Solar Panels UK - is it worth it?

[Pete UK]

If that's from my image above? then its from 48 panels ... and my best ever winter day, "useful generation" for only around 4 hours in the middle of the day, and breaks down roughly like this:

For context: I have 48 panels, and average use is ~50kWh a day

April 1782 kWh : 5 "low days" 25-ish kWh, most are around 60kWh, and 7 are 80-ish kWh

(June, July, August around 2,200 kWh)

January 388 kWh : 14 "low days" < 3kWh, 5 days 5-ish kWh, 7 days 10-20kWh, 5 days > 20Kwh

December 257 kWh - 12 "low days" < 3kWh, 14 days 6-10 kWh, 5 days 15-ish kWh

Someone with, say, 16 panels might only get 1/3rd of that, dunno how much is needed before the systems will actually start?

So apart from the occasional "perfect" winter day, in Winter the norm is "rubbish" - I would characterise whatever I get as a bonus, rather than anything that actually contributes to my consumption. Just don't want anyone to assume that the 4 winter months contribute anything useful - particularly as that occurs at a time of greater electricity use (even if only more lighting for the long winter nights)

Yep - agree winter is rubbish compared to summer. The point I was trying to make was that even, say a “4kW” a day generated is 4kW added to the 38kW (/whatever battery size you have) downloaded overnight from grid in the battery I (/you/anyone) wouldn’t have to buy at 42p peak. And you’d use at least 4kW in winter from 0530 till useful generation starts, So that’s £50 a month saved; If it were only an average of a 4kW trickle per day.

I’m not sure of your usage profile or situation but;
On the excellent winter days where your getting 10-20kW or 20kW that’s £4.20-£8.40 or £8.40 per day, so that’s 7 days saving you (using 15 average) £42 total and 5 days saving you a total of £42. Assuming you can use/store that extra.

In other situations, A 4kW trickle generated could stretch the time before you start using peak by 8 hours at 500w background or 4 hours at 1kW background drain.
Plus (or minus ) probably out of the whole 50kW you’d use on a winters day maybe 10-12kW (in our case) of that might be going in a car which would be off peak already.

I’m just rambling really but it seems that with a high useage one just has to accept the fact that in winter you’re never going to have a big enough battery (unless you go mad on kit, but you still need the time/ grid power/ approval/ ability to charge it in the off peak window) and are going to have to pay for some peak price kW’s. But that’s ok. Every little helps though and all adds up.

 

[WannabeOwner]

Yep - agree winter is rubbish compared to summer.

You are right. My concern was that someone reading this, contemplating changing from Gas to Heat Pump, may be thinking that Solar PV will provide some Leccy to run the Heat Pump. For that to be the case, in Winter, we would need the UK to be a lot closer to the Mediterranean!

But as you rightly point out, having spent all that capital on a Solar panels whatever is generated in Winter is during "core daylight hours" and can all be offset against peak tariff rate

Over last year I got:

2,200 kWh Jun/Jul
2,000 kWh May / Aug
1,800 kWh Apr / Sept
1,000 kWh Mar / Oct
750 kWh Feb
250 kWh Nov, Dec, Jan

So the deep Winter months (@40p/unit) are worth £100/month to me, but Mar-Oct are £400-800 a month

 

[Mrklaw]

Well - they’re unlikely £400 a month as you won’t use that much peak electric. Some of that would have been exported for a low rate and some off peak for eg car charging etc.

The two may be closer than expected in terms of value

 

[PITA]

I’m just rambling really but it seems that with a high useage one just has to accept the fact that in winter you’re never going to have a big enough battery (unless you go mad on kit, but you still need the time/ grid power/ approval/ ability to charge it in the off peak window) and are going to have to pay for some peak price kW’s. But that’s ok. Every little helps though and all adds up.

Well I went 'mad' ... found the answer, and it seems to work really well

My objective was to get a really well balanced system, for 'us'. Close to zero peak-rate grid use.

But... Winter was the problem.

Even if you have massive battery storage, with little to no Solar being generated, you have to get it from the Grid.

Problem here, is getting it from the Grid at Cheap Rate fast enough during the short low cost period. On top of all the other Grid download demands you'll start to add.

This is why we upgraded to 3 Phase Supply.

Now we can charge multiple Powerwalls, multiple electric cars, and power the home during Winter on cheap rate.

3 Phase became the game changer to stay at cheap rate.

This Winter will be even better for us, because Intelligent Octopus runs for 6 hours (11:30 to 05:30). So in the Powerwall App on Time Based Control - Allow Grid Charging... it means the Powerwalls only need to bridge 18 peak-rate hours now (not 20 hours on the old 'Octopus Go' tariff). Those extra two hours make a good difference.

This winter, during that 6 hours we'll be charging at 35 kW during the night with 3 Phase pumping two cars and home storage.

The Solar Array will just be in the background trickle charging the base load.

 

[PITA]

I have to add though, according to our DNO ... our house is at the maximum allowance now, even for 3 Phase. Without opening up a can of worms with Commercial Grade Supply infrastructure.

So, I'm testing them to the limit

What's worrying about that, is I only have two electric cars, a heat pump, and two Powerwalls. A standard 3 bedroom detached house.

... and I've maxed them out... Good Luck anybody else.

 

[WannabeOwner]

they’re unlikely £400 a month as you won’t use that much peak electric

Yup, I had that in my original draft, must have removed it Doh!

I did some sums ... my use-case is around 2.5 kW during the day, 2kW at night, and say 300kWh / month in the car.

2,200 kWh Jun/Jul

Assuming no export ...

Off Peak equivalent usage : 2kW x 4 hours x 31 days = 250kWh plus 300 kWh for the cars = 550kWh @ say 10p = £55

Rest is daytime usage & charge PowerWalls : 2,200 - 550 kWh = 1,650 kWh @ say 40p = £650. Total saving £700

 

[DaveNN]

It's a long thread, forgive me if I've gone over well trodden ground.
Going overboard with batteries will probably require a chunky inverter.
Like others , mine will cope with about 3kw ( with just over 10kw battery storage BUT with a dod of 90%),
We use about 170kwhr a week during the winter, with over 90% of that at (now) 7.5ppkw.
The rest is when the iron, for example, is used in the morning.
Weirdly, we have a constant draw of..I will assume it's the inverter..about £1 a week. ( I will have to investigate).
We load shift quite a bit and have taken advantage of smart charging occasionally.
I've tested my 4.05kw array today, ran the cables to the loft and bird proofed the panels accordingly.
I wire up next weekend.
My Sofar Solar inverter/ battery controller are quite basic, with about a 10 mins data logging lag.
What I'm trying to get my head around is the smartest way to maximise my solar/ minimise my grid draw.
I can assume that I have to juggle my battery charge timing and take advantage of any dawn sun ( if it happens)..
Would:-
Home,
Storage
Car
Hottub ( as an example) be logical?

Any advice/tips would be welcome and appreciated..

Onto the ROI
With batteries alone at 7.5ppkwhr, I'm looking at 4 yrs ROI.
The cheap rate electricity does skew the panel ROI .
As noted a vast percentage of our use is at 7.5ppkwhr.
I would guess at a ROI of about 10yrs ??

Any comments?

However, if and when we sell up..the panels etc will be ripped out if I don't enjoy a 100% return on my costs, in the house sell price.

 

[Mrklaw]

for battery you mainly want in summer to not charge if you don’t need to - get to around 7-7:30 and it should start charging again. then you’d be on solar with the battery as a buffer if demand spikes etc, then after the sun sets the battery should get you through to the next day. I have a 9.5kwh battery so not much different from you and I think on a good day like recently we start using the battery around 7pm a little as the solar drops, and its down to maybe 55-60% the next morning at 7. So thats about 4-5kwh used through the evening and the night including dishwasher overnight and often a washing load on. I have it set not to charge which is fine if it stays sunny during the day.

in autumn I expect to set it to not drop below maybe 30-50% during off peak and charge to that if needed as the sun gets less so it’ll top up to get through to reasonable production and then charge up, but I’d monitor a bit to work out the right amount - with the aim to get through to off peak without using any peak grid.

Winter I’d set to charge to 100% during off peak, and then just hope the battery manages with a bit of top up from the sun but inevitably I’ll use some peak rate more often during this time.

summer with lots of excess hopefully, I have it mainly so if there is extra washing/drying can be done, do that. If not and its looking good I’ll put it into the car - 10-15kwh is a decent percentage while I’m wfh.

 

[yessuz]

I thought they had to reply within 45 days?

45 business days?
which is 2 months?

 

[DaveNN]

for battery you mainly want in summer to not charge if you don’t need to - get to around 7-7:30 and it should start charging again. then you’d be on solar with the battery as a buffer if demand spikes etc, then after the sun sets the battery should get you through to the next day. I have a 9.5kwh battery so not much different from you and I think on a good day like recently we start using the battery around 7pm a little as the solar drops, and its down to maybe 55-60% the next morning at 7. So thats about 4-5kwh used through the evening and the night including dishwasher overnight and often a washing load on. I have it set not to charge which is fine if it stays sunny during the day.

in autumn I expect to set it to not drop below maybe 30-50% during off peak and charge to that if needed as the sun gets less so it’ll top up to get through to reasonable production and then charge up, but I’d monitor a bit to work out the right amount - with the aim to get through to off peak without using any peak grid.

Winter I’d set to charge to 100% during off peak, and then just hope the battery manages with a bit of top up from the sun but inevitably I’ll use some peak rate more often during this time.

summer with lots of excess hopefully, I have it mainly so if there is extra washing/drying can be done, do that. If not and its looking good I’ll put it into the car - 10-15kwh is a decent percentage while I’m wfh.

Winter is the easy one

Summer is almost as easy.... not likely to use the tumble dryer, for starters.

I needed a new hobby perhaps energy monitoring could be it?

 

[RagingWhisky]

I have to add though, according to our DNO ... our house is at the maximum allowance now, even for 3 Phase. Without opening up a can of worms with Commercial Grade Supply infrastructure.

So, I'm testing them to the limit

What's worrying about that, is I only have two electric cars, a heat pump, and two Powerwalls. A standard 3 bedroom detached house.

... and I've maxed them out... Good Luck anybody else.

Yikes!

Is this "maximum allowed" based upon a theoretical power draw or amperage?

I'm on single phase/100A fuse and fly very close to the sun on that - have considered 3-Phase as the next step, but wouldnt want to get caught out!

 

[RagingWhisky]

Winter is the easy one

Summer is almost as easy.... not likely to use the tumble dryer, for starters.

I needed a new hobby perhaps energy monitoring could be it?

And if you can, have your batteries in an insulated enclosure or indoors! as the winter weather this past November-March absolutely nuked performance!

My one regret is not having internal space, or an enclosed secure shed to have batteries installed within - ended up instead making "insulated jackets" for the batteries instead on the house north wall.

 

[Avendit]

And if you can, have your batteries in an insulated enclosure or indoors! as the winter weather this past November-March absolutely nuked performance!

My one regret is not having internal space, or an enclosed secure shed to have batteries installed within - ended up instead making "insulated jackets" for the batteries instead on the house north wall.

That is one thing I hadn't considered! Good point. Charge/discharge doesn't change much for me, but how low they will let me go is definitely restricted in winter with the temp.

Hmmmm. Woolly jacket time I guess!

 

[RagingWhisky]

When the temps dipped to 5C or below, the charge rates of the units just fell off dramatically.

Normally our two inverters could feed the battery banks at a peak of 12,000w when all temps are perfect, however at 5C and below speeds would 'start' per unit at 1000w, then after 40minutes up to 1500w, then another 45minutes to 2000w each as the batteries slowly warmed up due to the charge.

Was utilising Octopus Go originally for th 4-hour cheap rate, but have since jump over to intelligent as the 6-hours off-peak made the difference.

 

[yessuz]

45 business days?
which is 2 months?

this is part of the email I got from Otovo:

Unfortunately, we have not yet heard back form the DNO, but this is to be expected as the average application wait time is between 35-45 working days (wait times depend on each DNO's internal processes so it can be less than this average). It has only been 26 working days since we submitted your application, so we´re still within that window.

 

[WannabeOwner]

including dishwasher overnight

Most days I have excess / export (unless car has been somewhere and has battery space to mop up excess PV), so I have dishwasher on during the day, rather than at night, and run it on" intensive" program rather than "Eco" so that it gets properly hot and cleans itself better

have your batteries in an insulated enclosure or indoors!

My PowerWalls are in "furthest unheated room" (its modern build, thus reasonably well insulated; Rads are set to 5C and very rarely come on). The PowerWalls lift the temperature by at least 2C in that room (compared to "Before PowerWalls"), which is helpful in Winter. Beware of that extra waste heat in Summer ...

An opposing view is that if you were unfortunate enough to get a runaway fire then NOT indoors would be an advantage!

smartest way to maximise my solar/ minimise my grid draw.

No idea how it scores on a "smartest" scale ... but what I do is

I use solcast.com.au for solar prediction (note that [unless/until they've changed it] their onscreen display is using "old algorithm" and their CSV download the "new algorithm", so best to use the CSV yourself rather than their graphs)

I download CSV (every hour or so) and use that to attempt to predict SolarPV. I then attempt to run down battery to "zero" shortly before sunrise (but ONLY IF the prediction looks like dramatic sun).

Based on that I decide how much (if at all) I charge overnight on Off Peak - basically I want the PowerWalls to hit 100% during the day - and also whether car charging will be needed. I also take into account if I need the car charged for a long-ish trip in the next few days, and if so I prioritise that so that it is definitely at 90% prior to departure (including Off Peak charging if PV hasn't done the job).

Yesterday PV went over 500W at 05:50, the PowerWalls dropped to 6% at 06:45 (which was the point at which PV started exceeding household requirement). PowerWalls charged steadily until 12:45 and then more rapidly until 100% at 14:45 - cars were already full - and then at 18:00 PV started producing less than house (and fell below 500W at 19:30)

Today's prediction was a bit less than yesterdays, so I aimed for 15% at 07:00, fell to 12% by 09:30 ... and is currently 31% at 15:30 ... and clearly not going to get anywhere near the 100% I would like and that would carry me through the night,

At a minimum I want enough in PowerWalls to get me to start of Off Peak. So prediction was a bit rubbish today If the cars had needed charge I would have been set PowerWall Off Peak charge higher - if the PowerWalls fill up "early in the day" (either very sunny, or had some Off Peak charging overnight) then any excess would go into the car ... so that would be "evens". But if the cars don't need anything I'm taking an aggressive approach to PowerWall level, so they have enough "soak up" capacity ... and I'm probably losing (and winding up paying Peak rate for my aggressive stance ) too often. My algorithm is in Beta... and just like FSD it needs some work yet!

 

[Mrklaw]

maybe of interest

 

[DaveNN]

And if you can, have your batteries in an insulated enclosure or indoors! as the winter weather this past November-March absolutely nuked performance!

My one regret is not having internal space, or an enclosed secure shed to have batteries installed within - ended up instead making "insulated jackets" for the batteries instead on the house north wall.

I have ripped out the downstairs cloakroom and now have all my eco kit in there.

 

[ElectricPolice]

Most days I have excess / export (unless car has been somewhere and has battery space to mop up excess PV), so I have dishwasher on during the day, rather than at night, and run it on" intensive" program rather than "Eco" so that it gets properly hot and cleans itself better



My PowerWalls are in "furthest unheated room" (its modern build, thus reasonably well insulated; Rads are set to 5C and very rarely come on). The PowerWalls lift the temperature by at least 2C in that room (compared to "Before PowerWalls"), which is helpful in Winter. Beware of that extra waste heat in Summer ...

An opposing view is that if you were unfortunate enough to get a runaway fire then NOT indoors would be an advantage!



No idea how it scores on a "smartest" scale ... but what I do is

I use solcast.com.au for solar prediction (note that [unless/until they've changed it] their onscreen display is using "old algorithm" and their CSV download the "new algorithm", so best to use the CSV yourself rather than their graphs)

I download CSV (every hour or so) and use that to attempt to predict SolarPV. I then attempt to run down battery to "zero" shortly before sunrise (but ONLY IF the prediction looks like dramatic sun).

Based on that I decide how much (if at all) I charge overnight on Off Peak - basically I want the PowerWalls to hit 100% during the day - and also whether car charging will be needed. I also take into account if I need the car charged for a long-ish trip in the next few days, and if so I prioritise that so that it is definitely at 90% prior to departure (including Off Peak charging if PV hasn't done the job).

Yesterday PV went over 500W at 05:50, the PowerWalls dropped to 6% at 06:45 (which was the point at which PV started exceeding household requirement). PowerWalls charged steadily until 12:45 and then more rapidly until 100% at 14:45 - cars were already full - and then at 18:00 PV started producing less than house (and fell below 500W at 19:30)

Today's prediction was a bit less than yesterdays, so I aimed for 15% at 07:00, fell to 12% by 09:30 ... and is currently 31% at 15:30 ... and clearly not going to get anywhere near the 100% I would like and that would carry me through the night,

At a minimum I want enough in PowerWalls to get me to start of Off Peak. So prediction was a bit rubbish today If the cars had needed charge I would have been set PowerWall Off Peak charge higher - if the PowerWalls fill up "early in the day" (either very sunny, or had some Off Peak charging overnight) then any excess would go into the car ... so that would be "evens". But if the cars don't need anything I'm taking an aggressive approach to PowerWall level, so they have enough "soak up" capacity ... and I'm probably losing (and winding up paying Peak rate for my aggressive stance ) too often. My algorithm is in Beta... and just like FSD it needs some work yet!

View attachment 942420

It’s all solar ‘roulette’ as I term it.

The aim, like you, is minimal peak usage period. If that means I put more into the battery to protect myself then so be it. The aggressive approach as you rightly put it is counter productive as I end up paying more for peak usage, but have done this many times. I don’t use apps, just BBC weather, which is more roulette.

Quite simply last night I charged the car for todays 140 mile trip up to 90%, which obviously drained the battery and then set a 30 minute boost charge of the batteries from 05:00-05:30 to last until solar began its magic. 30 mins gets me 2kWh hence 15p. The previous day I misjudged and the peak usage cost me 21p for 2h before solar matched the house load. Obviously very early sun as only used about 0.5kWh in 2h.

This whole way of working is dynamic and changes with the seasons so for the average Bob like me who hasn’t programmed the arse off some API or ZX81 coding algorithm is now becoming tiresome. I simply follow seasons and aim to make sure the batteries are full and can run for as long as possible until off peak kicks in.

In peak summer like the weekend just gone, I too wash and dishwasher on short programs in the day to get as many runs in as possible. With 2 grown up partying daughters our washing is immense. In winter everything is on at night including a full battery charge to last as long as possible through the day and evening. Load shifting for me is always between 90-95% off peak.

One last point as regards this DNO approval for larger inverters, I got caught up in this when I first had my install, nobody explained it to me that there was a 3.68kW limit so naturally I was pretty pi$$ed when I thought I could have paid an extra £100 for a 6kW hybrid inverter. We occasionally have usage which peaks above 3.68, yes the dishwasher hits its drying cycle just when the kids airfry a bowl chips, or the dreaded Sunday roast; however, it comes back to the extra cost which when I’ve looked into it is negligible in the grand scheme. Bit like buying a seven seater for the few occasions a year the grandparents visit! Never enjoyed spirited country lane driving in my old Zafira!

Anyhow, this is my scenario. Everyone on here has there own so all I’ll finish with is don’t fret it, get what you can afford and what covers the majority of your needs. Unless you spend megabucks to cover every eventuality and invest time and effort into tracking the solar cycles you’ll still be way better off than sitting on a flexible tariff.

I’m a novice at this but Octpus tracker has me down at £552 for the last quarter on IO compared with £1,382 on flexible. That is without the additional IO hours that the tracker can’t map. I’d call that a decent return!

 

[PITA]

Yikes!

Is this "maximum allowed" based upon a theoretical power draw or amperage?

I'm on single phase/100A fuse and fly very close to the sun on that - have considered 3-Phase as the next step, but wouldnt want to get caught out!

The National Grid have new rules on domestic supply.

From what I've been told they don't do 100 Amp fuse installations on new installs anymore. Neither Single Phase or 3 Phase.

So... if you've got a 100 Amp fuse already installed, that's OK... you got in just in time.

If you have a 3 Phase supply upgrade, they will only install an 80 Amp fuse Cutout (80 Amps per phase). With 100 Amp Switch & 100 Amp Smart Meter.

There is one exception, which I tried to exploit, but was turned down point blank.

The only other option presented to me was a 3 Phase Commercial upgrade, which involved even thicker cabling, a new 200 Amp Cutout which does not fit a meter box, and cast doubt over a Smart Meter that would be allowed to handle it all on a Domestic tariff.

It opened a right can-of-worms.

So I accepted that 3 Phase and 80 Amps per phase is my limit... and most peoples limit now, without the costs spiralling into the stratosphere.

This has to handle two 22kW fast chargers (64 Amps, per phase), plus two Powerwalls charging over 6 hours (20 Amps)... so you can see why I wanted some more wiggle room.

Now admittedly, my 22kW chargers only charge at 11kW because of vehicle restriction. But that won't always be the case.