PV Solar - what the view in the UK in 2021?

[Glan gluaisne]

With our 4kW array and 3.6kW inverter, we also have a solar diverter to send all surplus electricity to our immersion heater rather than the grid (we are all electric). Having storage batteries would make no sense as we have no surplus energy, and none goes back to the grid. During summer when it's hot, the air-con is working hard to keep us cool (for free).

We have a bit over 6 kWp of PV, an all-electric house, and a diverter to store heat in a "thermal battery" to heat our hot water (it's a phase change sodium acetate based thermal storage unit). Likewise, having batteries makes no sense, I can't quite get the very cheapest system available to cover it's purchase cost, with me doing the installation, before it dies from old age.

We also find that running the house cooling systems from free electricity in summer is probably the best use we get from the PV, along with water heating and a bit of summer car charging. PV really doesn't deliver much for the time of year when we use most of our electricity, and delivers way too much at the time of the year when we don't use much. It's not at all uncommon to find that, on a hot summer's day we're sitting with the thermal battery fully recharged by mid-morning, the car charged, the house cooling system running and we're still pumping over 4 kW to the grid in excess generation.

If there was an affordable way to store around 2 MWh or so of electricity, then we could store enough excess during the sunny months to keep us going through the winter months, but such a technology doesn't yet exist, and if it did it probably wouldn't be batteries. Something like a very much larger version of our thermal battery might work, as that has a much longer life than batteries, with seemingly no degradation with age.

 

[26ct2143]

We have a bit over 6 kWp of PV, an all-electric house, and a diverter to store heat in a "thermal battery" to heat our hot water (it's a phase change sodium acetate based thermal storage unit). Likewise, having batteries makes no sense, I can't quite get the very cheapest system available to cover it's purchase cost, with me doing the installation, before it dies from old age.

We also find that running the house cooling systems from free electricity in summer is probably the best use we get from the PV, along with water heating and a bit of summer car charging. PV really doesn't deliver much for the time of year when we use most of our electricity, and delivers way too much at the time of the year when we don't use much. It's not at all uncommon to find that, on a hot summer's day we're sitting with the thermal battery fully recharged by mid-morning, the car charged, the house cooling system running and we're still pumping over 4 kW to the grid in excess generation.

If there was an affordable way to store around 2 MWh or so of electricity, then we could store enough excess during the sunny months to keep us going through the winter months, but such a technology doesn't yet exist, and if it did it probably wouldn't be batteries. Something like a very much larger version of our thermal battery might work, as that has a much longer life than batteries, with seemingly no degradation with age.

Generate in summer for winter use... now that's what I call long term energy storage.
Do the old compress air into tanks and release to a generator later trick... lol

 

[Dilly]

We have a bit over 6 kWp of PV, an all-electric house, and a diverter to store heat in a "thermal battery" to heat our hot water (it's a phase change sodium acetate based thermal storage unit). Likewise, having batteries makes no sense, I can't quite get the very cheapest system available to cover it's purchase cost, with me doing the installation, before it dies from old age.

We also find that running the house cooling systems from free electricity in summer is probably the best use we get from the PV, along with water heating and a bit of summer car charging. PV really doesn't deliver much for the time of year when we use most of our electricity, and delivers way too much at the time of the year when we don't use much. It's not at all uncommon to find that, on a hot summer's day we're sitting with the thermal battery fully recharged by mid-morning, the car charged, the house cooling system running and we're still pumping over 4 kW to the grid in excess generation.

If there was an affordable way to store around 2 MWh or so of electricity, then we could store enough excess during the sunny months to keep us going through the winter months, but such a technology doesn't yet exist, and if it did it probably wouldn't be batteries. Something like a very much larger version of our thermal battery might work, as that has a much longer life than batteries, with seemingly no degradation with age.

What we need is ‘cloud’ storage. Pay in the summer excess to your supplier and draw back out in winter. Maybe one day...

 

[26ct2143]

What we need is ‘cloud’ storage. Pay in the summer excess to your supplier and draw back out in winter. Maybe one day...

The whole market is pretty complicated already lol.
I generate for the grid here (my own use first then grid), my tariff is such that every half an hour's electric is a different price to the previous one.
Makes billing interesting.
Then you have the TRIADs which are 3x half hour periods in winter. If I happen to be generating in a triad period, that half an hour of electric could earn about £500 for 20kwh. But if I'm offline, I'd be charged at that rate for the half hour period (total would depend on how many kwh I used)

 

[Dilly]

The whole market is pretty complicated already lol.
I generate for the grid here (my own use first then grid), my tariff is such that every half an hour's electric is a different price to the previous one.
Makes billing interesting.
Then you have the TRIADs which are 3x half hour periods in winter. If I happen to be generating in a triad period, that half an hour of electric could earn about £500 for 20kwh. But if I'm offline, I'd be charged at that rate for the half hour period (total would depend on how many kwh I used)

I think my head would explode trying to keep up with that

 

[KendoNagasaki]

You solar guys must be much better with your electric consumption than me....
Just checked my daily consumption is about 27kwh/24hours.
And that is house only (no cars on that)

Yours must be much lower.

We have a bit over 6 kWp of PV, an all-electric house, and a diverter to store heat in a "thermal battery" to heat our hot water (it's a phase change sodium acetate based thermal storage unit). Likewise, having batteries makes no sense, I can't quite get the very cheapest system available to cover it's purchase cost, with me doing the installation, before it dies from old age.

We also find that running the house cooling systems from free electricity in summer is probably the best use we get from the PV, along with water heating and a bit of summer car charging. PV really doesn't deliver much for the time of year when we use most of our electricity, and delivers way too much at the time of the year when we don't use much. It's not at all uncommon to find that, on a hot summer's day we're sitting with the thermal battery fully recharged by mid-morning, the car charged, the house cooling system running and we're still pumping over 4 kW to the grid in excess generation.

If there was an affordable way to store around 2 MWh or so of electricity, then we could store enough excess during the sunny months to keep us going through the winter months, but such a technology doesn't yet exist, and if it did it probably wouldn't be batteries. Something like a very much larger version of our thermal battery might work, as that has a much longer life than batteries, with seemingly no degradation with age.

something like gravitricity at a home or community scale I suspect rather than batteries
Storing renewable energy in mineshaft weights may be cheaper than using batteries - Revolution-Green
watching them with interest

I do love the massive weighted trains in the US but they are about as practical as building your own pump storage hydro. ARES North America

 

[Glan gluaisne]

About 33 tonnes of sodium acetate trihydrate, with a suitable nucleating agent, stored in a large insulated container, with an electric heating element plus a heat exchanger to extract the heat, would just about do it. The stuff stores roughly 220 kJ/kg of sensible heat, or about 61 kWh per tonne, with a phase change temperature of about 58°C.

It will sit at about 58°C until all the liquid has turned to solid, when it will start to cool down, a temperature that is just about ideal for heating hot water or running a heating system. 33 tonnes of the stuff would have a volume of about 23m³, so would fit into a basement sized area. That's about the size of a small to medium sized road tanker, so one of those buried under a house, or in a garden, with loads of insulation around it, would seem to make this a possibility, albeit and expensive and disruptive one.

We use about 150kg of sodium acetate trihydrate to store around 9 kWh of heat to run our hot water system. It's a lot smaller than a hot water tank of the same capacity, plus it has much lower heat losses. There's an internal heat exchanger that flash heats cold water to around 55°C on demand, all done passively, just by opening any hot water tap and starting the water flow. A 3 kW electric heating element heats the sodium acetate up and keeps it in it's liquid state when fully charged.

 

[Dilly]

About 33 tonnes of sodium acetate trihydrate, with a suitable nucleating agent, stored in a large insulated container, with an electric heating element plus a heat exchanger to extract the heat, would just about do it. The stuff stores roughly 220 kJ/kg of sensible heat, or about 61 kWh per tonne, with a phase change temperature of about 58°C.

It will sit at about 58°C until all the liquid has turned to solid, when it will start to cool down, a temperature that is just about ideal for heating hot water or running a heating system. 33 tonnes of the stuff would have a volume of about 23m³, so would fit into a basement sized area. That's about the size of a small to medium sized road tanker, so one of those buried under a house, or in a garden, with loads of insulation around it, would seem to make this a possibility, albeit and expensive and disruptive one.

We use about 150kg of sodium acetate trihydrate to store around 9 kWh of heat to run our hot water system. It's a lot smaller than a hot water tank of the same capacity, plus it has much lower heat losses. There's an internal heat exchanger that flash heats cold water to around 55°C on demand, all done passively, just by opening any hot water tap and starting the water flow. A 3 kW electric heating element heats the sodium acetate up and keeps it in it's liquid state when fully charged.

Can’t help wishing I was younger sometimes... the future will be amazingly innovative, if we have one !!

 

[Mr Miserable]

I keep revisiting the maths for PV and battery and still cannot make it work.
(Even harder since the money stayed in TSLA!)
I love the concept though.
I keep revisiting @Glan gluaisne 's posts in the hope that one day I will understand them.
I should have tried harder at skool....

 

[pdk42]

Thanks for all your replies. Reading through them I’ve come to the conclusion that it’s going to be hard to make a financial case for it, even with a 10 year or longer pay back period. Pity. If I had the cash to build a new house though, I’d definitely look to some of the more ambitious ideas, like thermal battery storage, or ground source heat pumps.

 

[twlr]

It's hard to make a financial case for a Tesla but I still have one.

 

[Cardo]

I have two arrays. The original 3.9kWp array faces almost bang on south and was fitted before FiT came to an end. The 6.5kWh battery we had fitted at the same time added £3.5k to the cost. Payback is around 12 years. The battery delayed the payback, but gives me good feels as it means I use more of my generated electric.

The second array is totally cost inefficient. It’s a 2.7kWp on west and east roofs and a south facing roof that shades in the afternoon. It was all the suitable roof space I had left. I’d guess this will pay for itself during its lifetime, but I won’t make money unless electric costs increase considerably. The reason for this was I wanted to be able to charge our EVs more on solar, as I was finding on the original array we frequently hovered just under the 1.4kW surplus required to charge the cars. The new array will increase the length of the generating day and the peak in the middle of the day.

 

[Spacey73]

So I'm sat here reading this whilst stripping apart 32.4v 3Ah 100whr electric lawn mower packs (£84 on ebay each) that I bought for £3.50. I bought 120 of the damn things.

So far I have hooked up 5kwh of them in a 48v (14S) configuration with a passive capacitor based BMS that is always balancing between the highest and lowest cells shunting energy across at 5amps max....unlike normal BMS's that only balance at 4.23v which is not good for battery.

I discharge only to 20% and charge only to 80% which will give a good 10 years of battery life hopefully from these 1860 cells. Some of my old ebikes with 18650 packs are still running after 8 years and they have been hammered but they only have about 60 to 70% of battery left in them...charging to 80% stops tendrils from forming it's why the older model S's are doing so well.

This should give me a 12kwh system at 48v, house uses 700w just running background stuff but now I have a load of bitcoin farms going that adds about 800w but it also heats the house up

Gas has not been turned on this winter as the constant heat is very good at heating a small 3 bed house.

Solar is 4.8kw system currently wired up 2 in series but I will change that to 3 in series, no feed back outside of house and only uses what the house needs minus 100w that it draws from grid.

This keeps us going for about 4hrs in Jan and any surplus when the battery is full goes to the bit coin farms.

Battery and all connectors cost under £450 for 12kwh and solar panels were bought new from bankrupt business 400w panels for £1,000 for 12, Invertors (3kw) were £350 and the Solar Inverter 6kw was £300.

£2,100 for a 12kw batter, 4.8kw solar and all the inverters etc to go with it. Buying up bitcoin miners that are so cheap because they cost too much to mine with for when the surplus energy needs to go somewhere in spring/summer.

Profits from the little bitcoin farms at the moment are £400 to £600 a month but will probably settle down to £300 to £400 soon..... job done

 

[Drew57]

@Spacey73 until I read the above I thought I was quite savvy, owning a Tesla, solar, inverter, batteries, charger & all?

So let me get my old head round this.... lots of lawnmowers for £3.50 and something about hammered ebikes can farm bitcoins and tendrils & heat the house up at the same time for -£600/month. If I had the slightest clue I'd say sign me up.

Your comment about bitcoin miners being so cheap at the moment does make sense though what with all the pandemic layoffs but £2,100 for some batter? - surely it's only eggs milk & flour.

....I had to check that I was still on the UK/Ireland site as most of that might as well have been written in Martian

Sorry could't resist, blame my nurse - she put me up to it.

 

[Spacey73]

Ha, made me laugh... basically I bought a load of brand new lawnmower batteries for £400 (bankrupt stock Bosch) and built a Tesla Powerall sized pack. Pics will explain better... 3 BMS for emergencies plus cut off on inverters and a constant cell ballancer...then into a junction box with trips etc.... powering bitcoin farms that heat the house for ..at the moment £600 profit a month.

 

[browellm]

Absolute madness. I love it.

 

[Medved_77]

Ha, made me laugh... basically I bought a load of brand new lawnmower batteries for £400 (bankrupt stock Bosch) and built a Tesla Powerall sized pack. Pics will explain better... 3 BMS for emergencies plus cut off on inverters and a constant cell ballancer...then into a junction box with trips etc.... powering bitcoin farms that heat the house for ..at the moment £600 profit a month.

I really hope you have a fire extinguisher near by

 

[Spacey73]

Sounds wackier than it is...excuse the wires as it's still in prototype stage, once I add the rest of the cells it's going into a proper cabinet with tidy wiring and better connections. But even as it is it has ROI'd already and not failed once.

RE the fire extinguisher: It's in a small concrete outbuilding/shed with nothing really flammable (liquids or vehicles) also I've built over 200 high powered ebike and e motocross bike batteries with no issues. If you don't discharge them below 3.15v or charge them higher than 4.07v they last for a very long time.

The pack can technically put out 40kw of power easily but I'm only asking 4kw peak but mostly sits at 1.5kw.

All individual packs are fused and an overall 3 x BMS in parallel as emergency cut offs. Then you have a constant delta balancing shunt and the cut offs from solar inverter and AC Invertors. I check cells daily

 

[Drew57]

I really hope you have a fire extinguisher near by

I heard he's cornered the market for B-stock SodaStreams

 

[Glan gluaisne]

When shifting some boxes around in the garage a week or so ago, I found a box full of old packs, still in their original packaging, that I'd bought as spares for the larger pack that runs my (solar powered) electric boat. Must have been sat in the box they were delivered in for at least four years, and got tucked away on a shelf when we moved house:

Rather surprisingly I found they were all fine, still in balance to within about 20mV, after all this time. Rather than let them go to waste they are now destined to be fitted in an old ammo box, together with a flying capacitor BMS, charger and a small 230 VAC inverter, as there've been a few occasions recently when a mains power bank would have been handy. The ready built ones are expensive for what they are, but I reckon my little ~1kWh, 300W, one will outperform a friends ~£400 portable power bank, and cost a lot less (looking at making a DIY inverter/charger for it).

On the topic of cell safety, I had a couple of incidents in the early days when I started out making electric bikes, back around 2002, but with a decent BMS and a bit of care these things are safe enough. My electric motorcycle pack probably has the toughest time, as that can supply a few hundred amps for a short time, mainly because I wanted to not use a higher pack voltage, and get embroiled in the additional safety stuff that applies to higher voltage systems, like those in most EVs. The mean power a motorcycle uses isn't very high, anyway, so high current's only drawn for a few seconds at a time.