Posted by: @mrkfm

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Hi. Wondering if someone can offer some basic advice on this subject to a novice.

I've been reading up about battery storage and seen videos etc where this is being promoted as an option without solar as long as you have a cheap overnight tariff.

Is this worth looking in to now?  Or do I need to wait for gov deregulation first?  I noticed Octopus are looking at selling these themselves but this seems a way off.

Are the Ecoflow Stream 5000 or the DJI Power 2000 options for saving without waiting 10 years to break even? No one seems to add the cost of an electrician doing an install to the return on investment.

And do both need a "fuse spur" to be able to export the power back into the grid?  

I get the feeling we've gone a bit off piste rather quickly here, so I'm going to throw some generalisations towards you, @mrkfm. Everything @transparent and @jamespa have mentioned is good, solid advice but the fused spur issue is perhaps a bit of side show rather than the main event and you did ask for a basic introduction.

Eventually, a battery is only useful for timeshifting; buying at one time and using at another. Whilst there is value in being able to use that power during a power cut, the benefit is almost always in the difference in cost between the leccy when you buy it and the leccy price when you want to use it. This much is blindingly obvious and I'm sure not news to you.

You obviously need to be on a tariff with at least two prices to allow for this time shifting to work, and the simplest is a standard "economy 7" style tariff. Right at the moment, in my region, the peak rate is 33.47p and the cheap rate is 14.17p. I'm going to assume your domestic consumption (apart from heat pump and EV) is about 9 kWh; it's a fairly safe assumption for most. I'm also going to assume your domestic consumption is pretty evenly spread throughout the day, so doing the sums on that means that if you had a big enough battery to tide you over the 16 peak hours so you could make all 9 kWh cheap ones, you'd save about £420. To achieve that would take a battery of slightly more than 6kWh and a typical bundle of a battery like that with a single phase inverter would be about £2,500 (without fitting), and therefore a payback on kit alone of just under 6 years. The bundle I'm using for this exercise is from Fogstar and whilst I'm quite interested in their batteries I am in no way making any kind of recommendation.

If you had a heat pump (I'll use the averaged-out consumption of mine of 12.8 kWh/day), the same sums would give an annual saving of slightly over £1,000. However, that's rather a lot of smoke and mirrors, since the heat pump isn't heating the house for quite a lot of the year. Averaging out the months when it is really necessary gives a daily figure more in the region of 21.7 kWh, so in order to service that with cheap rate leccy would need a battery more in the region of 32 kWh. A typical battery/inverter bundle (from the same supplier as before) is around £5,200 and a payback on kit alone of just over 5 years.

As @transparent pointed out, tariffs fluctuate so these figures are very rough and ready based on the huge assumption of the difference between peak and cheap rates remaining fairly constant for the next 5 years or so. It is also true that you could adopt several supplementary strategies to further reduce the net cost of the energy you buy in such as:

• Adding solar panels and using what you generate, storing what you generate and/or exporting what you generate. All pretty obvious.
• If you size the battery for a heat pump, in summer you will have a lot of spare capacity which you could use to buy at cheap rate and then export back to the grid when the export rate is higher than the cheap rate. Not likely to be cost effective whilst cheap rate is around 14p.
• Redoing the sums with different tariffs, particularly time of use ones. Octopus Go, for instance, has a cheap rate of 9.5p in my region.

Bear in mind, of course, that having an EV will have no bearing on the benefit of having a battery, but it may limit how much you can draw from the grid to charge said battery.

Any qualified sparky should be able to install a battery and inverter pretty easily and you can expect around £400 as a day rate. Many sparks are also set up (themselves or through subcontractors) to install solar panels although you'd want to be a bit careful about who you choose there to make sure your roof remains weathertight after such an installation.

Anything like this that is connected to the grid is likely to require that the energy distributor (UK Power Networks in my case) is informed about the installation and quite probably in advance. Your installer should be able to do this for you or at least guide you through doing it yourself. In fairness, I found the red tape far more of a challenge than any other part of getting my installation done.

Overall, forget any projected savings quoted by anyone trying to sell you something and concentrate on doing the maths yourself. That way you are far more likely to understand the assumptions you're making and the compromises you're accepting.

Does that help?