Our Warmstone Heat Battery replaces the boiler in your home... and can be installed as a straight boiler ‘swap out’.

1.7t ... Straight swap... Sure

Posted by: @editor

I came across Caldera a few months ago that make heat batteries. An interesting concept  - they weigh an impressive 1.7 tonnes.

CALDERA.CO.UK "https://www.caldera.co.uk/warmstone-heat-battery"

Hi Mars,

An interesting concept, and not that different from electric storage heaters, but with the addition of radiators or UFH. Obviously their claims of cheap renewable energy have gone out of the window, but I suppose that a system with solar PV combined with an Octopus GO type of tariff may prove to be cost effective.

How much does a system like this cost and are there any grants provided?

Hi Mars,

I have just had a look at the Caldera FAQ's.

No grants at the moment and £12000 to install. Not really a cost effective solution.

@derek-m, yes, it is quite pricey, and still runs on electricity without the benefits of a heat pump's COP. Their own 'wizard' on the website states it's probably not suitable for houses that are 3+ bedrooms, which essentially prices it out of the equation because you can get a smaller heat pump unit installed for less than that with the benefit of a grant. Maybe they'll come down in price as they scale their business and production.

CENTRICA.COM "https://www.centrica.com/media-centre/news/2022/centrica-and-glen-dimplex-to-run-uk-s-largest-trial-of-domestic-smart-storage-heaters/"

Trial of modern storage heaters with time of use tariffs.

I think OVO did a similar trail but didn't continue it. 

I really don't understand how something so simple could cost so much.  I think "heat batteries" have a place - perhaps (a small unit) in a passive house, or similar, where I've often heard that the heatload is so small it's hard to justify a conventional heatpump system.  

It is curious that Octopus Go and EDF have 4 hour electricity prices which are 4x cheaper than the day rate, matching the cop improvement of a heatpump.  So, at the moment, a heat battery on a cheap tariff is financially (but not in CO2 terms) on a par with a heatpump operating on a flat tariff.  Of course, you could get a massive heatpump and run it in those 4 hours - but it would have to be huge and expensive.  Or a battery system, charging up in the small hours, but again such a large upfront investment makes it unlikely.

I was really intrigued by this when I saw it on the Fully Charged youtube channel.

Although designed as direct replacement for oil/lpg, I feel there could be a place for mains gas replacement too.

I really like how they store such a large amount of energy. It's quoted to store 100kWh of heat and can hold it for around 23 days.

So I thought if you have solar pv creating all that excess energy toward the end of summer, it could be channelled into this and be stored ready for when the heat is needed. Then only when the demand starts to get high would you need to start thinking about charging off peak. 

The coldest month and highest energy use for our household in last 3 years was Jan 2021 (avg 4C in Cambridge), the daily average was just under 98kWh of gas that month (DHW and heating). So the need to use daytime power to top up should be very rare. They do quote approx 5hours for a total recharge, so the right tariff would need to be found.

I been doing some basic modelling on our past 3 years home usage to help me calculate the potential financial benefit of introducing solar and an alternative heating solution. I found that the savings/bill cost (around 2-300 gbp cheaper than gas/elec/solar) was virtually the same as if I'd installed a new heat pump with a SCOP of 4.5  based on the following:

• Current household heating usage of 12,500kWh
• ECO 7 tariff of 0.075 (to charge tank and batteries full each night - 5-6 months running on solar) / Day tariff 0.44
• PV array of 8.47kWh and battery storage of 9.6kWh

Add into the fact it's virtually maintainence free, quoted 20year lifespan and just plugs straight into the existing system (with cylinder) without need for upgrades, it's not a totally unreasonable option at all. However, I do concede that the low eco tariff is pretty important here! In the video they said it was 12k, but with the intention to bring that down to 10k with higher volume production. 

Biggest challenge is actually getting one! They have apparently halted the start of larger scale commercial production:

"We had planned to upgrade our factory in 2022, enabling us to start mass production, but took the difficult decision to pause both the factory upgrade and sales of Warmstone units. This decision was influenced by turmoil in the energy markets leading to the removal of most off-peak and night-time electricity tariffs, heating oil going from being a relatively expensive fuel to one of the cheapest, and difficulty finding skilled installers." (from their website)

I like it's simplicity, I just wonder if it will catch on and get to the volume it needs to make there business sustainable...

@squeakysim

I don't wish to burst your bubble, but I looked at the Warnstone units some time ago and came to the conclusion that they are too expensive and not that practical in many situations.

They weigh 1850kg so are not exactly an indoor device and would require quite a reasonable base outside, or maybe in the garage. To fully charge 100kWh would require approximately 4.6 hours at 90 amps. Transport can confirm, but I feel certain that you would require DNO approval, even assuming that the main supply fuse is rated at 100 amps.

You would still need the radiators etc. of a water based heating system.

If you wish to have an off-peak electric heating system, you could get 5 x 19.8kWh storage heaters for less than £4000.

@derek-m that was a very big poke at my bubble! 😂

I agree, it’s definitely not suited to as many situations as other options.  I guess that’s another reason why it’s suited to be a good replacement for lpg/oil, as you would have a base already setup, which we do from the first boiler we had.

I had no idea about the potential power issue though, something for further investigation (should they become available!).

Not sure the storage heater comparison is really a fair one. I don’t profess to have any real knowledge of storage heaters, but I’m pretty sure they can’t store heat as long as this can? Or provide hot water for that matter. 

I certainly don’t know that this is a viable alternative, but I’d love to find out more should it ever start production!

@squeakysim

I try to be objective, when I look at any new idea. If the Warmstone unit was more competitively priced then I may have been more favourable, but I try to consider what may be the more cost effective solution. Before I wrote my reply I had a good look at the present offering of electric storage radiators, and I was quite surprised to read that they now have some degree of inbuilt intelligence, and can vary the amount of charge taken from the grid dependent on the estimated amount required for that particular day. They could possibly also be more readily charged from your solar PV.

True, the electric storage radiators cannot provide hot water, but that could easily be remedied with the addition of a Sunamp heat battery, or a hot water cylinder which also contains a small ASHP, which is now also available.

@derek-m The cheapest and best heat energy storage is a thick concrete slab with a well designed low temperature under floor heating system