Solar energy collection and storage - Solar Energy Sciences and Engineering Applications - page 134

Table 4.4.1 Large-scale interseasonal solar heating systems with output > 4MW th (adapted from
Dalenback, 2010 ).

Collector Nominal Power In operation

Area (m 2 ) Output MW th since 1996 Location Country

18,300 12.8 1996 Marstal Denmark

10,700 7.5 2009 Broager Denmark

10,073 7.0 2009 Gram Denmark

10,000 7.0 2000 Kungälv Sweden

8,012 5.6 2007 Braedstrup Denmark

8,012 5.6 2008 Strandby Denmark

7,300 8.1 2003 Grailsheim Germany

7,284 5.1 2009 Torring Denmark

6,000 4.2 2008 Soenderberg Denmark

5,670 4.0 1997 Neckarsulm Germany

• latent heat storage material must not corrode or react with heat-transfer surfaces

or solar energy collector materials.

• supercooling behaviour of the latent heat storage material on solidification should

usually be limited and consistent over numerous freeze/thaw cycles.

• toxicity and flammability must satisfy regulating requirements

In a thermochemical energy storage system thermal energy separates chemical bonds
reversibly. The displacement of the chemical bond energy requires absorbs heat energy
resulting in thermal energy storage. The chemical products a useful thermochemical
heat storage reaction are unreactive at ambient temperatures. As temperatures increase
the chemical bonds are reestablished forming the original chemical with the release of
stored heat. Highly endothermic chemical reactions can achieve very dense energy
storage per unit material mass. The energy remains stored until it is recovered by an
exothermic reaction.

4.4.5 Analytical representation of thermosyphon
solar energy water heater
In a thermosyphon solar water heater a hot water store is located above and connected
by dawncomer and upriser pipes to the solar collector. The height difference between
the collector and store inhibits nocturnal reverse circulation (Norton and Probert,
1983).
A finite difference transient heat transfer and momentum analysis in which the
thermal capacitances of both the collector plate and the cover are implicit can be
applied to the liquid (i.e., water) circulating through the collector, upriser, hot water
store, and downcomer of a thermosyphon loop (Hobson and Norton, 1988). All fluid
properties and heat-transfer coefficients can be assumed to be temperature-dependent
based on either the ambient or mean component temperatures. These coefficients can
be updated at each timestep in a numerical calculation. An appropriate store model
includes a simulation of buoyancy-induced mixing between stratified layers that occurs