Please check my parents Solar plans

[Deleted User]

The bit that I am struggling with is the lack of Social Energy price information. For example, who would want to export battery power at 5.68p/kWh only to buy it back at 14p/kWh. This would presumably take place at peak periods when the supplier would be making £s. Some Octopus battery exporters on Agile Outgoing were making £2/kWh over the last few months.

My situation is similar to your parents. My array generates about 6000kWhs per year. To cover the lack of solar in the Winter months, the battery requires about 800kWhs from the Grid. We consume about 4000kWhs/year so it follows that we export about 2800kWhs a year to the Grid. My import cost is £40 a year and I generate about £154 (@5.5p/kWh) in SEG payments. The £114 difference between export and import covers my daily standing charge so my electricity is free. 

I could increase the saving by a further £100 a year if I switched to the Tesla Energy Plan. Tesla would take over control of my battery with an estimated matched import and export of 3900kWhs/year. The Plan is run by Octopus on behalf of Tesla at 11p/kWh import and export. So far, I am sticking with what I have as repeated charging/discharging isn’t good for battery life.

So how much is my array/battery saving me a year? I could play ‘man maths’ and choose the highest fixed price tariff in the land and would be lots but I would only be kidding myself.

Petriix

Batteries do not pay for themselves within their usable lifetime under normal usage patterns. Social energy are not transparent in their 'energy trading' payments so it's impossible to calculate the benefits. I'd steer well clear.

A typical 6kWp array should cost around £5k fully installed. That would take around 14 years to break even in normal circumstances. Get quotes from small, local installers without the glossy brochures and pushy salesmen. My panels were installed by a couple of guys with a van and a ladder in around 3 hours.

Solarchaser

Petriix said:

Batteries do not pay for themselves within their usable lifetime under normal usage patterns. Social energy are not transparent in their 'energy trading' payments so it's impossible to calculate the benefits. I'd steer well clear.

A typical 6kWp array should cost around £5k fully installed. That would take around 14 years to break even in normal circumstances. Get quotes from small, local installers without the glossy brochures and pushy salesmen. My panels were installed by a couple of guys with a van and a ladder in around 3 hours.

I know you love to bang the drum about batteries never paying for themselves, but your statement above cannot be proven.
Simply put, no-one knows how long batteries will last at this point. 
Most have a 10 year warranty sure, most cars have a 3 year warranty,  does that mean you scrap them after 3 years?
Most power tools have a 1 year warranty etc etc etc.

Can you get a 10 year roi with batteries, yes!
Are you likely to, no!
Normal useage just now makes it likely to be a ~15 year payback, optimised usage likely a ~12 year payback. 
However with TOU tarrifs more likely to be the default in the coming years, there is a higher than average chance that batteries will fall into a 10 year roi.

You said useable lifetime,  but no-one knows what that is yet.
Solar panels were seen as a 20 year max proposition,  but there are many lasting past that.

Finally most people agree £1/w is a decent price for solar, so a 6kw system should be able to be got for £6k. You might be lucky and get it for £5k, but you would need to be really lucky.
More often than not its more like £6k for 4kw.

Small companies are more likely to phoenix themselves which makes any warranties invalid, so sometimes its better to go with a larger company for more piece of mind.

Social energy to me seems like a scam, so I agree with you on that point.

Petriix

Solarchaser said:

Petriix said:

Batteries do not pay for themselves within their usable lifetime under normal usage patterns. Social energy are not transparent in their 'energy trading' payments so it's impossible to calculate the benefits. I'd steer well clear.

A typical 6kWp array should cost around £5k fully installed. That would take around 14 years to break even in normal circumstances. Get quotes from small, local installers without the glossy brochures and pushy salesmen. My panels were installed by a couple of guys with a van and a ladder in around 3 hours.

I know you love to bang the drum about batteries never paying for themselves, but your statement above cannot be proven.
Simply put, no-one knows how long batteries will last at this point. 
Most have a 10 year warranty sure, most cars have a 3 year warranty,  does that mean you scrap them after 3 years?
Most power tools have a 1 year warranty etc etc etc.

Can you get a 10 year roi with batteries, yes!
Are you likely to, no!
Normal useage just now makes it likely to be a ~15 year payback, optimised usage likely a ~12 year payback. 
However with TOU tarrifs more likely to be the default in the coming years, there is a higher than average chance that batteries will fall into a 10 year roi.

You said useable lifetime,  but no-one knows what that is yet.
Solar panels were seen as a 20 year max proposition,  but there are many lasting past that.

Finally most people agree £1/w is a decent price for solar, so a 6kw system should be able to be got for £6k. You might be lucky and get it for £5k, but you would need to be really lucky.
More often than not its more like £6k for 4kw.

Small companies are more likely to phoenix themselves which makes any warranties invalid, so sometimes its better to go with a larger company for more piece of mind.

Social energy to me seems like a scam, so I agree with you on that point.

I've never seen any actual figures that back up that 15 year ROI for batteries, let alone anything shorter. But I take your point about the potential longevity. I just wouldn't advocate making a long term investment based on something significantly outlasting it's warranty.

My gripe with batteries is that I'd really love to have one, but there's no way I can make the numbers work. I generate far more than I could ever use in the Summer and use far more than I can generate in the Winter so I would only ever be able to halve my total imports with optimal use.

I would need a 15kWh battery to enable a full shift to off-peak and, with the higher standing charge, my total savings couldn't exceed £250 per year. I'm not sure what 15kWh battery systems cost £3750, which is the price it would have to be for my £250 saving to give a 15 year ROI.

I'm sure a really high user would be able to double my annual savings, pushing the budget close to a Powerwall so maybe a 15 year ROI could just about be achieved by someone with an existing solar PV array that receives deemed export payments. However, any new solar installations are dependent on metered exports for their SEG payments so the savings calculation has to account for the loss of 5.5p per unit that is stored rather than exported.

I'm all ears if you want to show me some actual figures which contradict me. Maybe there's something I'm missing.

Petriix

By the way, my EV has a 7 year warranty. And, while I will hopefully save around £10k over that time in comparison to driving a diesel car, I'm under no delusion that it will actually pay for itself in that period (or ever). It's a bigger picture and I'm willing to swallow the cost of the depreciation in order to have the luxury of a new car for the same overall cost of ownership of a much cheaper second hand ICEV. I'm sure people have similar reasons for investing in a battery that may never break even.

Solarchaser

I won't pre-empt my full calculation for the year that will happen at the end of this month (I will have had 17kwh for a year at that point.) I can tell you that if you are looking for a decent roi then a powerwall will never be a great example.

My own example is two lux running in Parallel  with 8x 2.4kwh pylontech batteries.
All together has cost just over £6k.

But if we take your own example of using solar for half the year on 15kwh, and assume you would never use a tou tarrif, so for arguments sake say you switch the batteries off between October and April but empty and fill on solar every day between April and October then that's 15x (365/2) x 15p/kwh  [change it to whatever you pay for leccy]  =£410 a year saving.  For my £6k makes around 15 year payback. 

Now I don't know what you pay for leccy, at the moment 15p is generally seen as the average.
But you asked for figures while providing none to base it on, that's my general answer with your proposal and what I paid for my batteries and inverters. 

Petriix

Thanks for showing your figures. 15p seems very high; I've never paid more than my current rate of 12.4p. My total annual bill is less than your suggested saving, but I guess you took 15kWh as my average daily usage whereas it's actually my peak usage. I average under 6kWh of imports and around 3.5kWh of self-consumption of my solar generation (excluding the EV). I know that I am a low user so not the best candidate for batteries.

I generate over 10kWh just under half of all days on average so let's assume that I can cover my usage for half the year, although I do use more electricity in the winter with the dryer in action when the weather is too cold to air-dry the washing. So I could self-consum another 5.5kWh for 180 days saving me 5.5 x 180 x 0.124 = £122.76. This ignors that I already divert around 1000kWh per year to the EV with my Zappi.

If I was getting SEG payments rather than deemed exports then the saving would be 5.5p less per kWh, so around £70 per year. Even if the battery allowed me to self-consume all 3500kWh that I generate instead of the 1250kWh I currently use (excluding the EV), that's 2250 x 0.124 = £279 per year with deemed exports or just £155 on SEG.

If I went with Octopus Go then I could switch 90% of my imports to overnight at 5p, but it would add £50 to my standing charge while saving me £75 on the unit costs (again, excluding the EV because a battery system doesn't impact that), so a total saving of £25 over sticking with a single rate.

Like I said, I'm sure a high user (with a bigger PV array) could maybe double my savings, but it's still not looking good without deemed exports.

Solarchaser

I've always said batteries are borderline for low users, and you are a very low user, so looking from your point of view, batteries would struggle to make sense even at £100/kwh, so you will be waiting a while.
I picked 15kwh because thats what you said you would need, in reality you would opt for less than half that, and so the price of most of the kit would half with it.

But let's be honest, you don't spend enough on electricity ever be seriously interested in batteries.

Petriix

Solarchaser said:

I've always said batteries are borderline for low users, and you are a very low user, so looking from your point of view, batteries would struggle to make sense even at £100/kwh, so you will be waiting a while.
I picked 15kwh because thats what you said you would need, in reality you would opt for less than half that, and so the price of most of the kit would half with it.

But let's be honest, you don't spend enough on electricity ever be seriously interested in batteries.

The thing is, my actual total usage isn't all that low: (approximate kWh)

• House: imports 1750, self consumed solar 1250
• EV: imports 1000kWh, self consumed solar 1000kWh

So that's around 5000kWh.

Obviously I manage to use a good proportion of my generation already, which is why I left the EV out of my calculations. My point is that it is extremely unlikely that *anyone* can make a reasonable financial argument for domestic battery storage with a *new* solar PV installation.

If using the high price of 15p per kWh and ignoring the lost SEG payments just about makes a 15 year ROI for someone with usage of 5500kWh, what do those calculations look like for someone with normal usage (UK average is apparently 3700kWh) and not paying way over the odds for their imports?

I've analysed the data from my own 3.42kWp array (south facing, no shade) and, assuming daily use of 10kWh, the total shortfall of days when generation is under this is just over 1000kWh. That means, even with an infinitely big battery, I would still need to import 1000kWh. You could probably halve that if you double the array size so still 500kWh imported.

Let's argue that imports could all come from Octopus Go at 5p so £116.25 per year including standing charge for the 'with battery' scenario. Without the battery, let's assume that we could just about cover 40% of usage (like I do), although it might be more with a bigger array. So we're importing 2220kWh at a reasonable rate of 13p plus 15p standing charge = £343.35. That's a saving of £227.10 per year *before* considering the SEG payments lost which, at the low rate of 3p would wipe another £51.60 off your savings.

So, an average electricity user with a new PV array would be able to save £175.50 per year by adding a battery of sufficient size to hold a whole day's consumption. This is the information that we should be giving to anyone who comes on here asking whether a battery would be a good investment. The answer should always be that, unless you're a very high user, it's almost impossible that a battery system is right for you. If they happen to have an unusual situation where the numbers look better then it's worth taking a closer look to be sure, but it's definitely the exception rather than the rule.

Solarchaser

I think you make good points in general, but none in absolutes, and thats my problem with your continued stance.

If you say most people can't make battery roi in 10 years I'll agree with you totally, if you say most people may not make roi in 15 years I'd probably still agree.
However the problem is your blanket view of it not working for anyone.

It's like me saying to you, you will NEVER use more than than third of your solar power because previous to batteries I was only using a third of my solar power, yet from your self consumption it looks like you are managing something like 40% (assuming the array makes 3000kw or similar), so good for you, but many people cannot do that.

So if you take away your ev (a big house battery that you can drive rather than run the house with)  then you buy 1750kwh a year, that makes you a very low consumer, add on your self consumed solar and you are at 3000kwh a year, still a low user. 

I appreciate the fact you removed the EV, I think you are right to do that as it throws out the averages since so few households have them.
I'd muse that in 10 years with far more widespread ev usage the average electricity usage will rise significantly. 

Anyway back to the batteries, if you stop talking in absolutes we have general agreement. 

What do I mean by that, well let's tale your idea of doubling your solar array, well let's say dno says you can't export more than 3.6kw, so you double the array (at say £4k for arguments sake) but make very little more solar because its export limited, so that extra seg you were gonna get as roi for the extra solar is a no go, however the battery can now work to sup up that restricted export, so your 3.4kw array thats doubled to 6.8, anything over 3.6kw is denied export, but fills your battery, that makes it not a seg reducer at all.

And so if we then say that as most of us advise when getting solar to go as large as possible, but realising that it's very unusual to get a free pass on export from the dno, the stuff going into the batteries would all have been lost by derating the mppt to reduce export. 

I mean, sure we could argue about how much export you would actually lose, and how much the batteries would take that could have been exported on a marginal sunny day, but thats back to my point really., which is if you stop talking in absolutes then I mostly agree.... as will most folk.

Finally you have several times quoted a powerwall,  but the powerwall is one of, if not thee most expensive batteries, why not quote things that are much cheaper?
What about buying a sofar and 2.4kwh battery for £720 second hand... thats my story.
Forget about the two batteries I bought brand new, because that doesn't suit my narrative right now 🤔

So if we take it that I only ever used a third of my solar you could Likely argue that I could save 2kwh for I dunno, say 250 days of the year.
Let's go with your 13p, so 26p a day over 250 days is £75 a year saving, there I'm under a 10 year roi.
If we want to say I'm on seg at 3p (6x250 =£15) then that saving is £60 a year and so I'm at a 12.5 year roi.
If we want to say seg is 5p then its a 15 year roi.

So I fall back to my place before, just because you as a low user, and self consuming (with ev) over 70% of your solar cannot make batteries work, doesn't mean no-one can.

I WILL be under 15 years roi, so your statement that no-one can be is just wrong, so please drop the absolute statements.