Pros and Cons of DIY battery storage in the UK vs commercial offerings

[di_sjo]

This thread is specifically about the practical pros and cons of DIY battery banks in the UK versus the commercial offerings out there.

I've been debating energy storage solutions for a number of years. I am an electronics guy so building my own pack does not phase me, however I am unsure of what the benefits are of a commercial solutions, such as the Tesla Powerwall, pylontech etc. The cost per kwh is obviously significantly different.

For example, take the following two products for comparison:

Tesla Powerwall 3 - £7500 - 13.5 kWh - 55p/Wh

GivEnergy AIO 6.0 - £5500 - 13.5 kWh - 40p/Wh

Fogstar Energy 30kWh 48V Rack Battery Bundle - £5999 - 30 kWh - 20p/Wh (or 23p/Wh with hybrid inverter)

Seplos V4 kit (314Ah) - £1699 - 15kWh - 11p/Wh

Now of course this isn't an apples to apples comparison as the TPW has an inverter built-in. Even if I add a 10kw hybrid inverter in (~£1k) that only brings the Seplos cost up to 18p/Wh, still significantly cheaper than Tesla, and GivEnergy for example.

Now I appreciate the more expensive options are part of a complete eco system. They're big brands, with big warranties, and big backing. I get it, it's convenience, peace of mind, potentially more scalable and serviceable in 3, 5, 10 years time.

Maybe I need to look at it from the point of view of the downsides of DIY/cheaper solutions (I consider the Seplos kit as effectively DIY). What can't you do with this type of solution? How terrible is integration? How well are these EVE cells really holding up? The DIY forums seem to have some confusion around the right way to handle these cells, e.g. compression etc. I want peace of mine when I go to sleep, not keeping one ear open for a fire alarm.

If I think of it in terms of my own personal use case, I am looking for maybe 40-50 kWh of storage. I have two EVs which I charge mostly at night (with two Zappis), during the Octopus cheap rates. My base load is around 300-400W and i'm looking to potentially add an ASHP and/or air conditioning. I will want to automate this, perhaps with Home Assistant, to make the best use of the battery storage (import/export to earn revenue), whilst balancing the needs of my personal consumption. In this kind of scenario, should I be looking more towards a DIY solution with specific component choices, in the assumption that the big shiny commercial offerings are not as flexible as i'd like (yet)?

My assumption is that I am currently stuck between a rock and a hard place - I want ultimate flexibility, but also peace of mind (from a reliability, consistency and safety perspective). This is probably why i've not invested yet - but i'd appreciate opinions from you guys (please not just 'i made my own battery and its great').

 

[jgh]

Being able to control it is pretty much up to the inverter facilities. The battery is secondary.

WRT to sleeping with one ear open... I think UK regs are now requiring battery storage to be not within the house
(on new installs; mine's in the loft).

 

[kommando]

The new guidelines do not prohibit batteries being inside the house, what is not recommended is to have the battery located on an escape route or in habitable rooms. So an integral garage or utility room is ok as long as they are not on a planned escape route.

Full document

https://www.pluginsolar.co.uk/wp-content/uploads/2024/04/PAS_63100_2024.pdf

 

[DIYrich]

First consideration is what solar, if any, do you have. try to build a system compatible with your solar.

EVE (assuming that is what comes in the box) is a reputable brand. You want Grade A cells.

You also have to decide if you want Communications with the inverter, or if you will run in voltage mode. Voltage mode will work with any battery. Communications adds a little bit, since the charge curve for lifepo4 batteries is so flat. Consider the integration of the inverter and battery.

I would go with the Fogstar or Seplos. In either case, you don't have to worry about compression, since that is part of the design of each, and you can't change it.

Fogstar is off the shelf 5kWh rack batteries by a UK Company. Get a communicating inverter, and you are good to go. If you have any problems, you have local support. If a battery dies, it is easy to replace one (although a replacement in 5 years may not have compatible communications, but no big deal). If they offer a nice app, you may be able to see a lot of detail of the condition of each battery. As a UK Company, you can probably trust that it really contains Grade A EVE cells.

With a rack battery, if you go camping, you can pull a battery, attached 3kW inverter, and you have portable power.

Seplos is cheap, buying from China is a risk.. You will learn a lot in the build process. If a cell goes bad, it can be replaced. If you are going to build 45kWh of storage, you might want to source the cells yourself. For the 48 cells, you might be able to get 52 matching cells, and that would give you 4 spares to swap out. If you source the box separately, it would be easier to get a BMS that is compatible with whatever inverter you buy.

 

[jgh]

Thanks, kommando. I see a loft is not:

6.5.5 Batteries shall not be installed in any of the following locations:
g) voids, roof spaces or lofts;

 

[kommando]

Thanks, kommando. I see a loft is not:

6.5.5 Batteries shall not be installed in any of the following locations:
g) voids, roof spaces or lofts;

Or a basement, but how many houses in the UK have a basement. Mine is in an attached workshop at the furthest point away from the house with a 2ft wall in between house and workshop. Also has a fire alarm which as well as sounding off also sets the phone alert off and CCTV I can see away from the house.

 

[di_sjo]

Bump

 

[kommando]

Fogstar now do full DIY kits for not much over DIY money, their website is silent on warranty on these kits

SEPLOS V4 Kit and x16 EVE LF280K Grade A Bundle

The SEPLOS V4 DIY battery bundle with EVE LF280K Cells is a complete solution for building your own 48V solar battery system.

www.fogstar.co.uk

Whereas the made up ones can be 8 years.

Fogstar warrants the Fogstar Energy 48V 15.5kWh ("Product") to be free from defects in cells, BMS and workmanship for a period of eight (8) years from the date of purchase ("Warranty Period").

As my DIY builds are still early on I cannot offer any other advice.

 

[Neil H]

I have two seplos masons totaling 30kwh for nearly two years and not had any problem with them and will be adding I aslo set up the seplos facebook page a year ago

 

[mpeterson]

There is a middle way between DIY and home made. I am not being paid in any way, just a customer. If you search for Gobelpower you will find that they offer 280Ah 16s LFP packs for about the same price of DIY. However, you will need to open it when it arrives to check all internal connections. These come with pace 200A BMS. They ship to the UK and deal with customs for you. If you want to run the octopus intelligent Go A2A Heatpump thing you would need two of those, happy days. Warranty, well as I said, it's something between buy and DIY, as inverter, I highly recommend Victron MP2 5000 70, the DNO had no issues with connecting it grid parallel, and you can do the application yourself without issues because it has the necessary certification for the UK.

 

[di_sjo]

Being able to control it is pretty much up to the inverter facilities. The battery is secondary.

WRT to sleeping with one ear open... I think UK regs are now requiring battery storage to be not within the house
(on new installs; mine's in the loft).

Yeah, i'm somewhat nervous about having it in the house. I do have an attached garage which is reasonably isolated from the house but not 100% - the consumer unit is in the garage and all the wiring goes back into the house, via a link-connected space (downstairs bog/utility room). There is also a pathway around the rear/side of the house, with a small shed at the bottom - but that is basically 1200mm between the rear of the garage and next door's house exterior wall, and I am also uneasy about building out a battery store right next to someone elses property.

The new guidelines do not prohibit batteries being inside the house, what is not recommended is to have the battery located on an escape route or in habitable rooms. So an integral garage or utility room is ok as long as they are not on a planned escape route.

Full document

https://www.pluginsolar.co.uk/wp-content/uploads/2024/04/PAS_63100_2024.pdf

I'll take a read, thanks for sharing.

First consideration is what solar, if any, do you have. try to build a system compatible with your solar.

EVE (assuming that is what comes in the box) is a reputable brand. You want Grade A cells.

You also have to decide if you want Communications with the inverter, or if you will run in voltage mode. Voltage mode will work with any battery. Communications adds a little bit, since the charge curve for lifepo4 batteries is so flat. Consider the integration of the inverter and battery.

I would go with the Fogstar or Seplos. In either case, you don't have to worry about compression, since that is part of the design of each, and you can't change it.

Fogstar is off the shelf 5kWh rack batteries by a UK Company. Get a communicating inverter, and you are good to go. If you have any problems, you have local support. If a battery dies, it is easy to replace one (although a replacement in 5 years may not have compatible communications, but no big deal). If they offer a nice app, you may be able to see a lot of detail of the condition of each battery. As a UK Company, you can probably trust that it really contains Grade A EVE cells.

With a rack battery, if you go camping, you can pull a battery, attached 3kW inverter, and you have portable power.

Seplos is cheap, buying from China is a risk.. You will learn a lot in the build process. If a cell goes bad, it can be replaced. If you are going to build 45kWh of storage, you might want to source the cells yourself. For the 48 cells, you might be able to get 52 matching cells, and that would give you 4 spares to swap out. If you source the box separately, it would be easier to get a BMS that is compatible with whatever inverter you buy.

Thanks for replying, lots of point. I'll comment on each one:

Solar- No solar yet but on the to-do list, so spec is to be defined.

Comms - I'd prefer comms, i'm an IT guy, so like the data, and control. I'll also be building out a Home Assistant setup at some point.

Compression - This is an interesting point. Is there anything to say that Fogstar and/or Seplos has simply ignored it? Is it really a thing? Do other commercial/professional grade units consider this? I've not really seen any research or analysis on this yet. I've not looked too hard though. With watching plenty of if DIY'ers on youtube mess around with compression, I do wonder how scientified the approaches are.

Warranty - Yes Fogstar is a UK company but aren't they really just importing stuff from China and re-packaging it? None of it is designed or build, as such, in the UK.

Grade A cells - You mention this twice, I will research, but I am working to the assumption that the difference between grade A and B is more about capacity than reliability.

Or a basement, but how many houses in the UK have a basement. Mine is in an attached workshop at the furthest point away from the house with a 2ft wall in between house and workshop. Also has a fire alarm which as well as sounding off also sets the phone alert off and CCTV I can see away from the house.

Yes, no basement here, but a douple of outdoor'ish options as above. I'd prefer to not even need to consider CCTV to monitor batteries, and that doesn't feel like a 'fit and forget' type solution. How many people point a camera at their Tesla Powerwall for example?

I have two seplos masons totaling 30kwh for nearly two years and not had any problem with them and will be adding I aslo set up the seplos facebook page a year ago

Thanks for sharing.

There is a middle way between DIY and home made. I am not being paid in any way, just a customer. If you search for Gobelpower you will find that they offer 280Ah 16s LFP packs for about the same price of DIY. However, you will need to open it when it arrives to check all internal connections. These come with pace 200A BMS. They ship to the UK and deal with customs for you. If you want to run the octopus intelligent Go A2A Heatpump thing you would need two of those, happy days. Warranty, well as I said, it's something between buy and DIY, as inverter, I highly recommend Victron MP2 5000 70, the DNO had no issues with connecting it grid parallel, and you can do the application yourself without issues because it has the necessary certification for the UK.

Appreciate your insight. Typically I would be in this kind of space too, I would choose a spec that I considered meeting my requirements, and then I would procure and build out myself, or contract to someone to build exactly as per my spec, project-dependent. In this case though, with peace of mind probably my #1 priority... not sure the middle-ground is going to cut it. Hrm.

 

[kommando]

Yes Fogstar is a UK company but aren't they really just importing stuff from China and re-packaging it?

Yes, but you can take Fogstar to UK small claims court but not a Chinese company if the warranty is not met. They have to still be in business but that holds for any company.

 

[di_sjo]

Yes, but you can take Fogstar to UK small claims court but not a Chinese company if the warranty is not met. They have to still be in business but that holds for any company.

True. I wonder how Fogstar perform when it comes to problems?

 

[kommando]

I wonder how Fogstar perform when it comes to problems?

Can be tardy if busy but never seen a problem not sorted out yet. I buy the case elsewhere but all my cells have come from Fogstar.

 

[solarob]

I have two seplos masons totaling 30kwh for nearly two years and not had any problem with them and will be adding I aslo set up the seplos facebook page a year ago

Hi Neil,
I've just ordered 2 Seplos v4 MB31 kits from Fogstar as the Black Friday price is ridiculously low at about £87.50 per kwh.
Do you have a thread regarding your setup? I'm looking at a Sunsynk 8.8kw hybrid inverter for my system, what have you used? Any issues to report?
I will try to take a look at your seplos FB page soon!

*edited to add that I've asked to join the FB group. Hopefully it is the correct one!

 

[Lawrence_SoCal]

This thread is specifically about the practical pros and cons of DIY battery banks in the UK versus the commercial offerings out there.

I've been debating energy storage solutions for a number of years. I am an electronics guy so building my own pack does not phase me, however I am unsure of what the benefits are of a commercial solutions, such as the Tesla Powerwall, pylontech etc. The cost per kwh is obviously significantly different.

...snip..

My assumption is that I am currently stuck between a rock and a hard place - I want ultimate flexibility, but also peace of mind (from a reliability, consistency and safety perspective). This is probably why i've not invested yet - but i'd appreciate opinions from you guys (please not just 'i made my own battery and its great').

I'd state the issue differently.
As, LFP battery tech, from reputable vendors, is all largely similar now (wasn't a couple of years ago.. see Will's latest video

in regards to comments about build quality).
To me, the decision matrix starts with your automation/other requirements, and then your micro-interconnect device (MID) [ie, typically a hybrid inverter, but could be other... the device that is grid-forming and can disconnect house from power grid in an outage and allow batteries to power home]. From there, you are going to want a compatible battery. This will be a MUCH narrower list to pick from. NOT picking from said list should definitely impact your peace of mind. Not many, but if you look in this forum, you will come across rare stories of houses burning down... for me, spending a little more for a properly engineered, certified code-compliant system which will be in-house seems like cheap insurance (and avoids homeowners insurance from denying a claim, if that were to become necessary)

And then you have considerations like
- solar PV curtailment when grid down, house battery(s) ESS at/near full, and PV production greater than house load. Frequency shifting is a low-tech, crude, brute-force approach, that has, on occasion/certain circumstances, damage home electronic device(s). Integrated direct communication compatibility seems preferable, but tends to be limited ... fingers crossed this gets better with new Vehicle to Grid/Home standards
- do you want your setup to support

• Vehicle to X (V2G, V2H, V2x .. grid/home)?
• excess PV EVSE charging
• etc

all of which require some level of cross system communication . You could use HA, but you are introducing communication latency, and an extra point-of-failure or two (fine, as long as you plan accordingly).

When looking at it as above, the actual battery choice really isn't that big of a question, in my mind. really just a capacity desired and local code question. the real driver are overall system expectation/requirements, expected system longevity (vs early component replacement)

 

[Neil H]

Hi Neil,
I've just ordered 2 Seplos v4 MB31 kits from Fogstar as the Black Friday price is ridiculously low at about £87.50 per kwh.
Do you have a thread regarding your setup? I'm looking at a Sunsynk 8.8kw hybrid inverter for my system, what have you used? Any issues to report?
I will try to take a look at your seplos FB page soon!

*edited to add that I've asked to join the FB group. Hopefully it is the correct one!

What name have you registered with?

 

[SeaGal]

My assumption is that I am currently stuck between a rock and a hard place - I want ultimate flexibility, but also peace of mind (from a reliability, consistency and safety perspective). This is probably why i've not invested yet - but i'd appreciate opinions from you guys (please not just 'i made my own battery and its great').

For the reasons in bold, assuming you have the skills and knowledge, I would (as I did) DIY.

My battery pack has the added advantage of coming with an on-site, 24/7 support contact for not additional subscription fees. And unlike the companies you have named, I am cautiously optimistic that my installer will still be around in 15 to 20 years time. If she isn't, then a) I've documented everything I can and b) it's no longer my problem

I think UK regs are now requiring battery storage to be not within the house

Not regs, just recommendations for fire safety. Some good points in that document, but also a lot of questionable points too, IMHO.

The new guidelines do not prohibit batteries being inside the house, what is not recommended is to have the battery located on an escape route or in habitable rooms

 

[solarob]

What name have you registered with?

All good Neil, I was the Rob that joined yesterday. A very useful resource!

 

[wookey]

I highly recommend Victron MP2 5000 70, the DNO had no issues with connecting it grid parallel, and you can do the application yourself without issues because it has the necessary certification for the UK.

When did you do this? Before or after May 2023? And which DNO? After that G100 Issue 2 took effect, for which Victron haven't actually issued a compliance certificate for the MPII yet. It may be that DNO's are still accepting the Issue-1 certificate they did in practice? I ask because I have installed just this and am wondering if the DNO is going to quibble about Issue 1/2 certification or not. I'm also not sure if Victron have actually implemented the new back-off state-machine required for issue 2 in the MPII firmware or not. (It could be done with node-red on the GX if not).

 

[mpeterson]

When: March '24
DNO: SSEN
G98 application/notification
Certificate that I used is attached
They were very nice. Replied within a few days, it is notification only anyway.