Skip to main content
Observer Ethical awards Winners 2011

YouGen Blog

What is the best solar hot water panel for a small space?

Posted by Gabriel Wondrausch on 31 July 2009 at 8:47 am

Question from YouGen user: I have a 7 year old Solartwin panel on my roof which I believe is performing poorly and is not metered. The company say that the harder water is likely to be too much for the panel and that it needs an indirect panel. Thus I feel I need to replace it. It is a landscape shape high on my roof, now surrounded by PV panels, so its replacement needs to fit the same space. Given the space constraint, what is the best panel/system to install? I cannot easily find outputs per square metre gross.

Answer: To maximise the solar gain from a limited area you are probably best using an evacuated tube collector as they have a higher yield per square metre than a flat plate collector.

This is due to the increased insulation provided by the vacuum. By containing the absorber within a vacuum, heat loss from the absorber is almost completely avoided. This also increases the yield in low radiation and cold conditions as the absorber is not susceptible to the ambient temperature.

An evacuated tube collector will have an output of approximately 600-650 kWh per m2 per year compared to approximately 500 kWh per m2 per year for a flat plate panel. But as panels come in all different shapes and sizes it could be that a flat plate panel will fill the available space better than a evacuated tube panel.

There are various institutes that publish test data from various collectors. Most comprehensive is the SPF Swiss test facility. It has information on collector outputs as well as collector sizes.

If the roof space is too restrictive solar thermal panels can sometimes be mounted in different locations than the roof. Different types of panels have various mounting options. Most can be mounted on A-frames, some can be mounted on flat walls, and we have mounted panels on pergolas in the garden which can make a nice feature.

About the author: Gabriel Wondrausch is founder and director of SunGift Solar, which installs solar thermal and other renewable energy systems in the South West of England.

If you have a question about anything in the above blog, please ask it in the comments section below.

Like this blog? Keep up to date with our free monthly newsletter


4 comments - read them below or add one


samComment left on: 23 October 2009 at 9:04 am

One installer has offered to solve my space problem by installing a 16 tube Logical Energy evac tube system on my South facing roof the wrong way round ie with the tubes running horizontally. He didn't convince me that he knew this would work. Does anyone have experience of this? And will it receive as much thermal energy like that?

report abuse

Renewable Energy Market

Renewable Energy MarketComment left on: 20 October 2009 at 9:58 pm

In my humble opinion as an experienced installer of a variety of solar thermal panels I would shy away from direct solar thermal systems for a variety of reasons including hard water and poor gains in the UK climate.

I have found that the most effective collectors are the Ritter or similar CPC direct flow (compound Parabolic Collectors) and yes I know they collect leaves in some locations, though when the gutters of the house are cleaned the lower part of the panel where the leaves collect can also be cleaned. Indirect diluted antifreeze filled systems pressurized to 2.5 bar will give the best gain through an unvented cylinder.

report abuse

Gabriel Wondrausch

Gabriel Wondrausch from SunGift EnergyComment left on: 31 July 2009 at 1:46 pm

In response to your comment:

Firstly, to see the output of a collector you want to look at the “Typical solar yields (solar savings)”. You can then download a PDF on each tested collector.

The majority of collectors are manufactured in Europe but mostly with components sourced from other countries. It is therefore fairly difficult to determine the quality of a particular panel without physically seeing and using it. This is where we can help. As installers we have dealt with many different systems and can offer advice on the different panels available. I would recommend getting it touch if you would like to talk about the collectors we recommend and why.

report abuse


samComment left on: 31 July 2009 at 8:52 am

Thanks for this. May I check my understanding a little more? The SPF is quite hard to use. Should it be be the tested solar yield that I am reading? IN addition this lists mostly swiss and german models some of which say they are marketed in UK. How then to identify the quality panels - noting an earlier blog on quality manufacture - (many don't have published quality standards) and installers in UK who can manage specific kit?

report abuse

Leave a comment

You must log in to make a comment. If you haven't already registered, please sign up as a company or an individual, then come back and have your say.