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Discussion Starter #1
Hi all

Been considering a solar hot water diverter, not something expensive like the Zappi kit, but something like a Solic 200 or Solar iboost. Some details below about our set up:

6.2kw of south facing solar installed. Export is not limited at the inverter.
Installed post FIT, so the deemed 50% export does not apply to us.
We are signed up with Bulb for the smart export guarantee (SEG), so since 1 Jan we are being paid 5.38p per unit exported.
We use gas to heat our water at present, paying 3.2p a unit with Octopus.
The gas boiler is less than a year old (Worcester Bosch), an S plan condensing “system“ boiler set up, NEST thermostat.
We do have a working 3kW immersion heater installed in the cylinder as a back up for hot water should the boiler fail.
Family of 4 in the house, 1 bathroom.

Is it as simple as this not being worth doing (financially) as we get paid more to export surplus that we pay for gas?

If we did get one, would it cover all our hot water needs, or would we be boosting with gas still / running out of hot water if not careful.


Thanks for any advice.
 

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We have had a hot water diverter as long as we have had the solar panels. The installer's electrician said it was the first one he'd seen.

So we are getting the 50 percent assumed feed in tariff payments anyway. It is just saving us gas, which was costing us about 4p per kWh when I did the sums.

It is set up with the thermostat at a slightly higher setting than the gas system. So, on a sunny day, it does all the water heating but on a bad day the gas system does a top up in the evening.

It's a nice feeling when the supplier's computer queries your summer gas meter readings for being impossibly low.

However, to answer your main question, just export the electricity at that nice high price and saver yourself the cost and complexity of extra kit.

You are probably saving the grid from burning the same amount of gas as you would have saved yourself, so don't get conscious-stricken about the effect on the environment either.
 

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Sounds like the SEG would negate the need for an iBoost? I've got solar, a battery and an iBoost which is a useful device for mopping up some surplus going back to the grid but you don't really need that. Only really useful to me in the summer, not enough solar in the winter for the iBoost to do much.
 

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I've got a Solic diverter and it's a solid no nonsense bit of kit, so no problems on that front. I also have a large thermal store.


If your hot water tank is small and your heavy usage is 15ish hours after the tank is heated, is morning showers, you may not have enough hot water to make it worthwhile.
 

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Also I installed a factory 2nd Solic so what I paid for the total installation maybe 1/5 if what a std install would cost.

The factory 2nd allegedly had a scratch on the casing: I couldn't see it.
 

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Discussion Starter #6
I was erring towards the Solic due to the long warranty and seemingly basic and hopefully more durable design, did notice the eBay graded items at a discount so would buy that route provided they had the original warranty still. The iboost would be an easier install though.
Even then, I’m not sure it’s worth the extra outlay and added complexity, and so far the replies above seem to agree.
 

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How big was your storage cylinder.?

Where in the tank is the 3kW element installed.

The answer to these questions might rule out the installation on technical grounds without even looking at the cost effectiveness.
 

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I was erring towards the Solic due to the long warranty and seemingly basic and hopefully more durable design, did notice the eBay graded items at a discount so would buy that route provided they had the original warranty still. The iboost would be an easier install though.
Even then, I’m not sure it’s worth the extra outlay and added complexity, and so far the replies above seem to agree.
It is basically wrong to turn energy into heat, but if you make your own peanuts you might as well eat them yourself if nobody will pay for them. This does not seem to be the case here.
 

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100 litres of heated storage sounds a bit small for a family of 4. However you could crank up the storage temperature. Problem then is the risk of scalding for small children ( unless you have mixing/ tempering valves for your hot water taps or distribution).

Personally I'm a fan of maximising your own consumption of electricity and minimising one's own fossil fuel or gas consumption. For example I burn zero gas from March to September.
 

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Cost wise it probably isn't worth spending the money if you are getting paid for actual export.
It is good to be able to switch off the boiler when the heating goes off and not need it until autumn, but we don't have a gas supply to the house and on earlier deemed export so our hot water from the surplus generation is 'free'
 

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Yes if you have FIT with deemed export, no in your case as you don't have it.
 

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Yes if you have FIT with deemed export, no in your case as you don't have it.
In my opinion it's actually pretty marginal even if you have deemed exports:

Remember that you are not actually saving money at the expensive kWh rate for imported electric; you are only saving the cost of the gas that you would have actually used to heat the water which is usually lower than 1/4 of the price.

In my house we use the hot tap for at most 2 hours per week - this includes baths and showers which are run directly off the combi gas boiler. It's a 25kW boiler so this adds up to around 2500kWh at a total cost of up to £75 per year at £0.03 per kWh for gas.

With a solar diverter - assuming that I already had a tank and immersion heater - I would probably only be able to save up to half of that because you still need hot water on cloudy days and in the winter. So total savings would be a generous £40 per year.

The cheapest diverters seem to start at around £200 although I am unsure of the total cost including installation. Assuming it costs £300 all in and is guaranteed for 10 years, that's a potential saving of £100 in the first decade. If it lasts another 10 years, it might save you another £400, but it's far from guaranteed. If the diverter fails after 6 years then you have the potential expense of getting an electrician to remove it so that you can send it back for repairs and then the cost of fitting the replacement which would almost certainly swallow all of the savings that you made.

Now, you might use more hot water in your house and you might have nothing better to do with the energy; and, regardless of the financial savings, you may prefer to reduce your demand for fossil fuels. However, the likely result of you exporting surplus solar energy is to reduce the grid's demand for gas generated power so even that argument is uncertain at best. This also assumes that you don't have anything else to use that surplus generation such as an EV with a Zappi or equivalent and that battery storage doesn't become more affordable in the next decade.

I won't be buying one!
 

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It won't be financially viable to install a solar diverted gadget in your current circumstances.
If you're a sucker for gadgets and MUST have one whether you actually need it or not, fill your boots.
From personal experience, I'd reckon your solar array would only heat your hot water tank sufficiently for 6 months of the year.
 

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I bought a "Solar iBoost" when my timer gave out, since it can fill the role of timer as well as diverting "excess generation".
It has since been replaced by an "Eddi" as part of the install of our new hot water system using a Sunamp phase change thermal store - so I have one going spare that I must get around to putting on eBay or similar one of these days.

Economically it doesn't sound worthwhile for you, but might still be worth it if you wish to reduce your "personal" carbon footprint, particularly if you can get a cheap deal on a suitable (used) unit.
 
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We had an Optimersion fitted when we had the PV fitted about 5 years ago. In the summer the only gas we use is for cooking and to top off the hot water before we get up so the water is hot enough to get washed. We're on a FIT that pays regardless of how much we export so whether its more cost effective than fossil fuels isn't a consideration for us. It paid for itself within the 1st year so I'm happy and as mentioned, it does reduce my carbon footprint regardless of whether or not I'm saving money.
 

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It paid for itself within the 1st year so I'm happy and as mentioned, it does reduce my carbon footprint regardless of whether or not I'm saving money.
I'd love to see your calculations for how it paid for its self. As shown above, I calculated that I could only save around £40 per year. Was it particularly cheap, or do you use an enormous amount of hot water? I'm genuinely curious to see the numbers in terms of kWh saved.
 

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Not every one is on a gas combi boiler.
We don't have gas and have a hot water tank. Being able to heat all our hot water from April to September means I can switch the boiler off when the heating goes off for the summer. I haven't experimented with running just the hot water for long during the summer so I don't know how much it costs to heat our hot water but with a wood pellet boiler the saving will be over £100 for the 4-5 months the boiler is off, plus a smaller contribution for the rest of the year. I did try out for a few days when we first had the boiler fitted and for heating hot water only it was very inefficient, between £1-2 per day.
 
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