PV with battery storage on 3 Phase

[tdansmith]

Hi, 

 

I am in the process of pricing up a PV install with battery storage. Due to space constraints, I suspect I will end up with 10-12 panels, and was therefore thinking a 3.6kw hybrid inverter would suffice and also get me below the G98 threshold. I would compliment this with battery storage - initially 15kW which would cover our current needs, but with potential for expansion if I install a heat pump. The battery would store energy from PV, but would also allow us to charge at cheaper night rates and discharge during the day when rates are higher. 

 

My situation is slightly complicated by the fact that we have a 3 phase supply. Currently we use only a single phase for our whole house, but in time we may reserve a second phase for the heat pump, and potentially an EV charger on another.
 

I understand the principal of net metering, and we have an Octopus smart meter that would accommodate this, so in theory we can place a single phase PV inverter (and battery storage) on any of the phases and this would be able to offset use on any of the three phases. However, I do not fully understand if single phase inverters / battery controllers are smart enough to monitor usage on all three phases and hence discharge an appropriate amount to offset the combined usage. As an example, if the inverter and battery are on phase 1, but I am using 5kW on phase 2, will the battery be aware of the usage on this different phase and discharge 5kW on phase 1 to offset this? I understand that the Tesla powerwall 3 may be able to perform this task, but is this true of any other systems? The Powerwall is quite an expensive solution (£/kWh), and I was initially looking to get something like a Fox or Givenergy as these are cheaper and seem to be very good. If I am limited to Tesla it might be cost effective to instead get a 3 phase inverter from Fox/Givenergy - which would surely be able to monitor use across all phases.

 

Hopefully this all makes sense, and apologies for my ignorance! This is all quite new to me, but I am keen to understand more. 

Edited December 3 by tdansmith

[Marvin]

Hi @tdansmith

 

Sorry if you know all this. Just some thoughts off your original posting..

 

The SSE, (Distribution Network Operator: DNO) valuated our system by the maximum the certified inverter would allow into the grid, not by how many panels we have (In fact the inverter allows about 25% more panels than that its limited wattage).

 

Think carefully about future requirements! its costly to upgrade.. for several reasons..

 

I'm not sure about the design of the system your considering but please check that the battery storage capacity in your design would not be included in your DNO's calculation of how much power could flow back to the grid. ( as I understand it it batteries need to be controlled by the inverter and the inverter is limited, not the inverter and then the batteries meaning that both lots could go back to the grid)

 

Not sure that you would not end up potentially crossing phases trying to supply from batteries more than one phase. Sounds like a high end inverter to do that....

 

Storing 15kW is only half the consideration. You also have to consider the maximum power level. Batteries have a limited percentage of their stored power that they can efficiently discharge. In my opinion low and slow is the order of the day....

 

Here's a tool to help you see what a 3.6kW system would do over the year. Start by zooming in to your home and then adding your proposed data. 

 

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

 

I would suggest you look at the potential supply month by month and your requirement month by month.

 

Good luck 

 

M

 

 

 

 

 

[SteamyTea]

2 hours ago, tdansmith said:

I would compliment this with battery storage - initially 15kW which would cover our current needs

 

1 hour ago, Marvin said:

Storing 15kW is only half the consideration.

 

1 hour ago, Marvin said:

check that the battery storage capacity in your design would not be included in your DNO's calculation of how much power could flow back to the grid

 

A fantastic example of why there is a difference between kW (power) and kWh (energy).

 

Would be highly unlikely that a 3.6 kW inverter could pump out 15 kW of power to the grid, even if the DNO approved it.

 

Apart from cost, and some minor charging issues, the size of the storage (kWh) makes little difference. Like putting a larger fuel tank in a car, it does not affect the engine power, or how fast you are allowed to drive.

 

As for the 3phase, this is a bit more technical.  Net metering is meant to get around this, but not sure how well it does it.

Ideally, a 3P system has balanced phases i.e. they all draw the same power at the same time. This is hard to do in practice as no one wants to turn on 3 lights, or 3 kettles, when you only need the use of one.

This is especially hard if you have neighbours that are still on single phase and may be drawing power as well.

I can see this becoming a bit of a problem as we transition to all electrics domestic heating, but engineers are clever people and will be testing systems already.

 

So what to do.

Can you run everything off a single phase, with some time shifting maybe i.e. car charging but not DHW heating (that takes more power, even via a HP than space heating).

 

Then when 3Phase is the normal, upgrade the PV and Inverter/Battery.

[tdansmith]

Thanks for your comments, and correction on kW vs kWh - I blame writing the post on a phone

 

You are of course correct that I am looking for a 15kWh battery and was originally looking to spec a 3.6kW inverter.

 

In terms of balancing a 3 phase demand - yes, in theory this would be ideal, but I’ll let them worry about that on the supply side. 
 

The main question I’m looking to answer is whether it is possible for an inverter and battery on a single phase to offset usage on all 3 phases - beyond the Powerwall 3, which apparently does this.

 

If the answer is no, I may well stick to using just a single phase, including the future ASHP and EV charger, but it does seem a wasted opportunity. 

[SteamyTea]

19 minutes ago, tdansmith said:

The main question I’m looking to answer is whether it is possible for an inverter and battery on a single phase to offset usage on all 3 phases

Ask you supplier, they should know about this, failing that, ask the DNO.

[Dillsue]

On 03/12/2024 at 18:58, tdansmith said:

The main question I’m looking to answer is whether it is possible for an inverter and battery on a single phase to offset usage on all 3 phases - beyond the Powerwall 3, which apparently does this.

From previous forum discussion I belive that export on one phase offsets import on the other 2 phases, but only if the export and import happen at the same time. If you export and import at different times both get logged by the meter but don't offset each other in the meters registers.

[Dan F]

On 03/12/2024 at 18:58, tdansmith said:

The main question I’m looking to answer is whether it is possible for an inverter and battery on a single phase to offset usage on all 3 phases - beyond the Powerwall 3, which apparently does this.

Victron does too, and I'm sure others do too, includig Sonnen. Just need to check datasheets .