Solar, is it worth having a battery in my case scenario?

shamanicone

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan), I've been allowed 3.9 Kwh export by my DNO and I use 3200 Kwh average electricity a year. 

I currently don't have a heat pump or EV.

Is it worth my while having a battery at this stage based on my usage please (I've been quoted approx £3k extra for a Tesla PW3 and backup gateway over the panels)

Thanks 

nakie999

Yes, based on your usage, a battery may not give you strong value right now. You use about 3200 kWh a year and you do not have a heat pump or EV that would increase your evening demand. Most of your solar generation would be during the day when usage is lower. In that case much of the stored energy might not be used fully.

A battery becomes more cost effective when you have higher evening use or when you plan to add an EV or heat pump in the future. If you think you will add either within the next few years, the battery could make sense later. For now, you can install the panels and monitor your actual export and usage patterns. This gives you real data so you can decide later with more confidence.

Screwdriva

Your usage is low but the Powerwall 3 has access to intelligent flux, which should hasten your payback window. 

Not sure what you've been quoted but a 6.5kWp (13 X 500W bifacial Eurener panels) paired to a PW3 should cost < £11.5K installed, with bird netting and 10 year workmanship warranty. 

shamanicone

Screwdriva said:

Your usage is low but the Powerwall 3 has access to intelligent flux, which should hasten your payback window. 

Not sure what you've been quoted but a 6.5kWp (13 X 500W bifacial Eurener panels) paired to a PW3 should cost < £11.5K installed, with bird netting and 10 year workmanship warranty. 

9.5k for 13 x aiko gen 3 panels, PW3 & gateway, bird netting

Screwdriva

I’d ask them to swap panels for Eurener and go for it! 

I’d check their workmanship warranty duration too. The price seems a bit too good to be true so I'd suggest caution - there are cowboy installers who will surprise add on after the initial quote has been agreed to.

QrizB

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan)

I don't know why anyone would choose to pair a 10kW inverter with only 6kW of panels. Is there a reason for this?

shamanicone said:

I've been allowed 3.9 Kwh export by my DNO ...

So, without  battery, you're going to be clipping the top third of your idealised generation curve. Admittedly this is probably only 10-15% of your potential kWh, but it's not going to help the economics.

shamanicone said:

Is it worth my while having a battery at this stage based on my usage please (I've been quoted approx £3k extra for a Tesla PW3 and backup gateway over the panels)

Add the PW3 and you should be able to minimise the lost generation from your export limit. You'll also have the option of self-powering through the night & minimising import, and/or importing at cheap times and exporting at expensive ones.
You could even end up with a zero (or negative) electricity bill, like @Solarchaser in this thread:

https://forums.moneysavingexpert.com/discussion/6636785/can-you-run-an-all-electric-house-for-free

ed110220

QrizB said:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan)

I don't know why anyone would choose to pair a 10kW inverter with only 6kW of panels. Is there a reason for this?

shamanicone said:

I've been allowed 3.9 Kwh export by my DNO ...

So, without  battery, you're going to be clipping the top third of your idealised generation curve. Admittedly this is probably only 10-15% of your potential kWh, but it's not going to help the economics.

shamanicone said:

Is it worth my while having a battery at this stage based on my usage please (I've been quoted approx £3k extra for a Tesla PW3 and backup gateway over the panels)

Add the PW3 and you should be able to minimise the lost generation from your export limit. You'll also have the option of self-powering through the night & minimising import, and/or importing at cheap times and exporting at expensive ones.
You could even end up with a zero (or negative) electricity bill, like @Solarchaser in this thread:

https://forums.moneysavingexpert.com/discussion/6636785/can-you-run-an-all-electric-house-for-free

One reason for oversizing the inverter relative to the PV would be to size it for the battery. There's no particular reason why your battery sizing should be the same as your PV sizing, especially as PV sizing is often constrained by space.

We've got 4.8 kW of PV on an 8 kW inverter. A 'standard' 4 kW inverter would be fine for the solar, but would only allow storing up to 20 kWh in a five hour cheap rate overnight window which wouldn't be enough if you had ASHP. You'd also be importing from the grid even if you had energy in the batteries if your load was above 4 kW, which again it easily could be with ASHP.

Martyn1981

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan), I've been allowed 3.9 Kwh export by my DNO and I use 3200 Kwh average electricity a year. 

I currently don't have a heat pump or EV.

Is it worth my while having a battery at this stage based on my usage please (I've been quoted approx £3k extra for a Tesla PW3 and backup gateway over the panels)

Thanks 

Hi, like others have mentioned, a 10kW inverter is too big for 6kWp of panels, you'd really want about 5kW.

But that said, a 3.9kW inverter would be too undersized, and would lead to some clipping and loss.

Based on that, and what looks like a really good price for the PV + PW3, I'd say go for it. Even if the PW3 has to be capped to avoid export greater than 3.9kW, it will still be able to absorb the full ~6kW of generation from the panels, by storing it in the batteries (so long as the batts aren't full).

Plus the battery gives you a big potential benefit in the winter, where you could charge it with cheap rate leccy, then run the house off that through the day. Combined with the PV and storage in the sunnier months, you should be able to avoid almost all use of day rate leccy.

Of course this requires you to find and switch to a dual rate tariff, but it should save you. And having a battery and cheap rate leccy, should make other options in the future better, such as an EV charged cheaply overnight. Or something I'm a big fan off, and that's adding an air con unit, an air to air unit (A2A). With one of these, you can use spare PV to warm the house in the Spring and Autumn, when heating demand is low, and even pre-heat the house overnight on cheap rate in the winter, to reduce use of the gas central heating (GCH). [I've now gone a bit further, added a second A2A unit, and removed the GCH.]

So, for the price, and the better use of the large PV array, and future options, I think the battery is a good option for you, with potential future proofing built in.

shamanicone

Martyn1981 said:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan), I've been allowed 3.9 Kwh export by my DNO and I use 3200 Kwh average electricity a year. 

I currently don't have a heat pump or EV.

Is it worth my while having a battery at this stage based on my usage please (I've been quoted approx £3k extra for a Tesla PW3 and backup gateway over the panels)

Thanks 

Hi, like others have mentioned, a 10kW inverter is too big for 6kWp of panels, you'd really want about 5kW.

But that said, a 3.9kW inverter would be too undersized, and would lead to some clipping and loss.

Based on that, and what looks like a really good price for the PV + PW3, I'd say go for it. Even if the PW3 has to be capped to avoid export greater than 3.9kW, it will still be able to absorb the full ~6kW of generation from the panels, by storing it in the batteries (so long as the batts aren't full).

Plus the battery gives you a big potential benefit in the winter, where you could charge it with cheap rate leccy, then run the house off that through the day. Combined with the PV and storage in the sunnier months, you should be able to avoid almost all use of day rate leccy.

Of course this requires you to find and switch to a dual rate tariff, but it should save you. And having a battery and cheap rate leccy, should make other options in the future better, such as an EV charged cheaply overnight. Or something I'm a big fan off, and that's adding an air con unit, an air to air unit (A2A). With one of these, you can use spare PV to warm the house in the Spring and Autumn, when heating demand is low, and even pre-heat the house overnight on cheap rate in the winter, to reduce use of the gas central heating (GCH). [I've now gone a bit further, added a second A2A unit, and removed the GCH.]

So, for the price, and the better use of the large PV array, and future options, I think the battery is a good option for you, with potential future proofing built in.

Martyn1981 said:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan), I've been allowed 3.9 Kwh export by my DNO and I use 3200 Kwh average electricity a year. 

I currently don't have a heat pump or EV.

Is it worth my while having a battery at this stage based on my usage please (I've been quoted approx £3k extra for a Tesla PW3 and backup gateway over the panels)

Thanks 

Hi, like others have mentioned, a 10kW inverter is too big for 6kWp of panels, you'd really want about 5kW.

But that said, a 3.9kW inverter would be too undersized, and would lead to some clipping and loss.

Based on that, and what looks like a really good price for the PV + PW3, I'd say go for it. Even if the PW3 has to be capped to avoid export greater than 3.9kW, it will still be able to absorb the full ~6kW of generation from the panels, by storing it in the batteries (so long as the batts aren't full).

Plus the battery gives you a big potential benefit in the winter, where you could charge it with cheap rate leccy, then run the house off that through the day. Combined with the PV and storage in the sunnier months, you should be able to avoid almost all use of day rate leccy.

Of course this requires you to find and switch to a dual rate tariff, but it should save you. And having a battery and cheap rate leccy, should make other options in the future better, such as an EV charged cheaply overnight. Or something I'm a big fan off, and that's adding an air con unit, an air to air unit (A2A). With one of these, you can use spare PV to warm the house in the Spring and Autumn, when heating demand is low, and even pre-heat the house overnight on cheap rate in the winter, to reduce use of the gas central heating (GCH). [I've now gone a bit further, added a second A2A unit, and removed the GCH.]

So, for the price, and the better use of the large PV array, and future options, I think the battery is a good option for you, with potential future proofing built in.

So (as you are probably aware) the inverter is built into the PW3 (hence the larger size than required). The DNO has capped my export but not limited the inverter, my understanding is that means I can fill the battery at full throttle as it were, meaning about 2.5 hours for the PW3 to fully charge.

I'm going for a tariff that will charge me 7p overnight and pays 15p export - it's not intelligent, but I think I can set the PW to max this anyway (hopefully).

My thinking was also the future, and probably a later move to a heat pump (something that might be forced upon us anyway in the not too distant future) and who knows what is coming down the line geo politically (so a bit of self reliance might not be a bit thing if things get complicated in that regard). 

My last swaying factor towards going for it is I'm going to pay for it all over time on 0% credit cards - so it's not like it's going to take a huge chunk out of my growing savings. 

Thanks for the input

QrizB

shamanicone said:

So (as you are probably aware) the inverter is built into the PW3 (hence the larger size than required). 

We're all aware of that, but couldn't understand why you first posted:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan)

... when you hadn't yet decided on whether to have a PW3.

If the plan all along was to have a PW3, why then ask:

shamanicone said:

Is it worth my while having a battery at this stage based on my usage please

You can hopefully understand our confusion.

shamanicone

QrizB said:

shamanicone said:

So (as you are probably aware) the inverter is built into the PW3 (hence the larger size than required). 

We're all aware of that, but couldn't understand why you first posted:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan)

... when you hadn't yet decided on whether to have a PW3.

If the plan all along was to have a PW3, why then ask:

shamanicone said:

Is it worth my while having a battery at this stage based on my usage please

You can hopefully understand our confusion.

QrizB said:

shamanicone said:

So (as you are probably aware) the inverter is built into the PW3 (hence the larger size than required). 

We're all aware of that, but couldn't understand why you first posted:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan)

... when you hadn't yet decided on whether to have a PW3.

If the plan all along was to have a PW3, why then ask:

shamanicone said:

Is it worth my while having a battery at this stage based on my usage please

You can hopefully understand our confusion.

QrizB said:

shamanicone said:

So (as you are probably aware) the inverter is built into the PW3 (hence the larger size than required). 

We're all aware of that, but couldn't understand why you first posted:

shamanicone said:

Hi, I have room for about 13 x 460w Aiko panels with a 10 Kwh inverter (and that's the plan)

... when you hadn't yet decided on whether to have a PW3.

If the plan all along was to have a PW3, why then ask:

shamanicone said:

Is it worth my while having a battery at this stage based on my usage please

You can hopefully understand our confusion.

"If the plan all along was to have a PW3, why then ask": Because nothing is written in stone, and no plan cant be unplanned if you are having second thoughts. I ran some calculations through an online ROI calculator that made me think again (or at least, look for further opinions if this was the right move). 

It's an expensive investment, and I don't like to rush into things without very careful consideration.

No harm in asking for second opinions is there?