It is self-evident that a solar system will produce more in summer and less in winter. When buying solar, you want to know how much solar you will get in the depths of winter as well as the height of summer.
Unfortunately many quotes only contain energy generation estimates that are averaged over the year.
So when buying solar, how do you find out how much energy the system you are considering will generate throughout the year?
The quickest and easiest way is to use an online solar estimator called PVWatts.
Here's an example:
Steve, who lives in Castle Hill, Sydney asks:
"Would you be able to let me know what the typical output would be from 7.8 KW and 10.8 KW systems by month i.e. Jan, Feb etc."
Sure! Here's how I do it...
1. Go to PVWatts
2. Put in your location. This is a US based site, so be sure to put the state too to help it know you are an Aussie.
I will type: "Castle Hill, NSW" and then hit "GO >>".
3. Check the location is in your part of the world (within a few hundred km is fine - there are a limited number of data collection locations in Australia). Then hit the big orange arrow pointing right.
4. Enter your site details.
- DC System size: is how many kW of panels
- Tilt - is tilt from horizontal. Your roof is probably 22º. (Don't fret over this - unless you have a flat roof or a super steep 45º roof. Use 22º if you are not sure).
- Azimuth: This is the roof direction. This defaults to 180º because the website is made in the Northern Hemisphere. Your panels are probably North (0º) or West (270º) or East (90º) - or somewhere in between.
Then hit the big orange arrow pointing right.
5. Bazinga! Here are your results by month. The numbers you need are in the "AC Energy" column:
6. If you want the daily figures (which are much more useful to get a feel for how they'll offset your daily consumption), then cut and paste the numbers from the webpage into your favourite spreadsheet. I'm going to use Excel. Here I've pasted the numbers in and divided by 30, 28 or 31 days depending on the month, to give a column of daily generation.
I've also pasted the results for a second system (10.8kW) for Steve to compare with the 7.8kW system: