Solar Hot Water

Collectors on your roof heat water, or a heat transfer fluid, using energy from the sun. That heat is moved into a storage cylinder, so you draw on water that has already been warmed for nothing before any element or burner switches on.

Because the sun does not run to your schedule, every system keeps a booster, usually an electric element, gas or a wetback, to top the cylinder up when solar has not got there on its own.

There are two collector types. Flat plate panels are robust and cost less, and they suit a roof with good sun and steady demand. Evacuated tubes hold their performance better in cold and overcast conditions, and individual tubes can be replaced if one fails, which often makes them the better call in Canterbury.

Then there is where the cylinder goes. A close-coupled system sits the cylinder on the roof above the collectors and circulates without a pump. A split system keeps the cylinder indoors or at ground level and uses a pump and controller, which is more flexible, tidier to look at, and usually the sensible choice for a retrofit or a roof that will not carry the extra weight.

A well-sized system will typically cover somewhere between half and three-quarters of a household’s annual hot water. That is a real saving, but it is an annual average. Output is strongest through summer and modest in the middle of winter, which is exactly when you want long showers, so the booster covers the gap.

Solar also rewards households that use a decent amount of hot water. If there are one or two of you and demand is low, the numbers work less well, and a hot water heat pump may give you a better return for less on the roof. We will tell you if that is the case.

Solar hot water is roof work, structural work and plumbing work at once, so it usually needs building consent and has to be installed to comply with the Building Code. We handle the consent side, the roof penetrations and flashings, the cylinder, the pump and controller, and commissioning at the end.

Frost is the part that gets skimped. A system specified for a warmer part of the country can split a collector or a pipe run on a hard Canterbury frost, so we set systems up with proper frost protection appropriate to the site rather than to a catalogue.

A lot of the solar hot water in Christchurch went on during the subsidy years, which makes plenty of it well over a decade old and out of warranty. Some of those brands have left the New Zealand market and some of the installers have too, so we regularly take on systems we did not put in.

Common faults are the circulating pump, the controller or its temperature sensors, heat transfer fluid that has degraded and turned acidic, cracked or clouded evacuated tubes, scale through the collectors and cylinder, a failed tempering valve, or a booster element that has quietly died while the solar side kept working. Very often no hot water on a solar system turns out to be the boring part rather than the panels.

We will test the system, tell you what is actually wrong, and give you a straight answer on whether it is worth repairing, including when replacing it with a hot water heat pump or a modern cylinder is the better use of your money.