6. Solar thermal energy (How to capture solar heat?)
To date, most solar thermal energy systems are combined with short-term heat storage. This is a well-insulated water tank for service water and / or heating water. The hot water from the sunlit roof is passed through the tank and releases its heat. Such systems are often designed to save the heat requirement of a few days.
A plant for service water typically contributes about 60% of the annual heat requirement, a combination plant for hot water and heating about 30%.
But how can you heat completely CO2-neutraly?
The energetically ideal solution is a combination of solar thermal energy, photovoltaic, heat pump and downhole heat exchanger systems. The heat pump requires electricity that can be generated with a photovoltaic system. If the water is already preheated, the heat pump needs less power.
Excess heat, which the solar panels produce in summer and autumn, can ideally be transferred via the downhole heat exchanger and stored underground, so that less heat is consumed by the heat pump in winter.
A hybrid collector (or "PVT collector" of photovoltaic-thermal) combines solar cells to generate electricity with an underlying collector. In a hybrid module the collector harvests a little less heat. However, in return the electricity yield can be increased by this combination. The reason: the more solar cells heat up, the lower their electricity yield. The collector dissipates the heat in summer and thus cools the photocells.
To date, hybrid collectors are not used very often, yet. In Switzerland, an innovative use of hybrid collectors for an office building is being tested (Mojic et al., 2018). In combination with a thermally active ground plate that acts as heat storage, the hybrid collectors should not only be used for heating, but also for cooling. In the summer month, when the ground plate heats up too much during the day, the collector can release heat into the cooler air during the night. Solar thermal energy thus becomes an important building block within a well thought-out overall concept.
Literature and Links:
- DIW (2016): „Eigenversorgung mit Solarstrom“ – ein Treiber der Energiewende? DIW Roundup 89. Download: https://www.diw.de/sixcms/detail.php?id=diw_01.c.523544.de
- Paschotta, Rüdiger (2018): Photovoltaisch-thermischer Solarkollektor. Online in RP-Energie-Lexikon: https://www.energie-lexikon.info/photovoltaisch_thermischer_solarkollektor.html
- Mojic, Igor et al. (2018): Deckung des Kälte- und Wärmebedarfs mit thermischer Aktivierung der Fundamentplatte und PVT Kollektoren. Online: http://www.spf.ch/fileadmin/daten/publ/OP-I-3-1_1148_Mojic_et_al._Deckung_des_K%C3%A4lte_und_W%C3%A4rmebedarfs.pdf
- Zenhäusern, Daniel et al. (2017): PVT Wrap-Up. Energiesysteme mit Photovoltaisch-Thermischen Solarkollektoren. Online: http://www.spf.ch/fileadmin/daten/publ/PVT_WrapUp_Final_mit_FR_Zfsg.PDF
- Zenhäusern, Daniel et al. (2017): PVT Wrap-Up. Energy systems with photovoltaic-thermal solar collectors. Online: http://www.spf.ch/fileadmin/daten/publ/PVT_WrapUp_Final_EN.pdf
The panel for download as pdf (559 KB)