Solar Panels UK - is it worth it?

[gidster99]

Hi guys - I am also trying to figure out if it makes sense to go with a solar / battery combination.
The biggest challenge I have with regards to electricity (I have plenty of other non-electrical challenges, but we won't go into those here! ;-) is that I use too much of it - around 11,000 KwH per year. I have looked into how much per day, and it is between 26 - 32 KwH per day.
I have had a couple of solar quotes - and it seems my roof is not ideally set up for solar: too many velux windows / dormers etc.
So the best they seem to be able to fit will generate around 4,500 KwH per year (obviously with much of that generated over the brighter months). So that is around 6,500 KwH short of my needs
So I am wondering what my options are? I was naively thinking I can just get lots of battery storage - say around 30 KwH and simply charge the batteries using a low overnight rate and live off the batteries / solar during the day.
However, I have just been told this might not be so easy to do as my batteries may only allow me to power a certain amount of things at once... and once I go over this amount (which might be around 4KWs) I will be drawing from the grid.
Is my plan foiled? Or is there something that can be done - someone mentioned I might be able to set up a second inverter in parallel and thereby double my power output... This sounds like it might work...But would appreciate your thoughts - especially if any of you have done something similar.
Or should I simply try and move over to Octopus Agile and fit enough battery storage to allow me to run off battery during the expensive evening hours and just live with the Grid for most of the day, with its hopefully lower rates? I guess if I were to do this, we would need to try and make sure not to use heavy loads during the time we are on battery power... Right now I do not have a smart meter, so it is difficult for me to know what my maximum power usage is like.
Anyway, if anyone does have any thoughts on this I would be interested to hear them as this all seems to be less straightforward than I would like!
Many thanks!

 

[Mrklaw]

what is causing your usage? And what are your demand spikes - i.e how many kw instantaneously to consider? if its a shower for a few minutes don’t fuss it, but if its continuous it needs consideration.

load shifting you’ll also have issues charging 30kwh of batteries in a 4 hour off peak window for example. but you could potentially use multiple inverters to get more charge/discharge speed. Eg if you have 3.6kw max if you doubled up you could get 7.2kw demand handling.

Also load shifting you’re only getting the cost between off peak and peak - so eg 40p peak/7.5p off peak you’re saving 32p/unit rather than 40p for solar - that needs factoring in.

 

[gidster99]

what is causing your usage? And what are your demand spikes - i.e how many kw instantaneously to consider? if its a shower for a few minutes don’t fuss it, but if its continuous it needs consideration.

load shifting you’ll also have issues charging 30kwh of batteries in a 4 hour off peak window for example. but you could potentially use multiple inverters to get more charge/discharge speed. Eg if you have 3.6kw max if you doubled up you could get 7.2kw demand handling.

Also load shifting you’re only getting the cost between off peak and peak - so eg 40p peak/7.5p off peak you’re saving 32p/unit rather than 40p for solar - that needs factoring in.

At this point I am not clear what is causing my usage - at least not specifics... This afternoon I started taking regular readings from my electric meter and working out an hourly use in KWs... Today is washing day, so my worst period was with the washing machine on for one load and the tumble drier for the prior load... There may have also been some dishwasher action as well as some lights and the Computer etc... Anyway, the worst period today was using the equivalent of about 3 KWs per hour... So a single inverter of 3.6 KwH might be too little for me, forcing me to look to double them.

I am also waiting for a gizmo by Efergy which I think I clamp on to my mains feed - and I am hoping that may help me better understand my current electric use.

I think the current plan is to load up as much solar as I can - but as mentioned, this seems to max out around 4,500 KwH over the year... So this battery plan is to handle the remaining 6,500 KwHs of power still needed. I suspect the amount I would save would also be slightly worse than your example as I think I would "lose" some power in the trip from grid to battery to appliances. But it is to effectively try and get as much power from solar / battery charged at 7.5p that I am striving for.
But even from what I am seeing so far, it looks likely that I will need to factor in this double inverter. Which I have no doubt will add to the cost !

 

[MrT3]

Anyway, the worst period today was using the equivalent of about 3 KWs per hour... So a single inverter of 3.6 KwH might be too little for me, forcing me to look to double them.

If that is your worst then a 3.6 kWh inverter would be fine.

what are you trying to achieve, saving money or being self sufficient? Using more than you generate isn’t a bad thing as none is wasted being put back into the grid, so payback period is shorter/more accurate.

 

[yessuz]

you do not have smart meter or you are not on the Octopus GO (IO...|)? because these give you exact power consumption each 30 minute slot.

with smart meter home display you can see instant power usage. so you always can see that kettle on = 3kw. but it's short burst.

my house, on the light load (only 2 laptops + monitors / wfh) is about 350w. for example. but I can see that it can be more when thumble dryer + overn is on. for example induction hob is same as car charging... roughly 7 kw at max)

but you should be able to identify why such a massive usage.

ps. my max load was like 12 kw at peak

 

[Mrklaw]

At this point I am not clear what is causing my usage - at least not specifics... This afternoon I started taking regular readings from my electric meter and working out an hourly use in KWs... Today is washing day, so my worst period was with the washing machine on for one load and the tumble drier for the prior load... There may have also been some dishwasher action as well as some lights and the Computer etc... Anyway, the worst period today was using the equivalent of about 3 KWs per hour... So a single inverter of 3.6 KwH might be too little for me, forcing me to look to double them.

I am also waiting for a gizmo by Efergy which I think I clamp on to my mains feed - and I am hoping that may help me better understand my current electric use.

I think the current plan is to load up as much solar as I can - but as mentioned, this seems to max out around 4,500 KwH over the year... So this battery plan is to handle the remaining 6,500 KwHs of power still needed. I suspect the amount I would save would also be slightly worse than your example as I think I would "lose" some power in the trip from grid to battery to appliances. But it is to effectively try and get as much power from solar / battery charged at 7.5p that I am striving for.
But even from what I am seeing so far, it looks likely that I will need to factor in this double inverter. Which I have no doubt will add to the cost !

definitely get your half hourly readings, or do readings yourself to build a picture. We do washing machine and dishwasher overnight, often 1-2 tumble dryer runs during the day and we use maybe 12-15kwh unless we’re charging the EV. The only stress for a battery is the tumble dryer if its on for a couple of hours you don’t want to put something else on - but a kettle is done in a couple of mins so thats fine. So either wait for solar so you have battery+solar to cover load or just pause the dryer/wait for the other thing.

I’m hoping you’re mis-calculating as from your descrioption you seem about double what you perhaps should be using. Unless you have a big detatched house with electric underfloor heating on all day or a tropical room

 

[gidster99]

you do not have smart meter or you are not on the Octopus GO (IO...|)? because these give you exact power consumption each 30 minute slot.

with smart meter home display you can see instant power usage. so you always can see that kettle on = 3kw. but it's short burst.

my house, on the light load (only 2 laptops + monitors / wfh) is about 350w. for example. but I can see that it can be more when thumble dryer + overn is on. for example induction hob is same as car charging... roughly 7 kw at max)

but you should be able to identify why such a massive usage.

ps. my max load was like 12 kw at peak

Correct: no smart meter yet. I have requested one but have been told I can't have it yet which is annoying (I'm trying to get them to change their minds! )

In the meantime I have ordered a Home Energy Monitoring gadget which I'm hoping will let me know my maximum draw etc.

 

[Mrklaw]

Correct: no smart meter yet. I have requested one but have been told I can't have it yet which is annoying (I'm trying to get them to change their minds! )

In the meantime I have ordered a Home Energy Monitoring gadget which I'm hoping will let me know my maximum draw etc.

read your meter as often as you can on a typical day - weekend or even just a few times during the day (more is better) to build up a picture.

 

[Pete UK]

Hi guys - I am also trying to figure out if it makes sense to go with a solar / battery combination.
The biggest challenge I have with regards to electricity (I have plenty of other non-electrical challenges, but we won't go into those here! ;-) is that I use too much of it - around 11,000 KwH per year. I have looked into how much per day, and it is between 26 - 32 KwH per day.
I have had a couple of solar quotes - and it seems my roof is not ideally set up for solar: too many velux windows / dormers etc.
So the best they seem to be able to fit will generate around 4,500 KwH per year (obviously with much of that generated over the brighter months). So that is around 6,500 KwH short of my needs
So I am wondering what my options are? I was naively thinking I can just get lots of battery storage - say around 30 KwH and simply charge the batteries using a low overnight rate and live off the batteries / solar during the day.
However, I have just been told this might not be so easy to do as my batteries may only allow me to power a certain amount of things at once... and once I go over this amount (which might be around 4KWs) I will be drawing from the grid.
Is my plan foiled? Or is there something that can be done - someone mentioned I might be able to set up a second inverter in parallel and thereby double my power output... This sounds like it might work...But would appreciate your thoughts - especially if any of you have done something similar.
Or should I simply try and move over to Octopus Agile and fit enough battery storage to allow me to run off battery during the expensive evening hours and just live with the Grid for most of the day, with its hopefully lower rates? I guess if I were to do this, we would need to try and make sure not to use heavy loads during the time we are on battery power... Right now I do not have a smart meter, so it is difficult for me to know what my maximum power usage is like.
Anyway, if anyone does have any thoughts on this I would be interested to hear them as this all seems to be less straightforward than I would like!
Many thanks!

I’m in a similar situation to you. I’ve done a lot of head scratching. Do you have an EV?

We use about 19,000kW a year.

 

[Mrklaw]

if you can fit more than 4-6 panels and can afford it, get some (and ideally a battery to take your solar self-use from 40-50 to 90%). Even if you don’t have space for enough to cover your home usage it still helps. although I’d have thought higher usage would go with larger homes so larger roofs, I realise some will have odd layouts.

likewise a battery also adds options for load shifting off peak tariffs which provide decent savings

Car if you wfh and can’t use the solar (eg daytime my use is around 300w if the tumble dryer isn’t on and the battery is done charging) you can throw it in the car, but otherwise just charge off peak and assume thats not covered by the solar. Not an issue if your home use is high anyway.

 

[WannabeOwner]

the best they seem to be able to fit will generate around 4,500 KwH per year (obviously with much of that generated over the brighter months).

Suggest you check PVWatts to see how your generation is spread over the months. You can do separate figures for the direction or each face of your roof. Even if you don't figure out the actual; area of your dormers it would get you a ratio between each face, and Summer / Winter months

Winter is going to give you "nothing" (UK mid-Winter insolation is 90% less than mid-Summer), so knowing which months are high, and how much, might help your decision on Solar (e.g. vs. "Just battery")

North Facing roof (if you have South / North) is worth considering. Should give you around 80% (of South) in mid Summer (unless you have a steep roof)

South generates most at PEAK, but East + West starts earlier / finishes later and, for me, I think is best as it provides power to house for "more of the day" and thus a shorter solar-night to have to run off battery.

my batteries may only allow me to power a certain amount of things at once

I have 2x PowerWall. Max draw is 10AMPs (as is max charge either from Solar or overnight/Off Peak). Other batteries will have different limits. My PowerWall charge (overnight) drops if something else (e.g. charging EV) is using a lot of power, so whilst they will will to 100% in 4 hours slot they won't if car is charing at same time (depends on your supply, 3-Phase probably doesn't have that problem etc. etc.)

You may need to make sure you have 100AMP fuse / get it upgraded.

At this point I am not clear what is causing my usage - at least not specifics

Need to find that When I whittled mine down the "WTF is using that last bit" was a stonking big transformer that was heating!! the under stairs cupboard ... and provided low voltage for the front door bell installed in 1960 !!

Also found my fridge-freezer was on for "hours" each day. Cleaned out the filter which solved that (and made the kitchen a lot quieter )

I have ordered a Home Energy Monitoring gadget

I recommend getting a Smart Plug (or several), which has Energy Monitoring. e.g. TPLink Kasa or Tapo (bit more functionality, but more money). You can also use them to turn stuff off - e.g. TV etc. when you go to bed (you can have a "Good night" routine, which will cause a forest of them to turn stuff off - - e.g. "Alexa Goodnight")

Separate from that and once you have your "Home Energy Monitoring gadget", then throw your breaker switches - all off, then back on one-by-one to see if anything spikes your monitor and is consuming "constantly" - aquarium tank etc.. That's obviously not so useful for things that are on a timer / intermittent. Hopefully SmartPlug will help you log how much Washing Machine uses and how often it is on and so on. (Some white goods you will be able to move to overnight use when you have an Off Peak rate)

 

[gidster99]

definitely get your half hourly readings, or do readings yourself to build a picture. We do washing machine and dishwasher overnight, often 1-2 tumble dryer runs during the day and we use maybe 12-15kwh unless we’re charging the EV. The only stress for a battery is the tumble dryer if its on for a couple of hours you don’t want to put something else on - but a kettle is done in a couple of mins so thats fine. So either wait for solar so you have battery+solar to cover load or just pause the dryer/wait for the other thing.

I’m hoping you’re mis-calculating as from your descrioption you seem about double what you perhaps should be using. Unless you have a big detatched house with electric underfloor heating on all day or a tropical room

I am afraid I am definitely not miscalculating my overall energy use as it is consistently around 11,000 / 11,500 KwH per year.

We are lucky enough to live in a substantial house. And we also have a self contained flat in the loft which is rented out to tenants ... and we include their electricity in their rental price. So I'm sure that at least partially explains the high energy use. But yes: the electricity bill is eye-watering!

I’m in a similar situation to you. I’ve done a lot of head scratching. Do you have an EV?

We use about 19,000kW a year.

Hi Pete, yes we do have an EV.
But I have excluded it from the above as it is charged via a separate phase of electricity (the house happened to come with 2 phases) ... I think, as this is already on a very good overnight tariff, that the EV will not be impacted by my solar

if you can fit more than 4-6 panels and can afford it, get some (and ideally a battery to take your solar self-use from 40-50 to 90%). Even if you don’t have space for enough to cover your home usage it still helps. although I’d have thought higher usage would go with larger homes so larger roofs, I realise some will have odd layouts.

likewise a battery also adds options for load shifting off peak tariffs which provide decent savings

Car if you wfh and can’t use the solar (eg daytime my use is around 300w if the tumble dryer isn’t on and the battery is done charging) you can throw it in the car, but otherwise just charge off peak and assume thats not covered by the solar. Not an issue if your home use is high anyway.

The plan is to stuff as many panels on both sides of the roof as possible (ie even the less sunny side)...but that still only takes me to about 1/3rd of my usage. But yes: every little helps, and I think the incremental cost of adding more panels once the scaffolding is already up and the electricians are already on site is worth it.

 

[Pete UK]

……We have a non ideal roof. Just signed to get 27 420w panels, 2x GivEnergy 5kW inverters, 4x GivEnergy 9.5kW batteries.

Planning on IO (6 hours of off peak) to allow to charge car and solar batteries fully over night.

For us, the Solar will generate just shy of 7,000kW per year, the car uses 4,500kW and the rest (7,500) will come from off peak via the batteries. (And unfortunately, some peak in winter).

What will save us the most is the batteries.

Even discounting the solar, if you charge the batteries fully overnight at 7.5p but you have to export some, due to solar generation, you’ll get 5p per kW back. So your ‘insurance’ cost of charging the batteries off peak ‘too much’ will be 2.5p per kW. For us that’s 36kW x 0.025 = 90p a day !

If however, we don’t charge them at all and it’s a bad summers day and we don’t generate 36kW and we have to buy it at peak, it’s going to cost us 36x 42p = £15.12 a day, for that mistake.

So it’s better to overcharge at night and then put up with having some export at 5p, then trying to be a super smart arse and getting it wrong. You have to get it right far more times than getting the charging wrong.

It’s a learning curve but other than 100% charging in winter, we expect to lower the overnight charge after Feb to say 80%, then slowly reduce to maybe 20-30% over the summer months. TBC !

Our DNO application wait is coming up to a month now…. Grrr.

 

[WannabeOwner]

the EV will not be impacted by my solar

It can soak up any excess - e.g. mid day in the Summer when your battery is full and you are still generating, or if your Solar can generate more than 10kW at peak (i.e. more than House + Battery-charge can use)

that still only takes me to about 1/3rd of my usage

Might be 100% (or more) of your day time summer usage ... you still need to power the house during the night in summer

I think the incremental cost of adding more panels once the scaffolding is already up and the electricians are already on site is worth it.

Yes, definitely, even a North side (if roof not too steep)

 

[gidster99]

……We have a non ideal roof. Just signed to get 27 420w panels, 2x GivEnergy 5kW inverters, 4x GivEnergy 9.5kW batteries.

Planning on IO (6 hours of off peak) to allow to charge car and solar batteries fully over night.

For us, the Solar will generate just shy of 7,000kW per year, the car uses 4,500kW and the rest (7,500) will come from off peak via the batteries. (And unfortunately, some peak in winter).

What will save us the most is the batteries.

Even discounting the solar, if you charge the batteries fully overnight at 7.5p but you have to export some, due to solar generation, you’ll get 5p per kW back. So your ‘insurance’ cost of charging the batteries off peak ‘too much’ will be 2.5p per kW. For us that’s 36kW x 0.025 = 90p a day !

If however, we don’t charge them at all and it’s a bad summers day and we don’t generate 36kW and we have to buy it at peak, it’s going to cost us 36x 42p = £15.12 a day, for that mistake.

So it’s better to overcharge at night and then put up with having some export at 5p, then trying to be a super smart arse and getting it wrong. You have to get it right far more times than getting the charging wrong.

It’s a learning curve but other than 100% charging in winter, we expect to lower the overnight charge after Feb to say 80%, then slowly reduce to maybe 20-30% over the summer months. TBC !

Our DNO application wait is coming up to a month now…. Grrr.

So with 2 x 5KW inverters does that mean your battery can power up to 10KW of appliances at once?

 

[Pete UK]

Forgot to highlight that the inverter charging rates (/supply rate) and the battery charge/ discharge rates are very important. Pay close attention !

For example; although the GivEnergy Gen 2 hybrid inverter is 5kW, it will only charge the batteries at 3.6kW! And only power the house at 3.6kW, but you can get 5kW from the solar (it peaks at more actually); 3.6 to the battery and 1.5 to the house. Or less to the battery and more to the house.

So with 2 inverters, you’d be able to power 7.2kW to the house from the batteries when the sun is down, without any peak price electricity needed from the grid (as long as you have enough battery storage!). This only has to last you till the start of your off peak period again. For IO that’s 11:30pm. But if there is no solar all day, then it has to last from 05:30-23:30 !

Also look at the depth of discharge (usable kW) from the battery. The GivEnergy 9.5kW packs have 100% (although they have a 4% reserve, so 96% ). That’s why I used 36kW for 4 instead of 38kW in my example above.

You will (like me) probably still have to buy some park in winter, can’t get around that. But make sure you can store enough off peak/ Solar to fully cover most of the year.

 

[yessuz]

So with 2 x 5KW inverters does that mean your battery can power up to 10KW of appliances at once?

Pretty much

 

[yessuz]

But seriously what are those 10kw appliances?

Dishwasher, washing machine uses the most power during the start of the cycle, i.e. when heating up the water. After it is heated up - it's mostly kist motors.

Same for tumble dryer - most of power consumption during full cycles in the first half.

Under floor heating is about 150w per m2 (well my bathroom is...)

Electric towel rail is ~400-600 w per rail. But fornthis I changed standard thermostat which is only on/off to the one with timer or power setting, so I can turn it on for 2 hrs only

I managed to get loke 12 kw consumption ONLY once, when I started the dish washer, washing machine, car charging floor and towel heating all at once

Maybe your tenants do the Bitcoin mining? If power is already included, I Know I wouldn't be saving at all ))

 

[Pete UK]

Yes and no,

10kW if the solar is producing but only

7.2kW if from only from the batteries !

 

[Rooster6655]

Hi guys - I am also trying to figure out if it makes sense to go with a solar / battery combination.
The biggest challenge I have with regards to electricity (I have plenty of other non-electrical challenges, but we won't go into those here! ;-) is that I use too much of it - around 11,000 KwH per year. I have looked into how much per day, and it is between 26 - 32 KwH per day.
I have had a couple of solar quotes - and it seems my roof is not ideally set up for solar: too many velux windows / dormers etc.
So the best they seem to be able to fit will generate around 4,500 KwH per year (obviously with much of that generated over the brighter months). So that is around 6,500 KwH short of my needs
So I am wondering what my options are? I was naively thinking I can just get lots of battery storage - say around 30 KwH and simply charge the batteries using a low overnight rate and live off the batteries / solar during the day.
However, I have just been told this might not be so easy to do as my batteries may only allow me to power a certain amount of things at once... and once I go over this amount (which might be around 4KWs) I will be drawing from the grid.
Is my plan foiled? Or is there something that can be done - someone mentioned I might be able to set up a second inverter in parallel and thereby double my power output... This sounds like it might work...But would appreciate your thoughts - especially if any of you have done something similar.
Or should I simply try and move over to Octopus Agile and fit enough battery storage to allow me to run off battery during the expensive evening hours and just live with the Grid for most of the day, with its hopefully lower rates? I guess if I were to do this, we would need to try and make sure not to use heavy loads during the time we are on battery power... Right now I do not have a smart meter, so it is difficult for me to know what my maximum power usage is like.
Anyway, if anyone does have any thoughts on this I would be interested to hear them as this all seems to be less straightforward than I would like!
Many thanks!

There are a few factors which will make or break whether its worth it for you:
-Cost of install
-How you are paying for it
-How much of the generated solar you will use
-How much you will use from the batteries
-Life expectancy of the install
-Warranty/reliability of installer

I would be looking at separating the savings of the solar and the battery so that you can work out whether having both or them individually will be worth it for you, despite some saying that solar is a no brainer, that isn't the case for everyone especially those who are also looking at financing it which will take a considerably chunk out of it. Feel free to send more details and I can try to work out some calculations.