Adding batteries to solar PV

[John_S]

I have been considering adding batteries to my solar PV, especially now that prices are trending downwards. I have a FIT eligible 2.1kW system installed in 2010. My original SMA 2500 inverter is still going strong. Presently I divert excess solar PV to my HWC. I am on the Intelligent Octopus tariff and use about 6kWhs peak rate per day. I have applied for an export MPAN and then will switch to metered export as I can heat my hot water at 7.5p instead of from foregone export at 15p.

My choices appears to be to get a new hybrid inverter to cover both the batteries and the PV or to get a stand alone battery charger/inverter.

Hybrid
Pros
Likely to need a new solar inverter sometime, so get a hybrid one now.
Possibly simpler with the DNO as I just notify them of a like for like replacement.
Cons
My inverter is in the attic and I would prefer to install the batteries on the ground floor. Thus long DC cables needed. Alternatively, install batteries in the attic but then a new AC cable would be needed. either way, installing the cable would be disruptive and would require some redecoration.
Would probably need a 3kW hybrid inverter and not sure about loss of efficiency with 2.1kW PV

Standalone
Pros
Easier installation. Two separate systems ensure resilience.
Cons
Extra cost if a new solar inverter is needed
More DNO approval required. Export limitation to take into account solar.

I am thinking in terms of a Solis 3.0kW RAI inverter charger and two Pylontech US5000 batteries from Bimble Solar as I can collect from Lewes.

I appreciate that there will be times when I shall still need to draw peak rate from the grid. Also, that the economics of this might be marginal especially if vehicle to grid becomes a reality and is compatible with my existing charger.

Any comments, suggestions, pitfalls to avoid etc.

John

[Lincs Robert]

Don’t forget that with either hybrid or AC coupled solutions that you will also have to run a CT sensing cable so that either inverter can monitor the house for import/export so that it can do its thing. The length of this cable isn’t an issue as it can be done with Cat5/6 data cable extending the cable supplied with the inverter which will probably only be about 5m or so long. An option for both an extended AC cable and data would be to go external to the property to avoid/minimise the redecoration you mention. I’d avoid long DC cable runs as it’s simply bad practice and you would also have to extend the BMS/CAN cable from the master battery to the inverter. Long DC cables will also be much more expensive than the comparable AC cable which would be a 4 or 6mm cable, even if you have to go down the armoured route.

A number of us have batteries installed in roof spaces.

Hope these comments help.

Rob

[nowty]

Hybrid Con - If the new inverter has capability of battery grid charging, then its ineligible for FITs unless you go down the road of agreeing with FIT provider and replacing your FIT generation meter with a Bi-Directional Generation meter. Even if you find a DC (only) coupled one, fitting batts to FIT inverter your going to lose a little FIT income due to DC power loss round trip.

Second inverter is easier, G99 FastTrack approval is little more than a tick box exercise. It will also give you more combined AC power when the solar is generating. You will also be able to add more solar to the second inverter with no FIT issues and get more export income.

[Moxi]

Hi John,

I would just say that the Solis inverter doesn't have the best control interface for dealing with charging and discharging off peak power from the grid, there are some threads about this on the forum. It is also reported that it has a limited daily capacity to change settings before it locks up.

I don't use mine to charge from the grid, instead I charge 14kWh of pylons from any available insolation and this works form me around 10 months of the year with notable contribution to house loads and completely off grid import for 8 to 9 months of the year. In this respect the Solis is a great piece of kit that just works silently in the background.

As reference the house is a small 3 bed stone cottage in North West Wales, 2 adults 3 kids, background load is 450W.

Moxi

[John_S]

Thanks.

Are there any alternatives to the Solis?

As far as I can see, the Sofar ME3000SP is only available as a used unit and I cannot find anyone selling the Luxpower 3600.

I am not worried about the the Solis having a basic interface. Once it is all set up and working, I won't be wanting to tweak it constantly, except for eventually exporting when I get paid a couple of quid per kWh.

[openspaceman]

I am not worried about the the Solis having a basic interface. Once it is all set up and working, I won't be wanting to tweak it constantly, except for eventually exporting when I get paid a couple of quid per kWh.

The issue with the solis standard interface is that you can only set the amperage at which you charge the battery off peak rather than charge flat out and stop at a chosen SOC, Ideally one would vary the SOC to allow enough to carry one through th next day and allow some room for solar PV input.

[John_S]

The new Octopus export tariff totally changes the thinking. I don’t want to charge from solar. I want to export excess solar and earn 15p per kWh. I am happy to charge at 7.5p per kWh with Intelligent Octopus.

These new tariffs totally change conventional thinking.

John

[nowty]

The new Octopus export tariff totally changes the thinking. I don’t want to charge from solar. I want to export excess solar and earn 15p per kWh. I am happy to charge at 7.5p per kWh with Intelligent Octopus.

These new tariffs totally change conventional thinking.

John

Exactly, I'll probably be charging the EV and heating water all summer on the IOG tariff and setting to constantly export out of cheapslot times day and night. I'll have to turn the battery charge rate down for the solar too, in order for more overspill into the grid during the day.

Its turned everything I've been doing towards self use on its head.

[Moxi]

In that case John the Solis is probably good option for your application, as I say it’s proven reliable with me but it doesn’t lend itself to tariff following logic unless, like some here, you link it to alternative interfaces and then there can still potential issues.

Moxi

[robl]

We’ve got 4kWp of FIT PV, and recently got a completely independent hybrid inverter and battery. We got a sunsynk 3.6kW Ecco, and a 15kWh eve280L system from fogstar - it’s a very good value kit - you need to be quite careful assembling it, if in doubt get assistance. It can charge to a given SOC from the grid in the Octopus Go time, and it can make use of any excess PV from the original fit system. The rest of the time it’s setup to null the grid connection, to minimise any grid power taken or given outside of the go time. It can operate as an ups - we didn’t bother with that, i think that’s for South Africa and California, where the grid is a bit dodgy - ours is great. We converted our fit deemed generation to Seg export ages ago, financially dubious, but honest. Note this is a one way process I believe.
The worst I’ve noticed is that the sunsynk setup is a bit cryptic - other than that I’m very happy with it