Solar water heating
Practical Action
Dedicated solar storage volume:
Flat plate:
30-45litres per m2 of collector absorber
Evacuated tube:
40-60litres per m2 of collector absorber per person
NB: The above are figures quoted for the UK and should be used in conjunction with solar
irradiance values for the region being considered.
(Capturing solar energy, 2009)
In the UK and other countries with a similar climate, the optimum solar water heating systems
are those which have been designed to supply 100% of the hot water demand experienced
during the summer. Due to the reduction in solar radiation available and increased hot water
demand likely during the winter months, it is usually assumed that systems are not best
designed to cover 100% of the winter load.
The following table has been extracted from the CIBSE Knowledge Series publication
‘Capturing Solar Energy’, which provides a guide to the hot water demand experienced in
different types of building.
Hot water demand (litres / person / day)
Type of Building Service Catering
Total
House
--
30-50
School/College
- Average
36
6
- Large
7 18
13
Hotel/Hostel
- Average
80 14
137
- Large
303 62
464
Office
- Average
3 10
8
- Large
10 33
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Table 5: Typical daily hot water demands (Capturing Solar Energy, 2009)
From this table, the hot water demand in a certain type of building can be approximated, i.e.
the daily hot water demand for a 4 person household can be calculated as:
4 people x 30 litres/person/day = 120 litres/day
The CIBSE Knowledge Series publication ‘Capturing Solar Energy’, 2009 contains tables and
explanations describing the steps involved in sizing the various components of a solar water
heating system, i.e. the collector, storage requirements and heat exchanger. Guidelines are
also listed approximating the hot water demands for different types of buildings.
Maintenance Tips
Although the complexity of a solar hot water heating installation can vary, encouraging
maintenance at regular intervals is advisable as this will help to reduce the occurrence of
significant failures over the life-cycle of the system. Below is a list of visual checks that could
be carried out on an annual basis:
Check the collector for any sediment accumulation and damage
Check any joints and connections for leaks or damage
Check the pressure levels of the working fluids
If the system contains a pump, check for any damage and that both the pump and the
associated valves are fully operational and for any damage
Check that any controls and temperature sensors are producing plausible results
Check any required safety notifications are still in tact
(Capturing Solar Energy, 2009)
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