Solar Panels UK - is it worth it?

[GRiLLA]

Yeah it's definitely mainly the hot tub.

But our load will be higher than average even without it (compared to houses where people are out all day) as 2 of us work from home so 4 monitors, 2 PCs, lights (even in daytime we sometimes need lights on as back of our house is quite dark). Multiple kettle boils for tea/coffee. Etc etc etc Each probably small on its own but adding up

Do you WFH in the hot tub? I must admit to having never looked into (or been interested in) hottubs, but are you keeping it hot all the time? That seems nuts.

For comparison I WFH, 2 kids are home both playing on gaming PCs a lot, plenty of other use brings us to maybe 12KWH, when they go back to school it'll be more like 8KWH and my 9.5kwh of available battery hopefully should cover it in winter.

I have 16 405w panels, today we've generated 28KWH, the battery is full, dumped a load into the car and sold 7KWH to the grid.

 

[Chimpy McChimp]

Do you WFH in the hot tub? I must admit to having never looked into (or been interested in) hottubs, but are you keeping it hot all the time? That seems nuts.

For comparison I WFH, 2 kids are home both playing on gaming PCs a lot, plenty of other use brings us to maybe 12KWH, when they go back to school it'll be more like 8KWH and my 9.5kwh of available battery hopefully should cover it in winter.

I have 16 405w panels, today we've generated 28KWH, the battery is full, dumped a load into the car and sold 7KWH to the grid.

Yes. You have to keep it on all the time. Unless you know you aren't going to use it for a while then it makes sense to turn off and drain it. Otherwise it cools down then costs more the heat up (the ramp up is very energy hungry). It doesn't actually heat 24/7 but as it starts to cool, the heater switches on. It's very well insulated (snow and ice can sit on the lid and it be 40oC inside). But it is trying to keep over 1000 litres of water water warm when ambient air is probably mid teens to low 20s at best in Scotland.

 

[GRiLLA]

Yes. You have to keep it on all the time. Unless you know you aren't going to use it for a while then it makes sense to turn off and drain it. Otherwise it cools down then costs more the heat up (the ramp up is very energy hungry). It doesn't actually heat 24/7 but as it starts to cool, the heater switches on. It's very well insulated (snow and ice can sit on the lid and it be 40oC inside). But it is trying to keep over 1000 litres of water water warm when ambient air is probably mid teens to low 20s at best in Scotland.

Can't you heat it to hotter during a cheap rate overnight, then let it get cooler during a more expensive daytime rate? Why do you have a flat rate?

 

[MrT3]

It's cost us 54p this month and we have used it a lot.

Per load?

A A+++ rated heat pump dryer typically uses 1.3 to 1.5 kWh per full load, so around 45p with current prices.

 

[GRiLLA]

Per load?

A A+++ rated heat pump dryer typically uses 1.3 to 1.5 kWh per full load, so around 45p with current prices.

I've had an A+++ heat pump dryer for about 10years now, but I notice it would be F under the new ratings and a new A would be about 500wh a load.

 

[MrT3]

I've had an A+++ heat pump dryer for about 10years now, but I notice it would be F under the new ratings and a new A would be about 500wh a load.

A++ would be F in the new ratings but virtual no dryers on the market use the new ratings because they were all launched before the change - either way you won't really find anything rated better than A+++/E on the market (maybe a £2500 Miele is an E or possibly scraping into a -D) and they will consume over 1 kWh on a full load. They may only draw around 500w but will take up to 3 hours to dry a load.

 

[Chimpy McChimp]

Can't you heat it to hotter during a cheap rate overnight, then let it get cooler during a more expensive daytime rate? Why do you have a flat rate?

Doesn't work like that unfortunately. Max temp it goes to is about 42. Which is uncomfortable. 40 is okish

I fixed with EDF a while ago till September 24. Can't remember the standing charge or gas rates but leccy is 19.23p per kwh. No cheap rate. Just the flat rate charge.

Managed to get locked in not long before rates went crazy so have been protected. The solar and battery were part of a plan to protect us once we had to switch. Maybe rates will have come down significantly (I haven't really kept an eye on them TBH. Just been content knowing I'm fixed for a good while yet).

Been doing other stuff to keep costs down (like replacing our 30 year old boiler that was set up to heat hot water constantly. I would love to know how much we are saving now but thanks to EDFs F up of our smart meter I can't track it like I can with electricity. But getting off topic.)

 

[Chimpy McChimp]

A++ would be F in the new ratings but virtual no dryers on the market use the new ratings because they were all launched before the change - either way you won't really find anything rated better than A+++/E on the market (maybe a £2500 Miele is an E or possibly scraping into a -D) and they will consume over 1 kWh on a full load. They may only draw around 500w but will take up to 3 hours to dry a load.

It's a Samsung.
TBH. I put in our electric rate into the smartthngs app and it tells me how much we spent. I have no idea if it is accurate or not. But I think I did 3 loads one day after holiday and the notification said 54p for the month. Which thinking about it, given I'd been away, the 3 times may have been the only times I'd used it that month.

I do know it's a lot cheaper than our old fashioned tumble dryer A full load straight out of machine takes around 2.5h. Max. But when you work from home you can get through several loads a day (If needed)

 

[Mrklaw]

you’re probably good with what you have. An off peak tariff with load shifting into overnight might get you down to an average of 16-17p/kwh but 19p flat is pretty competitive right now

 

[Chimpy McChimp]

It's a Samsung.
TBH. I put in our electric rate into the smartthngs app and it tells me how much we spent. I have no idea if it is accurate or not. But I think I did 3 loads one day after holiday and the notification said 54p for the month. Which thinking about it, given I'd been away, the 3 times may have been the only times I'd used it that month.

I do know it's a lot cheaper than our old fashioned tumble dryer A full load straight out of machine takes around 2.5h. Max. But when you work from home you can get through several loads a day (If needed)

Quick update. 1 load was 12p (tariff 19.23p per kwh)

 

[Pete UK]

Now I've had time to think (overthink???) Does it make sense for the battery to charge from grid then charge house as I have a flat rate. Seems like unnecessary charge/discharge cycles on the battery.

As others have said. No, not until you’re on a cheap rate tariff.

Leave the GE battery in ECO mode only for now. No timed charge/ discharge. That way you’ll just capture all the solar and make use of it.
Not sure if you have an EV or not? - but If you find the battery is getting to 100% from solar and you’re exporting for extended periods, then it’s time to put some in the car if it’s at home and you have one? If you have a smart charger, like a zappy then you can use that in eco+ mode. If you have a dumb charger, you can charge it but with the amps cranked right down.
Yesterday for example; I set my model Y to charge at 5A (1,200w) from 9am and over 4 hours I added about 6% - which got me to 90%; (Then everything went out to the grid for the rest of the day!) If I am closely monitoring it, I crank up the amps until I’m not exporting any more (basically what the zappy does but manually).
I generate the most from my east array so 9am till 1pm is when the whole system it’s at its highest generation normally. But you can vary that according to your set up!

I was kind of in the same boat as you after my install. Still on a fixed rate with OVO for a month due to various reasons. What I did was set up the car to charge over the (imaginary) off peak period to see how it would work as if I was on IO (or similar). But also left a bit of space for Solar car charging when I anticipated the batteries were going to get to close to 100% and was going to be exporting that day.

The battery/ batteries make a big difference. Even if you “only” have a 9.5kW battery, you’ll be able to get more out of it than that during the day. Because when you’re on a cheap overnight rate, you can charge it (if needed), and use some of that till the sun comes up. So in your case the house and hot tub will use maybe 2-3kW? until you start generating, then the solar will charge it up to 9.5kW again during the day, and solar will power your house/tub during the day, so you’ve effectively gained 9.5kW from a maybe a mix of cheap rate/ solar plus the 2-3kW from solar! This will be more obvious during the shoulder seasons.

Are you using 24-30kW during the summer only or is that an average year round daily use?

 

[Chimpy McChimp]

As others have said. No, not until you’re on a cheap rate tariff.

Leave the GE battery in ECO mode only for now. No timed charge/ discharge. That way you’ll just capture all the solar and make use of it.
Not sure if you have an EV or not? - but If you find the battery is getting to 100% from solar and you’re exporting for extended periods, then it’s time to put some in the car if it’s at home and you have one? If you have a smart charger, like a zappy then you can use that in eco+ mode. If you have a dumb charger, you can charge it but with the amps cranked right down.
Yesterday for example; I set my model Y to charge at 5A (1,200w) from 9am and over 4 hours I added about 6% - which got me to 90%; (Then everything went out to the grid for the rest of the day!) If I am closely monitoring it, I crank up the amps until I’m not exporting any more (basically what the zappy does but manually).
I generate the most from my east array so 9am till 1pm is when the whole system it’s at its highest generation normally. But you can vary that according to your set up!

I was kind of in the same boat as you after my install. Still on a fixed rate with OVO for a month due to various reasons. What I did was set up the car to charge over the (imaginary) off peak period to see how it would work as if I was on IO (or similar). But also left a bit of space for Solar car charging when I anticipated the batteries were going to get to close to 100% and was going to be exporting that day.

The battery/ batteries make a big difference. Even if you “only” have a 9.5kW battery, you’ll be able to get more out of it than that during the day. Because when you’re on a cheap overnight rate, you can charge it (if needed), and use some of that till the sun comes up. So in your case the house and hot tub will use maybe 2-3kW? until you start generating, then the solar will charge it up to 9.5kW again during the day, and solar will power your house/tub during the day, so you’ve effectively gained 9.5kW from a maybe a mix of cheap rate/ solar plus the 2-3kW from solar! This will be more obvious during the shoulder seasons.

Are you using 24-30kW during the summer only or is that an average year round daily use?

The 24-30 is just over last month or so. But when the hot tub is on. It's not on all the time but when we were doing that calculations for solar we figured we were at 11,000kwh roughly per year. But we had only had the model Y a short time so most likely a bit higher usage than last year.

 

[Pete UK]

The 24-30 is just over last month or so. But when the hot tub is on. It's not on all the time but when we were doing that calculations for solar we figured we were at 11,000kwh roughly per year. But we had only had the Y a short time so most likely a bit higher. But I'm. My worried about the car part as no matter what I do (charge from grid or solar or battery) the savings are massive over the diesel cars I had previously.

We use about 19,000kW pa (majority in winter)

If it helps, over the last 12 months with the model Y we used;

4,077kW to do 12,700 miles.

3,564kW was from home charging (87%)
367kW was from supercharging (9%)
147kW was from ‘other’ public charging (4%)

By far the highest price per kW was supercharging.

We managed to put 182kW from Solar in the car in July (~ 750 miles or ~ £150 in petrol at 35mpg). Which covered all the car charging. Which was pretty sweet. And exported 180kW. Turns out that in summer we don’t use the car as much! We used about 20kW per day in the house in July all from Solar. It is more like 75kW in December and Jan (including car charging)

I think you’ll need to get your calculator out to work out what’s best. Certainly for us pre-Solar/ batteries but with the EV it wasn’t worth going on a cheap rate, as the higher house peak rate usage back then far outweighed the smaller EV charging rate usage. But Octopus rates have changed since then, so now IO would have worked out better than a fixed rate for us. With your solar generated you might find things aren’t as clear cut. 19p per kW is still pretty reasonable though, so I’d stick with that while it lasts if it was me.

We’re all at the mercy of fluctuating rates so all the ROI and savings calculations you do etc are pretty hard to quantify in advance. Then they change overnight. For sure the EV savings from a fossil fuel car are huge though. So petrol savings should be taken into consideration against any increased electricity cost.

I’m pretty happy on IO now. Worst case for us will be Dec/Jan if we’re consuming 75kW per day.

Roughly I reckon a winters day will be;

£3.45 @ 7.5p:
10kW charging the car.
36kW charging GE batteries (4% reserve)

free:
4kW from Solar(?)

£8.10 @ 30p
27kW house

So £350 in Dec now, compared to previously when I was paying £800+ at 34p or what would be £715 at current Octopus rate of 30p/Kw

 

[Pink Duck]

Remember that kW is the unit for rate of energy transferred (power), kWh the unit for energy amount stored/moved (capacity).

 

[Chimpy McChimp]

Thanks for sharing your maths. I did do some back if a fag packet stuff earlier this year. We currently pay 320 per month (regardless if winter or summer) for gas and electric and is probably about right for our usage on our tarrifs. I think with our new boiler and the solar and battery I reckoned I would shave over £100 per month off.

But it's all a bit "who knows" as we have no smart meter for gas to track how much our bills dropped with new boiler. With the solar it's been a bit easier to calculate (kind of) and I'm finding myself looking at the weather forecast and the sky and cursing clouds.

Our tarrif only includes 6 monthly billing so have to wait and see.

All in all I know I'm going to save money. But will need to review real data over time once we have had the panels for a while.

 

[Avendit]

I live in a Passive Haus, so the only buzzword I know is "PHPP". Its basically just a monster spreadsheet, but I don't know if it is available without purchase etc. or if, for a layperson, the vast amount of information (about materials used for construction of the house etc.) is viable. With PHPP (and presumably? the APPs that are available) its then possible to do What-If - swapping windows for triple glazed, adding insulation, and so on. That would help with what benefit you could get from "improvments"

I use this super simple u-value calculator and a spreadsheet to do u-value whatif calculations: uvalue01.xls

the Uvalue is just W/m2K - Watts, per meter square of surface, per kelvin (ie degree C). If you have a wall with a make up that results in a uvalue of 1, and its 10mx2.4m thats a value of 24w per deg C. Assume a 20 degree temp difference in the winter and that's 480W. This is just a unit value, but I believe can be taken as per hour, and adjust units to get 0.48kwh, per hour. Multiply that out and you get 11.5kwh per day, 80kwh per week. How you scale that to years is up to you (note that the kwh here are not electric units, but heat. Could be supplied by electric at 1:1ish direct heating, electric heatpump at 3:1, or gas at a cheaper per unit cost. However you generate it however, that's how much heat you need to put into the room to keep it at the 20 degrees difference from outside. And thats just a single wall!

This is why sorting insulation first is so important. Take that same wall, but built to Passivhaus standard with a uvalue of 0.10 and that 80kwh per week becomes 8kwh per week, 1.1 per day.

 

[Avendit]

This is why getting your cavities filled was so government supported. My walls of 2 layers of 10cm bricks and a 10cm gap without insulation would be a uvalue of 1.3. Just adding cavity fill brings that down to 0.3ish. Instant quarter of the heat loss through all your walls. I've then added external insulation to most of my walls to bring it down to 0.18

Over 150 square m of wall, per 24 hours adds up to a huge difference in how hard it is to heat. At current prices had we not done any of our renovations we would be paying £1000 a month for power + heating. Instead, I expect to pay ~£1200 for the whole year.

Do remember to draft proof tho. No point carefully insulating all your walls and roof etc if the hot air can just go around them.

 

[Mrklaw]

This is why getting your cavities filled was so government supported. My walls of 2 layers of 10cm bricks and a 10cm gap without insulation would be a uvalue of 1.3. Just adding cavity fill brings that down to 0.3ish. Instant quarter of the heat loss through all your walls. I've then added external insulation to most of my walls to bring it down to 0.18

Over 150 square m of wall, per 24 hours adds up to a huge difference in how hard it is to heat. At current prices had we not done any of our renovations we would be paying £1000 a month for power + heating. Instead, I expect to pay ~£1200 for the whole year.

Do remember to draft proof tho. No point carefully insulating all your walls and roof etc if the hot air can just go around them.

but also make sure your rooms can breathe and have enough air changes. And your cavity isn't stopping your walls from breathing to prevent damp.

all gets very circularly complex very quickly. Used to just figure 'oh they slapped an air brick over there ok' but now I have no idea. We had secondary glazing fitted upstairs for free by heathrow for the extra night flights. As part of that, because it blocked up the tricklevents, they put big electric vents on the walls - I guess big as they're sound insulated maybe? But they actively pull air in and you have little icons to show how many are in the room etc. But in my living room I have a chimney that is pretty open to the outside, plus a hefty air-slot down by the back wall. That almost feels like too much ventilation.

 

[Avendit]

but also make sure your rooms can breathe and have enough air changes. And your cavity isn't stopping your walls from breathing to prevent damp.

all gets very circularly complex very quickly. Used to just figure 'oh they slapped an air brick over there ok' but now I have no idea. We had secondary glazing fitted upstairs for free by heathrow for the extra night flights. As part of that, because it blocked up the tricklevents, they put big electric vents on the walls - I guess big as they're sound insulated maybe? But they actively pull air in and you have little icons to show how many are in the room etc. But in my living room I have a chimney that is pretty open to the outside, plus a hefty air-slot down by the back wall. That almost feels like too much ventilation.

true, you do need to maintain some air exchange. I love my MVHR, but we went overboard when specing our retrofit.

I do believe its about taking control of ventilation maybe? ie uncontrolled leaks bad, trickle vents you can open/close (or automate these days! Just the first one off google: Automatic Ventilation from Glidevale Trickle vents) are good. Control all your other leaks (like capping off that chimney if unused) so you are deciding how much air to swap, and not having it dictated by how windy it is outside.

 

[WannabeOwner]

like capping off that chimney if unused)

We only had one "open" chimney here, in old part of the house. We were fortunate that the house was very airtight (concrete floors and roof, no timber floors / joists), so chimney was the main source of air leakage.

When we did major refurb we put a wood burning stove in (Passive Haus type, i.e. it has a pipe to get its air from outside, rather than from the room - which would require "air brick" to outside - nuts!)

Anyway, until then we had a board that we fitted in the chimney to block it up and prevent air flow when the fire was not in use (don't forget its up there when you light the fire!).

I think there are inflatable balloon things which are stuffed up the chimney. I expect that would be worth doing for chimneys that are unused, or infrequently used, or during off-season.