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Hi, I'm considering installing a home battery storage system linked to solar panels. My main aim is to reduce our electricity costs and power our Leaf. I like the idea of being able to store energy when the sun's out or it's cheap (we have Octopus Agile) for use in the house and to top up the car. I've seen a few users describe having a system and wondered if anyone would share their spec/design and experience of installers?

I'm quite cautious about this and have been thinking and researching it for a few years. The number of variables to such as system mean that the selection of the wrong components could mean the final system doesn't do what it should. Add to this the expertise of an installer to put together an effective design concerns me. I'm sure there are folk out there who have developed such systems and know what works. Finding them is the problem.

For info, I live in Newcastle upon Tyne so I know solar isn't the best all year vs Southern locations. We have a gas combi-boiler (no hot water storage)for our hot water and central heating. Roof space is sufficient for a 4kw PV combination system of east, west and south generation.

I'd welcome any thoughts, tips, advice and comments.

40KWh Tekna, love it!
 

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Peugeot e-208
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I have a similar situation to you. Roof space for a 4kW array, although I only have W or E, not S. Also combi boiler and also in Newcastle!

I concluded that cost wise, it's very difficult to make the numbers add up - either for the pv or the battery. Likewise, the embedded carbon in all of the kit and installation for a small-scale solar is pretty high. I concluded that the money would be better spent elsewhere (ie invest in commercial solar), and the time and effort would be better spent make much lower tech adjustments. (Do your washing on a sunny day, avoid the evening peak, etc).
 

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2018 Nissan Leaf 40kWh Tekna - love it
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Yes, I agree with mad rich. Doing the cost/benefit calculations never seems to provide any financial advantage. I would suggest you do these calculations yourself and make your own mind up.
The problem with using a tariff like agile is that its very difficult to do the calculations on what you might save.
I was looking at how I might move all my daytime electricity onto the night rate on economy 7 (which I already have for heating) and payback was 20 years. I concluded that I would rather spend that money on other things. The electricity suppliers love it. Someone else paying for what they should be investing in.
 

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Nissan LEAF30
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Not just is the payback a long period but you have to question the life of the batteries and ancillary equipment - most is only warrantied for 10 years (such as the Tesla Powerwall2 at 80% in the UK).
 

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MG EZS 2020
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I was looking at how I might move all my daytime electricity onto the night rate on economy 7 (which I already have for heating) and payback was 20 years. I concluded that I would rather spend that money on other things.
Is this using a battery set-up only? My roof has an extra eave from the shape of my bedroom window which cuts into the space available for panels. I thought that I may use just a battery and, say, Octopus Go to shift my electric to the Go times and run electric heaters/water from the battery. Is this feasible?
 

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jim5452
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I have PV and have tried to justify batteries, but even taking into consideration the high rate of AGILE at the moment, there appears to be no way from a monetary point of view the they can be justified, taking in to consideration the losses going into the battery and further loss taking out, plus the cost per cycle.
So if I do decide to ignore cost it will be from the nice toys angle like other none essential items.
I better stop before I talk myself into getting one
 

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Yes, but look at the payback period. If you save the difference between peak and off-peak on Go that is less than 9p/kWh. If you consider a nominal system to store 1kWh per day that amounts to a saving of £32.85/year ignoring round-trip losses. Looking at prices in general to purchase a battery storage system, ignoring fitting, you'll be lucky to find storage at under £500/kWh so roughly a break even point of 15 years in an optimistic case. Factor in the roundtrip losses (15-20% minimum), fitting costs, finance costs etc. and it goes out further. All of which take you to at least the 20 years suggested by @EdH above.
If you are on Agile and seeking to offset the peak cost of 35p/kWh with "free" stored solar then things look a little better.
 

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Peugeot e-208
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When I asked a friend about it, he talked of 'using a £5,000 battery to store £2 worth of electricity' which rather put things into perspective.

For what it's worth, here's some research I shared with a few friends when I was (we were) considering it last year. I see I put a plug in for Fully Charged!

Calculate your yield here.

I reckon on my West facing roof, a 4kW array would yield 2850 kWh/ year. More than my annual usage of 2350kWh.

(South facing is best, obviously, but West is better than East because it's more likely to match evening household demand.)

Turn that into a rough model of monthly variation here:

Suggests that I would be in surplus between March-September, subject to being able to store enough energy to smooth out intra-day demand and day-to-day variation in sun.

Cost? Slate roof is the most expensive to fit to, fixed costs like scaffold accounts for at least 20% of the total cost (making smaller scale installation expensive). North of £6k for 4kW! 25 year guaranteed to 80% capacity, 40 year useful lifetime for the panels (but much less for the inverter - expect to replace once for £800). For what it’s worth, the Energy Saving Trust calculator above gives a ball-park saving of ~£195/ year (without batteries). Seems high.

Feed in tariff has ended now, but there may well be government incentives around the corner.

Battery cost is decreasing all the time, but currently cost-neutral at best over ten year lifetime of batteries. Wait a few years? But you have to balance this against the fact that VAT on batteries is 5% if you install at the same time as your panels, or 20% if you retrofit!

Alternative - much smaller battery to cover your use in the ultra-peak period of 4-7pm (charge from solar or off-peak grid) combined with a suitable tariff from your supplier. Or electric car + vehicle to grid technology.

System needs some clever design, and canny usage - matching demand with supply wherever possible. Timers for dishwasher/ dryer etc is a start. For example if you plug your car into a typical home charger (7kW) that's more than your 4kW array is producing, so you're importing from the grid even if it's sunny. Bad! Smart chargers are available which constantly monitor your household use and solar input, and aim to divert only the remainder and no more in your car, though you can up it to full speed if necessary.

Robert Llewellyn (he played Kryten on Red Dwarf!) is a somewhat surprising authority and enthusiast on EVs and renewable. V informative YouTube channel.

The house at the end of my street has gone solar, and I’m going to quiz them too.

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And here's his response:

I would step back in your questions one level, why are you thinking solar energy?

Is it to save money? Is it to achieve a cost neutral energy profile over the medium term? Is it to save carbon emissions from electrical generation at grid supply level?

You can model the ass of these things and the reality is you will not get a meaningful answer, the shape of the efficiency degradation curve if the key to long term performance and this is never know, panels are rated as % output at 10 yrs or similar, the key is if it degrade fast initially then plateau it will totally blow the model out the water. Similarly the costs is driven by the mechanism of installation and maintenance, you have a warrantee on the panels for a replacement part not a replacement installation, ie one panel fails they deliver a new one but you have the full scaffold cost to replace it. Similarly balancing string voltages on the panels etc will have a big impact as will the inverter performance. On batteries, this is similar, a £5,000 battery to store £2 of electricity is hard to make work on a pure financial calculation, further the battery tech is fairly heavy for environmental footprint, lithium comes at a big cost. If the battery is part of a total energy solution, ie a smart charging car that can sit at home in daylight hours, that does make the calculation more favourable.

If you are looking to save money don’t do it, switch your appliances to more efficient ones and turn off a few lights..

If you want to save carbon that is a totally different question, simple option is to go for a low carbon grid supplier, it can be argued that centralized renewable development has a lower whole life carbon impact than de centralised, ie invest in a solar farm don’t fit a domestic solar install.

However, what that calculation does not allow for is that by adding 4kw to your roof, it is an extra 4kw that was not previously available. It also works as a valuable tool to help us learn to monitor and use our power more intelligently. Add 4kw to your roof, use it wisely, try to reduce your total demand. Look at the numbers for the cost, expect it to be at a moderate cost and moderate financial risk over 10 years and if you can make your peace with that then do it.

Alternatively, group together and finance an installation of the roof of a commercial/school building that is under construction as a revenue generating/off setting scheme… this was popular as an investment mechanism under EIS tax etc lots of people lost there shirts on it but it is probably the best way to go if you follow the economics and science of the status of tech.

Short answer is probably switch off some lights, eat less meat, don’t fly places…. Sounds a bit dull though..
 

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Yes, I agree with mad rich. Doing the cost/benefit calculations never seems to provide any financial advantage. I would suggest you do these calculations yourself and make your own mind up.
The problem with using a tariff like agile is that its very difficult to do the calculations on what you might save.
I was looking at how I might move all my daytime electricity onto the night rate on economy 7 (which I already have for heating) and payback was 20 years. I concluded that I would rather spend that money on other things. The electricity suppliers love it. Someone else paying for what they should be investing in.
Yes even ‘want to buy it man maths’ returns a ROC of about the likely life of the battery kit before any ROI. At best it’s a bet on future electricity cost rises.

I have a programme of more and better insulation instead.
 

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Ioniq 38kwh 2020
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I would love solar but I can't even make the sums add up on them now the FIT has gone. So no chance with a battery storage. My electricity use is only around £350 (maybe £500 max now I've got an EV) per year. That's a long payback (even if I generated enough energy for my own use I'd still need to buy some energy and pay standing charges) even without factoring in things like replacing the inverter at 10 years average, or cleaning and maintaining the panels.
 

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I’ve heard of people who buy a sofa for £5k or even a new kitchen for £10k and never make their money back on it. :)

I’m getting a battery (LG RESU 10 kWh) fitted next week. In terms of pay pack, it’s around 8 years. I think in the UK it would be more like 14 years.

In terms of Solar PV side, I’d get as big an array as you can. The marginal cost for additional panels isn’t much when you consider the install cost, inverter, etc.

You’re not really going to charge the car from the battery. This is just for overnight use until the sun comes up.

It’s worth taking some detailed notes about your daily energy consumption so you can understand how much you use and when. This will help when you come to size your battery.

Don’t forget that energy use reduction is a key part of this. You might be able to get your overnight energy use down to 5 kWh, in which case a 6 kWh battery might work.

Then if you’re like me you’ll need the whole suite of MyEnergi products:
  • Eddi to divert spare energy to the hot water tank and pool pump, pool heater.
  • Zappi for using excess power to charge the car (only works when you have the car at home of course)
  • Hub to monitor it all.
Like I say, you don’t have to do it just because it saves money. Many people buy an EV because of the experience, not because it saves money.

What’s wrong with doing this because it feels good and you get satisfaction from reducing your demand on the grid?
 

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I don’t see the cost benefit unless your house is so remote that paying to add it to the grid would be prohibitively expensive.
 

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I’ve heard of people who buy a sofa for £5k or even a new kitchen for £10k and never make their money back on it. :)
One tends to get a benefit of owning a sofa or kitchen.

There's no benefit to a solar & battery installation if it's not saving money or carbon!
 
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One tends to get a benefit of owning a sofa or kitchen.

There's no benefit to a solar & battery installation if it's not saving money or carbon!
Then why do people buy expensive sofas and kitchens, or things that look nice?

Plenty of benefits from fitting a home battery.
 
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