Solar Panels

BarbaraG2000

I installed 3.9kWp panels and a 5.2kWh battery in December - the worst possible month for solar generation.  The battery wasn’t commissioned until the first week of January. It still saved me 15% off my December - January bill.  Last month it was nearly 80%, once payment for export is taken into account.

Crucially, I have an EV, and am on the Octopus Go tariff, with 4 hours of very cheap electricity every night.  That means I can charge the battery during that period as well and use cheaper electricity through the following day, topped up by whatever solar is produced.

At this time of year, the saved solar in the battery is seeing us through the night with minimal grid import apart from when we charge the car.  Yes, solar can produce enough to charge the car - I added enough for 60 miles to mine on Saturday.  But not all days are that good and obviously it depends how many miles you do and how much the car is at home to take advantage.

markin

 

Ally_E. said:

Based on April price hike, MSE was saying it would take 13 years to break even if one installed solar now. That's a long time to wait. Obviously with the October hike that number will go down, but still a long time. Will you be in the same house still to see the break even point?

Sounds unlikely, maybe based on the worst SEG of 1.5p and selling 90% or something daft, The higher the price the quicker the payback if you at least use use 30% and yourself most do.

QrizB

markin said:

 

Ally_E. said:

Based on April price hike, MSE was saying it would take 13 years to break even if one installed solar now. That's a long time to wait. Obviously with the October hike that number will go down, but still a long time. Will you be in the same house still to see the break even point?

Sounds unlikely ...

MSE's numbers mostly hang together:

https://www.moneysavingexpert.com/utilities/free-solar-panels/

Spend £6500, generate 4000kWh/yr. Use 30% (1200kWh) at 28p/kWh, save £336. Export 70% (2800kWh) at 7.5p/kWh, earn £210. Total value £546//yr, payback time 11.9 years.

Benny2020

Depends whether you think electricity prices will fall, stay flat or rise.
Its also best for the country and environment if we generate part of our own needs.
EV's rolling out will probably be another thing to think about.

brewerdave

Benny2020 said:

Depends whether you think electricity prices will fall, stay flat or rise.
Its also best for the country and environment if we generate part of our own needs.
EV's rolling out will probably be another thing to think about.

And as more people buy EVs, two things are going to happen 1. Companies like Octopus will increase the price of the o/n "cheap" rate (they already claim its a loss leader) 2. The Govt. are going to need to replace the lost petrol tax revenue - either higher tax rate on leccy or road mileage pricing. Both of these will alter the maths of payback on panels, batteries and EVs

[Deleted User]

brewerdave said:

Benny2020 said:

Depends whether you think electricity prices will fall, stay flat or rise.
Its also best for the country and environment if we generate part of our own needs.
EV's rolling out will probably be another thing to think about.

And as more people buy EVs, two things are going to happen 1. Companies like Octopus will increase the price of the o/n "cheap" rate (they already claim its a loss leader) 2. The Govt. are going to need to replace the lost petrol tax revenue - either higher tax rate on leccy or road mileage pricing. Both of these will alter the maths of payback on panels, batteries and EVs

I agree. The whole point of the smart grid is to better balance demand and supply. If this is ever achieved then tariffs will revert back to something like we have at the moment: that is, one unit price. 

FWiW, I can well see Octopus putting an end to their Go and Go Faster tariffs as it brings even more EVs and EVSEs into the Intelligent Octopus tariff fold. This is an overnight tariff when Octopus decides when to charge depending on the customer’s EV requirement.

MWT

[Deleted User] said:

FWiW, I can well see Octopus putting an end to their Go and Go Faster tariffs as it brings even more EVs and EVSEs into the Intelligent Octopus tariff fold. This is an overnight tariff when Octopus decides when to charge depending on the customer’s EV requirement.

The half-hour slots they select for the charging are not necessarily overnight, which can be interesting as whenever those slots are, the customer gets all their consumption at the low rate, not just the charging.

Net result is you get 6 hours at the low rate every night and the possibility of additional low rate periods on top of the base 6 hours.

They do have that tariff very well locked down though, people will not be getting onto it without a compatible EV/home charger.

scarletjim

QrizB said:

markin said:

 

Ally_E. said:

Based on April price hike, MSE was saying it would take 13 years to break even if one installed solar now. That's a long time to wait. Obviously with the October hike that number will go down, but still a long time. Will you be in the same house still to see the break even point?

Sounds unlikely ...

MSE's numbers mostly hang together:

https://www.moneysavingexpert.com/utilities/free-solar-panels/

Spend £6500, generate 4000kWh/yr. Use 30% (1200kWh) at 28p/kWh, save £336. Export 70% (2800kWh) at 7.5p/kWh, earn £210. Total value £546//yr, payback time 11.9 years.

Please excuse my ignorance, I'm only just starting to learn about solar panels now, but simple question: why would someone only use such a tiny amount of the electricity generated by their panels? Is it simply because the calculation above assumes no battery, or are there other factors to consider?

Our house uses about 6200kwh per year, and as a result our electricity bill is currently something like £2,000 per year, presumably £3,000py from October. Gas bill is similar (underfloor heating, cooking hobs etc, but primarily winter costs for gas).

If we had a system that generated 6000 kWh/yr, and a battery to store it, would we be able to basically reduce our grid electricity usage to zero (or presumably zero plus standing charge)?

If we had a system that generated even more, could we use the extra via the battery to heat our water at night, thereby reducing the gas costs too?

I ask all of this because all of the online calculators only suggest a bill saving of maybe £400-500py, and I don't understand why we wouldn't be saving far more than that...

Would appreciate any layman-level education that anyone can provide, as the various solar panel websites don't go into this kind of detail... Thanks.

Reed_Richards

scarletjim said:

If we had a system that generated 6000 kWh/yr, and a battery to store it, would we be able to basically reduce our grid electricity usage to zero (or presumably zero plus standing charge)?

No.  The easiest way to understand why not is to ask yourself "Why is it cold in winter?". The answer is because we have much shorter and often cloudier days so we don't get anything like the amount of solar radiation that we get in summer.  This translates into much less solar power in winter.  We also tend to consume more electricity in winter, although in your case it may not be that much more.  Of course if you had a 6000 kWhr battery you could do it but that would be the size of a house and more expensive than a house.    

QrizB

Reed_Richards is entirely correct in his post above.

scarletjim said:

If we had a system that generated 6000 kWh/yr, and a battery to store it, would we be able to basically reduce our grid electricity usage to zero (or presumably zero plus standing charge)?

To put some numbers on that, at current domestic prices a 6000kWh battery would cost around £3M*.

Typically, domestic batteries are only sized to move electricity around within the day (from daytime to nighttime) - or, at best, from one day to the next. If you had a system that could generate 6000kWh/yr you might have a 10-20kWh battery to go with it, at a price of £7-15k. This would be enough to reduce your electricity bills to close-to-zero for 4-8 months of the year, but you wouldn't be able to cover your use in the remaining months.

The additional saving could be £400-£600/yr, so you'd need your battery to last for at least 12 years before it would pay for itself.

* You'd be unlikely to pay domestic prices for a 6MWh battery; you're in industrial territory, equivalent to two Tesla Megapacks, so you might get the price down to £3M. I don't know if that includes the cost of the concrete slab and associated switchgear, though.