – stations. www.isentropic.co.uk/

I will be looking at energy storage generally in my next Blog, with heat storage being one option. Whatever the initial impetus for developing storage, solar heat technology could certainly benefit.