Sanity check - Solar + battery install

DougMLancs

That quoted kit is almost what I’ve got and I paid £9500 5 months ago. Whereabouts are you in the NW @Andy0321? If you’re in Lancashire I can recommend a good local installer. 

EcoScruples

Eon may seem like a safe pair of hands but as Screwdriva days, it's ridiculously expensive today.
I certainly would not have got a battery (or such a big one) had I known then what I know now, id have used the grid as a battery. Banked my export for the winter and installed more panels.

Andy6S

Hi guys and apologies for jumping in but I’m in a similar position to @Andy0321 in that I have been getting quotes for solar and battery storage but with the intention of also getting an ASHP.  

My thinking was to maximize the amount of battery storage so I could charge from the grid at cheapest rate in winter to power the ASHP and sell excess generated during summer back to the grid. However, reading some of the comments it appears that this may be the wrong approach.

As a newby I’m not sure if this should be a separate thread or not so apologies if I’m stepping on toes. Any advice greatly appreciated. 

QrizB

Andy6S said:

My thinking was to maximize the amount of battery storage so I could charge from the grid at cheapest rate in winter to power the ASHP and sell excess generated during summer back to the grid. However, reading some of the comments it appears that this may be the wrong approach.

With current electricity tariffs you can think of solar, storage batteries and heat pumps as three separate systems.

• Solar: generates electricity that you can use, or (if not needed) can be paid to export.
• Battery: can store electricity when it's cheap, so you can use it when it's expensive.
• Heat pump: can produce 3x more heat than the electricity it consumes.
  

Solar mostly generates electricity in the summer, when its warm and you don't need heating. At current prices, solar has the biggest financial benefit over its lifetime.

Electricity is generally cheapest in the middle of the night, or on sunny, windy summer afternoons. Batteries can break even and might make a small profit.

Heat pumps are mostly required in the winter, when it isn't sunny (but might be windy) and generally run all day long to deliver peak efficiency. Heat pumps might break even vs. mains gas, oil or LPG but are almost always cheaper than direct electric heating.

Andy6S

Thanks for the response QrizB. While I like the idea of considering them as separate systems but, as they operate together, to maximize their efficiency should we consider their potential impacts on each other? Should we think of them as an overarching energy system comprised of 3 sub-systems. 

For example I’m thinking of the ability to store excess energy from the roof in a battery and then use that stored energy to either power the ASHP or feed into the grid at the best price time bracket (16:00-19:00) dictated by the likes of Octopus Flux. 

 I must admit I don’t understand the concept of a “virtual battery” using the grid to replace local storage. Apologies if I’ve not done sufficient homework in that area. 

Thanks again QrizB. 

Alnat1

I think the "virtual battery" idea is simply, rather than spending cash on a real battery, just export as much as you can in summer, get plenty of credit with your supplier from the export payments, then use the credit over winter when the sun doesn't shine so much.

Reasoning behind this seems to be, say a battery is £2500 and has an expected 6000 cycles then it "costs" 42p a day to fill and empty it. In order for a battery to be worthwhile, it needs to be able to make you or save you that extra 42p a day. 

For me, with a battery, I'm pretty sure that I save this amount after dark most days and definitely in winter when the oven's on to cook in the evening and I'm having tea and toast for breakfast. With Octopus Flux as my summer tariff I can send extra to the grid when prices are high in the evening (tbf my SW facing panels are often sending lots 4-7pm anyway). Agile is my winter choice, so I can fill up the battery with cheaper overnight/afternoon electric to use at peak times. Last 28 days I've imported 2.99kWh av. per day at a cost of 8.34p/kWh and exported 6.43kWh av. per day at 15p/kWh, still enough to cover gas charges for HW/hob and the SC.

I have a real battery and a "virtual battery", my Octopus account has almost £500 credit which should cover the majority of my gas heating costs and the electricity I'll import over winter. I haven't paid Octopus for any energy since I switched to them April 22, just after solar/battery install.

I am considering ASHP and would probably add extra storage then. Another 4.8kW battery around £1500, need to "make" another 25p a day, already done by saving on the gas SC   

QrizB

Andy6S said:

For example I’m thinking of the ability to store excess energy from the roof in a battery and then use that stored energy to either power the ASHP or feed into the grid at the best price time bracket (16:00-19:00) dictated by the likes of Octopus Flux.

I can see it's an attractive idea but the economics don't really work that way.

Let's say your solar PV produces a spare kWh at noon. You can sell it there-and-then for 16.5p, or sell it later in the day for 27.5p. That's an extra 11p!

But ... if you look at recent calculations in this thread, your battery might be costing you 10p/kWh for every kWh cyle through it. All of a sudden your 11p bonus is only 1p, and that's before we worry about conversion efficiency.

Netexporter

My current thinking is that you need to hammer your battery. Aiming for 2 cycles per day may "shorten" it's (guaranteed) life to 8 years but you should easily get your capital returned within that time, if you use the optimal tariffs. If there is a Moore's Law of batteries, which does seem to be the case (probably not doubling, but significant) then in 8 years time you'll be able to get a technically superior battery for less real-terms cash.

Screwdriva

Well summarized by another wise forum member...

Andy6S

Guys many thanks for the various inputs, these will certainly help me form my decision making.