Solar Energy Perspectives - IEA

Solar Energy Perspectives: Buildings
Figure 4.6 Solar seasonal storage and district loop, Drake Landing Solar Community
Detached garages with
solar collectors on the roofs
Two-storey
single-family homes
Solar collector loop
Energy Centre
with short-term
thermal
storage tanks
District heating loop
(below grade) connects
to homes in community
Borehole seasonal
thermal storage
(long-term)
Source: Minister of Natural Resources, Canada (NRCan).
Key point
Comprehensive storage systems for solar energy make heating more affordable for a district.
Inter-seasonal ground storage, when not used in combination with heat pumps, seems more
appropriate for large installations in district heating and multifamily dwellings. This results
from the ratio of the surface area of the “envelope” of the storage over its volume, which
decreases as the volume gets bigger. Heat losses are a function of the area of the envelope,
and of the temperature. As heat is exchanged with the immediate ground environment and
spread over a larger volume, its temperature decreases. To minimise heat losses one must
either minimise the surface area through which heat exchanges take place – as in large
storage systems for district heating – or reduce the temperature to levels that make it usable
only with heat pumps.
Solar-assisted district heating is spreading in countries where district heating already provides
a large proportion of the space heating demand, such as Sweden, Denmark and other central
and Northern European countries. Despite the lower solar resource, the cost is only about
USD 56/MWh on average, as the solar fields are installed on existing district heating networks.
Other countries have ambitious scenarios with high penetration of active solar space heating
technologies (e.g. the “full R&D and policy” scenario of the European Solar Thermal Industry
Federation. see Dias, 2011). These largely rely on the development of affordable, efficient and
compact thermo-chemical storage systems for individual housing units.
Solar water heating and space-heating systems increase fourfold between the Baseline and
BLUE Map Scenarios – mostly based on SWH. One variant of the BLUE Map Scenario, the
BLUE Solar Thermal, assumes that low-cost compact thermal storage is available by 2020 and
that system costs come down rapidly in the short term. Active solar thermal technologies thus
become the dominant technology in 2050 for space and water heating. The BLUE Heat
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© OECD/IEA, 2011