PV and another heat pump

Wednesday, December 13th, 2023 at 08:06pm

It has been two months since I started to think more about my energy usage and now my energy profile has completely changed. Two weeks ago the air conditioning units were installed, but I have not yet mentioned that yesterday I had solar panels installed and today they completed the install of a heat pump hot water system.

The shape of my roof is not the easiest for solar panels, but they managed to fit twelve panels facing north. The panels are each 370W while the microinverters are 295VA (see this video) which even on an overcast day should cover my typical usage. The system has been running for 24 hours now (technically I should now turn it off and wait for the inspection) and it has been interesting to watch how much they generate versus what the weather is doing.

I opted for microinverters from Enphase (the only option in Australia for microinverters) because I like the idea better than string inverters and the tipping point was that there is an integration included in Home Assistant. So while it is good to have the provided online interface, it was also nice to be able to easily add the solar system. Once added I had thirteen new devices. One for the Envoy which is the controller/gateway, and then each individual panel. The figures I will be interested in are the panel generation, my consumption and how much I feed back to the grid.

My first side quest was to figure out why my smart meter was now saying I was consuming an amount of power that was simply not possible:

Screen shot from Home Assistant showing House power consumption is reported to be 4,294,966,779W

As I worked my way through the source of this number I quickly spotted the problem. The number in the XML from the smart meter adapter is in hex and very large numbers start with lots of F. Thinking back to computer science subjects at uni I remembered that is likely a negative number if we are dealing with a signed integer. After some number conversion a demand value of 0xfffffc09 was now coming back as -1015 which is both sensible and aligned with what the Envoy said I was feeding back into the grid. As I had published the script for this to github, it was right to push a fix.

While there was still some daylight (and there was some generation from the panels) I then played around some more in Home Assistant, including enabling the energy dashboard, but that is going to be a longer term task.

As well as installing the solar system yesterday, the electricians also did their part of the install for the new heat pump hot water system. Ready for plumbers to come today to decomission the old hot water system in the roof (still working after 50+ years…) and hook up the new heat pump and storage tank. Its power usage would have been high today as it was heating up the entire tank but once things settle down I will try to record how much it needs day to day.

The piece missing from the hot water install is the wifi module, once they come back to install that I will have a new source of data. There is no out of the box integration as there was for the Envoy system, but I hope I can figure out a way to extract data.

However a much more immediate result is that I have now had the first shower in this house with mains pressure hot water, no more low pressure due to the gravity fed system…

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