Above-average sunshine: that was what September 2025 gave us. It was already the umpteenth above-average sunny month in a row! It was particularly sunny and warm from September 5th to 7th and from September 19th to 20th. According to the KNMI (Royal Netherlands Meteorological Institute), there were 188 hours of sunshine in the month, which is well above the long-term average of 159.

RCD trips

Between the summer months, there were also occasional spells of wind and rain, particularly on September 15th, when the windspeed was uop to 9 Beaufort near IJmuiden. This gale-force wind and rain caused some customers' residual current devices (RCD's) to trip. This is an issue that sometimes arises whne the distribution panel has been modified by another contractor since the solar panels were installed. We've had to refer several customers to this article for information on the cause and solutions.

For the owners of home battery systems trading on the imbalance market, September was much better than previous months, even though Frank Energie's 'trading index' remained well below the average of 100: it was at 65 for the month. The greater volatility and unpredictability of autumn weather meant that imbalance trading began to bring higher yields. For example, on September 21st, when temperatures suddenly plummeted, the trading index was a whopping 233!

Fifteen-minute Prices on the Spot Market

On the market for dynamic electricity prices, there were some days with large differences between lowest and highest prices. Since October 1st, these differences may have become even greater, as the EPEX spot market now sets different prices every fifteen minutes instead of hourly. Some energy suppliers offer their customers the option of being billed at these 15-minute rates. In the image below, you can see that the electricity price on October 2nd showed significant fluctuations between 6:00 PM and 7:00 PM; you could potentially capitalize on this using a home battery system.

Unfortunately SMA has just announced another delay in the link-up between the Sunny Home Manager and the spot marketprices: this has now been pushed back to the first quarter of 2026. This delay is unfortunate, but we hope it will eventually result in the development of a robust system.

We're coming to the final and least sunny quarter of the year. The period when your home could run 100% on its own solar power is coming to an end, but even in the darkest months, there are still plenty of days with wonderful free solar energy!