Open Source Microinverter: Epilogue?

I discovered these blog postings by Ken Boak about a project for an open source microinverter that he collaborated with Trystan Lea.

Sustainable Suburbia: Micro Solar - The Future is Bright (Saturday, Oct. 3, 2015)
Part 1: Sustainable Suburbia: A Micro Solar Inverter - based on Arduino - Part 1 (Oct. 3, 2015)
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Part 2: Sustainable Suburbia: An Open Source, Micro Solar Inverter - based on Arduino - Part 2 (Oct. 3, 2015)
Part 3: Sustainable Suburbia: OpenInverter - An Open Source, Micro-Solar Inverter - Part 3 (Monday, Oct 4, 2015)
Part 4: Sustainable Suburbia: Open Inverter Part 4 - Getting the Draft Design into eagleCAD. (Tuesday, Oct. 5, 2915)
Part 5: Sustainable Suburbia: Open Inverter - Part 5, More Experimentation (Oct. 6, 2015)
Part 6: Sustainable Suburbia: Open Inverter - Part 6 - Thinking Allowed (Oct. 6, 2015)
Part 7: Sustainable Suburbia: Open Inverter - Part 7 - In search of Sine Waves (Sunday, November 8, 2015)
Part 8: Sustainable Suburbia: Open Inverter Part 8 - a General Purpose ATmega1284 Microcontroller Board (Thursday, Jan 21, 2016)
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I’m wondering what happened – lack of interest, a substantial technological roadblock, possible intellectual property roadblocks? Funding? Employer directive to stop? I could not find anything further on the topic.

Give it another go, John. I’ve bumped your user account level up a notch.

Hello @JohnPoole

It was a fun side project that Ken Boak and I (mostly Ken!) worked on one summer. I think at the time I thought I might put more energy into the idea and develop it into something to take forward at OpenEnergyMonitor but I think both of us ran out of time, Ken with a new job and myself with just core work here at OpenEnergyMonitor. Probably also biting off more than we could chew!

Your very welcome to take from it what ever you find useful and Im sure Ken would be happy to chat more about it if you had any questions.

I was trying to reach Ken Boak and ended up posting a comment on his About page in Wordpress, whether that will reach his attention or not remains to be seen. Do you know of a good way to reach him other than through Twitter or Facebook which require you to have an account to reach someone?
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@TrystanLea Thank you for the reply and information. I’m hoping I’ll reach Ken Boak.
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Hello @JohnPoole I will send you his email in a PM

Thank you. You’re welcome to send him an email providing my email address (which you have access to as a moderator?) and perhaps linking back to this thread; that might reduce the risk of my outreach ending up in his spam folder.

In the US, one of the things a grid-tied inverter must do is shut down within a prescribed
time limit (IIRC, it’s 200 mS) when the grid goes down.

That’s to prevent what’s referred to as islanding. i.e. continuing to backfeed the grid.

I’d guess that if nothing else, the anti-islanding issue is a show-stopper for this project.

If the inverter is not grid-tied, then none of these issues apply.

More info about anti-islanding here:

Would monitoring the other side for current be something easily done? I thought the technology was to determine what the phase is for the grid side and then match the phase. Ah… but once you match the phase and tie into the grid, then you have the task of continually determining if the grid is active and having to isolate your contribution. Interesting issue, maybe that’s is what is addressed in the patents?

Hello all,

I’m highly interested in such an open source microinverter ! ( Europe : 230V / 50 Hz)
As an electronics teacher in electronics (professional bachelor level), I might propose such a subject for a student’s work.
The level they are reaching allows us to propose CAD work, PCB assembling, firmware programming if not too sharp, and prototype testing!
But we’ll need support for schematic design and firmware evolution.

If anyone interested, do not hesitate to contact me!

That’s part of it.

Anti-islanding protects the folks working on the high voltage lines.

If you backfeed a transformer that normaly steps down 2400/7200/12470 to 240 Volts, it will
put that 2400/7200/12470 on the line its primary side is tied to. A lineman performing a repair
isn’t likely aware the line is live. (although proper training says treat ALL lines as live)

@Bill.Thomson Do you know if the Enphase IQ microconverters handler the anti-islanding sensing and regulation, or is that handled by another Enphase component downstream? I believe the IQ microvonverters can be signaled to go offline, but I imagined a controller downstream was managing and monitoring the grid status. It seems to me the monitoring of grid status and preventing backfeed when the grid is down ought to be a mature technology since before microconverters, you had converters for a series of panels that would feed into the grid. We installed a Sun Power system in 2013 and I remember that back-feed safety issue. I there there may be two issues: 1) backfeed, and 2) emergency stop (for firefighters). The emergency stop is something that was recently introduced in the last couple of years and I’m not sure all states in the United States have implemented that requirement into their code.

What I’m seeing with Enphase is you can have option A) generate with microconverters and they only work if connected to an active grid, B) if you want to have the ability to draw on the microconverters when the grid is down, you have to pay approximately $3,000 to isolate your “island”.

ALL of the inverters Enphase makes, and AFAIK, all they’ve ever made have anti-islanding
capability. So the answer to your question about the IQ8 and anti-islanding, is yes.

The IQ8 is a special animal compared to the rest of the Enphase product line.
It can be throttled, and it can support a micro grid.

More info about the IQ8 here:

The Sunpower system you desribed sounds like it’s a string inverter system.
i.e. one inverter fed by one or more series-connected “strings.” The downside to that scenario
as far as firefighters are concerned, is the high voltage DC produced by the PV modules regardless
of the state the grid is in. That DC voltage can range from 300 to 1000 volts, so I can understand
why they’d be concerned about it. WRT a string inverter system, an emergency stop should disconnect the DC side of the inverter as well as the AC side.

Given the requirement is part of the National Electrical Code, I’d say it’s a safe bet to say all 50
states have that requirement in place. Although it’s true the NEC isn’t law, AIUI, the vast majority
of AHJs (Authority Having Jurisdiction) follow the NEC. (The AHJ is the lowest level that has control
over the grid at the local level. It might be a city or town, an eletrical co-op, a corporate concern
or other entity)

Because of the anti-islanding requirement, all of the the microinverter manufacturers that sell in the
US market legally, produce products that have anti-islanding/rapid-shutdown capability.

The El Cheapo micros from China have historically NOT had anti-islanding capability.
However, it seems that the latest offerings from China do. Whether or not it actually works,
I cannot say.

That sounds like the Ephase Ensemble.
I’ve never looked at it, so I don’t know a great deal about it. But I can definitely believe the 3k-buck
price tag. I wouldn’t be a bit surprised if it was more that that.

Point of clarification for anyone reading this thread and NEC and law. The National Electric Code (reg. trademark by National Fire Protective Association (“NFPA”)) (“NEC”) is a model code, each state decides which version and to what extent it may adopt a model code. Just need to be clear that the NEC, but itself, do not have the force of law, it is a template for states to adopt and I’m guessing most do without much alteration, though it appears various version are currently in force in various states. I think the island safety standard is also known as Rule 21, however, I have to give up my privacy to the NFPA for “free” access to the code – not something I choose to do because I abhor organizations that set standards and then try to encourage governments to adopt the standards so they have force of law, but you have to purchase their editions. (It used to be that in order to know what the code was, you had to purchase the code from the organization, but that recently changed in California.) See Updated 2020 NEC Code Regulations by State |

Which is exactly what I was referring to when I said

It isn’t just the state that has a say in electrical energy supply matters.
Hence my mention of the Authority Having Jurisdiction (AHJ)

A state may have no law on their books prohibiting something, but an AHJ could have rules/regs
tighter than those of the state, effectively prohibiting that same “something” the state allows.

For anyone outside the USA reading this, do be aware of your local regulations.

In the UK, the “IEE Regs”, otherwise British Standard 7671 is invoked by Part 5 of Building Regulations, and those are law.

Anti-islanding is a requirement before you can legally connect any private generation to the grid.

On Friday, Jun 24, 3:32 PM PDT, I sent an email to Ken Boak. @TrystanLea had kindly provided me Ken’s email. I have not heard back, as yet.

Here is a quote ($18,400) from a company based in California selling Enphase products. I presume they have the necessary credentials to allow a customer’s self-built system to become activated assuming your purchase the “kit” and pay for the extra services. I had specified: 1) must not have batteries, 2) must work when grid is down (the predicted aftermath of Cascadia), must be something I can repair if damaged (by earthquake) and maintain.

This proposal looked tempting at first encounter, but the more I considered the design and started looking into the components, the more I became concerned about black box technology. I’ve witnessed how exploiters of some LoRa patents have positioned themselves in the market place to sell reasonably priced sensors using LoRa technology, but in order for sensors to work, you have to go through their cloud service. Looks like Enphase is doing the same thing – positioning itself between the mechanical part and in effect “renting” you the right to access and use your components as designed. John Deere tractors… ho ho, Russia commandeered some John Deere equipment in Ukraine and now they cannot operate it because John Deere manufactured the equipment to tie into their cloud.

So back to this topic: open source microconverter, it looks like if it could be approved for use with a grid, there are substantial hurdles to be overcome if you are to integrate such a home-built microconverter into an established electrical grid. It’s becoming tempting to just skip the goal of grid tie-in because of the barriers to entry.

I still would be interested in hearing from Ken in case there were some technical challenges he felt were insurmountable.

This has been a very engaging discussion. I’m reflecting on this and thinking: there needs to be an open source generic device that 1) assures synchronization to the specifications of the grid it attaches to and 2) acts as the shutoff to a grid.

What feeds into such a device, solar, wind, whatever, doesn’t matter and can be left to another component. Assume @TrystanLea and Ken’s project that caught me eye were working as desired, they still would have the barrier of legitimately interfacing into a grid. Other projects such as wind power generation face the same issue, once they’ve created DC, how can they export that into AC in a fashion that is compatible with the grid specifications and safety requirements. It would not be in a for-profit entity’s best interest to make a generic tie-in device, better to bury such design into the product in such as way that they only function with their product; this way they have a closed market with no competitors.

It’s worth noting that the discussed design above was only ever a very early stage design, grid synchronisation was only ever discussed as a wish list item in one of Ken’s blog posts and not something implemented in the design. The first goal would have been to complete a version that would have worked in an off grid context.

Talking of anti-islanding though, here’s a hackaday grid tie inverter project that specifically discusses this with an extended discussion in the comment section about safety Build Your Own Grid Tie Inverter | Hackaday

It’s probably worth looking around for other inverter projects as well as there may be some more mature projects around by now?

Care as ever is going to be really important with any mains voltage inverter design given the potentially lethal voltages involved and ultimately a good understanding of the relevant regulations involved.

It’s great that you are interested in this @JohnPoole and don’t wish to discourage you, but I would emphasise that our work in the above project was very much an early stage design and a long way from anything that ready for general use I would have thought? There’s a ton of knowledge, research, experience and as many are discussing here regulation compliance! built into commercially available inverters.

If your interested in potentially lower cost DIY solar systems using off the shelf commercial components this website from a UK supplier may have some inspiration there’s probably a US company doing similar?

There are quite a few open source solar related projects e.g: