Accurately measuring electricity usage

Hi, for quite a few years I’ve had a CT clip type electricity usage monitor (Current Cost ENVI from British Gas I think). However now I have has solar installed it seems to be at best not deducting the solar generation from the amount used or possibly even adding it on (looking at the spikes on the daily graph. The CT clip goes onto either one of the thick cables attached to the electricity meter. It doesn’t seem to make a difference which one I choose.

So is it possible to use my current equipment to accurately measure today’s grid usage, or do I need another piece of kit? I’ve got Solar Edge monitoring of the PV generation. I know I could read the meter every day, but I’d like to see the data in a graph of some kind. Ideally I’d like to see all of the data in one place - generation, self-consumed, exported and grid consumption.

Thanks!

Hi, for quite a few years I've had a CT clip type electricity usage monitor (Current Cost ENVI from British Gas I think). However now I have has solar installed it seems to be at best not deducting the solar generation from the amount used or possibly even adding it on (looking at the spikes on the daily graph. The CT clip goes onto either one of the thick cables attached to the electricity meter. It doesn't seem to make a difference which one I choose.

As you’ve discovered, a CT clamp on its own measures only current. It doesn’t know which direction energy is flowing. In order to measure True Power you need to also measure the voltage so that you can get the phase angle between the voltage and the current.

If your existing monitor doesn’t have ability to measure voltage then you’ll need a different bit of kit.

When you get a smart meter, it will do import and export accurately for you, but there’d be some work involved to get your solar generation figures in the same place.

Thanks.

There’s no way you’ll ever be able to track generation, self-consumed, exported and grid consumption with the standard gear or simple add-ons as you describe above. You can have your wiring rejigged and fitted with extra meters but it will cost you loads. Nerdishness has its cost!!! The best rule of thumb is one supplied by my son-in-law in France, where the installation of PV is wired differently to that in the UK: his system tells him he self-consumes very roughly one third of his generation and thus exports two-thirds. This self-consumption can be improved if you work from home and are punctilious about what appliances you use and when. Personally, I err on the side of caution and assume I use roughly 25% of what I generate. Doing so (and adding the savings to my accumulated FIT receipts and “deemed” export extra income) then helps me arrive at my break-even point - the point at which I will have paid off my PV system and am finally in profit.

There's no way you'll ever be able to track generation, self-consumed, exported and grid consumption with the standard gear or simple add-ons as you describe above.

I don’t see why not. A CT clamp on the incomer will tell you import/export. A second CT clamp on the output of the solar array will tell you total generation. Then some simple maths gives you the self-consumption.

The only issue is a typical consumer energy monitor can’t do it because it doesn’t measure the voltage, so it only ever approximates power use. Something like the OpenEnergyMonitor allows for voltage measurement and multiple CT clamps, and can do what the OP required inexpensively.

A smart meter will tell you import/export. The inverter on the solar array will typically tell you total generation.

The difference between the inverter figures and the export figures tells you how much of the energy you generated you used yourself.

A smart meter will tell you import/export. The inverter on the solar array will typically tell you total generation.

The difference between the inverter figures and the export figures tells you how much of the energy you generated you used yourself.

Exactly. I don’t know why willmow talks about having your “wiring rejigged and fitted with extra meters but it will cost you loads”. All you need is some simple inexpensive energy monitoring equipment, or your old meter replaced with a smart meter.

willmow writes with authority on this (here and in their other recent posts) but seems to be under a lot of misconceptions.