Using a PV energy diverter to heat a hot water tank.

[Marvin]

Splitting away from the  "Turning our heat pump off over summer and a general moan"  thread....

 

19 hours ago, Marvin said:  I would recommend checking out a solar diverter to anyone who has PV and a hot water tank with an immersion. 

 

Phil T Responded:

I did give this a lot of though and decided against as I get 15p fixed SEG, my heat pump is doing better than COP of 3 for DHW, so at my current variable electricity rates 33p it would cost me 4p/kWh to use a solar diverter instead of the heat pump, or cost me 8p/kWh assuming "Cosy" rate 21p/kWh, and that's before taking into account the up front cost of the diverter (a few hundred quid?). Have I got that logic correct or am I talking complete cobblers?

 

Hi @PhilT

No. Your thoughts make sense. You've checked out about a solar diverter and decided its not for you. I forgot all the possible setup differences which mean it is better for some than others: We do not have a smart meter. We do not get paid for exporting. We have one rate for electricity.

 

 

 

 

 

[billt]

It also depends how you go about it. If you make and install it yourself it can cost very little. In a previous house I made a 10 output diverter which worked on the energy bucket principle to ensure that no energy was exported, the electronics didn't cost much and I didn't have to pay an expensive electrician to connect it.

 

Here I use and even cheaper and simpler version, a Tasmotaised switch which is controlled by the HA system to switch on when when excess solar is being produced. It's not accurate as the system is off grid with batteries, so precision is not required.

[ProDave]

But for those that didn't want to pay for an MCS install, and / or do not for various reasons want a smart meter, there is no SEG payment available.

[Hobbiniho]

my sister has an immersun diverter powered by a wind turbine and she uses it to heat her hot water, she directs excess above the 3.8Kw to a combination of a electric panel heater and an old storage heater (not sure if this is the immersun or the wind turbine control that does this) meaning basically nothing is exported to the grid this has meant that only on the very coldest calm days in winter she has had to fire up the oil boiler, her electricity bill for the last quarter was about £10, unless you were an early adopter of solar like my dad you wont get any payments for the electricity you export so would benefit from self using as much as you can

[Radian]

On 19/01/2023 at 18:00, billt said:

It also depends how you go about it. If you make and install it yourself it can cost very little. In a previous house I made a 10 output diverter which worked on the energy bucket principle to ensure that no energy was exported, the electronics didn't cost much and I didn't have to pay an expensive electrician to connect it.

It sickens me how much the commercial offerings cost when you and I can knock something like this up for a few quid. I've been wracking my brains for a way to guide anyone how to safely assemble a diverter using "near" off-the-shelf parts but the main stumbling block seems to be a plug & play 16A (or better) ZC SSR module packaged like a shelley or tasmota.

[NSS]

38 minutes ago, Radian said:

It sickens me how much the commercial offerings cost when you and I can knock something like this up for a few quid. I've been wracking my brains for a way to guide anyone how to safely assemble a diverter using "near" off-the-shelf parts but the main stumbling block seems to be a plug & play 16A (or better) ZC SSR module packaged like a shelley or tasmota.

The key word in there is safely. Great that you and others have sufficient knowledge and skill to make your own, but I wonder if (God forbid) such a 'home spun' device were to have been installed in a property that subsequently suffered a fire, quite what the insurance investigators would conclude - irrespective of whether the device actually caused said fire.

 

Surely the cost of commercial offerings is in part due to the safety testing and certification they are required to undergo before being approved for use. For someone like me whose electrical knowledge just about stretches to rewiring a 3-pin plug, that peace of mind is worth the price.

Edited January 30, 2023 by NSS

[SteamyTea]

Back in the 1960's and 1970's it was not unusual to buy electronic kits for home assembly.

I wonder how many half fished  Sinclair amps and calculators there are in Grandad's lofts.

[billt]

9 hours ago, Radian said:

It sickens me how much the commercial offerings cost when you and I can knock something like this up for a few quid

 

That's the reality of the commercial world. You might be able to source the components for £50 or so and then spend several hours assembling it, but to make a commercial offering you have to produce an acceptable enclosure, ensure that it's safe, possibly have to pass compliance tests. Once you've produced it you've got to persuade people to buy it; if you sell it through resellers they'll want their 30-50% mark up and you can't undercut them with direct sales. It's a tiny market so there aren't likely to be economies of scale. £300 or so doesn't seem a totally unreasonable price. Then a man in the street is going to have to pay someone a couple of hundred quid to install it.

 

I've never understood why people think that it's worth while paying that much money to save a few pennies.

[Radian]

@billt @NSS I get all the wise words of caution and I agree wholeheartedly. I do design commercial products so do have a grasp of the costs involved. The key factor, as ever, is the volume of production. The solar market is relatively small but there are still over one million homes in the UK with installations and almost all could benefit if the upfront cost was low enough. With a stable design, 10% of that market would still yield sufficient economy of scale to align the margins with many other low-volume products. If it were my product, it would be the biggest selling line by a long stretch. One fact that may not be so obvious is that a product's profitability is massively dependent on its reliability. The friction of handling customer returns and warranty claims can soon erode the financial viability of a line. Companies can easily fail through the snowballing results of poorly considered engineering. The origins can usually be traced back to the decision to put too much investment in advertising to the detriment of design and testing.

 

As for a DIY step-by-step guide that could democratise the ownership of PV diverters, to save going off topic, I've started a new topic to discuss the prospects here.

 

[dpmiller]

I must admit I'm rather intrigued by Cool Energy's new offering

 

https://coolenergyshop.com/collections/myenergi-smart-ev-charger-solar-power-diverter/products/cool-energy-solar-power-diverter

 

It's *very* like the iBoost (display, buttons, menu etc) but much bigger and currently much cheaper. I was wondering if it might be fanless, and whether the current iBoost might [cough] disappear off the market soon...

[dpmiller]