Ditching gas, going electric immersion only, a wee project

Solarchaser

Where do I find charge stats?
Only thing I can find is charging history and thats only superchargers that are listed there

Heedtheadvice

......and now you are back posting after your 'holiday'....

How has your immersion system fared over winter ?

Solarchaser

I would say that the months of December and January highlight my bad decision in terms of opting for the smaller second tank, and because I still haven't either added another tank (decided I can't be bothered with the hassle/pain of doing that for the 2 months it's required) and i havent got round to moving the existing tanks to allow proper insulation surrounding them, 35kwh is not enough for those two months.

My work around for this has been to increase my battery storage size, and use that extra capacity to add 9kwh extra to the tanks around midday every day in December and January,  and this has worked perfectly to maintain the temperature above 50C for the whole day and crucially, heat the whole house to the point where everyone is comfortable without adding extra layers, which wasn't always the case in December and January a year ago.
So success, but I am still loosing a few degrees to lack of good insulation, and so still some work to do. This year!! (I hope)

Everyone who has come into the livingroom has commented on how nice the heated floor feels to, and I personally love it. Which is rewarding. 

Heedtheadvice

Thanks for the info. It was just curiosity to see how you fared.

So if I get this right you needed an extra 9 x 60 ( say ) 550kWh or so. At the recent cost of leccy that is about £150. ( ignoring your better Tarrifs to charge the batts)

That's still extra to buy but really hardly worth much more effort?

Hope you are quite content with your design/installation (admittedly not reaching your goal perfectly but well over 80% of need) .....and a success in my book. Well done!

Next step maybe add one of those salt heat stores  for your top up ? :-))

Solarchaser

I had similar calculations actually. 
If I was to heat an extra 9kw @30p over 60 days it was £162 and add another £54 to that for this month as I decided to add 6kw in Feb so its just over £200, but the tank is over £1k so at least 5 years payback, plus hassle.

I've trippled my battery storage now, so it should mean anything I'm adding is at say 9p, so more like £70 odds, making the difference more like 13-14 years.... ignoring the cost of the batteries, but they are mukti use, not just water

michaels

Do you have a TOU tariff with the batts?  Are you able to come up with a 'rule of thiumb' cost comparison between storing cheap overnight electricity as hot water as opposed to in batteries?!

Another thought, the batts have a round trip efficiency probably somewhere between 80 and 90% so possibly more loss than the lack of insulation on the tanks?!

Our peak usage on the coldest January day (about 0 max, -8 min) was 145kwh of gas and probably 20kwh of electric for space heating and hot water - guessing about 25kwh of that was hot water so it would need a pretty large volume of hot water to store that amount plus to 'charge' up in 5 hour cheap rate window would require 30kw connection (130A)!

Solarchaser

I'm on intelligent octopus, so 6 hours of 7.5p and the other 18 on 30p.

I dont really have a rule of thumb tbh.
My take is the batteries are a very nice to have, but the hot water is a must.
We need the hot water for .. well hot water, for the showers etc, but also for heating the house.

The batteries, just facilitate cheaper usage during the day.
I suppose you could argue the tanks do that also, as I could obviously heat the tanks with 30p electricity too, but the batteries for everyday usage are a nice to have, I have to buy electricity anyway, its nice to have it cheaper. With the tanks it's different because it needs to cost the same as, or less than a gas equivalent, or I'd be as well installing another combi.

My 800L is equivalent to roughly 35kwh, but thats assuming heat used only between 50 and 85C, there is an argument for using the tanks below that temperature,  definitely for space heating, but the family (wife) note the shower isn't as hot below a tank temperature of 50C, so that's my self imposed minimum.

I think I worked out my round trip on the batteries is 88%
With the tanks, my round trip is probably less during the really cold days because they are more affected by the increased delta of tanks at 85C vs outside temp of 0C or below, its hard to be definitive on loss as the tanks are only sitting at 85C for a couple of hours before the heating comes on in the morning.
Temperature sensors tend to report a loss of 1-2C between heat up and first use,  but the sensors are at one part of the tank, so it's hard to be definitive.
I was thinking maybe 80%, but that would mean losing a 1/5th of the heat, so I think perhaps 90% is more realistic, losing 3.5C from both tanks.
It gets used every day, and so I'd only really know if I heated them and didn't use hot water or heating for a full day, and compared the temperatures.
I'm not sure I can justify a couple of days away on the basis of testing my heating system efficiency. 

Between the morning heat up and coming on again mid afternoon for kids returning from school, id expect to see some temperature decline, and I do, usually 2-3C, but until I eliminate ways of cold getting to the tanks, I can't really say it's not just cooler water slowly circulating in the tanks away from the coils. I dont think it is, I think it's the tanks cooling, but thoughts arnt proof.

145kwh of gas usage in one day... wow, that's alot, but yeah the house needs what the house needs.

Reed_Richards

You may have said this before (it's a long thread) but how do your tanks and your batteries compare in terms of cost of the equipment per kW of output?  If you ultimately want heat out then water used to be a much cheaper way of storing it but battery prices have fallen so I've lost track of how they compare.

Solarchaser

I dont think I've ever tried to work that out tbh.
Battery prices have come down to where you can now get 15kwh for around £2k so £133/kwh (ignoring inverter and wiring)
If I take the smaller tank as it was an off the shelf 300L tank I can see online for £960 which is around 13kwh between 50 and 85C and so £73/kwh.(ignoring pump and plumbing)

So the water tank is a clear winner in cost for kwh, even with the recent drop in battery prices

michaels

Solarchaser said:

I dont think I've ever tried to work that out tbh.
Battery prices have come down to where you can now get 15kwh for around £2k so £133/kwh (ignoring inverter and wiring)
If I take the smaller tank as it was an off the shelf 300L tank I can see online for £960 which is around 13kwh between 50 and 85C and so £73/kwh.(ignoring pump and plumbing)

So the water tank is a clear winner in cost for kwh, even with the recent drop in battery prices

I guess you then have to divide the capital cost over the lifetime cycles where again presumably the tank beats the batteries again.

Against this, obviously the tank only stores heat whereas the batteries store electricity that can replace peak electricity use rather than just gas use and then there is the unknown question on efficiency.