Solar Panels UK - is it worth it?

[yessuz]

I think I’ve nailed my set up. Famous last words

Since swapping from OVO, Octopus IO has been charging my car perfectly so far using 26A selected in the car. Hitting the target every time. So this is working flawlessly; Some/ any of the excess solar battery energy stored at the end of the day (at 23:30 or later) is going into the car, down to a reserve percentage I set for the batteries on each GivEnergy inverter (10% right now) for each battery pair. Then when they hit that limit all the rest is coming from the grid at 7.5p (if needed - hasn’t been so far).

6kW is the max draw for the car whilst charging (at 26A) with about 2-500w background load and 1kW extra spare available for any spikes (whilst the car is actually charging) (otherwise it’s) up to the max of 7.4kW from the 2 battery inverters. The charging on IO seems to be biased towards the end of the 6hr period, so that’s preferable. I think.

Perfect way to automatically use up all the solar generated, have a buffer till sun-up and add any extra if necessary at cheap rate. And any high house demand (if any) over that is at cheap rate also.

I’ll up my reserve battery percentage in the app slowly each month as we get more towards winter, eventually to 100% as I’m fairly certain I won’t last the whole day on battery alone then.

You can get very granular with forecasts, automation, etc, to eke out the last penny and all credit for doing that but for me I haven’t got the time. I will charge slightly over what I might need for the day (as an insurance policy) and accept that very occasionally I may export a kW or two (or 10!) that cost me 7.5p for 4p and take the 3.5p loss on the rare occasion - it’s peanuts. Getting it wrong and buying kWs at 31p is not peanuts though. So I’ll err on the side of caution and not fret about any export.

I’ve got some loft insulation to implement and a few other changes (less electric underfloor Mat usage, somehow. Probably add a couple of rads to replace). Maybe ditch the gas?

Loving this IO tariff with my GivEnergy setup.

Spent £2 this month (July) on electricity. Plus the standing charge.

Going on the long journey from “I think I want Solar panels”, through the entire maze of requirements and options, installers, DNO, to fully operational, to being mesmerised watching the electrons flying around on the app has been a trip.

I’m just flabbergasted by the performance of the panels of today. I’m seeing full cloud cover, rain and 2kW plus being generated. They Start production at 1w 20mins before sun up, it’s just unbelievable how good they are these days. Obviously the no cloud, full sun day is better but Wow. Impressed. Never thought they’d work in those conditions at all. Thought they’d shut down completely.
All the looking at panel specs, fretting over minimum start-up voltages, clipping, orientation, G99 approval, was a non issue luckily.

This is all with the help of everyone on this forum. So thank you one and all for all your very helpful contributions. To help me through the maze.

So, to re-iterate the answer to the OP - YES Solar panels are definitely worth it in the UK.

(With the caveat of getting a proper, sufficiently suitable solar and battery system installed and and being on a decent tariff.)

Thanks again one and all and may the sun shine on your roof.

only if there is no excess load by the house (kettle, oven, dryer, etc). but then again, I feel that I better charge 90-80% of my target by grid, have some buffer for the evening/early morning use and top up remaining 10-20% of my target next day with solar.

have in mind - I quite often return home with battery at 20-30% SOC and I see that this is not entirely efficient to unload that 10 kwh battery to the car.

 

[kelvin 660]

We've got a plug-in Neff 3kW induction hob. Easy to install and saves getting special wiring installed. Works great and load shares each cooking zones, as required.

 

[Drew57]

@Pete UK - am I getting this right (apologies if not) but are you using solar to fill the batteries and then using IO to draw back out for car charging? If that is the case, fair enough but this does result in additional cycles for the batteries plus conversion losses DC-AC-DC whereas charging overnight on the IO tariff is just AC-DC (but at a cost).

Most of us seem to prefer not to drain house batteries when car charging.

 

[yessuz]

@Pete UK - am I getting this right (apologies if not) but are you using solar to fill the batteries and then using IO to draw back out for car charging? If that is the case, fair enough but this does result in additional cycles for the batteries plus conversion losses DC-AC-DC whereas charging overnight on the IO tariff is just AC-DC (but at a cost).

Most of us seem to prefer not to drain house batteries when car charging.

exactly

 

[WannabeOwner]

I can imagine a scenario where car is not at home during the day, house-battery stores PV - and has more capacity than would be required by the house overnight ... and thus car is charged (from house-battery) overnight - ready for the following morning commute.

Lots of losses involved though as @Drew57 says

 

[Pete UK]

@Pete UK - am I getting this right (apologies if not) but are you using solar to fill the batteries and then using IO to draw back out for car charging? If that is the case, fair enough but this does result in additional cycles for the batteries plus conversion losses DC-AC-DC whereas charging overnight on the IO tariff is just AC-DC (but at a cost).

Most of us seem to prefer not to drain house batteries when car charging.

Yes that’s sort of mostly correct.

I’ve got 38kW of battery storage, so that helps.

The batteries have an unlimited cycle guarantee for 10 years, so no worries there about the cycle count.
Also it’s a DC system (hybrid) so the batteries can charge from DC Solar directly, so no DC-AC-DC loss at that entry point. House use though, from the Solar through the hybrid inverter there is a DC-AC conversion. As is there from the battery to ‘house’ as you point out.

Yes, agree, there are some losses charging the batteries and then charging the car from the batteries but this the lower priority option and is free compared to a 100% loss if the energy gets exported out to the grid, as I’m not on a SEG for another couple of months. Also this is the only option if the car isn’t at home in the day.

Firstly;
I’m letting the solar run the home and charge the batteries up.
Then (maybe mid morning if/when things are looking good and I’m seeing 5kW or 6kW+ or so being generated, but not necessarily) I’m topping up to the car directly from excess Solar when able, with sometimes a bit of extra battery power added if at full rate, or more likely(usually) at less than 6kW (26A if I’m not 100% monitoring it or I might wind it down to 16A for example if I’m not looking at all, or a suitable level), (to avoid exporting and to allow the car and batteries to charge at the same time). This eliminates most of those losses.
This is when there is excess, the car is at home and it isn’t going to completely drain the batteries. (If it is, I limit what I add to the car).

If the car isn’t there, (I let) the solar batteries fill, and then the car gets charged up from them by the IO schedule overnight down to a minimum of 10% (or whatever level I set), then if they get that low, they pause and flip over to power from the grid at 7.5p.
However, they might not get down to that level, so I use no grid power but the car gets charged from all the solar generated that day and none is wasted.

I’m leaving 20-30% Solar battery (for now) if I’ve added to/ filled the car from Solar/ batteries in the daytime and it doesn’t need charging, to get me through to sun up background load.

For now in summer that’s the working plan.

Into winter it’ll revert gradually to;
1) Charging the car from Solar (if possible maybe on the odd day or two),
2) Next a bit of battery to car, if any left over on the overnight IO schedule.
3) Fully IO overnight charge the car. + Top batteries to 20, 30, 50, 80% as days get shorter.
4) Then fully IO charge charge the car and IO charge batteries to 100% and expect to pull peak rate from grid in the evenings or at some point.

Then reverse that plan into spring/summer.

Hope that makes sense.

 

[Pete UK]

I can imagine a scenario where car is not at home during the day, house-battery stores PV - and has more capacity than would be required by the house overnight ... and thus car is charged (from house-battery) overnight - ready for the following morning commute.

Lots of losses involved though as @Drew57 says

Yes - exactly this scenario.

Use it (with some losses) or it’s 100% wasted.

 

[JIBYC]

They should call it Work From Solar, not Work From Home.

 

[Drew57]

Into winter it’ll revert gradually to;
1) Charging the car from Solar (if possible maybe on the odd day or two),
2) Next a bit of battery to car, if any left over on the overnight IO schedule.
3) Fully IO overnight charge the car. + Top batteries to 20, 30, 50, 80% as days get shorter.
4) Then fully IO charge charge the car and IO charge batteries to 100% and expect to pull peak rate from grid in the evenings or at some point.

Then reverse that plan into spring/summer.

Hope that makes sense.

I agree and always do the same in winter. IO really comes into its own then & it's surprising how often there is reasonable generation on a sunny winters day especially as cold temperatures mean solar panels work more efficiently than during hot weather.

 

[WannabeOwner]

it's surprising how often there is reasonable generation on a sunny winters

Hmmm ... not sure I agree with "reasonable generation", but maybe I live in a greyer (Winter) area of the country

Having installed PV I take whatever I get in Winter, but I reckon it is trivial - depends a bit on how much your household uses, relative to your generation of course. The insolation in mid-Winter in UK is 90% less than mid Summer, which is reflected in my generation numbers. By February the days are longer, and the sun higher, so things are improving, but I reckon I need a wind turbine for the winter months !

Figures for Summer / Winter showing number of days and percentage (relative to "best ever Summer day")

Month	<1%	<10%	<20%	<30%	<40%	<50%	<75%	75%+
May				2	5	4	10	10
Jun			1	1		2	7	19
Jul					3	2	9	17
Aug				2	1	3	15	10
---
Nov		19	9	2
Dec	1	17	13
Jan	1	13	11	5	1
Feb		4	7	4	11	2

 

[Drew57]

Hmmm ... not sure I agree with "reasonable generation", but maybe I live in a greyer (Winter) area of the country

Having installed PV I take whatever I get in Winter, but I reckon it is trivial - depends a bit on how much your household uses, relative to your generation of course. The insolation in mid-Winter in UK is 90% less than mid Summer, which is reflected in my generation numbers. By February the days are longer, and the sun higher, so things are improving, but I reckon I need a wind turbine for the winter months !

Figures for Summer / Winter showing number of days and percentage (relative to "best ever Summer day")

Month	<1%	<10%	<20%	<30%	<40%	<50%	<75%	75%+
May				2	5	4	10	10
Jun			1	1		2	7	19
Jul					3	2	9	17
Aug				2	1	3	15	10
---
Nov		19	9	2
Dec	1	17	13
Jan	1	13	11	5	1
Feb		4	7	4	11	2

Yes, I suppose I'm in the "depends a bit on how much your household uses, relative to your generation" category.

• Looking at my Octopus bills for the four months below, our overall house electricity consumption averaged 12.69kWh/day (two wrinkly pensioners with gas heating and hot water with relatively few long journeys in our EVs).
• IO at 7.5p/kWh covered any PV shortfall and looking back over the highest bill month (January) we averaged £1.42 of electricity per day excluding standing charge - and this includes charging the cars!
• These are the number of days per winter month where <50% of our electricity needs were covered by solar generation (SSW PV was 5.1kW last winter, & will be 7.5kW for this) -

November 6 days <50% (1 day <95%) Average total electricity as per the bill £9.70/kWh
December 8 days <50% (2 days <95%) Average total electricity as per the bill £9.07/kWh
January 10 days <50% (1 day <100%) Average total electricity as per the bill £8.95/kWh
February 14 days <50% (4 days <100%) Average total electricity as per the bill £9.66/kWh

*All figures exclude standing charges or the impact of the Gov't Energy Price Guarantee discount which basically subsidised our gas (for which we have two systems in an original plus extended house & only heat each part of the house relative to usage during the day or evening).

Batteries are definitely the biggest contributing factor in winter (as well as a much maligned but extremely helpful wife who saves washing, ironing, baking etc for the days when the sun is forecast to be greatest. Christmas Day was the only time in 12 months where our oven actually used peak grid electricity and the first time for many months where she didn't use the air fryers in preference!).

 

[WannabeOwner]

where she didn't use the air fryers in preference!

I don't really have a way of comparing before-air-fryer oven usage power consumption to after, but when its just the two of us here it is now rare that we use the oven, so I guess it is making a big difference.

I'll have a look at my "Percentage of usage self-generated" days, I like that metric

Like @scdoubleu I'm also battling with Solcast's estimates being way off (during the poor weather we had during July), my algorithm has often seriously underestimated the amount to store overnight. I need to do a check of Solcast prediction against actual, in particular the time in morning when it is likely that I will generate more than the house uses - and start charging battery. My idea would be to get to that point (from Off Peak battery reserve) without having a huge buffer.

I wonder if just checking the weather forecast for [lack of] Sun would enable me to decide that Solcast is over optimistic and force a higher Off Peak charging buffer

 

[Mrklaw]

Yesterday I had solcast going ‘yeah 24kwh no probs’. Then in the givenergy dash you get the usual spikes in generation from cloud, then it fell off, then solcast bascially chopped off the top half of the bell curve for the afternoon.

You have to consider how inaccurate it is though - usually its been pretty good for me but when weather is spotty like showers popping up maybe its less accurate

if you have off peak, the difference between a bit of extra off peak charging from a false negative (charging too much) is a lot less than not charging and pulling peak at 30p from a false positive.

as much as I’m tempted to look at comprehensive automation, I think a relatively much simpler seasonal adjustment of the %charge is probably fine and the difference vs a solcast tracking daily adjustment is probably very small.

Solcast for me is a useful forward indicator for ‘can I batch some extra washing/tumble drying or consider drip feeding the car’ or ‘I’ll top the car up overnight and spread the washing out each night’

 

[WannabeOwner]

You have to consider how inaccurate it is though

I haven't processed the data I've been logging for a while, Need to find time to do that, and compare Solcast prediction against Solcast assumed-actual and my actual-actual.

 

[Pete UK]

if you have off peak, the difference between a bit of extra off peak charging from a false negative (charging too much) is a lot less than not charging and pulling peak at 30p from a false positive.

Yes, this is exactly what I’ve come to realise and was what I’ve been trying to explain (maybe badly?)

It’s almost a factor of x9 possibly more

- Because each 1kW at 31p imported at peak by a bad forecast costs just that but each 1kW imported at 7.5p and exported at 4p is only a potential 3.5p loss. And that’s if it’s exported (it might not be because you might be able to stick it in the car instead of letting it export ). So a very good insurance policy IMHO.

So, you can afford to ‘get it wrong’ (not wrong ) by slightly overcharging your solar batteries 9x more often before it costs the same as getting it wrong by undercharging once !

Or in other words, if your forecast gets it wrong 3 times a month you have to get it exactly right every day for the other 27 days to make up for it !

I don’t know how many or by how much over estimations can be out by - but if your forecaster under predicted by 10kW for several days a month that starts to add up if you have to import that at peak. A buffer that looks way ‘too big’ might actually save the day more often than not and be more cost effective overall.

It’d be interesting to see what data @WannabeOwner comes up with when he has the time to crunch it.

 

[WannabeOwner]

It’s almost a factor of x9 possibly more

Except that ... it depends on how often that happens

365 days x 10% just-in-case-buffer (assuming that it would be run down to 0% every day, if deployed) is also quite a lot of Off Peak juice

if your forecast gets it wrong 3 times a month you have to get it exactly right every day for the other 27 days to make up for it !

but that gets my attention!

 

[Pete UK]

Yeah, there are quite a lot of ‘if’s’ and ‘assuming’ parts involved in the equation!

For example; you could add more than you think you need. You don’t need it AND it doesn’t get exported. Or some of it does. Or all of it does. i.e. it gets exported in the morning because the morning was better sun but doesn’t get exported if the afternoon is better because you used it in the morning. Bit of a headache really !

 

[Mrklaw]

blimey the tale of two days.

Yesterday - generated 7.93kwh. one tumble dryer session and one dishwasher all day - nothing else heavy. Took me until 2pm to charge to 100% and I was already drawing from the battery around 6pm there was so little generation.

Today - on track for generating 30kwh. ended off peak at 50%, up to 100% by 11:30, put the car on, just stopped it after adding 30% battery, probably get another hour of generation.

 

[GRiLLA]

blimey the tale of two days.

Yesterday - generated 7.93kwh. one tumble dryer session and one dishwasher all day - nothing else heavy. Took me until 2pm to charge to 100% and I was already drawing from the battery around 6pm there was so little generation.

Today - on track for generating 30kwh. ended off peak at 50%, up to 100% by 11:30, put the car on, just stopped it after adding 30% battery, probably get another hour of generation.

8.2kWh yesterday, didn't get above 70% on the battery and hit my lower limit at 1am then pulled 1.6kWh before the sun came up.

33kWh today, wife found useful ways to use 20kWh, 10 went back into the battery and 3 to the grid.

Pleasure is that export will be 3x4.1p, import 1.6 x 7.5p, so I'm 0.3p up on the two days combined.

 

[Dilly]

Forecasts do seem to have been off-piste of late.
It hasn’t caused me import off-peak, though I did ponder charging a visiting EV overnight but held my nerve and waited for the sunshine.
I have run the boiler instead of the Eddi a few times, twice unnecessarily!

Still 3 days of sun, forecast or not, has put me on course to complete my 56th Megawatt tomorrow.