It's been a while since I last posted (...life etc!) but now is a time to look at some statistics for the first 12 months of the retrofit system.

As shown in the plots below, there's been a lot of activity. In the first 12 months (taken as April 2022 - March 2023) close to 6500 kWh of electricity were used by the house. Of that, a heft chunk came directly from the solar panels (2662 kWh) with a similar chunk coming from the battery (2183 kWh). Remember that the battery is filled both from the solar panels and also from the grid, so there's a bit of a mix in there. Direct import of electricity from the grid to power the house (hot water, cooking, heating, car and appliances) was 1654 kWh. As can be seen by the monthly breakdown, it is obvious that the majority of the imported electricity occurred in December (followed by January and February). That's the heat pump. More specifically, that's the heat pump with two cold snaps in December and January. More specifically still, that's before the heat pump was serviced and optimised (see post 11). 

The details for generation by the solar panels (below) are also interesting for the year. They totalled 7533 kWh for the year, and maxed out in June, July and August. In fact, it's likely that August was a bit too hot last year for them to run efficiently as the total monthly generation is down slightly on the previous two months. Or it could have been a bit cloudier - I don't have that information. It's also worth noting that December was really miserable - cloud and fog almost every day due to a winter anticyclone. This poor generation coincided with peak demand, which is not great.

Grid import (below) was brilliantly low from April to October) The combination of the draw from the heat pump and the low generation in the winter months is really obvious. Where possible we try to fill the battery on a cheaper tariff and then use that to power the heat pump, but that still wasn't lasting long. Hopefully next winter will be sunnier and warmer.

Lots of exporting to the grid too (below). At least in the summer months. If only we could get a better export price then we could likely offset our winter import costs. As it is, we have to go with the pittance on offer through the smart export guarantee.

And finally, battery usage (below). We maxed the usage in the winter months, as already explained. During summer, the battery rarely empties and is used to run the house from just before dusk to just after dawn. We are pretty much self-sufficient in the sunnier months if all the tech is working correctly.

For a bit of comparison, here is a chart for November 2022 - June 2023. We were importing right through to March but the first three months of sunnier weather (April - June) are looking good with the house being powered mainly by the battery and solar.

I thought that as I have the data I'd have a quick look at the amount of electricity that was taken from the grid and went into the hot water. The plots show this for each month in 20222 and 2023. Remember that the first year of useful and trustworthy data is from April 2022 to March 2023. The reason for the near zero values between April and October is because the solar diverter used excess solar generated electricity to heat the water tank - the only imported electricity is for the cleaning routines that occur at night (and often that comes from the battery).

Overall, not too bad. Again, a sunny winter would be even better. We haven't tried heating water via the heat pump which is an option, so that might be something to experiment with - I just think that will end up using more grid electric and costing more.

The following screenshots are from Hugo (see post 12) and show the cost breakdown for 2022 and 2023. The numbers are based on smart meter information linked to the rates we pay for imported electricity. This is only imported costs, not normalised for export payments. As is obvious, December came as a bit of a shock. The heat pump was running very hard at this time and similarly in January. I recognise that the costs are not huge compared to what some were having to pay at this time, but the change between October and December created a lot of concern as to whether the heat pump was the right choice. It probably is, but this coming winter will help inform that further.

All in all we are very happy with the solar panels, battery, car charger and hot water cylinder. I'm still a bit unsure about the running costs of the heat pump: and the fact that it's turned off for most of the year. This seems an expensive outlay but I guess we are helping discover the experience of installing and owning such kit and hopefully it'll be less expensive to run as the winters continue to get shorter and warmer (yay, climate change!).