What Are They And How Do They Work?
The solar panels we are talking about fall into two categories.
- Flat panel
- Vacuum tube
There is a third variety; however these are specifically for heating swimming pools and not for domestic hot water systems. The first is simply an insulation lined box with a glass or Perspex top and a micro-bore copper pipe serpentine in shape (wiggled like the pipe work on the back of your fridge), fitted to a copper base plate winding around the air space in the middle of the box.
The second is as its name describes. It is an evacuated toughened glass tube using the same principle as a thermos flask only in reverse, it takes heat in and keeps it there. The collector has between 12 and 30 vacuum tubes fitted into a receptor. More tubes means more collecting area so, the more efficient the collector is. The tubes have a heat sensitive liquid inside a copper core running through the tube which transfers the heat to the water circulating through the manifold to the hot water tank.
Flat panels are cheaper but less efficient; almost doubly so, especially in UK northern latitudes, whereas the vacuum tube types are much better suited to the UK north because of their round shape and the magnifying effect of the tubes. The reflective surface placed behind them increases efficiency too. They also do not lose heat by convection which flat panels do. With reduced manufacturing costs in the far-east, the prices of vacuum tube collectors have fallen dramatically and are now affordable by the average home owner.
Both will last around 20-30 years, both are virtually maintenance free and both will work on overcast days. But, the vacuum tube collector has a significant advantage because replacing individual vacuum tubes can be done without draining the system. If a flat panel fails then the system must be drained.
Depending on the annual cost of heating and hot water, the viability of a system can be calculated easily from utility bills.
Have a look at how you can save money in:
'Graphs & Charts > Costs Table'.