Newbie - please help me control a bigger Solar PV / heating system

Firstly - congratulations on a wonderful project and a what looks like a very helpful community. I’ve been searching for weeks (literally) to find what I need and this looks like i!. I’ve a lot of reading to do before I understand exactly what is possible. The monitoring part will probably be my first development and build but even before that, I need some help please with control. It’s a bit of a strange question so bear with me. Now to my problem …

I have 10kWp of solar PV and a 500L thermal store, primarily heated now by gas boiler, but there are also three x 3kW immersion heaters and I specified two sensor pockets for direct measurement just in case. I obviously want to use as much of the generated power as possible on the heaters without drawing power from the grid when the clouds com. Gas backup will remain the cheapest option for grey days and night time.

So far, so good, but even if I bought one of the off-the-shelf commercial units there’s nothing available in the UK to control multiple individual loads (at least from anyone willing to answer the phone to a technical question).

And then I found this:

It has six proportional or PWM outputs for SSRs plus two relay outputs, four temperature inputs, lots of other good stuff and will measure/control up to 100A of generated power. Sadly, I can’t get any technical advice from the Czech manufacturer and would be pretty much flying alone.

My problem is how to use it to power the three x 3kW heaters? More specifically, I’m not convinced that SSRs are the way to go and would prefer a triac circuit akin to that on the back end of the eMon.

Could I ask some kind soul to have a quick look at the website and the manual and tell me if I’m on the right track?

Many thanks,

Welcome to the OEM forum, Ian. And thank you for those kind words.

For what it’s worth, Some years ago I built a 3-immersion controller using the old emonTx V2 for a friend who ran a B&B. It was designed for only one triac to be on at any one time, but it shared the energy out between three tanks. It was never installed because his electricity supplier never changed the meter (so it unwound when he was exporting :grin: ). Then he became ill and retired. I still have the hardware.

The problem with the triac controlling in burst mode is flicker. If you’re on a strong supply, it’s less of a problem, but on a weak supply that’s shared with neighbours, it could give rise to complaints.

What exactly are your reservations about using SSRs? The switching element is almost certainly a triac, and we know that there have been fakes on the market - but provided you buy from a reputable supplier they should be fine.

The obvious first question for you: How good are you at programming? Because what I think you need will require bespoke software - for the logic of controlling the 3 heaters at least.

I’ll take a look at that manual later and come back when I’ve thought about it. I’ve quickly looked at the first page of the website and it certainly looks the part. But I suspect that you’re tied to exactly what the device can do, with little or no scope for customization. That’s where a system you’ve put together yourself scores.


I’ve looked at the manual.

On page 36, it gives details of the output modes. It appears that the SSR Mode does exactly what we call “Burst Mode” using an SSR as the power switch. That comes with warnings about flicker. There is also a PWM output, which is a truly proportional signal, that can be used to drive a “Phase Control” regulator. This is the sort that does not create flicker.

And there’s an API (Application Programming Interface) and reasonably comprehensive details are provided, so it looks as if, even if the device itself can’t control your three immersion heaters, there’s enough information that can be extracted so that another (computer / controller) device can do the calculations you need to control the immersion heaters. I haven’t checked every detail, but the temperatures and energy production & consumption values are available, and those are probably the main things you need. But one thing is certain - it will require a reasonable amount of programming knowledge to implement that logic; and knowledge of power electronics to implement the hardware.