Solar thermal

In this guide we investigate, score and rank the ethical and environmental record of 13 solar companies.

We also look at different types of solar thermal, different uses for the technology, and our recommended buys.

About Ethical Consumer

This is a product guide from Ethical Consumer, the UK's leading alternative consumer organisation. Since 1989 we've been researching and recording the social and environmental records of companies, and making the results available to you in a simple format.

Learn more about us →

What to buy

What to look for when buying solar thermal:

Subscribe to see which companies we recommend as Best Buys and why 

What not to buy

What to avoid when buying solar panels:

  • Does it score worst for carbon reporting and management? If it does, avoid it. Companies making renewable energy products ought to have their own house in order when it comes to carbon.

Subscribe to see which companies to avoid and why

Score table

Updated live from our research database

← Swipe left / right to view table contents →
Brand Score(out of 20) Ratings Categories Positive Scores

Our Analysis

Solar thermal is more simply known as solar water heating. According to a year-long study by the Energy Saving Trust in 2011, it can provide over half of a households' hot tap water needs over the course of a year, and 100% during the summer.

It is therefore a partial technology – you will still need something else to top up your hot water over the winter and for space heating. It doesn’t heat water to a high enough temperature to be used in traditional radiators, although it can make water warm enough to reduce the additional energy you’ll need from other sources.

It can manage the temperature required for underfloor heating but may still need supplementing.

Who’s in this guide?

We’ve featured the most popular and widely used brands. They are also all MCS certified. The companies are mainly small companies that specialise in renewable products and heating products.

There are a couple of bigger, more diverse electronics companies – Bosch and Haier. Plus, DIY giant Travis Perkins, owner of Wickes, makes a surprising appearance as the owner of Solfex.

Score table highlights

Pollution and toxics

Virtually all companies get a worst rating for Pollution and Toxics because they make electronics, like solar thermal controllers, and do not have a policy on the use of toxic chemicals such as brominated flame retardants, PVC and phthalates. AES and Navitron are the exception to these.

Carbon reporting and management

  • One company, AES, gets the best rating because it only makes renewable heating products, and it discussed its own climate impacts and what it is doing to reduce them.
     
  • The majority of the companies get our middle rating for carbon reporting and management, as they aren’t discussing how they were reducing their own impacts, but they do only make products focused on lowering carbon emissions, e.g. renewable energy products.
     
  • Five companies get our worst rating because they are more diversified companies with a lack of awareness of their climate impact and/or inadequate carbon emissions targets – Grant, GREENoneTEC, Viessman, Worcester Bosch, and Solfex.

Policy on the use of conflict minerals

All the companies got a worst rating for making electronic products, like controllers for solar water systems, but not having a policy on the sourcing of the conflict minerals used in them, minerals like tungsten, tin, tantalum and gold.

The only exception was Navitron which didn’t make any electronics.

How solar thermal works

Solar thermal works through water in panels on your roof, which absorb the sun’s heat. The hot water is then pumped to a hot water tank or cylinder to be stored until needed. It does not require bright sunlight in order to function; while that would be the ideal, it can still heat water even on cloudy days.

You can add solar thermal panels to most existing hot-water systems.

However, you’ll usually need to add an additional hot-water cylinder for the solar-heated water alongside the cylinder connected to your boiler or heat pump.

Or, to save space, you can change your existing cylinder for one with two heating coils.

Solar thermal can be combined with a conventional boiler or immersion heater to make the water hot enough to use in radiators, or to provide hot water when solar energy is unavailable especially during winter.

The downside is that it may not work well with a combi (water on demand) boiler. It depends on whether your make of boiler can accept pre-heated water.

Around half of combi boilers won’t do that. If you’ve got one of them you’ll either need to change it to a conventional boiler or use another technology, like heat pumps or PV instead of solar thermal.

What does it cost?

The cost of installing a typical solar water heating system is £4,000-£5,000. EST found that typical savings from a well-installed and properly used system are moderate – £60 a year when replacing gas heating, and £70 a year when replacing electric immersion heating.

But it may be eligible for the revised Green Homes Grant if you are on a low income. And, once it has been installed, you can receive payments through the Renewable Heat Incentive (RHI) per kWh you generate.

For applications submitted between 1 July 2020 and 30 September 2020, owners of a solar thermal heating system received the highest payments.

Type of renewable heating system Tariff (p/kWh)
Solar Thermal 21.36
Air Source Heat Pump 10.85
Ground Source Heat Pump 21.16

However, according to CAT:

“Bear in mind that the [green homes] grant value will be deducted from any RHI payments .... If you need to fund substantial insulation improvements, it would therefore be more cost-effective to use the grant for those.”

Homes with a hot water cylinder and high demand for domestic hot water, such as a family or house share, are the best suited to a solar thermal system. For a one-person household, with low hot water use, it won’t be as cost-effective.
 

The types, and installation details

There are two types of solar thermal panel, which are known as collectors:

  • Flat plate – resemble solar PV panels and sit flat on the roof
  • Evacuated tubes – a bank of glass tubes mounted on the roof tiles.

Evacuated tubes are more expensive than flat plate. They are often regarded as more efficient, but the Centre for Alternative Technology (CAT) says that with UK weather, there isn’t a big difference.

The Energy Savings Trust (EST) found that the main impact on a system’s performance are how well insulated the home’s hot water tank and pipes are.

One downside of solar thermal is that the panels have to be connected to the plumbing, so installation is not straightforward. Solar Guide thus says that a solar thermal system is best installed as part of a renovation or during the construction of a property. But, once installed, maintenance costs for solar thermal systems are generally very low and they will last for 20-25 years.

It is recommended that you find a professional installer rather than trying to do it yourself. The government mandated Microgeneration Certification Scheme is a quality standard covering installers of certain low-carbon technologies, in particular heat pumps and solar PV. Whilst not an absolute guarantee of quality, MCS offers a mechanism for best practice, advice and rectification.

Many incentive schemes like the Renewable Heat Incentive (RHI) require MCS qualified installers, so look out for the standard. For that reason, we have only covered MCS-certified brands in this guide.

Solar thermal vs heat pumps

Heat pumps can do space heating and hot water, so they are able to be more of a complete solution. But you can combine them, and there may sometimes be advantages to doing so. Air-to-air heat pumps only do space heating, so in this instance you could get solar thermal to help with your hot water.

Solar thermal vs solar PV

The market for solar thermal has declined since solar PV became cheaper and more popular. Many solar thermal companies stopped trading. Installing solar thermal systems was part of the short-lived Green Homes Grant, and solar PV isn’t, so check locally if there are any new or expanded green grant schemes which might be applicable.

Solar water heating is more efficient than using solar PV panels to heat water.

This means solar thermal panels will take up much less roof space than PV panels would for the same energy output, because you’ll need fewer of them.

In addition, there is a financial saving – solar thermal panels are generally cheaper than PV ones.

But because solar thermal needs a hot water cylinder and works better with a conventional or ‘system’ boiler, if you have a combi boiler and no hot water cylinder, solar PV may be better.

Of course, if you have a big enough south-facing roof, or you can mount panels at ground level where they’ll have a clear outlook, you can have both systems, either as two separate systems or Solar PV-T – which combines both.

But Solar PV-T systems aren’t yet as popular as solar PV or solar thermal systems and there are only a handful of manufacturers, none of which have been covered in the guides in this magazine. These hybrid systems are also not eligible for the Renewable Heat Incentive (RHI).

Make the most of your solar water system

Which? has the following advice:

  • Use as much hot water as possible from the solar-heated supply, rather than heating it up in an appliance using electricity. For example, fit a mixer shower (rather than electric) and check whether any ‘hot-fill’ appliances (which could include your washing machine) can take water from your solar system.
     
  • Use more hot water in the evenings – in showers, baths and washing-up. This is when water will be hottest, as it’s had most time to heat up.
     
  • Insulate your pipes and water tank to make your system more efficient.
     
  • Follow your installer’s advice on how to set the hot water controls to get the most from your system.
     

Other uses for solar thermal

Solar water heating can be used to provide warm water to a site which has no facilities at all: allotments, garden sheds, and campsites. The simplest is a ‘solar shower’ black pouch with a tap at the bottom, which costs less than £10 and provides ample hot water for camping.

Solar water heating is also popular for heating swimming and paddling pools.

Company behind the brand

AES Solar was established in 1979 and it says it was the first manufacturer of solar thermal collectors in Western Europe. It is a Living Wage employer. It says: “We manufacture and assemble the majority of our products from our headquarters in Forres. With the majority of our materials from the local, domestic, and European market, the environmental impact of the transportation is minimal. AES Solar is actively resisting the less sustainable trend of sourcing materials from Asia in order to reduce our carbon footprint and support producers closer to home.”

AES Solar is currently in the process of changing to an Employee Ownership Trust, a structure similar to the John Lewis model in which the Trust holds a controlling stake in the company on behalf of all its employees. It’s basically an indirect form of employee ownership.