Are these options realistic? (aka 'Rate My Solar Plan' :) )

Brimble

Usually on here I see people posting quotes, asking if they are competitive. I've approached it a different way - before talking to installers who potentially might want to sell me things that I don't need etc, I wanted to educate myself a bit first and do my own calculations based on the wealth of info provided kindly via many threads on here to see what set-up is likely to be most beneficial / desirable. As a result, I've put together 3 potential plans based on my expected overall usage, usage from my production, surplus sold back to grid, and hence financial benefits for:

1. Solar array 6.4kw
2. Solar array 6.4kw with iBoost (or similar)
3. Solar array 6.4kw with 6kwh battery (or similar size, depending what's available) (no iBoost)


Background info, sources and assumptions

I've used bills and regular smart meter monitoring to work out when I use fuels (both by month and by hour); I've used PVGIS modelling site to estimate production, and have then tempered it a bit by comparing to a few similar local set-ups; I've recognised that the spread of productive hours changes through the year The relevant roof is SSE-facing, no shade, and I'd estimate has about 30sqm of space available, so I guess 16 panels x 400W = 6400kw. If desirable, I could probably put 6 panels on a SWW-facing roof adjoining the main one, but we'll see if anyone suggests that being particularly useful. My spreadsheets show our (quite heavy - big house) usage, but to summarise it's about 6000kwh of electricity per year, pretty much spaced evenly throughout the year and throughout each day; plus 21000kwh gas, heavily weighted towards the winter and colder months. This is mainly for the wet underfloor heating system both upstairs and downstairs, plus of course a bit every day for water heating and cooking.


Calculations spreadsheet

https://www.dropbox.com/s/5lo7yda9vvakp3o/Solar research v1.0.xlsx?dl=0

The spreadsheet in the link above has all the detail, but in summary, I believe it is telling me the following, based on October 2022 standard rates (which are expected to be 80% higher than now):

• Production would be just over 6000kwh per year.
• Option 1 (solar only) would benefit me £1,365 per year (£1,156 replaced electricity (2215 units, 36% of my production), £208 sold back to the grid).
• Option 2 (solar & iBoost) benefit £1,564 (£1,156 replaced electricity, £335 replaced gas (another 2,517 units, additional 41% of my production, so using 78% in total), £72 sold back to grid). That's £199 more benefit annually than Option 1, with additional cost of iBoost.
• Option 3 (solar & battery) benefit £2,183 (£1,156 replaced electricity direct from solar, £913 replaced electricity from battery (another 1,748 units, additional 29% of my production, so using 65% in total), £114 sold back to grid). That's £818 more benefit annually than Option 1, with additional cost of 6kwh battery.

Payback time and current preference

Looking purely at payback time, Option 1 would be 5.5 years, Option 2 5.1yrs, Option 3 5.7yrs, however it shouldn't just be about that alone, and at present I'm edging towards Option 3 because a). it still gives considerably more benefit, and b). I expect the outcome would feel more 'satisfying' and would waste less. I appreciate that those payback times are way more ambitious than those usually quoted, but a). We have quite high usage, so can use more of what we produce; b). My calcs are based on costs from Oct 2022, which as we all know will be much higher than now; c). Nevertheless I may have errors or inappropriate assumptions that you guys can identify.

Questions

Before I start talking to installers:

1. Have I understood the basics correctly? Are there flaws or overly optimistic assumptions in my spreadsheet? (Happy to explain any workings that aren't clear). Does the formt make sense, am I missing any crucial factors?
2. Am I right to assume that 400W panels are generally considered to be best value for money & roof space at the moment?
3. Are my install costs likely to be in the right ball park? (Haven't got any quotes yet, but from what I've read on here have assumed about £7.5k for the solar set-up, £400 for iBoost if I take it, and £5k for the battery if I take that).
4. Note that I've stuck to price-cap tariffs for now - I appreciate that Octopus might improve the situation, but want to ensure I've got the basics right first.

I'm likely to have lots more questions, and being not very tech-savvy they might seem stupid questions to some, so to anyone who is prepared to help and/or follow the development of my plan, please be patient with me! I will be hugely appreciative of any help anyone is prepared to give.

Screwdriva

A few comments:

1) At current/ future gas prices, I believe a diverter makes sense. I'm not convinced a battery does however. See #3 below. 
2) 400W Black Panels from Sharp (made in Wales) and Hyundai (made in Australia via trade deal) are now affordable, well reputed brands!
3) I struggle to see any logical reason why Octopus Outgoing Agile wouldn't be the model of choice for export. Current average tariff is 3-4X the fixed tariff, making the grid act as a battery. 

Make hay while the sun shines!

2nd_time_buyer

Brimble said:

Usually on here I see people posting quotes, asking if they are competitive. I've approached it a different way - before talking to installers who potentially might want to sell me things that I don't need etc, I wanted to educate myself a bit first and do my own calculations based on the wealth of info provided kindly via many threads on here to see what set-up is likely to be most beneficial / desirable. As a result, I've put together 3 potential plans based on my expected overall usage, usage from my production, surplus sold back to grid, and hence financial benefits for:

1. Solar array 6.4kw
2. Solar array 6.4kw with iBoost (or similar)
3. Solar array 6.4kw with 6kwh battery (or similar size, depending what's available) (no iBoost)


Background info, sources and assumptions

I've used bills and regular smart meter monitoring to work out when I use fuels (both by month and by hour); I've used PVGIS modelling site to estimate production, and have then tempered it a bit by comparing to a few similar local set-ups; I've recognised that the spread of productive hours changes through the year The relevant roof is SSE-facing, no shade, and I'd estimate has about 30sqm of space available, so I guess 16 panels x 400W = 6400kw. If desirable, I could probably put 6 panels on a SWW-facing roof adjoining the main one, but we'll see if anyone suggests that being particularly useful. My spreadsheets show our (quite heavy - big house) usage, but to summarise it's about 6000kwh of electricity per year, pretty much spaced evenly throughout the year and throughout each day; plus 21000kwh gas, heavily weighted towards the winter and colder months. This is mainly for the wet underfloor heating system both upstairs and downstairs, plus of course a bit every day for water heating and cooking.


Calculations spreadsheet

https://www.dropbox.com/s/5lo7yda9vvakp3o/Solar research v1.0.xlsx?dl=0

The spreadsheet in the link above has all the detail, but in summary, I believe it is telling me the following, based on October 2022 standard rates (which are expected to be 80% higher than now):

• Production would be just over 6000kwh per year.
• Option 1 (solar only) would benefit me £1,365 per year (£1,156 replaced electricity (2215 units, 36% of my production), £208 sold back to the grid).
• Option 2 (solar & iBoost) benefit £1,564 (£1,156 replaced electricity, £335 replaced gas (another 2,517 units, additional 41% of my production, so using 78% in total), £72 sold back to grid). That's £199 more benefit annually than Option 1, with additional cost of iBoost.
• Option 3 (solar & battery) benefit £2,183 (£1,156 replaced electricity direct from solar, £913 replaced electricity from battery (another 1,748 units, additional 29% of my production, so using 65% in total), £114 sold back to grid). That's £818 more benefit annually than Option 1, with additional cost of 6kwh battery.

Payback time and current preference

Looking purely at payback time, Option 1 would be 5.5 years, Option 2 5.1yrs, Option 3 5.7yrs, however it shouldn't just be about that alone, and at present I'm edging towards Option 3 because a). it still gives considerably more benefit, and b). I expect the outcome would feel more 'satisfying' and would waste less. I appreciate that those payback times are way more ambitious than those usually quoted, but a). We have quite high usage, so can use more of what we produce; b). My calcs are based on costs from Oct 2022, which as we all know will be much higher than now; c). Nevertheless I may have errors or inappropriate assumptions that you guys can identify.

Questions

Before I start talking to installers:

1. Have I understood the basics correctly? Are there flaws or overly optimistic assumptions in my spreadsheet? (Happy to explain any workings that aren't clear). Does the formt make sense, am I missing any crucial factors?
2. Am I right to assume that 400W panels are generally considered to be best value for money & roof space at the moment?
3. Are my install costs likely to be in the right ball park? (Haven't got any quotes yet, but from what I've read on here have assumed about £7.5k for the solar set-up, £400 for iBoost if I take it, and £5k for the battery if I take that).
4. Note that I've stuck to price-cap tariffs for now - I appreciate that Octopus might improve the situation, but want to ensure I've got the basics right first.

I'm likely to have lots more questions, and being not very tech-savvy they might seem stupid questions to some, so to anyone who is prepared to help and/or follow the development of my plan, please be patient with me! I will be hugely appreciative of any help anyone is prepared to give.

Hey, nice work, on the useful analysis. Thanks

The savings on iboost and to a lesser extent the battery depend quite strongly on your outgoing tariff. 

If you go on Octopus Agile you could potentially get 3 times more for export (e.g. around 20p/kWh over the last year). This could mean you are effectively running the iboost at a loss if gas prices are below the export rate. Likewise it will diminish the value of the battery. So it might tip the balance in favour of option one.

However, Agile is the only export tariff that tracks market rates. So you have to ask "Will it be around forever, and will export rates on it stay as high as they are now"

I can see the logic behind option one and three - so it is a crystal ball decision  I went down the solar-only route with a similar usage/solar-array to you. If I did it again I would have got a battery. But financially so far it has not made too much difference.

Alnat1

You say electricity use is spread throughout the day, do you mean equally over 24 hours or is it more 7am-11pm when your family is awake? Deciding on whether a battery would work for you, think about this as daylight and dark hours and think how this changes with the seasons. Peak production will be between 10am-3pm, is this when you can use it?

When it's dark after 5pm you'll be importing from the grid to cook dinner, evening entertainment, run dishwasher, boil kettle, ironing etc. if no battery. If it's been a sunny day, excess solar will be gone. Would it benefit you to store that excess for use in the evening and maybe even run the baseload overnight? Mar-Sep with a battery you'll use minimal from the grid (150kWh since system install 3rd March for me).

Personally, a diverter for the hot water wouldn't give a ROI for us at the moment with gas prices being much lower per kWh than I get for export. We don't use much, couple of showers and hubby's shave and a bit for cleaning. Tank is heated 40 minutes a day, 3-4kWh of gas. I'd rather get paid Agile prices for our excess in summer and can boil a kettle for free if I need more hot water for cleaning. In winter the lower solar output will be needed for other things and we'd need to use gas to heat the tank anyway. It's totally different for those who get FIT payments.

My last plus for a battery with install is the VAT saving. You'll be annoyed with yourself if you don't go for it and want it later.

I think you might find quotes are a bit more expensive than you've anticipated but hopefully you'll get lucky.

Magnitio

I chose a similar solution to your option 3, but also installed a 1.5kW immersion that I can control on a timer. Due to the current high rates for exporting excess generation, which are far higher than the cost of gas, I haven't used the immersion much. However, it does provide some flexibility for the future.

On panel choice, as well as Sharp and Hyundai mentioned above, you might want to consider REC.

Your assumptions regarding installation costs might be a bit optimistic at the moment given the high demand.

ispookie666

Great analysis. I did similar, wanted panels all over my roof.  
I would say yes to battery and iBoost. You would be able to do load shifting when the sun is very low in the horizon, especially if you have access to Time of use tariffs.  

I have not pulled much from the grid since my battery went live (delayed install but was part of my solar) and planning to charge using E7. 

The only thing I would suggest - get a bigger battery! DNO might be your limiting factor if you are considering export to the grid. 

Brimble

Hmmm, this is very interesting - I'll respond on a few more specifics points shortly, but the main 'bone of contention' throughout pretty much all responses above seems to be whether or not to rely on Octopus Outgoing Agile. When I spoke to my wife about this yesterday, her response was "yes but then we're still very dependent on not just providers generally, but on a single provider, who could change everything at any point. How would we feel if we didn't get the battery, then Outgoing Agile was withdrawn or massively changed a few months later?". And I do see her point.

So whilst it is probably not the most cost-effective option, perhaps the most 'hedging' option would be to get the battery now (thereby avoiding the VAT), and make some use of it, but at the same time accept that, certainly for the short term, I should be on Outgoing Agile to make the best value from any production that I can't use to replace purchased electricity.

Brimble

A few other things that arose above:

Both @Alnat1 and @Magnitio have said that my costing might be a bit optimistic - thanks for pointing that out. Do you know what more realistic numbers might be? Does anyone know if prices tend to rise and fall in an annual cycle? (For example, extra demand from people getting excited late summer by all the sun they've seen, or people in Spring preparing for it, whilst people in Dec / Jan having other things to think about etc).

@ispookie666 has suggested I might want to look at a bigger battery. Just browsing randomly last week, I came across LG Chem RESU-10H which is 9.8 kwh for about £5k - might that be a good choice? Are there certain features on batteries that I should look to include or exclude?

Alnat1 also asked about my hourly / daylight electricity consumption. Having watched the smart meter carefully recently, and been through some (not that reliable to be fair) provider website data, I estimate our base load throughout the night to be about 0.5kw, and while we're awake about 0.6kw, with small spikes early evening if we use the oven when cooking, and late evening (TV and lights in lounge maybe?). In the spreadsheet I have tried to allocate my usage between daylight and non-daylight hours, including the obvious variations throughout the year - but do let me know if you think I've made an error or missed something.

Generally with the spreadsheet, did anyone actually look at it in detail? (Maybe not - no one likes looking at someone else's spreadsheet trying to understand their notes and thought processes, spreadsheets are such personal things...) But there were two assumptions in particular that I'm not comfortable with and so wanted to ask advice on:

• When looking per month at the amount of daylight use that I can replace with electricity I've produced, I've assumed I can probably use 80% of that - the 20% being over-production on extra productive days.
• When looking per month at the amount of surplus / unused that I can take to the battery, I've assumed I can probably take and use 90% of that - again the reduction being over-production that won't 'fit' in the battery.
• The reason for using 20% in the first one and 10% in the second one is recognising the smoothing that the battery provides, i.e. it doesn't have to use the electricity live, it can store it for later. But only up to its capacity of course.

Do those assumptions look reasonable? Does anyone with a battery have comparable data to share?

94JDH

Magnitio said:

I chose a similar solution to your option 3, but also installed a 1.5kW immersion that I can control on a timer. Due to the current high rates for exporting excess generation, which are far higher than the cost of gas, I haven't used the immersion much. However, it does provide some flexibility for the future.

On panel choice, as well as Sharp and Hyundai mentioned above, you might want to consider REC.

Your assumptions regarding installation costs might be a bit optimistic at the moment given the high demand.

Over on solar and battery forums on Facebook:

https://www.facebook.com/groups/2197329430289466/?ref=share

I don't know if the link works unless you subscribe though.

A user here has a similar spec (5.5k PV though) for just over £12k - so it still is possible.

silverwhistle

There are rather a lot of variables, aren't there?! :-)

As Alnat1 has pointed out, with the FITs I have the iboost was a no brainer but you also have to consider export rates as well.

As for what future prices will be, that's something professional modellers and hedgers are paid a lot to work out, but it could be that in a few years rates get a lot spikier on Agile Import. I used to be on it and saw the capped rate and the negative or nil price in the same day on a few occasions. Hornsea 2 goes fully live this month with 1.2G capacity, and there are other wind farms in the pipeline, which may help overall prices but will definitely increase variability at some times of the year.

Is an EV in your plans as that might impact on your home usage? 

Magnitio

Brimble said:

A few other things that arose above:

Both @Alnat1 and @Magnitio have said that my costing might be a bit optimistic - thanks for pointing that out. Do you know what more realistic numbers might be? Does anyone know if prices tend to rise and fall in an annual cycle? (For example, extra demand from people getting excited late summer by all the sun they've seen, or people in Spring preparing for it, whilst people in Dec / Jan having other things to think about etc).

I paid just over £11k for 6.4kWp panels and 10kWh battery in February. Quotes I have seen in the past few months appear to have increased by maybe 10-20%.

@ispookie666 has suggested I might want to look at a bigger battery. Just browsing randomly last week, I came across LG Chem RESU-10H which is 9.8 kwh for about £5k - might that be a good choice? Are there certain features on batteries that I should look to include or exclude?

Alnat1 also asked about my hourly / daylight electricity consumption. Having watched the smart meter carefully recently, and been through some (not that reliable to be fair) provider website data, I estimate our base load throughout the night to be about 0.5kw, and while we're awake about 0.6kw, with small spikes early evening if we use the oven when cooking, and late evening (TV and lights in lounge maybe?). In the spreadsheet I have tried to allocate my usage between daylight and non-daylight hours, including the obvious variations throughout the year - but do let me know if you think I've made an error or missed something.

That seems a high base load through the night and only a small difference during daylight hours. I know this can be controversial, but finding a way to analyse and reduce your usage will provide a great ROI. Same with gas.

Generally with the spreadsheet, did anyone actually look at it in detail? (Maybe not - no one likes looking at someone else's spreadsheet trying to understand their notes and thought processes, spreadsheets are such personal things...) But there were two assumptions in particular that I'm not comfortable with and so wanted to ask advice on:

• When looking per month at the amount of daylight use that I can replace with electricity I've produced, I've assumed I can probably use 80% of that - the 20% being over-production on extra productive days.

• When looking per month at the amount of surplus / unused that I can take to the battery, I've assumed I can probably take and use 90% of that - again the reduction being over-production that won't 'fit' in the battery.
• The reason for using 20% in the first one and 10% in the second one is recognising the smoothing that the battery provides, i.e. it doesn't have to use the electricity live, it can store it for later. But only up to its capacity of course.

It's not straightforward. For example, you'll get multiple dull days when you are not generating much and the battery is depleted. Then you will have very sunny days where the battery is full and you will export plenty. Unless you have a very large battery, you can't average out these fluctuations. A 6kWh battery doesn't last long with a base load of 500W.

Looking at your spreadsheet, I think it may be a bit optimistic on the amount of solar you would use without a battery unless you are able so shift some of your consumption to peak generation hours.

Do those assumptions look reasonable? Does anyone with a battery have comparable data to share?

Hi,

I have added some comments above. When I received quotes for my solar panels and battery, the payback periods quoted by the suppliers ranged from 13 to 18 years. With the increase in energy prices and optimising the use of our system, I am now projecting a ROI in under 8 years. If prices continue to rise as expected over the next 6-9 months, this may come down further. I'd certainly be happy if I can achieve the 5-6 years you are calculating.