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I am in the process of buying a house with solar that was installed back in 2011, so has a healthy FIT income. It also gets some cash each year from a community payback fund for a nearby windfarm. Between the two the estimated income will be about £1700 year, not including export paymemts or imported electricity savings. Since I'm out at work all day I'm very seriously considering a battery, both to store my solar and timeshift cheap overnight rates in winter. With the FIT income payback should be quite short.

I have a Zappi currently, which I plan to move to the new house (or if it's horrendously expensive to move consider a new one).

Initially I'd plan to charge battery with solar, where possible, and use that to run the house and small top ups for the car. If I'm home during the day obviously the car would be plugged into Zappi to top up from solar directly. I'd also move to a cheap overnight electricity tariff, probably Octopus Go, that I can use for the bigger car charges and charging the battery in winter.

The house currently has LPG heating, which I plan to change to air source heat pump after I've upgraded the insulation and probably the windows and doors. My hope is the battery would help for this as well, to time shift cheap electric. The solar inverter was replaced in May this year and is in warranty until 2022, so I don't need to budget for one of them in the very near future.

So my questions:
Any battery suggestions? I am tending towards a Tesla Powerwall 2, but struggle to give any good reason why!

Would it be worthwhile getting the same person to install my Zappi and the battery, preferably at the same time, so they have the headache of making everything speak to each other properly? Does anyone have experience of a similar setup? (I'm sure there's a Fully Charged episode about it that I'll rewatch)

Can anyone see any major flaws in this plan I haven't thought of yet? Or any suggestions?

It's slightly tricky in that I don't know exactly how much electric I'll be using, since I don't have baseline useage data for me and with the plan to move to electric based heating in future.
 

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One of the bosses of this firm is on here. They can do a quote for batteries and paybacks based on your usage and a variety of capacities. We had a look, but the payback for us was too long, despite having some 2011-vintage panels providing a similar income to yours.
 

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One of the bosses of this firm is on here. They can do a quote for batteries and paybacks based on your usage and a variety of capacities.
Thanks for the plug, it's much appreciated!

@Jayne your plans sound good but perhaps a little ambitious? You don't say what size of solar array the new house will come with, but unless it's very large it will be challenging to power everything you suggest, at least outside the summer months. Most people do not generate enough solar to power the house directly, fill a battery, charge a car and power an ASHP. You're right though that you can top up with lower price overnight electricity to make up some of the shortfall.

I've just bought a house in the country and installed 10kW of solar on the roof. But it's being decimated by the Aga which takes a huge amount of electricity so our battery is rarely filling up. Anyway, that's a story for another day (possibly involving an Aga being sold off).

With regard to the Powerwall I'd say it is a very good battery technically and about the best on the market for cost in terms of £/kWh. However it is rather large for the UK market and most households would struggle to fill it, and therefore make the best use of it. We offer a range of alternative battery systems and the most popular, the PowerBanx, can take from 1 to 8 batteries each of 2.4kWh. Most of our customers take 2, 3 or 4 batteries initially with a view to upgrading it later if they see a need. Prices start at £3k installed.


Would it be worthwhile getting the same person to install my Zappi and the battery, preferably at the same time, so they have the headache of making everything speak to each other properly? Does anyone have experience of a similar setup? (I'm sure there's a Fully Charged episode about it that I'll rewatch)
I wouldn't worry too much on that score - the Zappi will need a CT clamp installing around the power feed from the battery, but that's easily done - there's no other interfacing or connection between them.
 

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Thanks @Trevor Larkum, my plans for the house are certainly ambitious, I'll give you that.

I'm not actually expecting the solar to provide much more than day to day baseload in the house. Anything to the car would be a bonus. And since heat pumps are needed most when there's least sun, again, anything is a bonus. It's only around 4kWp with not much space to expand in future. It won't be the main source of electricity, but it is a pretty decent source of income (to pay for said battery.)

In my current house each month I use, very approximately, 10 kWh peak (weekdays 4-7pm), 100 kWh off peak and 200 kWh night (11pm-7am). Gas central heating and hot water, everything else electric. Majority of night use is car, which will increase at new job/house with longer commute.

If I'm honest the main benefit of a battery would be load shifting rather than solar storage. I'd prefer a battery sooner rather than later, but an issue is that the upgrades needed before heat pumps (ie more insulation and probably doors and windows) means I really don't know what size heat pumps will eventually be needed, which in turn means I don't know how much power it would be useful to store for them. Those bits will take at least a couple of years to sort. So the obvious options are either a big battery now or one that's expandable in future. Something that has decent power output would also be useful for the times I'd be running higher loads like cooking dinner while the heating is on. Again, not expecting to charge the car from it routinely. I wouldn't expect power cuts to be enough of an issue to worry about it acting as a UPS.

From an eco perspective I don't mind using grid electric. Nearly all grid generation nearby is either wind or hydro. If I can top it up with a little of my own solar then great. I like the idea of a 2nd life battery, but the main one I've seen is the Powervault eco which only has three years warranty.

I'll go have another read about the PowerBanx system. I would ask for a quote, but I'm sure I remember you telling someone in England they were too far north, so I'm pretty sure the Highlands will be way too far!
 

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We had an old gas cast iron boiler, used about 24,000kWh of gas to heat our home. With modest 100mm under 50% of ground floor insulation and 50% of walls insulated with 50mm of Celotex, draughts reduced, a ASHP now does DHW and heating for about 3,500kWh of grid electricity, plus use of 3,600 kWh of solar PV during the year. For 6 months the solar PV gives most of the power for DHW except for the final heating up to 50c.

This should give an indication of the power needed fir an ASHP, and ours is functioning in a 1930 solid wall detached house, so no new build warm place.
 

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I have considered a battery, but not sure that it will improve our costs nor improve our emissions. Just pleased that we have moved away from fossil fuel use at home, except for tiny amounts of mains gas for cooking.
 

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Discussion Starter #7
This should give an indication of the power needed for an ASHP, and ours is functioning in a 1930 solid wall detached house, so no new build warm place.
That is really helpful, thank you.

This is a 1980s detached self build bungalow built by a builder for his own home. Cavity walls are insulated, although I'm not sure how wide the cavity is or what they're filled with. No underfloor, but has 250mm loft. Hardwood outside doors and windows, original, very good condition but 30 yrs old (I've got a real dilemma about what to do them). Open fireplace. That giant airleak is going to get closed up. May replace with log burner, may not.
 

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I have considered a battery, but not sure that it will improve our costs nor improve our emissions. Just pleased that we have moved away from fossil fuel use at home, except for tiny amounts of mains gas for cooking.
The main benefit that you might get from a battery is load shifting. If you use a variable tariff, you could charge the battery at cheap rate and use it when grid electricity is more expensive. Depending on the size of the battery, all your usage could be at the overnight rate - for Octopus that's currently 5p per kWh. Of course you'd have to save a lot of money to offset the cost of installing the battery...
 

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Have you been on the myenergi forum? There are some complex set ups discussed on there and you might get some interesting ideas and find out how the Zappi will interact with the battery.

Most aren't doing it for cost saving reasons and with some it sounds like there's plenty of money being spent on batteries, cars, chargers and various tech to link it all together.
 

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Thanks @Trevor Larkum, my plans for the house are certainly ambitious, I'll give you that.

I'm not actually expecting the solar to provide much more than day to day baseload in the house. Anything to the car would be a bonus. And since heat pumps are needed most when there's least sun, again, anything is a bonus. It's only around 4kWp with not much space to expand in future. It won't be the main source of electricity, but it is a pretty decent source of income (to pay for said battery.)

In my current house each month I use, very approximately, 10 kWh peak (weekdays 4-7pm), 100 kWh off peak and 200 kWh night (11pm-7am). Gas central heating and hot water, everything else electric. Majority of night use is car, which will increase at new job/house with longer commute.

If I'm honest the main benefit of a battery would be load shifting rather than solar storage. I'd prefer a battery sooner rather than later, but an issue is that the upgrades needed before heat pumps (ie more insulation and probably doors and windows) means I really don't know what size heat pumps will eventually be needed, which in turn means I don't know how much power it would be useful to store for them. Those bits will take at least a couple of years to sort. So the obvious options are either a big battery now or one that's expandable in future. Something that has decent power output would also be useful for the times I'd be running higher loads like cooking dinner while the heating is on. Again, not expecting to charge the car from it routinely. I wouldn't expect power cuts to be enough of an issue to worry about it acting as a UPS.

From an eco perspective I don't mind using grid electric. Nearly all grid generation nearby is either wind or hydro. If I can top it up with a little of my own solar then great. I like the idea of a 2nd life battery, but the main one I've seen is the Powervault eco which only has three years warranty.

I'll go have another read about the PowerBanx system. I would ask for a quote, but I'm sure I remember you telling someone in England they were too far north, so I'm pretty sure the Highlands will be way too far!

Size of the curtailage?

Wind to balance out lack of sun in windy Highland winter?
 

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Discussion Starter #11
The main benefit that you might get from a battery is load shifting.
...
Of course you'd have to save a lot of money to offset the cost of installing the battery...
Yeah. That's why I've decided it's gonna be the solar FIT and windfarm community payback that'll pay for the battery. And savings on imported electricity just make payback quicker. One advantage of buying a house with solar already there, I don't need to pay for installing it! And I'm not convinced the house was valued any higher with having it to be honest. Their loss.

Have you been on the myenergi forum?
Good point. Not been on there in ages. I shall investigate.

Wind to balance out lack of sun in windy Highland winter?
I wish! Despite being well up the hill it's a relatively small plot and surrounded by trees/high hedges in a bit of a dip, so it'll be too sheltered. There's a house a couple of minutes down the road with their own wind turbine and a small (eight turbine) commercial windfarm about five min the other way so the potential is there. There's also a decent sized burn just the other side of my neighbours, but again not my land, so no option for run of river hydro either.
 

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Buy adjacent land plot?

Privately owned adjacent land?

Even if you don't meet the Scottish criteria for distance to boundary of your own curtilage, it's still possible to go down the planning approval route but you might need to go armed with windspeed data.
 

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Discussion Starter #13
Buy adjacent land plot?

Privately owned adjacent land?

Even if you don't meet the Scottish criteria for distance to boundary of your own curtilage, it's still possible to go down the planning approval route but you might need to go armed with windspeed data.
At the moment I'm filing wind under something that would be good but I'll see what my power useage is over the next few years and decide if it's worth persuing.

My uncle has a 6kW wind turbine with a big thermal store. He gets so much power he hardly knows what to do with it. There were so many delays in the planning process the big FIT payments he planned as a source of retirement income are now much smaller so it hasn't quite panned out the way he planned.

If something like the IceWind turbines actually worked, and were available, it could be an attractive smaller scale option to cope with more turbulent wind. But I really haven't seen much about vertical axis wind turbines that's very encouraging. Will speak to my cousin about it sometime. His company installs and maintains domestic wind turbines, among other things, so no doubt he'll have an opinion!
 
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