Is Power Generation Higher in the Rainy Season Than in Mid-Summer!? iChoosr Releases Annual Power Generation Data for Solar Panel and Battery Collective Purchasing Participants

The solar panel and battery collective purchasing project "Solar for All Our Homes," operated by iChoosr K.K., is currently deployed in 23 prefectures nationwide.

It is generally believed that power generation from solar panels is low during the rainy season, but in reality, stable power generation can be expected due to various reasons such as the length of daylight hours and temperature conditions.

We would like to introduce an example from "I-san," a resident of Sendai, Miyagi Prefecture, who is an iChoosr employee and a power industry veteran, and who installed solar panels and batteries through this project.

Summary of this newsletter: - Stable power generation can be expected even during the rainy season! - Because solar panels are sensitive to high temperatures, power generation efficiency may be higher in June than in mid-summer. - The installation of solar panels and batteries has led to the "visualization" of power usage within the home, improving the entire family's awareness of energy saving and resulting in annual electricity cost savings of approximately 180,000 yen.

Even in the rainy season, power generation does not drop drastically According to data from the Japan Meteorological Agency for Sendai, Miyagi Prefecture, where I-san lives, the average temperature in June 2025 was about 23 degrees Celsius, 4 to 5 degrees lower than in July and August, making it a relatively comfortable temperature. In addition, because June is the rainy season, it is generally perceived that "power generation is low."

However, in reality, for I-san's home in 2025, the power generated by the solar panels was at its highest for the year in June. Regarding this result, Nishihara, a senior project manager at iChoosr, states, "Solar panels have the characteristic that power generation efficiency decreases in high-temperature environments." Because solar panels are mainly composed of semiconductors, power generation efficiency drops when the temperature rises excessively. In mid-summer, the panel surface becomes hot, so even though there is more solar radiation, efficiency decreases. On the other hand, June is relatively mild, and it is the season around the summer solstice, so it is a season with long daylight hours throughout the year. Due to these overlapping weather conditions, stable power generation can be expected even during the rainy season.

A happy secondary effect of installing solar power equipment: Increased family awareness!? In I-san's home, since installing the solar panels and batteries, changes have been seen in the family's consciousness regarding daily electricity use.

I-san installed a monitor in the living room that allows the family to check the real-time supply and demand of electricity, "visualizing" the amount of power generated and used. As a result, the children, who previously did not change their behavior despite being told to save energy, began to check for themselves "how much electricity we are buying and how much we are selling," and became aware of energy saving on their own.

Furthermore, I-san analyzed data on "electricity consumption by time period" and "power generation" displayed on the monitor to optimize household chores. As a result, the family began to be conscious of using electricity in line with power generation hours, such as setting the EcoCute hot water heater and washing machine timer to run during the midday hours when power generation is higher, and finishing dinner preparations during the day. Through these efforts, the family was able to reduce the amount of electricity purchased and achieved a significant reduction in electricity costs of approximately 180,000 yen. Before installation (2022) annual electricity cost: 353,063 yen -> After installation average: 178,759 yen, difference of approx. 180,000 yen.