Generally, flat plate systems are cheaper, but there are many good reasons to pay a little bit more for evacuated tube solar hot water collectors. See below:
- They capture more of the sun’s energy at a given time because they have a greater surface area and passively track the sun around the sky.
- They require a smaller roof area to get the same amount of energy as a flat plate collector because of greater solar absorption.
- They weigh less so there is less load on your roof.
- They work more efficiently in overcast and windy conditions because of the vacuum insulation between layers of glass and highly insulated manifold.
- The vacuum insulation also means they are much more frost resistant, being passively protected down to -5°C.
- Flat plate collectors are more susceptible to hail damage.
- The tubes are durable – however, if one breaks, you can replace a single tube rather than the whole system.
- At the end of the useful life of the evacuated tubes they helpfully change colour when losing their vacuum so you can spot failure and they can be easily replaced without having to do any plumbing work for another 15+ year lifespan.
Diagram showing the passive tracking of the sun provided by tubes.
Diagram showing how the fluid only runs through the top manifold and less exposed to heat loss.