IEA SHC Task 52: Solar Thermal’s Role in 2050 Energy Mix

Photo: Riccardo Battisti

After consulting with industry stakeholders about what is realistically possible and economically viable, the task members set boundary conditions for all simulations, namely a 20 to 50 % share of users who are connected to a district heating network or have their own solar thermal system installed at home and as little as 5 % waste of solar heat resources because of overheating in summer. The designs for assessing solar thermal potential consisted of single-family homes with stand-alone heating solutions and solar district heating with short-term storage.

The simulations were based on the techno-economic EnergyPLAN model developed and maintained by the Sustainable Energy Planning Research Group at Aalborg University. This model simulates national energy networks – such as in the power, transport, and heating and cooling sector and in industry – by the hour. According to http://www.EnergyPlan.eu, the freeware “has been used in hundreds of scientific publications and reports” all over the globe.

The baseline year was 2010; the reference case was a business-as-usual (BAU) forecast, which expects that between 2010 and 2050, solar thermal will not make a larger contribution than it already has (see the chart below).

Next up were scenarios including more favourable developments, from reduced heat demand because of retrofits (Heat savings) and the expansion of the grid (District heating) to a high renewable share in heating and electricity (High RES).

Source: Aalborg University

The graph above shows the solar thermal potential of the four countries, assuming an average penetration rate of 35 %, meaning 35 % of all buildings are connected to a solar thermal plant either located directly inside the building or available through a solar district heating network. The two scenarios favourable to solar thermal are Heat savings and District heating. Italy shows a significantly higher solar share in the latter, because of many existing district heating networks (which supply 70 % of all heat) and only very few baseload heat plants in operation, for example, to process waste energy. Denmark’s district heating share is high too (60 %), but the country has already seen the installation of many baseload waste-to-energy systems, which decreases flexibility and leaves little room for new solar thermal units.

In the Heat savings scenario, reduced heat demand in buildings will lead to a potentially greater contribution of solar thermal to both domestic hot water production and space heating. A broader deployment of networks in the District heating scenario will increase solar thermal use because of added options to store and distribute heat among consumers and more flexibility due to hybrid systems, for example, heat and power and heat pump combinations. In the High RES scenario, solar potential decreases because of a wider use of other heat sources such as geothermal, industrial waste heat and waste-to-energy.

The researchers underlined the importance of analysing the entire network system at once to capture developments across energy sectors. A scarce resource such as biomass will be in high demand in all energy markets in the future, increasing the relevance of solar thermal supply. The simulations have shown that installing the maximum available solar thermal potential could reduce biomass demand by up to 2 % overall – or by more if the focus is only on the heat and power industry.

Obviously, the solar penetration rate is inextricably linked with the total solar thermal potential of both individual and district heating. The possible solar thermal share ranges from 5 to 8 % in overall heat production, assuming the above-mentioned rate of 35 %. This share will increase to between 6 and 12 % at 50 % penetration and decrease to between 3 and 6 % at 20 %. Table 1 below indicates that the solar thermal share rises significantly in the Heat savings and District heating scenario, as does the installed collector area, but the total solar yield decreases because of lower demand in general, which requires less capacity to be installed.

	Germany		Austria		Italy		Denmark
Penetration*	20 %	50 %	20 %	50 %	20 %	50 %	20 %	50 %
2010 baseline	25 TWh 3 % 72 Mm²	60 TWh 7 % 175 Mm²	3 TWh 3 % 6 Mm²	7 TWh 8 % 16 Mm²	9 TWh 2 % 28 Mm²	24 TWh 6 % 69 Mm²	2 TWh 4 % 6 Mm²	5 TWh 10 % 14 Mm²
Heat savings 2050	15 TWh 4 % 44 Mm²	38 TWh 11 % 111 Mm²	2.5 TWh 6 % 6 Mm²	5.5 TWh 12 % 16 Mm²	8 TWh 4 % 23 Mm²	19 TWh 10 % 57 Mm²	1.5 TWh 3 % 4 Mm²	3 TWh 10 % 10 Mm²
District heating 2050	16 TWh 4 % 45 Mm²	40 TWh 11 % 111 Mm²	2.5 TWh 6 % 6 Mm²	6 TWh 12 % 16 Mm²	12 TWh 6 % 32 Mm²	25 TWh 12 % 78 Mm²	1.5 TWh 4 % 4 Mm²	3 TWh 12 % 10 Mm²
High RES 2050	13 TWh 4 % 37 Mm²	26 TWh 7 % 77 Mm²	2 TWh 5 % 6 Mm²	4 TWh 8 % 11 Mm²	11 TWh 6 % 28 Mm²	20 TWh 11 % 59 Mm²	1.5 TWh 4 % 4 Mm²	3 TWh 11 % 9 Mm²

Source: Aalborg University

 

Annual solar yield [kWh/m²]	Germany	Austria	Italy	Denmark
Individual heating	330	402	451	314
District heating	410	500	560	390

Source: Aalborg University

Websites of organisations mentioned in this article:
Task 52: http://task52.iea-shc.org/
Aalborg University: http://www.en.aau.dk
http://www.EnergyPLAN.eu