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Fogstar battery for £5490
I’ve worked out that installing a 32 kWh Fogstar battery for £5490 with 6 kw inverter or a 48.3 kWh battery with 8kw inverter for £6900 should save me around £2000 a year charging up off peak on Intelligent Go. We use around 25kWh peak electricity a day and another 10+ on average off peak charging the cars daily (we tend to charge each usually 50% once a week, but if go on long trips this can be higher).
Does this sound like a plan? Seems I’d get a quick ROI. Are these batteries any good? Anything I need to watch out for?
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17 Replies
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Sounds great. It you add solar too every kW of solar adds 3 points to your house EPC and will enable you to maximise export at 12p per kWh which’s more than you are paying to charge batteries.
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yeah I thought the solar, once you basically get the electricity to 5 pence per kWh becomes more difficult to justify? Could I export on Intelligent Go? I thought I could maybe add that later.
Does this sound a good price? Should I go with bigger battery based on my useage or is smaller one enough?
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if you are a really heavy user go with the bigger battery providing the invertor can charge at a higher enough rate to fully charge it in your off peak period.
You need to use an MCS Supplier to install the solar so they can apply to the local DNO for export approval. The MCS paperwork is also used for proof re the EPC.
We charge our batteries to full each night so the solar runs the house, then tops up the battery and then exports. from 1st April we will be charging the battery at 4p per kWh and exporting solar at 16.5p per kWh but our export contract finishes end October this year so we will see what is available.
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You learn things once they are up and running.
My system is now 3 months old. Simplistically, on IOG I charge batteries overnight and they time shift home usage from peak to off peak.
Almost all of the solar gets exported.
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Yes, cheap batteries with good inverters are the only financially sensible way to do this. Do not be like me and get 3 Tesla PW3s. Solar wont ROI as fast as cheap batteries will.
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your logic is sound and it’s where is started in my deliberations.
Ignore your EV consumption when sizing the battery. As for the inverter I suspect either will do.
There are two main factors that influence the inverter size – only one applies to you
1. Household sustained peak load – if you run multiple 3kw cookers for hours a day then you’ll need a bigger inverter than if you run 1 cooker for an hour. The emphasis here being on sustained load. My main household peak load is around 3kw, although I have a 9kw electric shower in the morning. However as it only lasts 10 minutes a 9kw inverter would be overkill.
2. Size of the array on each string. Most inverters have limits in terms of the amount of solar they can take on each string input (MPPT) and in total across all arrays. It is industry practice to slightly undersize the inverter and whilst this can result in clipping, it’s a balance between an oversized inverter that may not generate well in low-light/morning/evening and an undersized one that could result in clipping. This post explains a little bit more
https://freedomforever.com/…/solar-academy-lesson-5
Lastly whilst not really a consideration, it’s important to be prepared to change the design depending on what limits your DNO may put on your system from an export perspective. Having a huge array and a large inverter that is restricted by your DNO to 3.6 kW export might be a waste unless you have a significant household demand that can consume the majority of what is generated and therefore you’re not losing much through an export restriction
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see my free home battery calculator here that you can use to work out a reasonably accurate payback period:
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That’s exactly what I’ve done 32kw storage bills literally gone down by 75%
I’d get a sunsync inverter as you can use the simple solar app with it and makes everything automatic unless your good with home assis
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One thing to watch out for is the max charging rate for your battery, ie can it be fully charged during the cheap rate period, if not, you don’t need such a big one. So, for example, our battery can only charge at a max rate of 3KW from the grid. Its 10KWh in size. The tariff we are on has 2 x 3hr cheap rates and 1 x 2hr cheap rate. So for us there’s not much point in getting a battery bigger than 10KWh
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thanks it says it can charge/ discharge at 300A by the looks of it, what is that is KW do you know?
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If your 25kwh daily consumption is consistent year round, 5 year payback on 32kwh battery makes a lot of sense.
Average UK house consumption is around 3000 kWh plus heat pump which could push it to 9-10k kWh annual. However the heat pump consumption is winter only so you have a higher winter average and a lower summer average. If that’s the case maybe a bigger battery would be better.
Download a years worth of historic data from your smart meter. You can analyse it yourself or also upload it to tools such as app.trent.energy and analyse for free.
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This is the battery specification
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I’m looking at a very similar setup. I’m pondering getting excess battery to export, but it seems there are potential issues with getting it easily controllable…
The package I’m looking at has the solis inverter, is this a practical solution? Is there a better alternative? I don’t currently have solar (cost/benefit with available space) but do charge an ev via zappi and on Octopus IG.
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I’d go for a bigger inverter to avoid any bottleneck. Mines a 3phase 10kw inverter so unlikely to ever be a problem.
But that’s a lot of battery storage. Do you really need that much?? Maybe, if you have a heat pump. But I use 12000 kWh Pa and the majority of that (with 7kwh panels and a 15kwh usable battery is just about enough)
With bidirectional chargers in the not too distant future your car itself could potentially give you a further 70kwh of storage.
The solar panels are relatively cheap nowadays. So it gives a bit of insurance against cheap overnight tariffs ever being pulled. And free electricity of Export and VPPs can help balance the grid and pay you an income.
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What’s your winter (say Dec to Feb) non EV average daily use.
Thats your battery size for running all day on EV rate (slightly less as you can ignore the consumption in the EV dip.
Anything more is likely to have a much lower RoI.
If you are likely to add a heat pump, you’ll want the monthly heat loss figures so you know what to allow extra for that.
My heat loss is tiny. My figure for January is 819kWh. SCOP of 4 : that’s then 205kWh which averages 7kWh (2.2kW heat loss at -5). It’s rare to have figures that low but you can scale.
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my daytime electric use is constant all year around as I don’t heat with heaters, that’s gas, and the only thing I have on more is lights but they are all LED. It’s about 25 kWh without the cars. We seem to be big electricity users, maybe it’s the 36 items I have connected to my wifi or the fact my wife runs washer and dryer basically 50% of the time!
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Same setup as me. Works a treat. Neednto be on IO Go and loadshift some things but it works.
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