Adding battery storage - feasibility and payback

teecee90

We had a 4kw PV system installed in 2015 with associated FIT rates. Bought an EV last year and intsalled a hypervolt charger and converted to IOG tariff - current fixed rates of 32.69 peak and 7.62p off peak and 51.33p standing charge. Outgoing Octopus tariff for export currently @12p. Peak annual usage is currently around 2100kwh per year.

Thinking of adding battery storage to reduce peak useage. Curret PV setup with non-hybrid inverter means it cant be retrofitted to the existing system, although I understand there are some battery systems that come with their own inverter. So my first question - is this correct? Could we add battery storage without having to replace any of the current PV kit (which seems to be going strong and I dont want to replace the inverter until its absolutley necessary)?

Second question - are there any calculators available to easily calculate the payback period if we were to add a battery?

Grateful for any advice.

Keep_pedalling

We have just done exactly that. We had a Fox EVO 10 installed which as it’s own inbuilt inverter. This has allowed us to shift 99% of our import to the cheap rate which is 6.6p pkWh on the IOG 12m loyal fix.

Screwdriva

This is currently my pick of the calculators out there.

Any plans for a heat pump in the near future? I ask as, with the recent reductions in export tariffs (regrettable, as the wholesale prices of energy do not appear to support this), your consumption appears too low to financially justify the cost of a battery. Said another way, the battery unlikely to pay for itself within warranty. And that assumes the manufacturer honours their warranty, which Fox has a reputation of not doing.

There is always the use case for relief power blackouts though.

teecee90

Just to clarify, no plans for a heat pump and I’m only looking for a payback calculator for the battery. The Solar PV system already paid back after just over 6 years (2022).

sheenas

The first step is to decide what size battery makes sense to you. Their are battery systems that come with their own inverter as you say and are basically hybrid system. I have just had a Plug-in Ecoflow battery installed with a power meter by a local sparky. Battery is 2Kwh and £610 from ecoflow with Ebay discount. £100 for the power meter and £150 for the sparky. I have the eon smart saver fixed tariff and the battery covers the 4pm to 7pm 38.77p/kwh period (plus some). I estimate this will pay back in 3.5 years and has been working well for 2 months now. I wanted to test the waters with the system and can add solar panels maybe in the spring now.

I personally don't think it makes financial sense currently to try and get 100% of you demand supplied with a battery. The real beauty of these systems is they are easy to upgrade with the need for an installer. Just connect up a 2wkh/4wkh etc etc expansion battery.

NedS

As your peak annual usage is around 5.75kWh per day (averaged over the year), you may find something like a plug-in ECOFlow Stream 5000 viable. ECOFlow are currently selling these for £1399 in the UK.

You could charge at 7.62p overnight and avoid import at 32.69p/kWh. Assuming a saving of ~24p/kWh (after conversion losses) and 5kW throughput per day, you may be able to save £438/year giving a 3.2 year payback period (best case scenario). Realistically it should pay for itself in 5 years.

Where you'd lose out is that if not wired in by an electrician, and simply plugged into a socket, you'd only have 800W output, so you would still draw from the grid for any high use such as kettle, electric oven etc, but it should at least cover all of your peak rate background usage up to 800W. If you are able to pay for an electrician to install it then the savings will be higher, but so would your upfront costs.

These devices seem ideal for low usage users like yourself where a traditional large home battery system is not economically viable. What do you think @Screwdriva?

sheenas

https://forums.moneysavingexpert.com/discussion/comment/82170762#Comment_82170762

The device needs a power monitor, else the device will discharge at 800w (or the Maximum) all the time during a scheduled discharge. The power monitor tells the battery/inverter how much power is required. The surplus is lost back into the grid.

Martyn1981

https://forums.moneysavingexpert.com/discussion/comment/82170780#Comment_82170780

You can set them to discharge what you want in 10W increments (upto 800W), and you can set several different periods/levels through the day. Mine discharge 280W for the 18hr high price period.

QrizB

You can set them to discharge what you want in 10W increments (upto 800W)

You can indeed, although without a power monitor (the Ecoflow one or a compatible Shelley) you won't be able to dynamically match your discharge to household load.

Nevertheless sheenas's experience is that the extra £250 for the meter and professional installation will be worthwhile. A total cost of £1650 (£2400+£250) for a 5kWh battery is still fairly competitive.

Screwdriva

https://forums.moneysavingexpert.com/discussion/comment/82170762#Comment_82170762

I didn't realize plug in battery storage was now legal in the UK..if this is case, sign me up!

I am not familiar on the difference between hiring an electrician to "install" it vs. just plugging it into a wall - how would that work in reality? Is the 800W limit imposed by the unit itself?

QrizB

I didn't realize plug in battery storage was now legal in the UK

That'll be because it isn't!

I am not familiar on the difference between hiring an electrician to "install" it vs. just plugging it into a wall - how would that work in reality?

The battery is supplied with a flylead with bare ends. This should be hard-wired into a dedicated circuit from your consumer unit. In addition if you spend the £100 to buy the Ecoflow power monitor (or a compatible Shelley device) that will also want installing in or adjacent to your consumer unit.

If the battery is on a new circuit (and most people won't have an existing one just lying around spare) then in England (and Wales?) it's notifiable under Part P of the Building Regs. Most councils charge a three-figure sum for Part P notifications, so it's potentially cheaper to have an electrician do the work and self-certify which avoids the council charge.

If however you were to fit a plug to the flylead, it would plug in just like a plug-in solar PV system does. In practice it'll work but you won't be able to register it as a plug-in system, won't generally get paid for export, and if it causes your house to burn down your insurer might decline to pay out.

Is the 800W limit imposed by the unit itself?

Yes, just like with plug-in solar.