DIY batteries on grid connected system?

[Crofter]

Prompted by the discussion about using an old Leaf in V2G mode, I'm wondering if it's allowable to build a battery yourself for an on-grid installation.

 

A couple of years ago I put together a 3.3kwhr LiFePO4 battery for about £400. That was for a 12v system. A 48v system either be cheaper per kwhr because you'd only need one BMS for the 16 cells. Prices have fallen a bit since then too.

 

Compared to an old Leaf, this is brand new cells, more appropriate cell chemistry, and it's cheaper.

 

I accept that there may be insurance issues, but in principle are there other hurdles, e.g. do the DNO need to sign off on what you're connecting? Not that the grid would see the batteries directly, of course.

[Dillsue]

31 minutes ago, Crofter said:

 do the DNO need to sign off on what you're connecting? Not that the grid would see the batteries directly, of course.

Thay don't need to approve what you're connecting so long as it's G98 type tested and on the ENA database. Just notify them once it's connected. Anything else needs prior permission via G99

[Crofter]

13 hours ago, Dillsue said:

so long as it's G98 type tested and on the ENA database. 

Well I guess that's a no then.

A set of cells and a BMS are not going to be type tested or appear on a database.

[JohnMo]

Not sure the above really answers your question.

 

14 hours ago, Crofter said:

principle are there other hurdles, e.g. do the DNO need to sign off on what you're connecting?

You are not directly connecting the battery or BMS to the grid, you would be using an inverter also.  The bit the DNO is interested in really is the inverter and how that works with the grid. So that would need to be certified.

[Kelvasco]

JohnMo is correct, 

 

You only require a G98-type approved inverter. The best, if you're going 48V, would be something from Victron. They publish their certificates online and you can send them to the DNO for approvals. 

 

It is a little dependent on what other onsite renewables you have (solar, wind) and how you use them (thermal storage, ASHP etc). As you could also look at something like Sunsynk/Deye hybrid inverter with G98 compliance to bring solar in and manage the overall energy controls better. Seems one of the bigger challenges (like a few on here have found) is managing the energy in and out of the battery system at the right times, if your DIY'ing something then DC coupling (with Synsynk/Deye type equipment) seems to make that easier. 

[Carrerahill]

29 minutes ago, Crofter said:

Well I guess that's a no then.

A set of cells and a BMS are not going to be type tested or appear on a database.

Design it, build it, put it to use and don't worry about the DNO, just don't take the p***. Especially if you won't allow any export of your battery power. 

 

I have said it once and I will say it again, there is no DNO police. 

[Crofter]

Thanks, that makes sense.

For background, I currently live off grid on a boat, with 1.2kw of PV, 6.6kwhr of DIY lithium, and MPPT charge controllers.

I gather in a grid tied domestic system you don't need the MPPTs, the inverter handles that?

What voltage do household batteries generally work at?

[Dillsue]

4 hours ago, Carrerahill said:

Design it, build it, put it to use and don't worry about the DNO, just don't take the p***. Especially if you won't allow any export of your battery power. 

 

I have said it once and I will say it again, there is no DNO police. 

And if the home built untested/certified mish mash doesnt shutdown when the grid is down,what happens to the linesman trying to fix the fault down the road?

[Crofter]

23 minutes ago, Dillsue said:

And if the home built untested/certified mish mash doesnt shutdown when the grid is down,what happens to the linesman trying to fix the fault down the road?

That's a very good point!