Solar Energy Perspectives - IEA

Chapter 4: Buildings
larger the collector area must be, but the cost-effectiveness of the marginal square metre of
collector area decreases as more energy must be dumped when it is not needed. Heat demand
for water is less variable during the year, although demand for hot water for body comfort
increases in winter while more heat is required to warm the mains water. All in all, combisystems,
even with large hot water storage tanks (1 000 m 2 to 3 000 m 2 ) usually cover only 15%
to 30% of the total demand for space and water heating – the higher range probably being
reached more easily in multi-family dwellings, thanks to some mutualisation of the demand.
Solar collector yield
Domestic hot water demand
Space heating demand
Cooling demand
Figure 4.5 Yearly pattern of solar yield versus demand for space
and water heating and cooling
Source: ESTIF, 2007.
Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Key point
The solar resource is minimal when the demand for space heating is maximal.
Worldwide, there are hundreds of examples of high-temperature seasonal storage, usually
with hot water tanks in the basement. One such example is the solar district heating system
developed at Friedrichshafen in Germany 15 years ago. Together with 2 700 m 2 of solar
collectors, it uses a long-term heat storage unit (designed as a cylindrical reinforced concrete
tank with a top and bottom having the form of truncated cones) entirely buried in the ground.
The system provides about half the yearly need for water and space heating of 570 housing
units, at a cost of USD 63/MWh.
A more recent example is the Drake Landing Solar Community development in Okotoks,
Alberta, Canada: 52 efficient houses, each with its own solar water heater, powered by solar
collectors on the garage roofs. Solar heated water is pumped into 144 boreholes, 37 m deep,
thus heating the ground to up to 90°C. During the winter, the hot water flows from the storage
field to the houses through a distribution network, where it exchanges heat with air blown in
the house (Figure 4.6). In this example, 90% of the space heating loads and 60% of the water
heating loads are met by the sun.
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© OECD/IEA, 2011