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Solar Thermal - a guide to life expectancy and maintenance

Posted by Gabriel Wondrausch on 7 November 2011 at 4:15 am

The UK will see a huge increase in solar hot water (solar thermal) installations, with the recent announcement on the Renewable Heat Incentive (RHI). When you’re investing in a new technology, you want to be sure that it’s going to be reliable and not over-costly in terms of maintenance and repairs.

Thankfully, solar thermal systems have been around for some time now (SunGift Solar has serviced some that are over 30 years old). They are tried and tested, and we have been fitting the technology for around seven years. However, to get the best out of your system there are some key things you should remember…

Regular servicing is essential

Just like your car, or any other mechanical equipment, servicing on a regular basis is essential, as there are components within a system – such as moving parts and valves – that must be kept in optimum working order. With regular maintenance, your solar thermal system will remain in a safe condition, run at its most efficient, keep down running costs, and generate the maximum amount of renewable heat.  A well-serviced and maintained system will also have a longer life-span.

We would therefore recommend that your get your solar thermal system serviced once every two years (some manufacturers require servicing to validate warranties others do not).

How much will servicing cost?

The cost of a service will depend on many factors and be heavily influenced by whether or not any maintenance is required. From our experience it is always much easier to service a system that has been fitted by us, as we are 100 per cent familiar with it and the way that it has been installed.  Servicing others’ systems can be time consuming, as unfortunately there are an abundance of poorly-designed and badly-installed systems out there that the original installer is no longer around to maintain.

When you receive a quote for the installation of a solar thermal system it is wise to ask the installer to include a price for a standard two-yearly service so that you know what the ongoing costs of keeping your system in top working condition will be. SunGift Solar’s current cost for a two-year service on a standard domestic system is £120+VAT.

What does a service include?

It’s essential that your service is well structured.  During a standard service our technicians work through a checklist to ensure that the system is performing correctly. It includes nine tests on the solar circuit and a variety of other electrical tests; checks on the collector’s fixings, pipework and insulation; examinations of the controller's parameters, wiring and functionality; and analysis of the cylinder’s position, controls and potential leaks.

Replacing fluid

One of the most important aspects of your solar thermal system is the heat transfer fluid. This will need to be replaced approximately every 12 to 15 years to ensure that the pH and antifreeze-protection levels are correct.

How long your system should last

A properly designed and installed solar thermal system should last in excess of 25 years, and we have experience of servicing systems still functioning that are over 30 years old. However, we also have experience of servicing systems less than one year old that are already too badly damaged to be of much use. It’s therefore essential that – if you are considering solar thermal – you choose a reputable installer that you have confidence in and that can give you all of the information that you need.

Photo by lightmanx5

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.

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5 comments - read them below or add one


monflyer58Comment left on: 6 October 2013 at 10:45 am

I have been cold called by company offering to service my solar thermal system ( I think they bought the customer list from my installer, who has gone bust).  They claim systems should be serviced every two years,  at a cost of about  £150 ( seems much in line with provces quoted in above article) . However, such an additional cost wipes out any csavings on electricity bills, and significantly impacts on the overall financial viability of solar thermal . Are these charges realistic, and/ or really neccessary ?   

I can easily check myself if the system is operating OK  ( though I can't tell if  may be slightly suboptimal) . However, it would need a major loss in output to justify a £150 service charge.  The one thing I don't know how to check is if the heat transfer fluid needs changing .  Any tips anyone ?  

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banjaxComment left on: 9 March 2012 at 12:02 pm

Would there be any caveats to utilising a GHSP as a means to prevent the fluid from overheating?

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banjaxComment left on: 1 March 2012 at 11:44 am

Does this mean that it is possible to use a Heat Pump as a means to prevent the fluid from overheating?

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ZCarlComment left on: 24 November 2011 at 7:54 pm

I just want to spread this news as well. 

There is a changes about about the building regulations.

As they said,

"the lower the U-value, the slower heat loss, thus it helps minimize your energy consumption".

Carl from Building Regulations Watford 

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nnw49Comment left on: 9 November 2011 at 10:30 am

One of the primary causes of failure in solar thermal comes from overheating the heat transfer fluid repeatedly.

There are two slightly differing types of fluid in use: straight propylene glycol water mix and a buffered solution of propylene glycol in water.

When the unbuffered solution is overheated repeatedly, it becomes acidic so starts to corrode the metalic components of the system.

 On the other hand, when the buffered fluid is overheated, it becomes like jelly - making it much more viscous. In this state it is quite hard to replace!

 Overheating in this context is >100C - which is quite possible in a pressurised system. It can take typically a couple of thousand hours overheating for the issues to start to happen.

 Hence, many suppliers suggest that the fluid be at least tested (for  pH and fluidity) every two or three years with replacement as necessary.

The problem occurs when there isn't anywhere to deliver the heat to - the DHW tank is at the desired temperature and the only option the controller has is to stop the circulation so the fluid gets very hot or boils in the collector.

The engineering solution to the problem is to prevent the fluid from overheating! If there are no other heat stores available, then a simple (large) radiator in the loftspace will suffice that the controller can divert the heat to when there is no demand from the DHW tank. Most controllers have the ability to control a single 3-port valve that would accomplish this.

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