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Solar – Assessing Potential within the Rural Area

Collector Surface Area

Starting from a calculated hot water heat requirement - taking into account the annual solar radiation, an average system efficiency and a desired solar fraction - the required solar collector area can be calculate as follows:

Where,

A_C        = Collector Surface Area (m²)
Q_HW    = Annual Hot Water Heat Requirement (kWh)
SF         = Solar Fraction
E_G        = Annual Solar Radiation (kWh/m²/year)
η_sys      = Average System Efficiency

For the initial sizing of a solar thermal system a desired solar fraction of 60 % can be assumed for temperate climates and 80% for tropical climates. Solar irradiation data is available from the European Commission Joint Research Centre (http://re.jrc.ec.europa.eu/pvgis/apps/radmonth.php?en=&europe). The average system efficiency for a glazed flat-plate solar collector system - taking into account collector, line and store losses – can be assumed to be 35 %.

Monthly Heat Generated by Solar Collector

The same equation rearranged can be used to estimate monthly heat generation by the solar collector:

Where,      

Q_SC  = Monthly Heat Generated by Solar Collector (kWh)
A_C     = Collector Surface Area (m²)
SF      = Solar Fraction
E_G      = Monthly Solar Radiation (kWh/m²/month)
η_sys    = Average System Efficiency

This provides a basic estimation which can be built upon using a solar thermal simulation program.

Simulation Programs for Solar Thermal Systems

A number of simulation programs for designing solar thermal systems are available, such as F-Chart, T*Sol, Polysun, GetSolar, RetScreen and Fresa. Demo versions are available for all the software’s and Retscreen is available as a full free download from www.retscreen.net .

 

References

• Planning and Installing Solar Thermal Systems: A Guide for Installers, Architects and Engineers. DGS (The German Solar Energy Society), Ecofys. 2005.
  
  
• Solar Thermal Systems: Successful Planning and Construction. Peuser F.A, Remmers K.H, Schnauss M. Solarpraxis. 2002.
  
  
• Solar Energy: Renewable Energy and the Environment. Foster R, Ghassemi M, Cota A. CRC Press. 2009.
  
  
• The Design and Sizing of Active Solar Thermal Systems. Reddy T.A. Oxford Science Publications. 1987.