Solar, Heatpump and Ev monitoring design

I’ve got an air source heat pump, Tesla and Nissan E NV200 electric vehicles. I’m looking to install Solar so want to get everything monitored so I can see what’s going on.

The Solar will be on the garage roof 20m (open air) from the house and the consumer unit for the EV is in a shed 10m from the house. The heat pump is on the main consumer unit. Everything is 240v single phase.

The solar will be 3.3 kw. The EV charging is 5kw. I’m not sure of the power consumption on the air source heat pump.

I’m new to all this, but I’m thinking of using two emonTx V3’s (one in the shed, and one in the garage) then a emonPi for the base station / heat pump monitor. Is this the most sensible solution?

I could feasibly monitor the EV at the main consumer unit too, but the feed out to the shed also powers the pond pump so that would skew the figures a bit.

There is only one line going out to the garage so monitoring that back at the house wouldn’t be very accurate hence the remote emonTX V3 (there are lights / compressor etc running off that line)

Any advice would be much appreciated! Sorry if my questions are a bit newbie

Don’t worry about that, Rick. Welcome to the OEM forum.

I think what you suggest will work - I’m wondering if you’ve thought about monitoring the house in any better detail?

What is WiFi coverage like from (say) the shed to the house? And how far is the shed from the garage? I’m wondering whether an emonTx in the shed is overkill - it has 4 channels and you’ll use maybe 2, when the house could have things you could usefully monitor separately - so is it an idea to swap the emonPi and the shed emonTx?

I’m assuming your incomer is in the house, and you need to measure that, then to get your general house consumption, you need a measure of everything going out and in on the shed feed and the garage feed. Measuring those at the distant end should be OK.

I’ll go with an emonTx in the garage. You have the PV infeed, and presumably general power there as well as lights and the compressor (that you might want to measure separately). Have you not got an EV charger there?

If you swap and have the emonPi in the shed, then you have two inputs there - one for the EV and one for everything else.

That leaves the house. One input for the main incomer, one for the heat pump, and two left over for future use.

If you have PV and you’re likely to export, you can disregard the possibility of using the optical pulses off your meter - a pound to a penny it won’t indicate exported energy.

Hi Robert,

Thanks replying, your solution should work as there is actually a WiFi repeater in the shed (so the Tesla can download updates) The shed is about 20m from the garage so hopefully the emonPi should be able to pick up both emonTx’s from there.

I’ve got an old fashioned analog meter in the house. I’m not sure if it has a ratchet to prevent it running backwards? In the longer term I’m planning on charging the cars when solar is at it’s peak - hoping to do this automatically but haven’t looked into it much yet.



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As far as I know. there was no hard and fast rule about ratchets. However, as soon as your PV is installed, you can expect the meter to be replaced, as your supplier may have a separate export tariff. That will be lower than the import tariff (as you’d expect) and they won’t want the meter to go backwards and effectively give you the same rate in both directions.

I wrote this only days ago - it happened in the days of FIT.

There’s been a lot here recently about automating the charging process, so there’s a lot of reading ahead for you.

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