Solar Thermal Collectors form the head end or energy capturing end of a Solar Thermal water heating system. There are broadly two types of collector, Flat Plate Collectors and Evacuated Tube Collectors.
When evaluating the two different technologies the three main things to consider are:
The available space on the roof or other mounting area
The location of the installation in relation to the sun
When the hot water demands are likely to be in terms of the time of year
What are Flat Plate Solar Collectors?
Flat Plate Solar Collectors can be descibed most simply as a heat absorbant material mounted in a sunny spot. The collector absorbs heat from the sun and then transfers that heat into fluid that is circulating around the system. Where a traditional boiler would burn gas, oil or coal to heat the water you would use the sun's heat, not needing to burn anything.
What are Evacuated Tube Collectors?
Evacuated tube collectors look a bit like strip flourescent lights, although they work quite differently. An evacuated tube system consists of individual tubes with fluid circulating through them absorbing the sun's heat. From there the system is much the same as the Flat Plate system mentioned above.
Flat Plate Vs Evacuated Tube
A flat plate system is generally slightly cheaper as they usually have less engineering costs associated with their manufacturer. Yet in ideal conditions, measuring peak performance a flat plate system could compete or even beat the performance of an equivelant evacuated tube system.
An evacuated tube system is likely to perform slightly better in lower light environments so you may find in a like for like comparison with an Evacuated Tube system, the tubes would squeeze a bit more heat out of the available sun in Spring/Autumn or on duller days.
Both have their uses and both work effectively in the UK, we don't believe that one technology is better then the other. In the debate between Flat Plate Vs Evacuated Tube we agree with both sides.
Cost Vs Performance
When evaluating collectors it's always useful to think about cost Vs Performance, for example if you had a large roofspace, a bigger flat plate collector could deliver equal performance or better when compared to a smaller, more expensive evacuated tube system.
or
If you had only a small amount of available space on a wall, roof or balcony you may find you get more energy per sqm from Evacuated Tubes.
Maintenance
Both Flat Plate and Evacuated Tube systems require very little maintenance. There are few moving parts and the inner workings are well protected from the elements. If something happens to the collector it's easy to swap out whole collectors and or individual tubes.
Both systems will perform better when clean and free of dirt/dust so if dirty and where feasable its worth washing them both in much the same way as you would clean a window using just water.
Most Solar Collectors have been designed to expell water and dirt effectively on their own so if you can't get to them and don't notice a drop in performance they are likely to be ok.