New or existing hardware project : PV hybrid inverter design?


Since I am bowled over by the level of work done on this forum, I’m wondering if anyone has come across a similar open source community that is working on PV inverter design, specifically hybrid inverters (that can integrate battery storage).
You’ve already nailed the monitoring and BMS side of things so it strikes me that some of you would lash off an inverter design before your morning tea break.

Best regards /Colm

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Hi Colm,

I’m in the US, so can only speak WRT the rules and regs we have here.
That said, it appears the EU has similar requirements.


In the US, it’s mandatory for a grid-tied PV system to cease energy production when it loses power from the mains to prevent back-feeding the grid. (referred to as anti islanding)

On top of that, there are at least two specifications (IEEE-1547 and UL-1741) a device must meet before it’s legal to connect the device to the grid.


I’m not aware of any such restrictions in the US, on an inverter that’s NOT tied to the grid.

To the best of my knowledge, that’s very close to the situation in the UK. I would expect the position in the EU to be similar.

Hello Robert & Bill,

Absolutely it would need to respect all EU legislation, all broadly similar to UK and US I think.
So, yes, it is more complex than monitoring or BMS equipment.
But the idea of an open-source design that meets all requirements and could be manufactured in a distributed manner ticks alot of boxes for me in terms of resilience, re-localisation, de-centralisation and a few more things.

Best regards / Colm

Getting UL certification can cost 5,000 to 50,000 USD, so I’d guess that’s one of the major
“stumbling blocks” keeping open source development from happening.


Much the same (though I don’t know the cost) for the UKCA and the CE marks.

The only saving grace is a CE mark wasn’t required (and the UKCA requirements are “largely the same as” the CE mark) if you built everything from a kit and it was for your own personal use (not even if you made it for a friend). That’s why Robin can sell kits of his Mk2 PV Router, but not sell the assembled unit (“fully manufactured goods”). (Even though his customers standard of construction could end up being far inferior and significantly less safe than his. There’s got to be logic in there somewhere, though I can’t see it.)

So without reading up on the marks and the requirements, it looks as if somebody could publish a design, they or somebody else could buy in all the parts and put them up as kits and sell the kit, for the end user to assemble.

I remember Robin making a comment about that quite some time ago.

I don’t know for certain, but I don’t think that’d fly over here.
Then there’s the other spec - IEEE 1547. Not sure how they would view a kit, but again, I suspect
it wouldn’t pass muster with them, either.

Good thing you didn’t include the term(s) “Grid Tied” in your description or else everyone would be thinking you were talking about a system connected to a utility grid and all the hassles which go with that.

I’m not sure there’s lots of advantages to a combined PV, Battery, Inverter, Charger setup when there are so many options using discrete components. Basically, use the PV to charge the batteries and run the inverter from the batteries. What to do with excess charge is another thing but heating water can help with the hotwater needs of the home.

Odd that you say that as a hybrid inverter is a grid-tied inverter.

A Hybrid inverter is an intelligent inverter that enables the storage of excess solar energy in a battery system for self-use. Hybrid inverters function like a common grid-tie solar inverter but can generally operate in one of several different modes depending on the application, this includes battery backup mode which provides a limited level of backup power in the event of a blackout. Most hybrid inverters can also operate without a battery and function just like a grid-tie solar inverter by exporting excess solar energy to the utility grid.


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Well I’ll be a monkey’s uncle… when I say “hybrid” instead of “Hybrid” I did not associate the terminology with a specific type of inverter. I hadn’t known that the inverters like the Victron which were Hybrid Inverters.

In that case, anything tied to the wires of those special government appointed electrical operators is going to be a PIA to get approved for operation. Making something which operates AFTER the Transfer Switch is thrown a bit less problematic.

Thanks for posting the link to school me on “Hybrid Inverter”.

I’m not following you there. Were you thinking it was a model designation?

Exactly. Hence my comments in post #2 of this thread.