Saturday, 1 October 2011

Sunshine on my solar makes me happy

Solar water heating has been around for so long that we all think we understand how
it works – but the technology has moved a long way from running a hose pipe across
your roof.

Sunlight will be providing us with power (more on this soon) and water heating during the summer months. Both systems use what are collectively known as solar collectors (usually panels) but quite different methods.
In our previous home we used a standard roof-mounted flat solar panel and water tank.
This was very effective during the warmer months, and provided the satisfaction of using free solar energy instead of mains electricity – but we were back to flicking a power switch for the booster throughout the darker months.

This time we are using the wonders of evacuated tube technology. Instead of a flat panel our roof will sport a bank of 24 glass tubes. Each of these is actually a double glass tube, one inside the other, with a vacuum in between them. Sunlight passes through these tubes to warm a copper pipe at their centre, and because the resulting heat cannot escape out through a vacuum, 97% of this energy is retained.
(This heat loss is one of the biggest drawbacks of the flat panelled system, and retaining it allows the evacuated tube system to continue operating even on cloudy days. Apparently the heat output is 25-40% greater than flat-panelled systems when averaged over a year).

A bulb at the end of the copper pipes transfers the heat to a water/glycol solution which is carried down to the exchanger coil inside our water tank, heating the surrounding house-hold water. A pump utilising less power than a light bulb then carries the solution back up to the roof for continuous heating. The pump is automatically controlled to keep the solution moving when it’s most needed, including at the onset of a frost to avoid freezing.

Our water tank will contain a second coil which is connected to our wetback system, generating heat when we light our fire in the winter months. This coil is connected to three radiators throughout the house, carrying heat where it will be most needed.
Having never lived in a modern, fully-insulated home before (our last house was a villa, with sash windows which seemed to transfer heat outside more effectively than any air pump) our only concern now is whether or not our house will be too warm.
Bring on the snow, 2012!

An impression of how the evacuated tube array will look in position.
Another advantage of this system is it’s ability to blend in with the roof profile.


  1. Hmmm, I haven't seen the evacuated tube array on the roof personally, but it can certainly help the heater and the tank keep the water warm. It may seem more complicated to build, but it may be more effective than usually heating systems.

    Richelle Loughney