Hardware advice; what to order!

Hardware emonTx
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Thanks for the initiative.

I used to live in UK so I understand the way you heat water.
I now live in South Africa and we heat water with electricity in a insulated tank with cold water coming in and hot out 200/300 liter tanks and we call it a “Geyser” - huge amusement for the Americans though.

Ok: I have 5Kw PV panels and a two inverters and 3 geysers in our household.

The SMA inverter pushes it’s electricity production to the IN line of my DB box and surplus is pushed into the grid for which I do get credit. But half what I pay for that Kw.

I need to measure Kw flow on the grid line and also MUST know in which direction it goes. (Getting from grid or feeding into the grid).
I then want to get the temp of the water in all three geysers.
I also have to have CT sensors on the geyser lines.

Armed with this readings on one platform, I want to make a few calculations to trigger a relay to switch on the geyser, so I can USE as much of power generated in daytime to STORE energy in the form of hot water.

So:
3 Temperature readers
6 CT sensors (Rather accurate) (to also reading AC / stove etc usage)
All readings dumped into a database so a program can read and make decisions.
emonCMS to show production, usage info on a PC screen reading emonCMS webserver on the Pi and to push to PVOUTPUT.ORG

What hardware do I need to order from you?
What would I still need (except the relays)

Anybody that would be willing to help with this project

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This sounds to me very much like a custom design is required, based on Robin Emley’s diverter. He might be able to supply you with a kit of parts - see http://mk2pvrouter.co.uk

I’m assuming that it’s all on a single phase?
So you have 2-off 5 kW panels, each feeding into a SMA inverter, those feed into a ‘pool’ from which you draw power for general household use and, in a controlled fashion, power for heating 3-off geysers. Any deficit or surplus is supplied/absorbed by the grid.

I designed a 3-way diverter, based on the emonTx V2 (which had readily accessible digital outputs) and MartinR’s PLL software for a friend who ran a Bed & Breakfast business (and he had 3 hot water tanks but only one inverter), but it was never installed because he had a meter that unwound when he was back-feeding the grid, so in effect he got both the feed-in tariff and sold the electricity back at the buying-in price! And now he’s closed the business and moved house.

Using present OEM “shop” ready-built components, it will be difficult to provide the outputs required to control the 3 relays to switch the water heaters. The emonTx V2 pcb is still available, but you’d need to source the remainder of the components, assemble that and construct triac drivers (or purchase solid-state relays) to do the power switching.

I think that is the route that I would go, use the old emonTx V2 to control the water heating and report the grid power only, and then add an emonTx V3 and an emonPi to monitor the temperatures (3 is no problem), the geyser and inverter powers (3 + 2). The emonPi will collect and record the data, and you should be able to send whatever you need onwards to wherever.

I don’t think the MQTT Relay will be fit for even burst-mode control as it contains a mechanical relay, but if you can guarantee that it would switch only a couple of times each day, it might be suitable.

Robin’s diverter doesn’t work that way. All the calculations are done inside the emonTx on a cycle-by-cycle basis, so it reacts almost instantly to, as far as possible, keep the nett grid power balanced at zero by varying the power drawn by the geysers.

There’s some food for thought for you. Come back and I can put together a parts list, based on what you decide.

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@Robert.Wall,
Thank you very much for your detailed comments.
You have summarized it perfectly.

I am not a electronic / electric engineer, just a very nosy hobbyist with ideas that I am convinced that should work.
I will need some time now to read/digest/research and then I will be able to ask informed questions or make appropriate decisions or comments.

some of the information makes perfect sense, some I have to get my head around :thinking:

Thanks again for your info.

Frits

4

I’m not surprised - I’ve been doing it for 50 years and I still have problems, the main one being the goalposts are continually moving. :persevere: