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Is Solar Thermal being overlooked?

In the age of the Heat Pump grant and battery storage, is Solar Thermal being overlooked?


We went to the Solar & Storage Live Show at The NEC in September of last year. One thing that stuck out for me was the absence of Solar Thermal. In fact the only mention in a hall of over a hundred exhibitors of Solar Thermal’s existence was a line on the side of City Plumbing’s stand that simply read ‘Solar Thermal.’ That was it!


On the day I briefly met an acquaintance of a colleague who scoffed at us when we told him what we did. ‘Just fit an iBoost (load diverter to the immersion heater, other brands are available) with the PV’ he said ‘why waste the roof space with a thermal panel?’


This passing comment stuck with me. Had I really worked and specialised in this area of the Renewable Energy sector for most of my adult life to have the technology I believed in best be trumped, superseded and usurped by a small device you just stick next to your cylinder and wire into your PV? I actually had to think about it for a minute… but the answer is a firm NO!


Thermal is the battery’s best friend!


In the emerging age of the battery, self storage, split EV tariffs and the energy crisis, Solar Thermal continues to stand up amongst the other renewable technologies.


Firstly, and perhaps most importantly heating water via Solar Thermal is 70% efficient versus 17% efficient when using an immersion heater via a load diverter. Surely there is somewhere better your electricity could go, like into batteries or back to the grid for the export tariff?


solar thermal and PV panels on a roof

I spoke to my friend and associate of 15 years, Graeme at Remote Power UK, near Bala in Wales, who specialise in all forms of renewable energy and off-grid projects, who had this to say: ‘Solar Thermal is the best way to go for water heating. A 3kW Immersion, however it’s powered, will not provide as much hot water as solar thermal and most immersion heaters are situated at the top of the tank, giving a far smaller dedicated solar volume than a cylinder with a solar coil at the bottom.


Solar thermal really comes into its own on larger systems with thermal stores in a commercial or domestic setting. It is just more efficient. It also pairs perfectly with air source heat pumps.’

This got me thinking, what are the best scenarios for Solar Thermal now?

Time to bring back the airing cupboard?


- Anyone getting a new hot water cylinder would be mad not to have one with a solar hot water coil. Even if they’ve no intention of using it immediately, it future proofs the system at a negligible extra cost and gives them the flexibility to move away from gas/oil/electric when the time is right. But that is pretty obvious and has been the case for over 20 years. Many just haven’t realised its an option or that the technology is out there. A cylinder is the battery of the heating side of the house (literally with a thermal store), it is as just a viable way of storing energy and having it ready on demand, so why not gain that energy using sunlight? I am speaking to more and more people who have bought houses with a combi-boiler who are frustrated there is nowhere in the house for a hot water cylinder now.

- People on the Feed-in tariff, probably only had 4kW of PV as that was the maximum for a domestic install, still have space on their roofs and are starting to see less and less return on their quarterly payments as the cost of gas and electricity creeps up. Time they pushed their house further off the grid?

solar hot water panels on a roof

- What if the roof is full of PV or they want to fill it? Solar Thermal can be ground mounted, or better still, wall mounted, to avoid taking up precious space on the roof. There might be an east/west gable where filling it with PV would create an issue with 3 strings, so why not opt for an east/west solar thermal system?


It almost seems counter intuitive to fill up a roof with PV to offset the electrical cost, just to then have to rely on gas or oil all year to heat up a hot water cylinder.

I caught up with Trudy Tarrant of Invicta Clean Energy in Faversham, Kent who said ‘Solar Thermal is just a no brainer. It compliments a PV system or heat pump well and is the best way to be heating water using renewable energy.’

- New build houses, and by ‘new build’ I mean the ones with tiny PV systems that aren’t enough to power a small torch but were thrown on so the developers could meet their EPC and carbon footprint targets. These houses, which I can see from my office every day, would be very difficult to add further PV to without ripping off the old system and inverter and starting again (and invalidating the FiT in doing so), but they’re perfect for solar thermal. The homeowners are probably scratching their heads wondering why their bills are still so high despite having some solar panels on the roof.


I suppose with this final point comes the issue of education and domestic habits. Once people learn how they consume their energy it becomes a lot easier for the renewable energy installer to understand their needs and find them a suitable solution. The act of ‘fit and forget’ is becoming a thing of the past for all technologies. People are needing to and wanting to gain an understanding of what they have, how it works and how they use it in an economical manner, my only advice is, leave some room in your mind and your roof for the Solar Thermal, so it may yet have its day in the sun!

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