[Question] Heat pump versus solar water heater in Cape Town

[smitty]

I'm looking into more efficient water heating for the Cape Town area.

There are a few things putting me off solar water heating, namely the months of May, June, July and August. Cloudy skies mean that the solar radiation reaching the ground is much reduced. The figures for Pretoria / Johannesburg are about 50% higher for these months.

This is making me lean towards heat pumps instead of solar water heaters.

Does anyone have any experience with this in the Cape Town or PE areas (which have very similar solar radiation figures) that they'd care to share?

[Justloadit]

IMHO I will say that the heat pump is the better option. I have a solar heated geyser, and get one heated load a day. When my daughters arrive, the first thing they do is bath, so by the time I get home, there is no hot water, and have to rely on the conventional element.

Under these conditions, the heat pump makes financial; sense.

[AndyD]

The most efficient system will always be a hybrid that uses solar when it's available then uses a heat pump to supplement when solar input is inadequate and finally uses a conventional element when the demand is too high for the other systems to be effective.

The problem is the complexity of hybrid systems and the initial purchasing and installation costs. The payback time will be very long and possibly beyond the life of the system itself so eventually you need to strike a balance between cost, payback time and your particular needs. As Justloadit suggested a heatpump with a traditional element as a backup would probably be a reasonable bet in Cape Town. It might be worth considering a separate solar powered pre-heating cylinder as this would operate independently and could be added later as a retrofit. This way it would keep your options open to improve your water heating efficiency in the future when increasing energy prices might motivate you to make future improvements.

[smitty]

I chatted to someone in Cape Town with a keen interest in energy efficiency (measures usage, has efficient appliances, put up a solar panel, etc) about his solar water heater. He confirmed that in winter it makes just about nothing although in summer it's meets his needs.

Obviously an electric element can be used to heat you solar water heater for those winter months but then that would push up your electricity usage. Saving for most months of the year isn't bad but just something to be aware of if you're looking into solar water heating.

If I can find someone with a heat pump in Cape Town I'll be sure to ask some more questions and report back here.

[desA]

Be sure to purchase a reputable heat-pump unit. Most of the stuff sold in SA is cheap, Chinese rubbish - which have poor reliability.