Publication date: Feb 25, 2025 Harnessing Weather Intelligence for Renewables to Optimize Asset Performance in Japan: Solar

Harnessing Weather Intelligence for Renewables to Optimize Asset Performance in Japan: Solar

Shulman Advisory, in collaboration with Atmospheric G2, is excited to share our latest article on the role of weather intelligence in optimizing solar asset performance in Japan. As the country’s most utilized renewable energy source, solar plays a critical role in Japan’s energy transition. In this article, we explore how advanced weather data can enhance forecasting, efficiency, and overall asset performance.

Let’s dive in. Harnessing Weather Intelligence for Renewables to Optimize Asset Performance in Japan: Solar

Importance for Japan’s Power Generation

Solar power plays a vital role in Japan’s energy mix, reducing reliance on fossil fuels and enhancing energy security. As of March 2024, the total installed capacity of solar power generation under the government-sponsored Feed-in-Tarrif (FIT) and Feed-in-Premium (FIP) programs were 73.8 GW, with the goal is to expand this to between 103.5 GW and 117.6 GW by 2030, based on Japan’s Strategic Energy Plan (METI). Solar power generation in Japan varies by region, with higher output in areas with ample available land or in warmer, sunnier southern regions. In October 2024, Fukushima recorded the highest generation volume at 157 GWh, followed by Hokkaido with 112 GWh (METI), both benefiting from abundant space for solar installations. In contrast, Tokyo, with limited land availability for large-scale solar power plants, recorded the lowest generation volume at just 0.46 GWh (METI). 

In an effort to grow solar power generation in Japan, the government initially implemented the FIT system in 2012, offering rates as high as JPY 42 per kWh. However, these rates have been gradually reduced over the years, with solar power projects over 50kW receiving JPY 8.9 yen per kWh in FY2025. The declining price trend has been accompanied by a push toward the FIP scheme, encouraging market-driven renewable energy integration with premium incentives based on wholesale electricity prices. As the FIP scheme encourages market-driven solar deployment, accurate forecasting and flexible operation are becoming increasingly important to ensure efficient utilization of generated power. 

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Understanding & Forecasting Solar Irradiance as well as Clear Sky Percentage

Solar irradiance, measured in Watts per square meter (W/m²) and as Global Horizontal Irradiance (GHI), helps assess solar power generation potential by indicating the total solar energy reaching a flat surface, including both direct and scattered sunlight. The clearer the day, the higher the GHI value, with the percentage of clear sky irradiance indicating how much of the potential maximum sunlight is received (100% meaning completely clear skies).

Accurately predicting GHI and clear sky irradiance helps optimize the efficiency of solar panels. During high irradiance periods, solar farms can maximize output, feeding more electricity into the grid. 

However, as solar power generation grows, curtailment rates are increasing during periods of high irradiance when excess electricity generation exceeds grid capacity, leading to restrictions on solar output. Addressing this issue requires improved grid management, energy storage solutions, and policies to enhance solar integration. When GHI drops due to cloud cover or rain, alternative energy sources may need to compensate. This forecasting helps balance power supply and demand, ensuring stable electricity generation. 

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Forecast Highlights for Japan

The 15-day solar irradiance forecast for Japan indicates variable solar power generation potential over the period, influenced by fluctuating cloud cover and irradiance levels. The solar irradiance forecast for Japan shows strong solar potential from February 24 to March 1, with high irradiance levels above 183 W/m² and low cloud cover, peaking at 100% of clear sky irradiance on February 25. From March 2 to March 5, solar energy generation drops due to increased cloud cover up to 93% and lower irradiance, reaching a low of 83.8 W/m² on March 4. Conditions improve slightly on March 6, with irradiance rising to 173.4 W/m² and reduced cloud cover at 61%, allowing for moderate solar potential. Fluctuations continue between March 7 and March 11, with irradiance ranging from 17 W/m² on March 11 to 193.3 W/m² on March 9, while cloud cover remains relatively high. The best days for solar energy are February 25, March 1, and March 9, while March 3, 4, and 11 will have the lowest solar potential due to heavy cloud cover. Monitoring these trends ensures efficient solar energy utilization and helps Japan maintain a reliable and sustainable power grid.

Atmospheric G2 also offers Japan solar generation forecast output at the city level and at the more granular hourly timescale – please reach out if you are interested in learning more at info@shulman-advisory.com.

Shulman Advisory in collaboration with AG2 aims to provide comprehensive climate intelligence services valuable for energy trading, asset management, and risk assessment, helping our clients make informed decisions based on accurate weather forecasts and associated risks. By integrating Shulman Advisory’s strategic insights and consultancy with Atmospheric G2’s actionable, data-driven forecasts, we offer a holistic suite of services designed to enhance decision-making and operational efficiency across the energy sector. We believe this partnership holds great potential value for Japanese power market players including power traders, renewable energy developers, grid operators and more.