distribution of plants related to year of
their commission is shown in figure 1.
The current developments include
mainly large-scale plants with diurnal
storage for residential heating but also
industries and heat-driven cooling applications in Southern Europe. There is
continued interest in developing plants
with seasonal storage, primarily in
Denmark and Germany.
Large-scale centralized solar
heating systems were introduced
in Europe in the late 1970s.
The majority of plants have been in
operation for 10 years or less. Although
the number of new plants commissioned decreased from 2003 and 2005,
there seems to be an increased interest
the past two years, with eight new
plants commissioned in 2006 and 2007.
Among European countries, Sweden
is still the leader in large-scale solar
heating with a total of 22 plants in
operation as of October 2007. Eight
plants – the first dating to 1979 – have
closed after 10-20 years of operation
and evaluation. (Many of these were
demonstration plants that had served
their purpose and would have required
considerable maintenance to operate
another 10-20 years.)
Applications and Technologies
The majority of Europe’s large-scale
solar heating plants supply heat to residential buildings. The largest plants
(minimum 2 MWth) are listed in table 1.
Two-thirds of these plants serve
existing buildings, especially in Sweden,
Denmark and Austria. Most solar plants
in Sweden and Austria are built in connection to wood fuel-fired heating plants.
Nonresidential plants include those
installed in industries and commercial
buildings.
The relation between what the total
load is and what portion of the load is
supplied via solar thermal energy relative
to the total load is often called ‘solar
fraction.’ In principle, large systems are
designed to meet ( 1) the typical summer
load (k W, MW) with a solar fraction of
about 5 percent, depending on the load
Table 1. Centralized Solar Heating Plants (minimum 2 MWth) in the European Union, October 2007.
Plant, Year in Total Area of Collectors Nominal Power Collector
Operation, Country Collectors (Capacity) Placement
sq m (sq ft) MWth
18,300 (196,980) 12.8
10,000 (107,639) 7.0
8,000 (86,111) 5. 6
7,500 (80,729) 5. 2
5,600 ( 60,278) 3. 9
5,500 ( 59,202) 3. 8
5,470 ( 58,879) 3. 8
5,470 ( 58,879) 3. 8
5,000 ( 53,820) 3. 5
4,900 ( 52,743) 3. 4
4,050 ( 43,594) 2. 8
3,575 ( 38,481) 2. 5
3,040 ( 32,722) 2. 1
3,000 ( 32,292) 2. 1
2,900 ( 31,215) 2.0
2,900 ( 31,215) 2.0
Source: Jan-Olof Dalenbäck.
Marstal, 1996, Denmark
Kungälv, 2000, Sweden
Braedstrup, 2007, Denmark
Nykvarn, 1984, Sweden
Graz (AEVG), 2006, Austria
Falkenberg, 1989, Sweden
Neckarsulm, 1997, Germany
Crailsheim, 2003, Germany
Ulsted, 2006, Denmark
AErøskøping, 1998, Denmark
Friedrichshafen, 1996, Germany
Rise, 2001, Denmark
Ry, 1988, Denmark
Hamburg, 1996, Germany
Schalkwijk, 2002, Netherlands
Munich, 2007, Germany
Ground
Ground
Ground
Ground
Rooftops
Ground
Rooftops
Rooftops
Ground
Ground
Rooftops
Ground
Ground
Rooftops
Rooftops
Rooftops
type; ( 2) the typical daily summer load
(MWh, GWh) with diurnal storage with a
solar fraction of 5 percent to 20 percent;
or ( 3) a larger part of the load using seasonal storage with a much higher solar
fraction of 50 percent to 80 percent.
The majority of European centralized
solar heating plants are designed to cover
the summer heat load – hot water and
heat distribution losses – using diurnal
water storages, but 20 plants are equipped
with seasonal storage and cover a larger
part of the load. The seasonal storages
comprise water in insulated tanks (above
or in ground) in 10 plants, the ground
itself in seven, aquifers in two and a
combination of ground and water in one
plant. Nine plants are designed to cover
the summer cooling load in heat-driven
cooling applications.
Typical operating temperatures
range from 30 degrees C (86 degrees F)
to around 100 C (212 F) for water storage.
The volume of seasonal storage in these
plants varies. In Germany, for example,
the Neckarsulm plant uses 60,000 cu m
( 15. 9 million gal) of in-ground storage
with a large number of U-pipes in boreholes; the Friedrichshafen and Hamburg
plants use buried water tanks storing
12,000 cu m ( 3. 17 million gal) and 5,000
cu m ( 1. 32 million gal), respectively. In
Denmark, the Rise plant stores 4,000 cu m
( 1.06 million gal) in an above-ground tank.
One of the earliest Swedish systems, the
Lyckebo plant that operated from 1983 to
2001, was connected to a 100,000 cu m
( 26. 42 million gal) water-filled rock cavern.
Most of Europe’s solar heating plants
have roof-integrated or roof-mounted
solar collectors, while 18 plants in Sweden
and Denmark have ground-mounted
collector arrays. More than 80 percent of
the plants are equipped with flat-plate
collectors, mostly large-module collector
designs. In a couple of cases in Sweden
and Germany, roof-mounted collectors
are designed as more or less complete
roof modules. Most plants have pressurized collector systems with an antifreeze
mixture – usually glycol and water – while
four plants in the Netherlands have
drain-back collector systems.
District Heating
In Sweden, the large-scale solar heating plants are used by district heating
systems and developers, mainly for existing
developments using both ground-mounted
collector arrays and roof-integrated or
mounted collectors. The oldest plant still
in operation in Europe is in Nykvarn,
Sweden, and dates from 1984. Recent
developments include decentralized solar
systems connected to the primary district
heating network in the city of Malmö.
The newest system, built by Kungälv
Energi AB, is a 10,000-sq-m (107,639-sq-ft)
ground-mounted collector array as a
complement to an existing wood chip-
