Is solar battery storage worth it?

Freepost

The tariff was just short of 26p/kWh then dropped in the last year to 21p/kWh but I was more interested in whether batteries made sense to store my unused power rather than export it. There is also the idea of having a smart meter installed and obtaining a higher rate for export, perhaps 15p/kWh for a 1000 units rather than the deemed 50% at 5p/kWh.

retireby50

Freepost said:

The tariff was just short of 26p/kWh then dropped in the last year to 21p/kWh but I was more interested in whether batteries made sense to store my unused power rather than export it. There is also the idea of having a smart meter installed and obtaining a higher rate for export, perhaps 15p/kWh for a 1000 units rather than the deemed 50% at 5p/kWh.

The tariff is kind of important. Simplistically speaking if your battery is replacing usage at 21p/kWh it's going to take longer to recover the cost of the battery than if it is replacing usage at 26p/kWh. You asked if your maths was correct in the original post, it was 1000*26p = £260 is correct. Maths isn't the challenge, it's how you might use your battery, what tariff you are on/will be on, how clever your system is (and can you optimally use it), whether you have an EV or not etc. Is your 1000kWh stored and used realistic for example (I commented on that above in another answer to your earlier post)...also using cheap rate to recharge the battery to replace higher rate usage....

Getting a higher actual export rate is a separate, but potentially related issue. What I mean is you don't need a battery to do that, but if you have a battery it impacts on optimising usage. I've sent you a message on another possible complication I've picked up on from this post.

pensionpawn

Is (solar) battery storage worth it? I have been trying to prove this since my (split, 4kWs due east, 3.12 kWs due west) array was installed in December 2015. I haven't been able to as all the scenarios I model do not repay a Powerwall (yes I know there are cheaper batteries out there, however I want high capacity, high peak o/p, full house coverage and Home Gateway too) within its warranty period. I too had a solar divert to heat water to store in my tank and until I migrated to Octopus Flux 18 months ago that method served me well on deemed export. However, as I export ~ 4.5 Mwhrs pa maths quickly demonstrated that I should export every spare watt and use gas at ~ 6p to heat my water again. The first 12 month on Flux reduced my annual energy bill, including S/C, to £54! My metered export was £655 more than deemed would have been. Even with time shifting, I still can't make the fiscal case for a battery. In May I had A/C installed into the house and in addition to not having to endure baking nights and uncomfortable sleep anymore, it will also heat the house with a cop of over 4. So I am just about to embark on an experiment of using the A/C to heat just the lounge through the autumn after the gas boiler has heated the house / water first thing in the morning and just before tea. I firmly believe that my first battery will be attached to five wheels, with one for steering, in the form of a VTH EV with a huge battery that can keep the house powered for days in an emergency. Time / cost will tell!

pete-20-11

Well, if Gary does solar’s latest YouTube is to believed, maybe one day we will have to pay to export our electric, or at least receive virtually nothing for exporting during the sunniest parts of the day. 

so at that point, being able to store the generation, or being able to use it by load shifting heavy appliance use to the daytime rather than overnight, might be needed. 

Guessing quite a few years away if it does happen. 

Martyn1981

pensionpawn said:

 So I am just about to embark on an experiment of using the A/C to heat just the lounge through the autumn after the gas boiler has heated the house / water first thing in the morning and just before tea. 

I've been doing that, using excess PV in the shoulder months to reduce GCH use, via our two A2A units. So just something extra you may be interested in - if you have cheap rate leccy, then you can take it a step further by running the A2A overnight during the cheap period to again reduce GCH need.

I have the unit running at 24C, with the door wide open, so heat spreads through the house.

The next step, bringing it back to batts, is that you can charge the batts on cheap rate, and run the A2A through the day too. Doesn't mean that the batts will be viable, but it may be another boost towards viability as costs steadily fall.

MouldyOldDough

pete-20-11 said:

Well, if Gary does solar’s latest YouTube is to believed, maybe one day we will have to pay to export our electric, or at least receive virtually nothing for exporting during the sunniest parts of the day. 

so at that point, being able to store the generation, or being able to use it by load shifting heavy appliance use to the daytime rather than overnight, might be needed. 

Guessing quite a few years away if it does happen. 

Surely if you are not going to be paid for excess electricity - it would be a simple job not to generate it - simply turn off a switch? 

pensionpawn

Martyn1981 said:

pensionpawn said:

 So I am just about to embark on an experiment of using the A/C to heat just the lounge through the autumn after the gas boiler has heated the house / water first thing in the morning and just before tea. 

I've been doing that, using excess PV in the shoulder months to reduce GCH use, via our two A2A units. So just something extra you may be interested in - if you have cheap rate leccy, then you can take it a step further by running the A2A overnight during the cheap period to again reduce GCH need.

I have the unit running at 24C, with the door wide open, so heat spreads through the house.

The next step, bringing it back to batts, is that you can charge the batts on cheap rate, and run the A2A through the day too. Doesn't mean that the batts will be viable, but it may be another boost towards viability as costs steadily fall.

Thanks for the suggestions. Flux offers a cheap rate between 2am - 5am however as I don't get up for work until 6:30am I don't think it will be cost effective / I'll see much benefit? I have UFH over 3/4 of the ground floor area and over the winter I have switched that on from 4:30 - 5:00 with the only noticeable effect being fiscal! Even though insulated with 10mm backboard it still loses energy quickly unless continually topped up, which then makes it very effective. I know I could leave the A/C on from 4:30, however with no one awake for at least 2 hours it's debatable how that would be more cost effective than my 2 year old Viessmann / Nest running and modulating down to 10% at 6p. I'll keep it in mind.

Qyburn

MouldyOldDough said:

Surely if you are not going to be paid for excess electricity - it would be a simple job not to generate it - simply turn off a switch? 

Simple, but storing it for use later sounds a better idea. Or store it when the grid doesn't want it, and export when it does. That would mean much bigger batteries than typically installed just now.

Qyburn

retireby50 said:

One of the problems with this discussion and working out what is best is there is a tendency (me included) to assume "our" situation applies to all. For example the above: I have an immersion diverter and it makes absolute financial sense (for me) as I am on the original solar tariff where get a low rate for an ASSUMED amount sent back to the grid (50% of my output).

Is there a reason you can't switch to metered export and get 15p/kWh?

Martyn1981

pensionpawn said:

Martyn1981 said:

pensionpawn said:

 So I am just about to embark on an experiment of using the A/C to heat just the lounge through the autumn after the gas boiler has heated the house / water first thing in the morning and just before tea. 

I've been doing that, using excess PV in the shoulder months to reduce GCH use, via our two A2A units. So just something extra you may be interested in - if you have cheap rate leccy, then you can take it a step further by running the A2A overnight during the cheap period to again reduce GCH need.

I have the unit running at 24C, with the door wide open, so heat spreads through the house.

The next step, bringing it back to batts, is that you can charge the batts on cheap rate, and run the A2A through the day too. Doesn't mean that the batts will be viable, but it may be another boost towards viability as costs steadily fall.

Thanks for the suggestions. Flux offers a cheap rate between 2am - 5am however as I don't get up for work until 6:30am I don't think it will be cost effective / I'll see much benefit? I have UFH over 3/4 of the ground floor area and over the winter I have switched that on from 4:30 - 5:00 with the only noticeable effect being fiscal! Even though insulated with 10mm backboard it still loses energy quickly unless continually topped up, which then makes it very effective. I know I could leave the A/C on from 4:30, however with no one awake for at least 2 hours it's debatable how that would be more cost effective than my 2 year old Viessmann / Nest running and modulating down to 10% at 6p. I'll keep it in mind.

Yep it's a fun numbers game, but with regard to cost, it's all about the COP, bout the COP (no treble).

So at night rate leccy, with lower COP, maybe half the cost per kWh(t) v's gas, and if you have a battery, then higher daytime COP may give you heat at 1/3rd the kWh(t) cost v's gas.

But again, not suggesting that a battery is cost effective (yet), just that combined with an A2A unit, there is another savings stream that would help a bit.