Monday, January 18, 2016

Power Monitoring and Solar

I've been wanting to monitor our use of electricity as part of the smart house project. I actually got started last spring by installing a current meter, but I never got the software working.

When we got the solar panels installed, the electrician removed my current meter in the process of upgrading the circuit breaker panel.

Last weekend, I installed TWO current meters: one on the mains, to measure current coming into and out of the house, and one on the solar panel lines, to measure current generated by the solar panels.

As it turns out, the OpenHAB has been updated to easily add my model of current meter to the system, so it was pretty easy (this time) to see and log the data. Here's the first day:

I knew we were using about 900 kWh per month from our electric bill, but it's kinda shocking to see the instantaneous numbers. It's also pretty interesting to see how many cyclical loads we have, and what a mess the solar power looks like.

Those big spikes on both Mains legs must be the hot tub - there's nothing else on our breaker panel rated to take that much energy.

I'll be rotating some smart plugs with their own energy tracking through the house over the next couple weeks, trying to nail down exactly what those other cyclical loads are. Primary suspects are the fridge, chest freezer, furnace blower, and electric heater.

I also want to accurately measure how much electricity the house is using, which seems difficult with the erratic solar input. It turns out current sensors like mine can't distinguish which direction the power is flowing, so I need to figure out another method.

It seems to me that consumption = |mains - solar|, and that when (mains - solar) is negative (i.e. when solar is greater than mains), the value shown on the mains is pure surplus being sent to the grid. Is there anything wrong with that thought process?

EDIT: So here's a scenario where the above idea wouldn't work: If the house is consuming 300 watts total, and 200 comes from solar and 100 comes from the mains, the 100 from the mains is consumption, not production, even though solar > mains.

Frustrating. Seems like I'll have to find a way to talk to the electric meter to do this calculation reliably.

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