Production of solar plants in charts
People often wonder, how much energy is produced by solar plants on not so sunny days or are they any good during the winter? What is the difference in production between years — can it be very different from one year to another or not so much? Solar plant owners, especially those on net metering contracts, want to know how the production goes in the current year compared to previous years. To answer these and similar questions, I’ve created a mobile application for Android called Solar Plant Charts, which is complementary to the official one from SolarEdge. Charts shown below answer these and similar questions. They show data from my solar plant in Ljubljana, Slovenia, peak power 10,8 kW.
Energy production in a year
This chart shows cumulative energy produced starting with the selected month. If we’d reset the energy counter on the selected month (for example on 1st Jan), its value would increase over the year as it is shown on the chart below. We can see that the slope is steeper during the summer months (I live in the northern hemisphere), while winter months show lower production, but it is not 0. In the last three years the production was very similar.
The red line for 2018 starts at 0 at the end of March, because that is the date when the solar plant started its operation.
By selecting some other start month, we can get a better view of the winter months.
It would be interesting to see this chart for solar plants on higher or lower latitudes, or at least outside Ljubljana, where fog in the winter limits production.
How big are deviations from the average?
This chart shows how much production in one year differs from production in another year. There is still not enough data to draw some good conclusions, but so far the biggest difference at the end of the year is about 200 kWh. However, during the year the deviations may rise to about 400 kWh. We can see that currently (July 2021, cyan line) the production is about 100 kWh below the average.
If I’d install a battery, could I go off grid?
This chart shows charge in the battery for the given battery capacity and average daily electricity consumption. The number in parentheses next to each year in the chart legend shows the number of days in a year when there would not be enough electricity to cover daily needs - when lines in the chart hit the bottom, it means the battery is empty. It is obvious that I can’t go off grid even with a 60 kWh battery. Battery with 470kWh would do the job, but of course such a battery is too expensive currently.
Please do not use this chart to make a decision to go off grid. Actual world is much more complex than taking an average, so you should consult an expert before making such a decision.
What are minimums and maximums of production per day over years?
The maximum values (red line) show maximum energy produced for the given day in all years from the range specified above the chart. For example, for the chart below productions are taken for 4. May 2018, 2019, 2020, and 2021 and then minimum and maximum values are shown. The chart shows that in the winter days there can be up to 40 kWh of electricity produced in a day (almost 60% of the max summer value), but also that there are not many such days in the given time frame. Most highs are recorded from April till June, while July and August have maximum values mostly below 70 kWh. The reason for this is decreasing efficiency of solar cells at higher temperatures.
This chart gets more informative when there is data for more years. When there is only one year selected, only one line is shown, because minimum and maximum have no meaning when dealing with a single value.
What does production per day look like?
For a quick overview of power per day (and indirectly weather) in one month, there are five charts shown on this page. Each one shows production for seven days (one week).
Let’s compare two months
Several questions can be answered by this chart, for example: At what time of the day does production start and end in July? What about January? What is the maximum or average power at a specific hour, which was measured in the given months?
Note also offset in time for 1 hour of June vs. January in the chart above. The reason is daylight saving time. Yes, we are still waiting for the EU Commission to make it a thing of the past.
Some statistics
Statistics usually get better when there is more data, and this is true also for this page. It shows the years with most and least energy produced, and the same for months and days. The days with minimum are not that interesting, except for one thing — we know there was snow covering the modules on the day when production is 0 kWh. Luckily it usually slides down the roof in a day or two.
Conclusion
We can see that there are many ways to present the data and each char tells a different story. If you have ideas for more charts, leave a post.
