Catharsis

We are heading for a cold snap this week, with a low of -15C forecast for Tuesday. What temperature does it make sense to turn up the thermostat so the oil-fired heat takes over from labouring heat pumps? Well, I'm glad you asked! I looked at our oil consumption for 5 years before we installed heat pumps. In the non-heating summer season, we used oil to heat just domestic hot water, to the tune of about 2.8 liters per day. We used a measurable amount of oil annually, so taking 2.8 * 365 from that total gives the annual oil consumption for heating only. The annual heating degree day total here is 3600, meaning that the daily outside temperature is, on average, 3600/365 (i.e. 10) degrees lower than our desired home interior temperature. My outside temperature sensor agrees, maybe a bit warmer. Oil is 10.7 KWh per liter, so (mutter, mutter) heating our house with oil consumes 4.48 KWh per heating degree day, or 186 watts per degree difference between inside and outside. I'm measur...

I've spent 'way too much time on it, but finally have data populating the Energy dashboard in Home Assistant. It's showing a decent story: This is mid-January, when sunset  is a mere 9.5 hours after sunrise, the sun is low in the sky, and we're using a bunch of electricity to run our heating system. Even so, when the clouds get out of the way, we're generating 30% of the electricity we're using. The heat pumps are consuming 75% of that generation.  When days get longer and it warms up, we should be generating a big surplus. Can I sell it to the neighbours? Spin up a giant flywheel in the backyard? Of course, this was a rare sunny day. The panels have been producing for a month now. Half   the production we've accumulated was on five days.