RedMod3
Member
While two is a couple, three will definitely not be a crowd.oh yes! Two Powerwalls are a certainty. They get lonely on their own
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Solar Panels UK - is it worth it?
- Thread starter jdwuk
- Start date
RedMod3
Member
We are not an average household; we are all-electric and choose to not use gas.
In peak summer 2PWs (27kWr) comfortably let up use just a little energy at the off-peak GO rate, we are essentially off-grid all day (average summer bills are Ā£40 incl EV charging). In this heat, our heat-pumps succeed in working hard to keep us comfortably cool.
In Spring and Autumn, with less solar, we will be able to just use GO off-peak only with 2PWs.
In Winter, our heat-pumps will be heating and using over 2kW 24/7; with 3 PWs we will be unable to just use the cheap GO rate and will want to avoid using peak power as much as possible.
All people have different circumstances. Some use gas, electric, oil or wood for heating, we just use our heat pumps. There will be circumstances where 1, 2, 3 or even 4 PWs will be a good idea.
like I said - for the average household. Are you a big house? Iād think an average sized home could manage with approximately double their usual electricity when adding in a heat pump - so 30kwh a day?
If I had the money Iād definitely go for enough capacity to have some buffer to avoid all peak if possible - and damn the payback period.
If I had the money Iād definitely go for enough capacity to have some buffer to avoid all peak if possible - and damn the payback period.
RedMod3
Member
2,000sq ft bungalow with 500sqft attached garage built 30 years ago, I have servers running 24/7 that are electric-greedy.
PITA
Model 3 Performance
Well... I now feel awkward as I need 50 kWh... so I'm looking at 4 in total.
Already got two, but holding off until Powerwall 3 comes out... then I'll jump and get to 50 kWh.
ACarneiro
Active Member
I think you grossly underestimate how much electricity the average household will need when energy intensive activities (heating, cooking and driving) which have traditionally been powered by energy-dense fossil fuels transition fully to electricity.well if youāre running a welding shop out back or a mini Amazon server farm thats fine
I agree, we are fortunate to be able to have the space to ground mount and went for 10Kw. This will likely increase as we add an extension, maybe a pool. We have outline for eco pods in the wood behind us. Battery storage is also key I believe
possibly. I thought the average house (I realise there will be outliers) is around 5000kwh a year for electric (non-heating) - so around 15kwh a day. For heating I assumed approximately the same again with a HP COP around 3-3.5. Many people won't be on heat pumps yet so 15kwh a day consumption would be enough.
During the summer you don't need a 15kwh battery, an 8 should be enough with solar to keep you mostly off peak. Yes in winter you may want more battery to move to off peak but then the math gets harder as the payback can stretch beyond the potential life of the battery if you're only leveraging it 3-4 months of the year.
Heating does change that but also even more biases load towards winter and you have excess in summer unused.
Avg UK household uses 8.5-10kWh of electricity and 33-38kWh of gas.
Take the lower end (for argument sake). Exc heating, 8kw battery will be enough to see typical household through peak period across the year.
33kWh of gas, to heat pump at COP 3.5 = 9.5kWh of additional demand. Now we are up to 17.5kWh and the small battery is not enough.
Disregarding the gas for cooking for a minute...
Average UK mileage has been falling and is now around 7000 miles. At 4m/kWh that's 1750kWh of additional demand or 4.8kWh/day.
Now we are up to 22kWh a day, and this is right at the lower end of average.....
So thats 46% higher than you were thinking already....
Take the lower end (for argument sake). Exc heating, 8kw battery will be enough to see typical household through peak period across the year.
33kWh of gas, to heat pump at COP 3.5 = 9.5kWh of additional demand. Now we are up to 17.5kWh and the small battery is not enough.
Disregarding the gas for cooking for a minute...
Average UK mileage has been falling and is now around 7000 miles. At 4m/kWh that's 1750kWh of additional demand or 4.8kWh/day.
Now we are up to 22kWh a day, and this is right at the lower end of average.....
So thats 46% higher than you were thinking already....
Its about in line - I hadn't factored in EV charging - that comes with its own storage battery so would be off peak and I wouldn't think most people would likely charge that with solar except if you have the space for a really big array.
9.5kwh for gas was less than I'd estimated, as was the main usage. So for electric a single battery would be enough. If you move to ASHP or similar, another battery may makes sense for that
It was 3-4 batteries I was starting to question. 1-2 I think absolutely makes sense
ACarneiro
Active Member
Iāve got 2 Powerwalls and Iām finding that in the depths of winter theyāre not enough to power my A-ASHP on ācheap juiceā all day long.
Of course, we are basing all our maths on the premise that cheap off-peak electricity will be available in the future which is by no means a given.
Itās entirely possible that, as EV adoption takes off, the āsurplus generation capacityā during the night goes away and companies stop incentivising any further load shifting.
Of course, we are basing all our maths on the premise that cheap off-peak electricity will be available in the future which is by no means a given.
Itās entirely possible that, as EV adoption takes off, the āsurplus generation capacityā during the night goes away and companies stop incentivising any further load shifting.
It seems very likely that incentives to load-shift will continue, but exactly when the load is to be shifted to may well change.
This could be good for batteries (if there's bursts of excess to mop up during the day), or bad (if the emphasis is more about shifting to different days).
For heating use, there's also the approach of storing the heat - with a well insulated building and a decent amount of thermal mass on the inside of the insulation layer (eg. UFH storing heat in the slab), you can afford to stop heating during the peak hours and rely on the heat already in the building.
I'm not so convinced of that beyond a few years. The supply system should be better placed to predict and cover demand fluctuations at scale than individual consumers. Indeed, part of the renewables landscape needs to be energy buffering to a much greater extent than at present. We will know if they are getting that right when we see low rates disappear.
EV owners already have a pretty flexible energy store if your EV at 50% soc is sufficient for your driving requirements.
With a high % of renewables coming online, there will always be surplus generation capacity at different times.
More likely is further evolutions of "intelligent" tariffs, combined with smart devices, that will soak this up.
Think of excess solar at midday or excess wind on a bank holiday - smart devices will pick up grid signals and dump excess into cars, batteries, how water diverters, etc.
This is interesting as I have been crunching the numbers on whether I could do exactly this with the combination of an ASHP and a second PW.
I think I could probably cover it even in winter, but of course, everyones calcs are different.
My peak gas usage for heating and hot water during Dec was 1330kWh, so COP of 3.5 is 380kwh or 12kWh per day... One PW capacity....
If you don't offer incentives, people will use power when they feel like it - it's cheaper to offer a small incentive to make people do things they can do easily than to build storage centrally. Conversely, central storage is likely to be cheaper than lots of small units, so the incentives are unlikely on their own to pay for powerwalls etc. But it's clear from the discussion here that most people's powerwall purchases aren't driven purely by rate arbitrage - there's the different economics associating the storage with solar, and people buying them mainly for security of supply with the economics just helping to make that luxury purchase more affordable.
ACarneiro
Active Member
Well, the COE will be significantly worse than spec as it gets colder, so maybe 3.5 is not quite the ideal number to model for a cold winter.
PITA
Model 3 Performance
Interesting comments...
We have an 'average' sized modern 3 bedroom detached house.
1 x 22 kW ev charger
2 x 8 kW electric showers
1 x 8 kW Heat Pump (air to air)
1 x 7 kW induction hob
1 x 7 kW ev charger
1 x 3 kW emersion water heater
1 x 900W microwave
2 x Chest Freezers, 2 Standard Fridge Freezers
60 x Connected Smart Devices
1 x 75kWh Ev Car (15,000 miles per year)
Our house uses about 18,000 kWh in a year
Now this is interesting, because if you see OFGEM and how they calculate the 'average home' it's only 2900 kWh per year. Ha! that's 8 weeks for us.
Solar Array is 7.2 kWp (5 kW inverter)
Battery Storage is 27 kWh.
>>>>>>>>>>>>>>>
So... cooking, washing, drying, heating, cooling, transport, lighting and entertainment is all electric.
... overall it's a very well balanced system actually, with almost no exporting.
But in Winter, when this house is pumping with life, we can use 100 kWh in a day.
As our battery storage has less capacity in Winter, due to cold battery management & the set minimum blackout level protection... we really need 50 kWh capacity to make it through a day.
The other 50 kWh can be downloaded at night on cheap rate to balance not using battery storage.
I fully expect the Energy Suppliers to move cheap rate periods, or severely restrict the time allowance. That's why I installed 3 Phase cabling.
We can download about 100 kWh in 4 hours. So 3 Phase will be really beneficial if we only have limited periods to 'grab what you can' at cheap rate (or between blackouts).
We can also fully function, including car charging at 7kW ... all off grid.
I'm looking to build an extension, which will allow an East Facing extra 4 kWp solar array. This'll bring us up to 11.2 kWp and hopefully 50 kWh storage plus 150 kWh in two Ev Cars. The kitchen will double in size with more 3 Phase level appliances.
It'll get lively
We have an 'average' sized modern 3 bedroom detached house.
1 x 22 kW ev charger
2 x 8 kW electric showers
1 x 8 kW Heat Pump (air to air)
1 x 7 kW induction hob
1 x 7 kW ev charger
1 x 3 kW emersion water heater
1 x 900W microwave
2 x Chest Freezers, 2 Standard Fridge Freezers
60 x Connected Smart Devices
1 x 75kWh Ev Car (15,000 miles per year)
Our house uses about 18,000 kWh in a year
Now this is interesting, because if you see OFGEM and how they calculate the 'average home' it's only 2900 kWh per year. Ha! that's 8 weeks for us.
Solar Array is 7.2 kWp (5 kW inverter)
Battery Storage is 27 kWh.
>>>>>>>>>>>>>>>
So... cooking, washing, drying, heating, cooling, transport, lighting and entertainment is all electric.
... overall it's a very well balanced system actually, with almost no exporting.
But in Winter, when this house is pumping with life, we can use 100 kWh in a day.
As our battery storage has less capacity in Winter, due to cold battery management & the set minimum blackout level protection... we really need 50 kWh capacity to make it through a day.
The other 50 kWh can be downloaded at night on cheap rate to balance not using battery storage.
I fully expect the Energy Suppliers to move cheap rate periods, or severely restrict the time allowance. That's why I installed 3 Phase cabling.
We can download about 100 kWh in 4 hours. So 3 Phase will be really beneficial if we only have limited periods to 'grab what you can' at cheap rate (or between blackouts).
We can also fully function, including car charging at 7kW ... all off grid.
I'm looking to build an extension, which will allow an East Facing extra 4 kWp solar array. This'll bring us up to 11.2 kWp and hopefully 50 kWh storage plus 150 kWh in two Ev Cars. The kitchen will double in size with more 3 Phase level appliances.
It'll get lively
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