ENERGY FACTOR
SOLAR PV
SOLAR THERMAL
HEAT PUMPS
Additional plumbing required?
No
Yes
Yes
Retrofit to standard electric geysers?
Yes
Some designs can be retrofitted
Requires modifications
Noise?
No noise
Some noise (pumped systems)
Yes
Works during power failures?
Yes
Yes, for some (thermosiphon and pumped with solar PV)
No
Frost issues?
No
Yes (requires more expensive indirect system)
Reduced performance
Winter performance
Good
Not as good
Not as good
Overheating and water wastage?
No
Yes (stresses system and wastes water)
No
Aesthetics
Good
Not good for thermosiphon and requires stronger roof
Good (if hidden)
Maintenance required?
No
Yes (every few years)
Yes (annual)
Price
Comparable or less expensive than pumped solar thermal. Less expensive than heat pumps
Thermosiphon solar thermal systems are cheapest
Most expensive
Lifetime
30+ years
10 to 15 years
10 to 15 years
Roof space required
Two to three times more than solar thermal
2-4m²
None (but requires space for system)
Lifetime cost of energy
Best
Good
Worst (continue paying for electricity)
Section 12B tax benefit for “build to rent” property developers?
Yes
No
No
Heat pumps require maintenance and have ongoing electricity costs, while gas is expensive and fluctuates with changes in oil price. There are several other considerations to take heed of when deciding between the different water heating options. The table above compares several factors for the three most popular alternative water heating options: solar PV, solar thermal and heat pumps. Based on cost and all the considerations in the above table, solar PV and solar thermal are clearly preferable to heat pumps. There are some situations where heat pumps are the only practical option – for example, multi-storey buildings with insufficient roof space for solar PV (carports can help overcome this issue). * Dr Sean Moolman is from PowerOptimal
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If upfront cost is the overriding consideration, thermosiphon systems (the systems with the tank on the roof ) are the lowest initial cost option. However, when system lifetime and maintenance cost are included in the calculations (when looking at lifetime cost), solar PV is the most cost effective. When taking winter performance, noise, power failures, maintenance requirements, overheating and water wastage into consideration, solar PV is advantageous to solar thermal. Whichever option is preferable to individual circumstances, it has never made more financial and environmental sense than now to switch to an alternative method of heating water.
