Newbir now looking hard at Battery solutions to maximise my PV output

Hi all,
Here goes! :-)
My wife and I have lived here in our1988 brick built 4 bed detached house for the last 26 years or so.
We invested in the max Solar PV array and get really good FIT payments which has recouped our investment in about 5 years and we get about £2.5k pa income from the array index linked on the really generous initial tariffs.
We have a 4kW array with a Fronius inverter. wee are South facing with a good roof angle.
Our energy supplier is OVO who we have bee pretty happy with but they have just hiked us from £150 per month for combined gas and electricity to £250!
We have loft insulation but lose a fair bit of heat from our two cat flaps!
A main consumption would be that we have our home office computers on 24/7 and TV, SKY et etc always on standby. We do not wish to change this!
Brand new double glazing throughout the house.
We have a living room fireplace now not used which is going to get a chimney blocking panel as i realize it loses a lot of heat.
I am considering getting something like a Powerwall or Givenergy system to help us out but wonder what the figures will work out to and payback period.
Gas is from a Combi 35kw Worcester boiler in the garage/workshop. We do have issues with the hot water being only just hot enough sometimes.
Our main bedroom en suite and guest shower has its own separate immersion fed from a loft cold tank via a high pressure pump and works extremely well.
I would welcome any advice at all regarding this and although not totally electrically competent I can understand most of the numbers.
Regards, Martin

Some key questions to ask yourself. How fast can you charge batteries? DO you have access to an overnight Tarrif?

You will need an AC Coupled battery, so the FiT PV system remains unaltered.

These can charge at 3kw, so you can just about charge 16kwh in a day from Solar.
You can double them up, 2 inverters and 2 batteries, giving you 6kw charge/discharge capability, if you r solar PV is large enough to make use, or you have access to a cheap overnight rate.
When I looked at batteries, I looked at what my base load was. Which is the background power consumption, mine was faily high at 600 -800W, like you I have IT, network gear, aswell as a fish tank, pond and 4 freezers.
We are also an all electric house, ASHP, electric range cooker.
I then asked myself, if I can charge them during the day, then run the house all night from battery, an charge the next, import would be kept to a min.

I went for 3x 5.2kwh batteries (As thats all that was on the shelf and not on huge back orders, i actually wanted 2 x 8.2kwh batteries)

I can on a good day charge these by around 4pm. So when its cooking time, we can run the cooker from solar+Battery during the lighter months. The battery should enough to last till next morning.
However as its cold at night the ASHP is still on, so drains my battery much faster.

We have only had ours 2 months, so yet to see if my theory is right, and we can indeed run the house 24/7 free of grid power in the Summer. 50% Spring/Autumn and best efort in teh winter.

martinking51

There is also a Facebook group for GivEnergy Owners. Where you will get lots of real world examples

https://www.facebook.com/groups/489882062425810/

As a rough rule of thumb, with solar panels alone you will utilise (i.e. actually consume in the home) approx 35% of what they generate. With batteries that should increase to 65% or more.

In March (a good month for sun hours) with a (in round figures) 5kW array and 10kWh of battery storage, we utilised 77% of what we generated. And made a reasonable sum from the Octopus outgoing agile tariff on what we could not use ourselves.

The best thing is that you need not lose your FIT income if you fit batteries, which is a massive win win.

Strikes me as disingenuous, bordering on fraudulent to get a 50% deemed export payment and then fit batteries to eliminate the export. Maybe HMG should think about this...

mrand31 friend of mine has had solar and battery storage for years and gets the deemed fit payment.
He rarely imports and often runs in island mode.

But whether you should get the fit will depend on whether you are following the rules of law or whether you are are wife of the chancellor.

mrand31 That's how the contracts were written by the govt a decade ago and they have another decade to run. Self consumption is a good thing for the network.

martinking51 Get an immersion heater controller first: water is a far cheaper energy store than a battery. Can you easily re-route all hot taps from the tank and away from the combi? Then cut your energy consumption and size the battery to suit. How much of your £250 bill is gas vs electricity?

mrand31 My understanding was that FIT was simply a mechanism for the government to remove the risk for early adopters to stimulate uptake of "green energy". I recently spent just a little bit more than a friend of mine who installed solar ten years ago. His system is 4kWp with one inverter, my system is 12kWp with two inverters and two 8kWh batteries. He gets FIT, I don't, but I benefit from the much lower cost of equipment because he (and many others) invested ten years ago.

I don't see FIT as payment for actual export, rather a ham-fisted way to compensate early adopters for their courage. I would have adopted ten or twenty years ago but couldn't afford it. The actual contribution of FIT-derived solar must hardly make any difference to the overall energy picture (@hoggy would probably be able to give some figures) but it does make a difference to the homes where solar was installed. If home owners then wish to improve their lot by making use of the technology, there's nothing to stop them. Indeed, I would expect both government and the generation/distribution industry to be glad that end-users are taking positive steps to load-shift (albeit driven by price) off their own bat.

Hi All,
Thanks so much for the very useful replies, much appreciated!

At this time we are on the OVO variable rate, our fixed contract having just expired.

Here is a better breakdown of our "permanently on" stuff;
55" Smart TV, Sky Q & Extra Box ; Denovo Network System; Dell Tower Computer + 2 Ext Drives, Canon Printer; BT Hub, O2 Booster; 2 x Alexa; 4 x GIGASET House Phones; Samsung Fridge Freezer (B Rated); Small Chest Freezer in garage. Solar Inverter. The en suite Immersion heater has an old thermostat so cuts in and out? Details of a suitable controller please?

Kitchen uses a 4 ring gas hob and a new basic single Neff Oven, Bosch Dishwasher; Tumble dryer (hardly ever used)

Our total usage in 2021 was:

Total Cost: £1179.79 of which Electricity was: £681.88 and Gas: £497.91
Total kWh: 20655.98 of which Electricity: 4388.31 and Gas: 16267.67

Our total usage so far in 2022 is:

Total Cost: £535.65 of which Electricity was: £259.31 and Gas: £276.34
Total kWh: 7944.44 of which Electricity: 1283.66 and Gas: 6660.78

Perhaps some of the more mathematically inclined can make something of these figures? :-)

Solar output Jun 20 to Sept 20: 1477.29 kWh
Solar Output Sept 20 to Mar 21: 1224.60 kWh (Dec reading missing)
Solar output Mar21 to Jun 21: 1382.42 kWh
Solar Output Jun 21 to Sept 21: 1463.50 kWh
Solar output Sept 21 to Mar 22: 1294.08 kWh (Dec reading missing)

FIT payments are around 55p per unit so very handy indeed!

Will these numbers allow a possible estimate of the size/ configuration of battery/ batteries that I will need?
Obviously we are not looking to run a washing machine during the night from this!

Who would be the best suppliers/ installers of this kit please? We are in South Dorset near Dorchester.
Regards and thanks to all.
Martin

Neff oven above is Electric, please pardon my omission. Martin

martinking51 You've provided a lot of detail but I'd put most of it to one side for now. If you're paying for 4,000kWh of electricity, that's only part of your actual consumption because you will also be consuming some solar. I know that our consumption is around 15-20kWh/day and our 2x8.2kWh batteries are at 50-60% by the time they start charging in the morning. Because of this, I know that when we have a few cloudy days, we don't have enough capacity to be self-sufficient and this means in the autumn and winter we will have to import from the grid to charge the batteries.

We've just signed up to EdF's EV tariff which is about 28p/kWh flat rate or 4.5p/kWh overnight (5 hours) and 39p/kWh the rest of the time but this is fixed until April 24 (you can swap between three EV tariffs as and when you like). With a 5 hour window and two inverters, we have enough time to charge both batteries to 100% each night from flat (8.2kWh/5 hours = 1.64kW charge rate, so less than the 2.5kW limit of the inverter). However, an AC3 would manage 15kWh, so almost enough for two batteries. You do need an EV (allegedly) to be on this tariff.

You could crunch some numbers to work out the RoI or just do it.

We fitted a log burner to our sitting room fireplace and that stops the draught. This would be an expensive solution to your draughty fireplace unless you wanted to keep warm and burn logs.

Immersion heater - plenty of discussions about diverting with iBoost or Eddi.

Hot water - check out the thermostat on your boiler and adjust the hot water to a higher temperature. If it's already set high, you might have to think about insulating the hot pipework from the boiler to where you use it.

Tim in regards to how much contribution households make to the grid - its not monitored by NG in any meaningful way (because live outputs not really possible from every house in the UK)
You just expect a depression in demand on sunnier days and you know roughly region by region whats likely going on where thanks to the DNO databases.
You still have to keep plenty of "spinning reserve" around to take the edges off between breaks of cloud and so on "just incase"

To be honest it's more of a hinderence to the grid as its completely the opposite of any other grid connected generation due to being so variable and uncontrollable - which (and this won't go down well) is why the SEG rates are so low.
That and locally its a pain to DNOs due to voltage rise on certain circuits.

Hi Tim,
Thanks for the reply.
We are unable to fit a liner to our chimney because the original builders (cowboys!) for reasons best known to themselves fitted a mixture of both round and square liners when doing the initial build. This was only discovered when we started to use the fire and found lots of CO emissions and black marks along carpet edges in upstairs rooms!
As a MUCH younger man I was able to carry endless buckets of weak concrete mix and add it via large holes made in the chimney breast working from downstairs all the way to the upper loft to seal the liners in situ. This worked out well and we have been able to use the fire in the past but now neither of us want the faff of logs and cleaning etc so will just block off the inefficient hole.

I assume from your post that you have or are getting an electric vehicle?
This is something we are also looking at but our priority at this time is to investigate a battery solution.
I will investigate immersion heater controllers and get back on this.

I guess that I am really looking to see is what kind of ballpark costs are involved in adding a suitable battery system to allow us to run our "always on" kit.
I think that we have the "standard" 4kW PV array in an almost ideal configuration, there might just be room for a couple more panels but presumably they would have to be separate from the existing system to avoid compromising out FIT payments?
Regards, Martin

martinking51 There are plenty of people on FIT who have fitted AC coupled inverters and batteries. The AC-coupled could divert your excess solar (if any) to battery for house supply in the evening and enable you to use cheaper overnight tariffs in the winter to charge the battery and supply the house.

Any internet search would find you retail prices for £2k to £5k+ for such a system but you'd have to get a competent electrical contractor to do the work for you to ensure compliance with building and wiring regs and manufacturer's warranty. I guess looking for someone to quote for the installation would be the best place to start.

An Eddi or similar for hot water heating would also be £500ish plus fitting but that would be a cheaper place to start. And yes we took delivery of an EV a couple of weeks after our solar was commissioned in January.

hoggy To be honest it's more of a hinderence to the grid as its completely the opposite of any other grid connected generation due to being so variable and uncontrollable - which (and this won't go down well) is why the SEG rates are so low.
That and locally its a pain to DNOs due to voltage rise on certain circuits.

I agree. My better half isn't bothered whether we get onto a SEG tariff or not as she sees it as an extension of us being self-sufficient (except in winter) and "free" energy for our neighbours, which it isn't of course because they still have to pay for what they consume. My Zappi keeps tripping on over-voltage and so I'm going to have to ask my DNO to either change me onto another phase or adjust the taps on the local distribution transformer just to get down to spec. In fairness, there's quite a large caravan site nearby and I expect at certain times, there's quite a big load from it. However, during the middle of the day, it's actually my export that pushes the voltage out of spec, not the grid. I've spoken to Givenergy tech support but they said that the inverter just bumps up the output by about 3V to achieve the export and so it's down to my DNO to make the change.

Hi Tim,
One of the main reasons I am looking on here is because I well remember the process of getting our solar PV installed about 10 or 11 years ago.
The number of firms that we looked at was astonishing and the attitudes and approaches to a customer looking to spend a lot of money was in the main a very disagreeable experience.
We had quotes ranging from £25k down to £9k!
One lot turned up and wanted £500 to do a survey and did not even know which way to work out where South was!
The level of expertise shown was mostly very low level and not at all confidence inspiring, the techno speak often being intended to intimidate.
When I pointed out to the couple of firms that we quite liked that we actually were looking with our neighbors either side to do a group purchase things got a bit more realistic. This finally happened and all 3 of us are happy with our systems.

I wish to arm myself with as much non commercially motivated knowledge as I can before expenditure.

I do , however, totally take your point about getting a quotation as a base line.

Are we saying that my existing Fronius inverter will have an "output" to the new battery when installed?
Is the Immersion gadget also compatible?
Is there an easy "rule of thumb" calculation as to the battery size needed based on the figures I have given?
Regards, Martin

martinking51 Your existing inverter sends the solar generation to the house consumer unit (via the MCS meter used to work out "deemed" export). Any new install will also be connected to the house consumer unit. A current transformer (CT) on the bit of cable between the house main supply fuse and the electricity meter (or between meter and consumer unit) will detect whether energy is flowing into (grid import) or out (grid export) of the house. The CT would be connected to the new AC-coupled system and it would "divert" the excess solar from being exported to charging your battery. You would be able to set up the AC-coupled inverter to discharge to the house when it detected grid import, or on a timer. Similarly for charging from the grid on cheap rate.

The immersion gadget does exactly the same, diverting export to heat the water (although obviously it can't divert hot water energy to your house when it gets dark, unlike the battery) and is significantly cheaper than the AC-coupled option. You could do this as a stepping stone on the journey to AC-coupled. However, be aware that if you have energy diverter devices, they can conflict unless they are configured so that one has priority over others. Setting an export threshold often helps, so you could divert to hot water if the export exceeds say 100W, divert to AC-couple if the export exceeds 200W and so on. Having kit that works well with other systems helps. Thus myEnergi have the Zappi EV charger and the Eddi hot water diverter and you can use the myEnergi hub to divert as you wish.

Working out how much battery you need requires you to know what your consumption is and then deciding if you want to have capacity to last for 24 hours between charges (from solar or cheap-rate) or if you're happy to accept that x% of the year it's 100% covered and for the rest of the year, you have to import ykWh of energy each day. You can model this to weigh up the pros and cons and do the RoI maths, or just pick a battery size and see how you go.

As I said earlier, I know (from our last 12 months daily meter readings downloaded from DCC) that our consumption is pretty steady at 15-20kWh/day. We are currently self-sufficient from solar as the weather has been good and the batteries usually charge to 100% by lunchtime and we can charge the EV during the afternoon. We use 6-8kWh from when the sun goes down to when we start generating again. That figure will decrease as the days get longer. When the days get shorter, say maybe November time, we will start consuming more than 10kWh overnight and it will only take a couple of dark days in the winter to put us 100% back on the grid. For that reason, we will plan to charge the batteries each night to last until the next charge period. Our installation was expensive, but we were able to put enough PV on the roof to supply everything.

Having large enough battery/batteries to keep you off standard-rate tariff all year round would be expensive and only you know whether that's desirable or affordable. However, to access dual-rate tariffs, most suppliers require you to own an EV. I can't tell you how much battery you need but I'm very glad that our installer specified 2x8.2kWh batteries for us as they seem to be just big enough to charge to 100% in winter during the EdF 5 hour cheap-rate window and last us the other 19 hours at typical house load. If we managed that, our electricity bill would still be for maybe 2,000kWhpa, mostly over winter, including about 300kWh for EV charging at night. If that was all at the EdF overnight rate of 4.5p/kWh, it would save about £470pa on the standard rate of about 28p/kWh. We are saving at least 4,000kWhpa by having the PV system in service the rest of the year and we are no longer putting petrol in the tank of one of our cars, saving about £1kpa.

Tim
Thanks so much for your effort and input.
I will digest this and get some quotes and try to get a better handle on how much we actually use each day.
Will come back when I have this to impart.
Regards, Martin

Tim,
May I respectfully ask how much the 2 x 8.2 kWh batteries were inc install?
Martin

martinking51 The cost is difficult to benchmark for your project as you'd be using AC3s but a google search gives a ballpark of £2.5k for battery (although they're not available for shipping currently) and £800 for AC3. Obviously, there's installation costs too but I'd have thought a budget of £7.5k would get you two AC3 and batteries.

Tim I was quoted £4300 to £5400 for 1xAC with 8.2kWh battery. Both figures include VAT.
Battery size is subject to the law of diminishing returns and it's easy to add an extra battery to the system later. I ended up with 2x5.2kWh due to availability - sufficient for short-term balancing (kettles and clouds), avoiding export on most days and charging for most of the 4 cheap hours on Octopus Go.

Was VAT not removed for these by Mr Sunak?

wilfleek I don't think so, it was only PV generation that attracted the lower 5% rate (or a battery installed as part of a PV installation, provided that the materials were no more than a certain percentage of the purchase price)

Article in Electrical Review, dated 24th March, states that the 60% materials limit has been removed, but that storage is only VAT exempt if it is being supplied as part of one of the listed technologies, most notably PV.
If this is the full story, who's up first to test this with a 16kWh battery system and a solitary PV panel?

martinking51 personally I wouldnt over think the requirements, as you will make lots of assumptions that will probably prove wrong once you get the system.

Your actual uasge will change once you have storage. Mine certainky did. You will load shift a lot of energy to overnight in the winter, and shift to the day in the summer. If you can't meet your demand during the day from PV and you can power devices at night then that is the same energy cost as charging the battery and then running in the day but without any losses. Moving whatever you can to only leave what is essential for the battery as its immovable makes the equation quite different
If you can, check the use of yopur energy. How much is peak and off peak? Thats a big factor in the sizing as its the difference between those wher ethe savings are.

The key question from my perpective is your peak power need and frequency of that need. That will determine the inverter size / quantity. You have an electric cooker. That will exceed ratings, but that will pnly be used for a limited time. The maths is then how often that happens and for how long to calculate if it is more cost effective to have a second invertor or just pay for the overage from the grid ( I chose the later as my xs is rarely over 4kw and only for short times when it does. When over 4kW its at cheep rate e.g. washer, dryer, EV. Charging the battery at the same time prevents the battery discharging into these devices )

For capacity I would just start with 8.2Kw. One inverter can have many batteries attached and they can be added at a later date. Just go with something that prove how it all works and deliver benefits without too much investment based on inconclusive evidence. After say a year ( so summer and winter cycle ) review and add more storage if required. Hopefully by that time storage prices will have come down and capacities will have gone up. Yes there is another installation fee, but as the hard work has been done already that should be nominal

for reference I use about 20kW/d. 4kW PV, 8.2kW storage, HW diverter.
In summer very little grid import even with hot water diversion ( so no gas ). In winter battery charged overnight and runs out about 3 hours before top up on Go Faster 5.
In my total record on GE portal, 2951kW generated of which 2110kW consumed ( which includes hot water ), 720kW battery charging, 119kW export

This information shows that if I had more storage I could only charge it if I had less hot water, robbing one system to use in another

If I was to do my system again I would oversize the PV but keep the 4kW limit as that straight forward to do. I would accept production cliping for the longer portion of the day producing more. Panels are cheep now vs 8 years ago, and oversizing wasnt really a concept at that time. I have space for another 2kW. I dont need the peek output but having max 3-4kw for a lot longer in the day would be very useful

Seye, Thanks so much for that very lucid outline which I will study in detail.
May I have details of the units you have and costs please if I am not being impertinent?!
What is your approximate location and PV aspect/azimuth?
Regards Martin