FIT 3Kwp System from 2014. Should I be adding batteries?

[Oldman22]

Considering the cost of energy now I am wondering if I should be upgrading my system to add battery power. Currently my 12 south facing Sharp ND-R250as single string panels are coupled to a Samil Solar river 3000TL inverter & is registered for FIT payments since Jan 2014.
I seem to have generated around 3.9MWh/yr in recent years with around 2.3MWh deemed exported my metering tells me.
I think I would have to be looking at AC coupled batteries to keep my FIT.
So can anyone please offer advice on suitable kit that can help reduce my energy bill? We use around 14kw/day in winter, most of that is 5pm onwards.

 

[johnb2713]

A lot will depend on what you want to achieve.
I use on off peak tariff (Octopus GO), I have just installed and setup a DIY AC coupled battery to join into my Solar PV system. The net result is all my electricity use now comes from off peak (7.5p kWh) or solar (free). My battery charges during the off peak period 00:30 to 04:30 and takes further charge throughout the day if surplus energy is available.
Essentially what you need is a Hybrid Inverter, a compatible battery storage unit of a size that fits your needs. Myenergi have just released a self contained unit (https://www.myenergi.com/libbi/) or you can select from the well know manufacturers the components required. Either way, it will save a lot of energy costs if done in conjunction with an off peak tariff. There are a lot of savings to be had if you DIY the battery build, my system cost less than £4200 to give 14 kWh and 5kW inverter power, it depends how competent you are with electrickery and delving into the unknown!

 

[Bob Smith]

Considering the cost of energy now I am wondering if I should be upgrading my system to add battery power. Currently my 12 south facing Sharp ND-R250as single string panels are coupled to a Samil Solar river 3000TL inverter & is registered for FIT payments since Jan 2014.
I seem to have generated around 3.9MWh/yr in recent years with around 2.3MWh deemed exported my metering tells me.
I think I would have to be looking at AC coupled batteries to keep my FIT.
So can anyone please offer advice on suitable kit that can help reduce my energy bill? We use around 14kw/day in winter, most of that is 5pm onwards.

You are correct, AC Coupled only. This is what I am in the process of doing.

 

[arwooldridge]

I think I would have to be looking at AC coupled batteries to keep my FIT.

Correct, and grid side of your existing FIT generation meter. It is not commonly known, I think, that a Hybrid inverter can be used in an AC coupled battery system. You either do not connect the PV inputs or can add extra PV(but not your existing FIT PV!) to them at any point. Hybrid inverters cost marginally more than Retrofit or pure AC coupled, but the potential to upgrade with more PV is worth considering. I think the small differential in cost is partly due to the production economies of scale as the Hybrids are now much more popular.

 

[johnb2713]

Correct, and grid side of your existing FIT generation meter. It is not commonly known, I think, that a Hybrid inverter can be used in an AC coupled battery system. You either do not connect the PV inputs or can add extra PV(but not your existing FIT PV!) to them at any point. Hybrid inverters cost marginally more than Retrofit or pure AC coupled, but the potential to upgrade with more PV is worth considering. I think the small differential in cost is partly due to the production economies of scale as the Hybrids are now much more popular.

Yes you run like this, I tried it briefly witha Growatt SPH6000 and it worked fine BUT the output when running on batteries only was reduced from 6kW to 3kW. Victron do an inverter designed for this application the Multiplus II series available from 3 to 10kW, great piece of kit and the one I chose for my DIY AC coupled battery.

 

[Oldman22]

Several questions, Johnb2713, what are the home insurance implications of all this battery power?
What wall space will I need to find in order to fit all the kit inc batteries lets say for a copy of Johns install. I only have 80x80cm of spare wall below my current pv setup.
How far away from the existing pv install (currently in my garage/workshop) can the new battery system be without causing excess cost or other complications.
Any easy way to work out what battery capacity to suit individual needs? Then to work out the payback period.
I am assuming that any battery add on should be fit and forget once "tuned" to meet individual requirements.

 

[johnb2713]

Several questions, Johnb2713, what are the home insurance implications of all this battery power?

None for me.

What wall space will I need to find in order to fit all the kit inc batteries lets say for a copy of Johns install. I only have 80x80cm of spare wall below my current pv setup.

You may be able to squeeze in there an inverter and a rack style battery.

How far away from the existing pv install (currently in my garage/workshop) can the new battery system be without causing excess cost or other complications.

Doing an AC coupled battery means it can be anywhere on your electrical system. You would need to have a suitable size of cable to meet your needs.

Any easy way to work out what battery capacity to suit individual needs?

I'm with Octopus Energy for my supply, they provide me with 1/2 hourly readings, this enabled me to analyse them over a whole 1 year period. I know my house has a steady 550w continuous load, ignoring the solar panels, that gives me a 13.2 kW per day consumption. A further 9.9 kWh per day was used on peak rate power, 20kW was used off peak.

Armed with the above info, when my Solar PV was installed a 7kWh battery was installed with the system, throughout the summer months we used very little peak rate power which saved a small fortune. It was clear that without the sun the battery wouldn't be big enough for the job so my DIY project commenced. I now have a total of 21kWh of storage and that seems to be just enough at this time.

Then to work out the payback period.

Using the DIY 14kWh battery I've just installed as an example.
Peak rate cost: 41.2p
Off Peak: 7.5p
Saving per unit: 33.7p per kWh
Assuming a unit cost of £4200 would give a payback time of 2.4 years assuming that all electricity to charge the batteries is purchased from the grid which it wont but the is the worst case situation, when excess solar is available then the figures get even better.

I am assuming that any battery add on should be fit and forget once "tuned" to meet individual requirements.

Yup, mine was switched on 24th December has had a couple if tweaks since them and now it just works! It is IMHO essential to have a dual rate tariff such as Octopus GO and then use it to the full to charge the batteries.

The system as a whole has worked for me very well, my payback including the solar PV and battery system is going to be under 3 years.

Its very difficult to size a system without being armed with their current use,

 

[Oldman22]

Thank you again Johnb for sharing your thoughts. My brain is currently swamped with info, most good but some questionable.
The more I looked at your system the more involved it looked & I wondered if I should look at how much a ready to fit battery store system would cost. The Libbi 3.68Kw inverter with 5Kw battery pack is around £5500, pretty much half the size of yours at a premium price when not on back order.

I asked a same county solar installer for a guide price and he they told me an AC coupled battery would make it part of the (current FIT) generation figure, if it was DC coupled it wouldn’t.
So correct info isnt always available!

I'm going to spend time at the weekend getting my solar/export/grid usage figures together and see if I cant get an idea what I would gain from various sized batteries.

This was news to me, "If you have a smart meter, your export payments will be based on actual export data. However, if you also have a home battery installed, your export payments will be estimated at 50% of what you generate. This is because your export meter cannot determine whether electricity exported from your battery was originally generated by your panels or taken from the grid."

Can I assume that purchasing a hybrid ac coupled inverter larger KW than the chosen battery pack would somewhat future proof by allowing another battery pack to be added later and maybe solar panels (separate from the original FIT panels)

Does the reduced or zero vat rate only apply to kit fully installed by contractors.

 

[johnb2713]

Thank you again Johnb for sharing your thoughts. My brain is currently swamped with info, most good but some questionable.

Exactly the situation I was in a year ago, I was drowning in opposing views and advice, a lot of advice was also incorrect.

The more I looked at your system the more involved it looked & I wondered if I should look at how much a ready to fit battery store system would cost. The Libbi 3.68Kw inverter with 5Kw battery pack is around £5500, pretty much half the size of yours at a premium price when not on back order.

My DIY battery has a 5kW inverter, 14kWh of storage for around £4200 including the little shed it lives in. Libbi is expensive as are most rady to run battery systems,.

I asked a same county solar installer for a guide price and he they told me an AC coupled battery would make it part of the (current FIT) generation figure, if it was DC coupled it wouldn’t.

Mmmmm that sounds like crossed wires, surely if it's AC coupled it is not part of the existing FITS system?

So correct info isnt always available!

So very true.

I'm going to spend time at the weekend getting my solar/export/grid usage figures together and see if I cant get an idea what I would gain from various sized batteries.

Do you have an off peak tariff like Octopus GO or and Economy 7 one? This is where batteries can make a killing for you. Utilita have a 5.3p kWh E7 tariff, if you can store enough for a days use then all of your energy would be at 5.3p

This was news to me, "If you have a smart meter, your export payments will be based on actual export data. However, if you also have a home battery installed, your export payments will be estimated at 50% of what you generate. This is because your export meter cannot determine whether electricity exported from your battery was originally generated by your panels or taken from the grid."

Says who? do you have a link?

Can I assume that purchasing a hybrid ac coupled inverter larger KW than the chosen battery pack would somewhat future proof by allowing another battery pack to be added later and maybe solar panels (separate from the original FIT panels)

I favour a larger inverter so that the system can supply the load from batteries. If you a 3.6kW inverter and switch the kettle and toaster on you will adding power from grid at peak rate costs. Going to a 6kW plus inverter that keeps you clear of the grid supply much better. The duration it can supply the load is determined by the capacity of the battery. My 14kWh battery was sufficient to cook the Christmas dinner and supply the house for most of the day. Both inverters were running at times I had over 12 kW discharge into my system.

Does the reduced or zero vat rate only apply to kit fully installed by contractors.

Yes and it only applies to solar PV installations. A battery or powerwall doesn't qualify. Solar Panels and battery does qualify. Madness for sure but I was luck enough to get zero VAT on my install.

 

[Bob Smith]

Says who? do you have a link?

I was going to ask the same question. As far as I know, this is not correct but would love to be proven wrong!!

 

[Bob Smith]

Yes and it only applies to solar PV installations. A battery or powerwall doesn't qualify. Solar Panels and battery does qualify. Madness for sure but I was luck enough to get zero VAT on my install

Yep, however, I suspect this is an opportunity for companies to increase their tariff.

 

[Bob Smith]

My 14kWh battery was sufficient to cook the Christmas dinner and supply the house for most of the day. Both inverters were running at times I had over 12 kW discharge into my system.

12kW to run the house... Well, that's my problem I do not know for sure what the required max power for my house is at a particular given time.
This winter we have hardly used our electrical underfloor heating (but this is a 3kW system!!!, so when it runs it runs and that for hours, so already 3kW taken...) so if I have it running, then the electric oven, I think these are the main two items that will run for a long period. When the washing machine is on it goes up to 2.5kW for maybe 20 minutes (depending on how hot the water must be). I have no idea about the dishwasher but I suspect the same.

So technically, this would mean that I need 3 (underfloor heating) + 3 (oven, does it take 3kW? ), + 2.5 (washer) = 8.5kW.
Of course, I could drain more but I can also stack things up in order not to use the dishwasher at the same time as the washing machine.

It is amazing how much power (not energy consumption) can be required at a time in a house...

I have never seen an installer discussing this at that level. Some asked about the kWh usage, but as you say @johnb2713 if your batteries can only deliver 5kW and you need 8kW then the 3kW will come from the grid even if you had enough kWh available in your batteries to run the show.

Now thinking aloud as I am currently targeting a charge/discharge of between 7 to 9kW. (This was evaluated based on what my PV will be able to give (not the kWp as I will have about 15.2kWp) ) I think I may get lucky that this will be largely sufficient based on the above even if I had not until now really considered this requirement (House Max Power requirement)

 

[Oldman22]

Says who? do you have a link?

https://www.which.co.uk/reviews/sol...nels/solar-panel-battery-storage-a2AfJ0s5tCyT

 

[johnb2713]

https://www.which.co.uk/reviews/sol...nels/solar-panel-battery-storage-a2AfJ0s5tCyT

Thanks Oldman22, I'll have a read.

 

[Bob Smith]

Don't want to be too critical but it is far to be complete.

What size solar storage battery do I need?​

The average home uses around 8kWh of electricity per day. The capacity of new lithium-ion batteries ranges from around 1kWh up to as much as 15kWh.

Ideally, you want a battery that will cover your evening and night-time electricity usage, ready to be charged up again when the sun comes up. You'll also need to bear in mind how much your solar panels can generate, as there's no point buying a battery that's bigger than they can fill.

With a battery that is well chosen for your home's energy use and your solar panels' output, you should find that you can have enough electricity to serve your evening needs for most of the year. You might find that you are still drawing on grid electricity for some of the longest winter nights.

You'll need to speak to a battery installer to discuss what will be the right size for your home.


They don't mention the possibility to use the grid to store energy, nor the maximum discharge, only talking about the kWh is not enough to decide.
They don't provide references to where they go their
"If you have a smart meter, your export payments will be based on actual export data. However, if you also have a home battery installed, your export payments will be estimated at 50% of what you generate. This is because your export meter cannot determine whether electricity exported from your battery was originally generated by your panels or taken from the grid."
from.
I personally don't believe it is true because I have never heard of it. However, once again, happy to be proven wrong.
There are people on the forum who probably are in this situation (exporting, having batteries and having a smart meter), who I hope can comment.

 

[johnb2713]

What size solar storage battery do I need?​

The average home uses around 8kWh of electricity per day. The capacity of new lithium-ion batteries ranges from around 1kWh up to as much as 15kWh.

No point in dealing averages, this exercise needs to be specific really.

Ideally, you want a battery that will cover your evening and night-time electricity usage, ready to be charged up again when the sun comes up. You'll also need to bear in mind how much your solar panels can generate, as there's no point buying a battery that's bigger than they can fill.

Oh yes there is, charge up off peak and use throughout the day.

With a battery that is well chosen for your home's energy use and your solar panels' output, you should find that you can have enough electricity to serve your evening needs for most of the year. You might find that you are still drawing on grid electricity for some of the longest winter nights.

Better to go bigger, charge from the grid, staying off the peak rate prices.

You'll need to speak to a battery installer to discuss what will be the right size for your home.

A quick analysis of energy use and times, you can easily work out what you need.

They don't mention the possibility to use the grid to store energy, nor the maximum discharge, only talking about the kWh is not enough to decide.

The inverter rating is critical to be able to stay off peak rate power and to be able to charge the batteries in the time window allowed. The capacity of the battery needs to match your demands or better.

They don't provide references to where they go their
"If you have a smart meter, your export payments will be based on actual export data. However, if you also have a home battery installed, your export payments will be estimated at 50% of what you generate. This is because your export meter cannot determine whether electricity exported from your battery was originally generated by your panels or taken from the grid."
from.
I personally don't believe it is true because I have never heard of it. However, once again, happy to be proven wrong.

I did have a read and yes, it is true.

There are people on the forum who probably are in this situation (exporting, having batteries and having a smart meter), who I hope can comment.

I have this setup and I get paid for what I export which I aim to keep low.

 

[Bob Smith]

No point in dealing averages, this exercise needs to be specific really.


Oh yes there is, charge up off peak and use throughout the day.


Better to go bigger, charge from the grid, staying off the peak rate prices.


A quick analysis of energy use and times, you can easily work out what you need.


The inverter rating is critical to be able to stay off peak rate power and to be able to charge the batteries in the time window allowed. The capacity of the battery needs to match your demands or better.


I did have a read and yes, it is true.


I have this setup and I get paid for what I export which I aim to keep low.

Hi John
I hope you realized what I wrote in italic was copied from Which website.

Regarding the statement that if you have home batteries installed your export payments will be estimated at 50%
You are saying it is true, yet you say you get paid for what you export. I don't get it.

 

[Oldman22]

Brains awash now with data.
I'm trying to collect data together to check what size battery store system I should aim for.

My Smart meter csv data dump tells me I used 2441kwh in 2021-22 & 2086kwh in 2022-23

49% of my daily usage is after 4pm with a surge around 5-7pm cooking, my unit cost is 35p

Daily gross consumption looks to be between 11kwh and 14kwh with the odd 21kwh (xmas day)

Solar generates around 15kwh up to 21kwh daily in sunny summer months with a lot being exported unused for peanuts.

I don't yet have an energy supplier who offers low rate overnight electricity to charge batteries but I guess there will be no problem changing to one who does offer this once I have a system that needs the low tariff.

So its looking to me like 10 to 14kwh battery pack and fast charge 5 or 6kw AC coupled inverter should with summer pv see me mostly grid free except for battery charging.

As to payback period I aim to spend no more than £5k. My current solar exports are worth £650/yr in battery charging mode. The grid use assuming my solar continues to perform is worth around £850/yr if I can use battery instead.
This works out at 3.3yrs to payback the cost of the kit assuming 5k max.

At the end of last summer I installed an 18k btu split aircon unit with heat pump, I've not had much chance to use it yet but that will tax my energy saving!

So am I on the right track so far?

 

[johnb2713]

Hi John
I hope you realized what I wrote in italic was copied from Which website.

Yes I did, Which really do get it wrong at times.

Regarding the statement that if you have home batteries installed your export payments will be estimated at 50%
You are saying it is true, yet you say you get paid for what you export. I don't get it.

The section refers to if you have export but no smart meter, you get a blanket payment of 50% of your Solar PV capability, if you have a smartmeter then you get paid for what you actually export.

 

[Oldman22]

Yes I did, Which really do get it wrong at times.


The section refers to if you have export but no smart meter, you get a blanket payment of 50% of your Solar PV capability, if you have a smartmeter then you get paid for what you actually export.

I'm going to have to disagree, my smart meter was installed well after my Solar install, I wasn't with the same provider for FIT payments and I'm still not so although I have a smart meter the FIT company does not have access to my export readings. I still get deemed 50%. I also recently enquired with my energy supplier re the latest mk2 if you like smart meters, they said if they installed one there is no obligation to inform any FIT provider that its been fitted. It would of course go on the national database so if a company wanted to find it, my current one is of course on that database but isnt read for export.