Tuesday, May 1, 2012

Solar year 4 ends

Phew, we made it! Every year we aim to produce more power with our PV system than we use at home. Normally we achieve this some time in February, 3 months before the end of our 'solar year'. This year we only made it with 1 week to go, having produced 13 kW more than we consumed (see chart below). The lines starting at the top are the running average of  power generated by our 1.1 kW Kaneka thin film system. The lines starting at the bottom are the averages of power used and the point where the two lines meet is where we break even.

Our other target is to reduce our electricity usage each year and unfortunately we didn't make it this year, missing out by  40 kWh (or about 9 days worth of power use).This breaks our run of 3 years straight of lower usage than previous years (6 kWh to 4.7, to 4.4, to 4.3 kWh per day). Last winter was our first year of  having solar hot water and this would have been a factor in our higher electricity usage this year. Our hot water system has an electric boosting system and I did a rough calculation that this used about 100 kWh over the cooler 5 months of the year. This equates to around 0.3 kWh a day over a whole year, so that would explain why we didn't cut our usage this year. The TV still only comes out once a week, but I don't think this has made much difference since we just use the computer more now. Still, we don't feel too bad about our consumption since it's a quarter of the average household in WA.

Solar generation was lower than any previous year, which I expected since we had a rainy, cloudy winter last year. I'll take rain over kWh any time thanks. Another factor in this would be that PV systems tend to lose some efficiency over time. We generated 4.5 kWh a day this year, after 5 in year 1, 4.7 in year 2 and 4.8 last year.

We followed our normal pattern of higher usage in winter, coupled with lower generation. The lines cross in spring when we begin to generate more power than we use. The annual bill won't break the budget this year, we got a credit of $94. Without PV we'd be up for a bill of around $500, so we made a $590 saving. For the first time we lost money with Smart Power this year (Smart Power is when you are charged a different tariff depending on the time of day you buy power in). This was because this was the first full year under the feed in tariff and there's a flat rate of payment for power fed to the grid (47 cents for us). We used to save a lot with Smart Power, mainly due to feeding lots of power into the grid at peak periods. Again, we fed in around three quarters of the power we generated. This was great for the bill since we qualify for the feed in tariff.

Another solar year gone, I can't wait until I have 20 years of data to play with...


  1. How can I get a copy of the excel spreadsheet template used for tracking this EXCELLENT data? moreland@iname.com

  2. Hi there - not sure if you're still monitoring this site... My wife and I are just about to install 6kwh of solar panels on our roof and I found your great little blog while searching for excel spreedsheets that have already been created so I can track our progress. If you don't mind, would it be possible to get a copy of the sheet you've created? chris_kuiters@paramount.com