Solar system savings - sense check

SuzeQStan

 

Grandad2b said:

We still have to get a handle on battery round trip efficiency - how much can you expect to get out for every kWh you put in?

 

We estimate a ‘round trip’ lost of about 20% for the battery charge in / out. So the 7p per kwh we charge the battery during cheaper TOU works out more like 10p per kWh by the time we hav stored & used it

Qyburn

Petriix said:

I've always said that iboosts or similar are a waste of money. Most people seem to pretend the diverted electricity would otherwise have been charged at peak rates to help with the confirmation bias. Slightly more complicated (and easier to pretend they're useful) for people on deemed export payments. 

It's not that complicated, on a deemed export tariff any electricity you use instead of exporting is free.

dai_bach

Screwdriva said:

dai_bach said:

In terms of what we have:
11 panels 435w. 4 South facing and 7 West/South West facing. Solar iBoost. No battery. Based in NE England.

Not sure what PGVIS forecasted for your location, but my initial gut instinct tells me 3900 kWh seems a bit low for a 4.8kW system, especially across S/ WSW aspects. For perspective, my system consistently generated the same with one less panel (10 bifacial panels spread across 3 aspects) and despite significant shading (2 panels shaded by a chimney for several hours a day). 

May I ask what brand the panels/ inverter system is?

As others have said, the iBoost is now financially redundant unless you're on FIT or have no other convenient way to heat hot water. 

Panels are Trina which I believe are probably not the best, but it's what I've got! Inverter is SolarEdge. I do have 1 panel that gets shading from a flue coming out of the roof, but the rest should be shade free. 

Interestingly, I just pulled out the order form and the estimated output quoted on there is 3,988 kwh so it's pretty close. Think I noted 435w originally but looking at the paperwork it says 425w so total system value of 4.675kW if that makes a difference to your thinking?

I've knocked the iBoost off now!

For the other comments - thank you all, plenty to think about.

We don't have an EV currently so don't think we can access any of the cheap overnight tariffs yet. Currently got 2 old diesels we are planning to run into the ground - will definitely consider an EV when looking at replacements when the time comes.

Martyn1981

dai_bach said:

Screwdriva said:

dai_bach said:

In terms of what we have:
11 panels 435w. 4 South facing and 7 West/South West facing. Solar iBoost. No battery. Based in NE England.

Not sure what PGVIS forecasted for your location, but my initial gut instinct tells me 3900 kWh seems a bit low for a 4.8kW system, especially across S/ WSW aspects. For perspective, my system consistently generated the same with one less panel (10 bifacial panels spread across 3 aspects) and despite significant shading (2 panels shaded by a chimney for several hours a day). 

May I ask what brand the panels/ inverter system is?

As others have said, the iBoost is now financially redundant unless you're on FIT or have no other convenient way to heat hot water. 

Panels are Trina which I believe are probably not the best, but it's what I've got! Inverter is SolarEdge. I do have 1 panel that gets shading from a flue coming out of the roof, but the rest should be shade free. 

Interestingly, I just pulled out the order form and the estimated output quoted on there is 3,988 kwh so it's pretty close. Think I noted 435w originally but looking at the paperwork it says 425w so total system value of 4.675kW if that makes a difference to your thinking?

I've knocked the iBoost off now!

For the other comments - thank you all, plenty to think about.

We don't have an EV currently so don't think we can access any of the cheap overnight tariffs yet. Currently got 2 old diesels we are planning to run into the ground - will definitely consider an EV when looking at replacements when the time comes.

Sounds fine to me, the generation for 2024 seemed reasonable.

I just played quickly played with PVGIS but had to guess at NE England, didn't want to go too far north, just in case, so dropped a pin just above York, and got an estimate of 4,086kWh*. But bear in mind that's just a guesstimate of average annual generation. Typically people on here average a bit better than PVGIS, but 2024 was a bad year.

*Guessed at a location, then entered 1.7kWp leaving default roof pitch at 35d and orientation at due south (azimuth zero), that gave 1,641kWh pa. Plus 2.975kWp, which I left at default 35d pitch, and orientation of +70 for approx WSW, that gave 2,445kWh pa.


Regarding the cars. When you are ready, and especially if you have off-road parking, then perhaps first think of getting an older, cheaper BEV (battery electric vehicle) with shortish range to replace one of the cars if it only does short jobs. That way you get to dip your toes in the waters and experience (gently) the fun and ease of a BEV. We bought a 70 mile range (if you drove carefully) secondhand Leaf back in 2019. Immediately became the car of choice, and the petrol Zafira got so little love, it sometimes had to be driven around the block to turn the engine over and dab the brakes. Best of luck.

Screwdriva

dai_bach said:

Panels are Trina which I believe are probably not the best, but it's what I've got! Inverter is SolarEdge. I do have 1 panel that gets shading from a flue coming out of the roof, but the rest should be shade free. 

Interestingly, I just pulled out the order form and the estimated output quoted on there is 3,988 kwh so it's pretty close. Think I noted 435w originally but looking at the paperwork it says 425w so total system value of 4.675kW if that makes a difference to your thinking?

Thanks for sharing. Your SolarEdge system gives you the benefit of panel level monitoring. Have a look in the app's layout tab to see if all panels are generating within 5% of each other (other than the shaded panel). I've seen too many malfunctioning Trina panels in my time, so one explanation could be that a panel or two may be underperforming relative to the others.

If not and all looks good then perhaps that generation is normal for your region. 2024 was an underwhelming PV year.  

Petriix

Qyburn said:

Petriix said:

I've always said that iboosts or similar are a waste of money. Most people seem to pretend the diverted electricity would otherwise have been charged at peak rates to help with the confirmation bias. Slightly more complicated (and easier to pretend they're useful) for people on deemed export payments. 

It's not that complicated, on a deemed export tariff any electricity you use instead of exporting is free.

Lol. Here's a thought exercise:

You generate 4000kWh per year. 
You self consume 1,500kWh for normal usage.

Scenario 1:

You divert 2,000kWh to your hot water via an iboost.   
You export 500kWh.
You earn (2000 x 6.79p) £135.80 for deemed export payments.

Scenario 2:

You import 2,000kWh (either gas or off-peak electricity) at 7p per kWh to heat water costing £140.
You export 2,500kWh.
You earn (2500 x 15p) £375 for a net gain of £135.

Oh look, that 'free' electricity actually cost you the opportunity to export it for 15p per kWh. Your iboost only saved you 80p over the course of a year. 

And the kicker is that your iboost will keep heating your water while you're on holiday in the summer, making your airing cupboard nice and warm. No one cares about wasting their 'free' electricity, but they still love to count all of those kWh in their "look how much my iboost has saved me" calculations. 

There are some edge cases where the numbers are slightly in favour of keeping deemed exports (no mains gas, no smart meter signal etc) but, for the majority, current market conditions are massively in favor of switching to metered exports. I also understand that the one way nature of that switch is off-putting. That's why I said it was 'complicated'. It's certainly not as simple as you claim. 

Reed_Richards

@Petriix, do you understand what "deemed export" is?  I had a solar system installed in March 2019, just in time to get in on the FiT.  For the next 4 years I continued with my old non-smart electricity meter and so had no means of measuring what my actual export of electricity was.  During that time my only choice was deemed export.     

Petriix

Reed_Richards said:

@Petriix, do you understand what "deemed export" is?  I had a solar system installed in March 2019, just in time to get in on the FiT.  For the next 4 years I continued with my old non-smart electricity meter and so had no means of measuring what my actual export of electricity was.  During that time my only choice was deemed export.     

I'm struggling to fathom which part of my more recent post could possibly imply that I don't understand what deemed export payments are. I've literally described the difference in my example. Unless there was something preventing the installation, presumably you could have chosen to get a smart meter installed during that period so it was actually your choice not to.

My system was installed in 2017. I was previously reluctant to get a smart meter and give up deemed exports. But these things both made sense with the former giving me access to very cheap overnight electricity and the latter (which I did a couple of years after the former) significantly increasing my income from my solar array.

The point being that, while you can earn 15p per kWh for metered exports of, say, 75% of your generation and buy the energy that you might otherwise have self consumed 'for free' at 7p per kWh, you are actually costing yourself money by using it yourself rather than exporting it. 

In my case, I used to leave my car plugged in on sunny days, diverting 1,000kWh over the course of a year. At peak I managed to self-consume 75% of the 3,500kWh I generated by doing washing/drying on sunny days and even running an electric heater on cold, clear days. 

Then the market changed. With 15p per kWh on offer for exports while load-shifting to 7p per kWh for imports, self-consumption became suboptimal.

Let's look at my figures from 2024 to compare what I could have done on deemed exports vs metered...

(Ignore generation payments because they remain the same regardless of the export element) 

I generated ~ 3,400kWh of which I exported 2,208kWh, earning £331. I load-shifted around 1,200kWh, costing £84. A net gain of £247.

If I'd stayed on deemed exports then I could have self-consumed that 1,200kWh on top of the 1,200kWh that I already used (for unavoidable stuff) and only exported 1,000kWh. I would have saved that £84 and the deemed export payment would have been (3400 x 6.79p / 2) £115.43.

So, in my case, giving up deemed exports and moving to using my Zappi overnight rather than in the day actually earned me ~ £132 extra. I suppose someone might have a Zappi and an Eddi or a home battery and get that self-consumption over 90% but that's still never going to quite make up for the lost earnings. 

Despite it clearly being more complicated for people on deemed exports, it's still a decent saving. For those already on metered exports, self consumption should only ever be for unavoidable peak usage. For anything that could be shifted to a cheap rate (like water heating, car charging and washing/drying), it makes financial sense to export for 15p and import for 7p.

Economy 7 offers a decent option for those without an EV. And, even for those with a home battery, I'd recommend only ever charging it from off-peak grid energy and never from solar unless it was to avoid genuine peak price imports.

Reed_Richards

@Petriix, I asked if you understood about deemed export because you didn't seem to understand @Qyburn's comment.  I did not get a smart meter before 2023 because when I asked around in 2019 nobody in my area had managed to get one that actually communicated.  The fitter who installed mine in 2023 said that it didn't quite communicate with the DCC but fortunately they were wrong.

Once you have a smart meter you need to become a supply customer of Octopus or Eon Next then move your FiT to Octopus (15p per kWh) or Eon Next (16.5p per kWh).  In my case this is proving troublesome because it seems Ofgem never knew I had a battery and want all sorts of paperwork that I was never given at the time of my installation.  After that, I need to apply for an export MPAN which others have reported may take some weeks to obtain.  I'll bet there are many people on the FiT who have been put off by all these hurdles and remain on deemed export.   

Petriix

@Reed_Richards there's a difference between contradicting something and not understanding it. Yes, there are some hoops to jump through but my intention is to help people make an informed decision so as to maximise their savings.

For clarity: you don't need to switch your FIT provider and it's usually easier not to. Once you opt out of the deemed exports they update the FIT register for your installation to show export as 'negotiated' which allows you to receive export payments from any other supplier.

You can (after a year and a not more than once per year) change that export status. If it becomes favorable in the future you could move back to metered export payments under the FIT scheme by changing your export status to 'standard tariff' which provides a nice backstop should these more generous rates disappear.