Solar Panel Q&A

[BillyStubbsTears]

Solar benefit split between usage, export payment and night-rate differential ended up being a touch over £250 for May.

That's good going. Ours, being a smaller system, can't match that. But we have saved £136 in May and I'm dead chuffed with that. With the amount of electricity we've used, we'd have paid £125 at standard tariff. Instead, we have paid £15 (we've imported only 25% of what we've used and on average, because that's mostly been imported at night to top up the batteries, we've paid less than 50% of the standard tariff for that) and received £26 back for what we've exported to the grid. So instead of paying out £125, we've received net £11.

[Superspy]

Remind me - is yours roughly 5kw and south facing?
Would be interested in a straight comparison of generation. Ours was 844kWh for the month.

Everything I've seen online suggests, for my roof pitch, a reduction of about 15% as a result of it being east/west.

[Colemans Left Hook]

Solar benefit split between usage, export payment and night-rate differential ended up being a touch over £250 for May.

That's good going. Ours, being a smaller system, can't match that. But we have saved £136 in May and I'm dead chuffed with that. With the amount of electricity we've used, we'd have paid £125 at standard tariff. Instead, we have paid £15 (we've imported only 25% of what we've used and on average, because that's mostly been imported at night to top up the batteries, we've paid less than 50% of the standard tariff for that) and received £26 back for what we've exported to the grid. So instead of paying out £125, we've received net £11.

it's not that long since we had these ambulance chasers. Yes it's a different world now

https://mis-sold-solarpanels.co.uk/?gclid=EAIaIQobChMIgoj11qSk_wIVEvDtCh0BdQ2_EAAYASAAEgIAafD_BwE

sadly we have to "get real here"   that £10,000 invested at 4,5% yields say £450 per year   that's £37.50 per month "rising steadily " as interest rates go up

 I won't waste my time mentioning other depreciating variables .

[Superspy]

Yeah, I didn't go ahead with a quote for solar on my previous house quite a few years ago because the vibe I got was just "this isn't realistic" - his numbers didn't make sense at the time, and I would have had to finance it at a stupidly high rate, and I'm glad I didn't.
Feeling much more confident about this system though. Yes it was 13k, but my savings for the first 8.5 months are about 1k, and that covers a full winter, not a summer.
It helps that I have significantly high usage in the summer vs winter months to take advantage of the generation though.

[BillyStubbsTears]

A few thoughts from me:

1) Putin's War has changed the financial case for domestic solar beyond recognition. When electricity was 10p/unit there was no way the financial case could add up. With electricity at 30p/unit, it's a no brainer. Personally, I think the days of 10p/unit are gone forever. Europe is never going back to living off Putin's cheap gas, so there will be far more demand for other power sources.

2) Including a decent sized battery in a solar power system also radically changes the financial case. There's a £3-5k increased initial investment, but it gives such flexibility on usage vs production times that it pays back very handsomely.
electric tariffs. Batteries allow you to buy at the cheapest times and sell at the most expensive. In simple terms, they give you power in the marketplace that you don't have without your own storage system.

[albie]

To add to that, those thinking that they will next get an EV.

How much are you spending on fuel at present, and how much of that can be displaced by charging up from your own solar?

The answer will be different for everyone, but don't forget to include that in your calculation.

[BillyStubbsTears]

Albie.

I'm not at all convinced that EV really changes the financial argument. For the following reasons:

1) Most domestic solar systems simply don't produce enough energy. It's been sunny most of today. We are close to the solstice. I've got a standard 4kWp solar system and it'll produce about 22kWh today. Of that, I'll need 11-12 for my own domestic use. So there's about 10kWh left. A Nissan Leaf as a random example does about 35 miles on 10kWh. So even in close to ideal conditions, I'd only just be able to get a typical daily car mileage from my system (based on a typical average of 10,000miles/year).

2) And that's assuming my car was plugged into my solar system while the sun was shining, and I didn't have it at work. If the car wasn't at home, the only way I could charge it from my own solar generation would be to store the solar production in a 10kWh battery - but I already rely on my battery to power the house after the sun has gone, so I'd have to buy a new one on top and that would cost me an extra £3-5k investment.


Where EV does make sense is if you can use an ultra-low import tariff overnight, like Octopus Intelligent, where you can get electricity at 7.5p/kWh for 6 hours a night. If you also have a decent size battery, you can charge that up overnight at the same rate and run the house off that during the day. That's a stone cold no-brainer for anyone with an EV. Unfortunately, I can't get that as I don't have off street parking and therefore can't get the EV charge point that is a pre-requisite for that rate.

[Superspy]

All depends on individual circumstances, not withstanding your point that my system is larger than average.

For someone like me, with a larger than average system and working from home, the EV will definitely be charged from the surplus solar.

Part of the problem is that taking it as a simple calculation of daily generation minus daily home requirement = surplus doesn't really work in practice because of the limited window in which the power is generated. If I don't use it in the middle of the day then it's exported and isn't available for me at night, so charging an EV at lunch time doesn't take away from power the house would use later, it kust takes away from the amount I'd export.

I reckon when my EV arrives I'll be dropping my 1400 per year fuel cost down by about 80 a month at least. However, it isn't really saving me anything in the grand scheme as the new car is more expensive than my current one.

[BillyStubbsTears]

SS.
Seems to me you are far better off just using/exporting your solar generated electricity, then charging the EV at low tariff times at night?

[BillyStubbsTears]

Just done some fag packet calcs based on those Nissan Leaf numbers.

The reported figures for the Leaf are that it does about 3.6 miles/kWh. If you charge up at 7.5p/kWh, that means you'd get 48 miles per pound.

At current petrol prices, you'd need an IC car that did 300 mpg to match that.

[Superspy]

SS.
Seems to me you are far better off just using/exporting your solar generated electricity, then charging the EV at low tariff times at night?

Ah, but the missing piece of the puzzle there is that I currently get 22p per kWh as an export rate but only because I'm on the Flux tarriff - which is dual income/outgoing tarriff. My night rate is about 19p to import.

So, if I was to move onto Intelligent Octopus to get the 7.5p night rate, I'd have to sacrifice the export rate down to 15p. So I'd be gaining 11.5p per unit for each unit imported over night, but losing 7p for each unit exported at all times. The amount I'm likely to be charging the car is very small compared to the amount I'll be exporting in summer (estimate 50kWh charging for May vs 350kWh export). In winter I'll be switching onto a more cheap-import focussed tariff. While the market is as it is I'm expecting to be swapping tarriffs every 6 months - export based with daytime charging in summer, import based with night time charging in winter.

[albie]

Solar car park canopies on the way:
https://www.bbc.com/news/business-65626371

Many opportunities to include solar on existing infrastructure, as well as buildings.

[albie]

BST,

You have bit of a tendency to extrapolate from your own situation, but that is not representative of all users.

You are not taking into account those who have solar, but do not have battery storage.
This might for some be because of the additional cost, and I think that they are the majority of solar owners in the UK today.

In this situation, storing electricity at lower night time rates is not an option.
If you have an EV, and bi-directional charging, the EV becomes the storage medium by default. It is called vehicle to grid (V2G).
You can then choose to use that energy for either transport or domestic consumption.

The point being that you have the flexibility to decide how best to use the resource. Behaviour then changes to match the incentives.
Given that most cars are parked for 90% of the time, that waiting time is a charging opportunity looking for an opening.

Again, the optimum solution will differ person to person...there is no right answer!

[Superspy]

Solar car park canopies on the way:
https://www.bbc.com/news/business-65626371

Many opportunities to include solar on existing infrastructure, as well as buildings.

Stuff like this seems like a no-brainer.

[mugnapper]

Solar panels - an eco-disaster waiting to happen? https://www.bbc.co.uk/news/science-environment-65602519

Trust the Beeb to temper your fun.

[albie]

The idea that a recycling industry will not emerge is just bonkers.

Once the volume of end of life panels becomes a significant number, then recycling the aluminium and other elements will be a valuable activity.
The panels should last 20 years plus, so the replacement date is not imminent yet for most installations.

All recycling operations need an input quantity to give a baseline to the business.

Article in the Times on the uptick in solar installs:
https://www.thetimes.co.uk/article/d7e405e6-fc70-11ed-aa31-73394e195d29?shareToken=9f47caea3f077a793c475a722752538e

[BillyStubbsTears]

BST,

You have bit of a tendency to extrapolate from your own situation, but that is not representative of all users.

You are not taking into account those who have solar, but do not have battery storage.
This might for some be because of the additional cost, and I think that they are the majority of solar owners in the UK today.

In this situation, storing electricity at lower night time rates is not an option.
If you have an EV, and bi-directional charging, the EV becomes the storage medium by default. It is called vehicle to grid (V2G).
You can then choose to use that energy for either transport or domestic consumption.

The point being that you have the flexibility to decide how best to use the resource. Behaviour then changes to match the incentives.
Given that most cars are parked for 90% of the time, that waiting time is a charging opportunity looking for an opening.

Again, the optimum solution will differ person to person...there is no right answer!

Albie.

I'm not extrapolating from my own situation at all. I'm looking at typical averages.

The average domestic solar installation is 4kWp. The average domestic electricity usage is around 10kWh/day. The average mileage is about 10,000 per year.

Do the maths. You said "How much are you spending on fuel at present, and how much of that can be displaced by charging up from your own solar?". I'm saying "Not very much if you think.of that as additional to your domestic requirements" (SS is a bit of an outlier that this doesn't apply to and of course there will be some like that - big system: work from home - but I'm looking at the average.)

I do get the idea that the car can be the storage and yes that does increase flexibility and may obviate the need for domestic batteries if you don't need all the car range every day.

My basic point though is that (for most people) to make the economics work for EV, the cheap overnight tariff is doing far more of the heavy lifting than the solar production. Which I think you agree with.

[albie]

BST,

You reckon " I'm saying "Not very much if you think of that as additional to your domestic requirements"...my point is that is the wrong comparison to make.

It is possible that the benefit from using solar energy to fuel a vehicle gives a greater benefit than only using it AFTER domestic needs are met. This will depend upon the future electricity tariffs, and displaced petrol/diesel prices.

This is particularly relevant when solar owners do not have battery storage.
These consumers can only use daytime gain by using the grid as a reserve, with a different rate applied to solar input and later evening usage.

The question is how to use the energy gain to best effect, by displacing the highest cost usage.
Looking forward across the expected lifetime of the panels, it is impossible to call this on the basis of current averages...this tells you very little useful information.

[big fat yorkshire pudding]

So what do we think the current saving per year is Vs cost to install? I still struggle with the payback period if I'm honest.

[BillyStubbsTears]

So what do we think the current saving per year is Vs cost to install? I still struggle with the payback period if I'm honest.

Depends on how the price of grid electricity goes of course.

At the moment, with current tariffs and some pretty active use of when to charge and discharge batteries, I reckon I've got about a 9-10 year payback period.

My advice to anyone thinking about this is to get the very largest set of panels possible. With hindsight, I wish I'd realised this when I had the panels fitted. With a bit more thinking about the layout, I could have got 13 rather than 10 panels on my roof. I was quoted £200 Inc VAT for each additional 400W panel at installation. From the figures I've got so far, I reckon each panel will produce at least 300Wh per year. At 15p feed in tariff, that's less than 5 years payback period for the additional panels. If you use that extra to offset importing from the grid, the payback period is only just over 2 years.

[Superspy]

So what do we think the current saving per year is Vs cost to install? I still struggle with the payback period if I'm honest.

I think I mentioned this in earlier posts, but the most important things to take into account when looking at payback periods in terms of the quotes solar companies provide are the assumptions they make for the variables.


My experience is as follows (in terms of the original quote):

- Assumed energy price inflation = 8%. This last 18 months has completely smashed that, but the decade previous averaged 5% a year, so this felt a bit disingenous and sales-pitchy to me. 5 minutes with a compound interest calculator will show that 5% vs 8% year on year is a HUGE difference, so this is a set of figures where you have to be careful of

- Assumed utilisation = 70%. Piece of cake to smash this in winter (I was getting 95%+ most of the time), but in the brighter months this is really hard to achieve with a bigger system. For May I only untilised about 59.5%. The reason this has such an impact is because the difference between the import and export prices is so big, even with the 15p export you can now get.

- Assumed export rate = 5p ish. Tied to the above point, post FIT (feed in tariff) but Pre Octopus doing Octopus things, export rates were trash. You could be in situation where you were paying 20p+ to import but only getting 5p back for export, so utilisation was a HUGE factor, because each unit you used knock 4 times as much off your bill vs selling it back to the grid. Now that export prices are a bit more favourable, utilisation isn't AS important, but it's still the biggest determining factor for how much money you'll save/make in one year.

That example BST gave is great because it's a nice and easy one that highlights just how much of a difference the current export rates make in terms of the "worst case scenario" of exporting everything extra panels generate and using none of it. Last year the best you could get on an export was half of that 15p...so worst case you were looking at the panels taking 10 years to pay back instead of 5. Massive difference in terms of long-term benefits of the system.


I've saved about £1k over the first 8 months or so of using mine, but most of that time has been over a winter, and I didn't get on an export tariff until November (when generation falls off a cliff). My overall savings for May were approx £250, and June, July and August should be the same or better, with September being roughly equivalent to March. If this happens, I expect my 1 year saving from the system to be approx £2k. That's a payback of 6-7 years even if energy prices stagnate.

Realistically, I think panels are a no-brainer (and the payback time is realistic) if you're at home all day, because that gives you the flexibility to maximise your utilisation. If you're not at home all day, I'm not sure what that picture would look like, but I would say batteries are a must. Ironically, they don't have as much impact as a result of the increased export prices - but if you're out all day then the bulk of your daily usage is going to be in the evening, so you need the storage solution to get your utilisation figure up.

[Superspy]

And to add - batteries are still hugely beneficial in the winter because of the cheap-rate night tariffs we've been talking about, where you all-but-ignore your solar generation and just max-charge the battery every night and use it through the day.

[BillyStubbsTears]

BST,

You reckon " I'm saying "Not very much if you think of that as additional to your domestic requirements"...my point is that is the wrong comparison to make.

It is possible that the benefit from using solar energy to fuel a vehicle gives a greater benefit than only using it AFTER domestic needs are met. This will depend upon the future electricity tariffs, and displaced petrol/diesel prices.

This is particularly relevant when solar owners do not have battery storage.
These consumers can only use daytime gain by using the grid as a reserve, with a different rate applied to solar input and later evening usage.

The question is how to use the energy gain to best effect, by displacing the highest cost usage.
Looking forward across the expected lifetime of the panels, it is impossible to call this on the basis of current averages...this tells you very little useful information.

Albie.

I'm not sure what your point is on the averages.

The average figures I gave are broadly right as of today. You have to start from somewhere if you're going to make a sensible assessment. It seems to me to be unlikely that those averages will change dramatically in the foreseeable future (except for one issue - see below).

I'm not sure I  get your comment about using the solar gain to offset your most expensive alternative. If you have an EV, both your domestic electic appliances and your car require electricity. If you're buying that electricity in, it doesn't matter whether you are buying it to roast a joint or to use in driving.

The point still stands that the majority of cases are going to require at least as much cheap electricity from the grid as the amount they can generate by domestic solar. That doesn't in any way belittle the benefit of domestic solar - it just sets it in a fair context. It's not likely to cover all, or even most of future electric needs.

And when you include heat pump central heating, the importance of cheap tariff imported electricity becomes even more dominant.

I agree that there's a big learning curve for all of us as we learn to adapt on how and when and where to store electricity, when to import it, when to use it and when to export it. It's a totally new world to get used to.

[BillyStubbsTears]

And to add - batteries are still hugely beneficial in the winter because of the cheap-rate night tariffs we've been talking about, where you all-but-ignore your solar generation and just max-charge the battery every night and use it through the day.

Bang on regarding the winter, but on the Octopus Agile tariff there's even a bonus in brighter months.

For the past several weeks, the import tariff overnight has been around 10-15p per unit tops, often much less. But the export tariff on Octopus Outgoing is 15p per unit 24/7.


So, you can charge up the batteries overnight at, say 10p per unit. Then during the day, run the house off solar during the day and battery once the sun has dipped, and export any excess solar to the grid for more than it cost per unit to charge the battery.

I honestly don't see how Octopus can make that business model work long term. Be interesting to see.

[albie]

Billy,

"It seems to me to be unlikely that those averages will change dramatically in the foreseeable future."

With regard to averages, high electricity prices are likely, particularly if the UK chooses to bankroll very expensive nuclear, paid for up front by a consumer levy.
This is the position of both Tory/Lab parties at present, and is ignorant nonsense from both.

Current average prices will very likely reduce in the price of installed solar, and the capacity/cost of batteries (both EV and standalone).
Both of these are falling down a technology experience curve, year on year. The average costs in these sectors are reducing, as a capital outlay and as distance travelled per unit of charge.

So the economics of self generation improves going forwards, in relation to buying from the private sector providers.

"I'm not sure I get your comment about using the solar gain to offset your most expensive alternative. If you have an EV, both your domestic electic appliances and your car require electricity. If you're buying that electricity in, it doesn't matter whether you are buying it to roast a joint or to use in driving."

It does matter what you are using it for, because that will determine the time constraint on the electricity used.
You might not want to cook a roast at 3am, but if you do not have battery storage then you cannot use the cheaper tariff.

The point here is those currently driving an ICE vehicle choosing an EV when it comes to replacement. I think this will be normal later this decade.
The price of petrol v the cost of electricity is another unknown, but climate policy suggests the leccy must become the cheaper.

At that point, the available solar resource can be allocated to the most pressing need. That may be in the home, or it may be for transport.
 
The private sector providers will only offer decent rates where it suits their business interests, failing regulation by government.

By all means use the cheapest method of meeting energy requirements, and time shifting demand is key to that.
An EV is just a bigger battery, which also works as a car!

[BillyStubbsTears]

Albie.

I never mentioned electricity prices, or relied on them in my reasoning. Did you read my first post in this exchange?

[Superspy]

The only thing you have to be careful of in the import cheap - export expensive game is accounting for round trip losses through the system. I believe this is why, on the flux tariff for example, there is an offset of a couple of pence between the night import and day export rate (19.4 vs 21.3) - the idea is you can't game the system, but if you choose to fill your battery overnight you won't be worse off either. It takes the management pressure off without screwing the customer.

[albie]

Albie.

I never mentioned electricity prices, or relied on them in my reasoning. Did you read my first post in this exchange?

Don't be silly, electricity prices are central to the whole debate.
Without an estimation of future grid supply costs, no assessment can be made for payback time or how to best use the leccy produced by your solar.

Interesting article on agrivoltaics on Reuters;
https://www.reuters.com/business/sustainable-business/with-agrivoltaics-we-dont-have-choose-between-solar-power-producing-food-2023-03-20/

 

[BillyStubbsTears]

Albie.

I never mentioned electricity prices, or relied on them in my reasoning. Did you read my first post in this exchange?

Don't be silly, electricity prices are central to the whole debate.
Without an estimation of future grid supply costs, no assessment can be made for payback time or how to best use the leccy produced by your solar.

Interesting article on agrivoltaics on Reuters;
https://www.reuters.com/business/sustainable-business/with-agrivoltaics-we-dont-have-choose-between-solar-power-producing-food-2023-03-20/

 

So you didn't read my post. Thanks for clearing that up.

[RobTheRover]

The batteries made a huge difference to the Energise Barnsley project I did. We fitted OAP bungalows with solar pv, and despite the tenants  mainly being in all day, utilisation was only around 45% of generation, and that was with an education piece on how to get the most out of the free power.  Adding just a 3kW battery took utilisation to over 75%, plus set up as a virtual power plant gave DSR and arbitrage opportunities.