Solar panels and battery - any real world reccomendations?

[Mercenary Keyboard Warrior]

If you have access to an Ev based cheap tariff your probably low risk in regards not being able to get another in the future

Bear in mind there are conversions losses AC->DC->AC but at 7.5p you don't really care

 

[tsinc80697]

So my quick workings, which please correct me if I've missed anything:

Our usage (10,000kWh pa) with Intelligent Octopus. We roughly use 0.8kWh 24/7 and an additional 0.2-0.4kWh during the day.

Rates
39.25p for 18 hours a day
7.5p for 6 hours a day

Usage
8,200kWh pa @ 39.25p/kWh = £3,219
1,800kWh pa @ 7.5p/kWh = £135

Current annual electricity cost
£3,354

If we installed 3 x 9.5kWh GE batteries we could draw down our daily requirements during the cheaper overnight period, and use this power during the day from the batteries instead of the grid. It would mean the batteries go from 100% to 15-20% every day, is this ok to do with these batteries?

Usage
10,000kWh pa @ 7.5p/kWh = £750

Forecast annual electricity cost
£750

Savings per year
£2,604

Three batteries & an inverter are ~£12,000, add ~£2000 for installation = £14,000

Over a 10 year period, before the batteries degrade(?) it would be a saving of ~£12,040 (£2,604 x 10 - £14,000)

If we added 4kW (10 panels) of solar panels to the install (which would produce ~3,400kWh pa), it would only save £255 a year (3,400kW x 7.5p/kWh) which seems pointless…unless the overnight rate price was increased.

 

[Welshman]

Yeah it would be completely dependant on the cheaper rates staying. They have been around for years though haven't they? (Economy 7 etc)

Our roof is quite big but the shape and direction isn't the best for fitting panels.

(We already have solar hot water panels which were fitted prior to us buying the house a few years ago)

We're on Intelligent Octopus at the moment so it's 7.5p/kWh for 6 hours a day so if we were able to use all of our energy from the batteries every day it would save about £2600/year.

It just looked pointless to add in solar panels when the cost of electric from the grid is 7.5p/kWh…but at 39.25p/kWh it's obviously a great saving.

but how much battery would you need to last the day....with only a 6hr recharge window??

 

[Mercenary Keyboard Warrior]

So my quick workings, which please correct me if I've missed anything:

Our usage (10,000kWh pa) with Intelligent Octopus. We roughly use 0.8kWh 24/7 and an additional 0.2-0.4kWh during the day.

Rates
39.25p for 18 hours a day
7.5p for 6 hours a day

Usage
8,200kWh pa @ 39.25p/kWh = £3,219
1,800kWh pa @ 7.5p/kWh = £135

Current annual electricity cost
£3,354

If we installed 3 x 9.5kWh GE batteries we could draw down our daily requirements during the cheaper overnight period, and use this power during the day from the batteries instead of the grid. It would mean the batteries go from 100% to 15-20% every day, is this ok to do with these batteries?

Usage
10,000kWh pa @ 7.5p/kWh = £750

Forecast annual electricity cost
£750

Savings per year
£2,604

Three batteries & an inverter are ~£12,000, add ~£2000 for installation = £14,000

Over a 10 year period, before the batteries degrade(?) it would be a saving of ~£12,040 (£2,604 x 10 - £14,000)

If we added 4kW (10 panels) of solar panels to the install (which would produce ~3,400kWh pa), it would only save £255 a year (3,400kW x 7.5p/kWh) which seems pointless…unless the overnight rate price was increased.

Few things, one GE inverter wouldnt be enough, they are limited on throughput to battery, think you may need two @katie279 knows more detail of the solution

GE quote usable, with maybe 4% reserved? But generally all are at least 90% usable with DOD (depth of discharge of 90%)

GE may not be your best bet, https://www.itstechnologies.shop/pr...battery-storage-system-with-40-96kw-batteries could be better

 

[tsinc80697]

but how much battery would you need to last the day....with only a 6hr recharge window??

Approx 27kWh

Few things, one GE inverter wouldnt be enough, they are limited on throughput to battery, think you may need two @katie279 knows more detail of the solution

GE quote usable, with maybe 4% reserved? But generally all are at least 90% usable with DOD (depth of discharge of 90%)

GE may not be your best bet, https://www.itstechnologies.shop/pr...battery-storage-system-with-40-96kw-batteries could be better

Ah ok. GE was really just an example as I had spotted their 9.5kWh batteries so if there are better/more suitable systems I'm all ears! The gen 2 GE inverters are 5kW aren't they? Is it more complex than 5kW x 6 hours = 30kWh?

Looks like there's a 30kWh GSL for £12k on ITS.

If we added solar panels would it reduce the price by 20% (0% VAT) from the GSL hardware or do installers generally not pass on the VAT saving?

 

[Journey]

If you are spending ~£3k on electricity per year then why worry about spending a few £k on some Solar panels that will last decades?

 

[tsinc80697]

If you are spending ~£3k on electricity per year then why worry about spending a few £k on some Solar panels that will last decades?

Because if I can get electricity from the grid for 7.5p is it worth spending ~£3k on solar panels that only generate 3400kWh pa. It would take 12 years to break even on the investment. But if I added panels it could potentially reduce the hardware costs due to the 0% VAT on hardware.

 

[HungryHippos]

Same advice I always give when this comes up, combo batteries and panels is best.

In your example you wouldn't even need the 3rd battery though, you just need it to last the day, and I'd wager 20kwh or so of batteries would do that, assuming the inverter is capable of charging them in the off peak window.

Money you theoretically save on battery VAT would go some way to adding panels, but depends on installer passing on the kit saving.

 

[Mercenary Keyboard Warrior]

Approx 27kWh



Ah ok. GE was really just an example as I had spotted their 9.5kWh batteries so if there are better/more suitable systems I'm all ears! The gen 2 GE inverters are 5kW aren't they? Is it more complex than 5kW x 6 hours = 30kWh?

Looks like there's a 30kWh GSL for £12k on ITS.

If we added solar panels would it reduce the price by 20% (0% VAT) from the GSL hardware or do installers generally not pass on the VAT saving?

Yeah technically a small solar install would save you the VAT on the total install

 

[Journey]

Because if I can get electricity from the grid for 7.5p is it worth spending ~£3k on solar panels that only generate 3400kWh pa. It would take 12 years to break even on the investment. But if I added panels it could potentially reduce the hardware costs due to the 0% VAT on hardware.

But the 7.5p rate no longer exists anymore, it is now 10p, 25% more than now, which you'll be paying when your 12 months ends.

 

[Mercenary Keyboard Warrior]

Same advice I always give when this comes up, combo batteries and panels is best.

In your example you wouldn't even need the 3rd battery though, you just need it to last the day, and I'd wager 20kwh or so of batteries would do that, assuming the inverter is capable of charging them in the off peak window.

Money you theoretically save on battery VAT would go some way to adding panels, but depends on installer passing on the kit saving.

Yeah this really.
It de-risks the install costs since at least you have some generation should the marginal pricing on units fall dramatically.

 

[Welshman]

you can also charge the battery for free during the day off the solar...therefore not needing as much of the 6hr cheap rate window

 

[tsinc80697]

But the 7.5p rate no longer exists anymore, it is now 10p, 25% more than now, which you'll be paying when your 12 months ends.

Ah didn't realise the rate had increased. If it does keep creeping up it would start to reduce the ROI on panels. It just seemed mathematically pointless if it remained at 7.5p/kWh. Even 10pkWh is still 8 years breakeven on panels.

 

[Twinz]

Our central AC unit requires a lot of surge current, making batteries more expensive for my application. Our electric is also not as expensive here in Florida.

I'm considering a small (seperate) 2-3 panel / battery / inverter system to take our refrigerator and well pump off-grid year round. I want it more for post-hurricane / storm power outages, but would want to run it year-round to offset the cost of the system.

 

[HungryHippos]

Ah didn't realise the rate had increased. If it does keep creeping up it would start to reduce the ROI on panels. It just seemed mathematically pointless if it remained at 7.5p/kWh. Even 10pkWh is still 8 years breakeven on panels.

It's a risk offset as well though.

In your example the 3rd battery is likely pointless, because you only need the battery power for 18 or 19 hours of the day, you'll never be reaching into the 3rd battery really, especially if you can load shift even more into the off-peak window.

The time when the panels will win hands down is if the cheaper off-peak tariffs are no longer as good. You could even wind up with expensive batteries that don't save you as much, then you have to go and buy panels, which means you may as well have done this from the start because of VAT saving of installation + you'd have been missing the generation since the installation by waiting.

Maybe speak to some installers and see what they come up with. You can always wire in a system that can take panels later should you want to do so, really it's your call on this one, I don't think battery alone is terrible it's just a riskier approach.

You may find it's best to remove those hot water panels and go with a new system that just does it all, including hot water diversion, especially if the hot water panels are taking up valuable south facing space inefficiently.

 

[Journey]

Ah didn't realise the rate had increased. If it does keep creeping up it would start to reduce the ROI on panels. It just seemed mathematically pointless if it remained at 7.5p/kWh. Even 10pkWh is still 8 years breakeven on panels.

You not accounting for exported power though in your cost analysis, and given the government and Ofgem announcement that they are going to be increasing export payments then you could be making money back on exported units as well.

 

[HungryHippos]

You not accounting for exported power though in your cost analysis, and given the government and Ofgem announcement that they are going to be increasing export payments then you could be making money back on exported units as well.

Oh I hadn't seen this, got a source? The SEG payments from Octopus are a complete travesty as it stands (though I understand why people on Go should not necessarily get quite as much, the 4p/kwh standard SEG is awful vs 15p/kwh if not on Go).

 

[katie279]

Few things, one GE inverter wouldnt be enough, they are limited on throughput to battery, think you may need two @katie279 knows more detail of the solution

GE quote usable, with maybe 4% reserved? But generally all are at least 90% usable with DOD (depth of discharge of 90%)

GE may not be your best bet, https://www.itstechnologies.shop/pr...battery-storage-system-with-40-96kw-batteries could be better

Hello! Yes, this sounds like it'd work fine for you - although the third battery might be overkill, I strongly suspect electricity use is going upwards, not downwards (eg heat pumps replacing gas, EVs replacing petrol etc), so wouldn't be a total waste over ten years.

With regards to inverter, make sure you get the Gen 2 as it allows a max of 3.6kw discharge and charge of the battery.

Your daily usage description seems a bit low compared to what you cite as annual usage, but basically the charge/discharge is the key as you'll only be able to charge 3.6kw X 4hrs per night which would be a max of 14.4kwh of battery per day. You can get a second inverter like I am to take it up to 7.2kw per hour.

PM me if any questions!

 

[Journey]

Your daily usage description seems a bit low compared to what you cite as annual usage, but basically the charge/discharge is the key as you'll only be able to charge 3.6kw X 4hrs per night which would be a max of 14.4kwh of battery per day. You can get a second inverter like I am to take it up to 7.2kw per hour.

They are Intelligent which has a 6 hour window.

 

[tsinc80697]

It's a risk offset as well though.

In your example the 3rd battery is likely pointless, because you only need the battery power for 18 or 19 hours of the day, you'll never be reaching into the 3rd battery really, especially if you can load shift even more into the off-peak window.

The time when the panels will win hands down is if the cheaper off-peak tariffs are no longer as good. You could even wind up with expensive batteries that don't save you as much, then you have to go and buy panels, which means you may as well have done this from the start because of VAT saving of installation + you'd have been missing the generation since the installation by waiting.

Maybe speak to some installers and see what they come up with. You can always wire in a system that can take panels later should you want to do so, really it's your call on this one, I don't think battery alone is terrible it's just a riskier approach.

You may find it's best to remove those hot water panels and go with a new system that just does it all, including hot water diversion, especially if the hot water panels are taking up valuable south facing space inefficiently.

The hot water panels will be going if we got other panels.

Regarding the 3rd battery my workings were:

Usage
~27kWh per day

5kWh during 6 hour cheaper period
21kWh outside of this

So we would need batteries with at least 21kWh capacity, and that would be going from 100% to 0% charge every day. If 90% of the capacity is usable then that means I would need 24kWh batteries. So a 3rd 9.5kW GE battery would be required, I think?