Solar Panels Changed Rice Farming in Japan

Don’t Put All Your Eggs in One Basket: How Solar Panels Changed Rice Farming in Japan

A long-term experiment in Japan has shown how farmers could produce both food and clean energy on the same land.

Researchers studied an agrivoltaic rice farm in Chikusei, Ibaraki Prefecture. The field was observed for six growing seasons, from 2018 to 2023.

Solar panels were installed above part of the rice field. Rice continued to grow below them. At the same time, the panels generated electricity.

The experiment produced mixed results. Rice yield declined due to shade. However, solar power created a valuable second source of income.

This is why the experiment reflects the proverb: “Don’t put all your eggs in one basket.”

What Is Agrivoltaic Farming?

Agrivoltaic farming is the practice of using the same land for agriculture and solar-energy production.

Solar panels are installed above crops or between cultivated areas. Farmers can then harvest food and generate electricity from one piece of land.

It is also called:

• Agrivoltaics
• Agri-photovoltaics
• Agri-PV
• Solar sharing

The system is especially useful in places where farmland is limited. Japan is one such country because much of its land is mountainous.

Where Was the Experiment Conducted?

The six-year trial was conducted in Chikusei city in Japan’s Ibaraki Prefecture.

Researchers compared two areas:

• Rice cultivated beneath solar panels
• Rice cultivated in a nearby open field

The agrivoltaic section covered around 1,416 square metres. Solar panels occupied about 27% of the area above the field.

The system had a capacity of approximately 57.96 kilowatts. The panels were placed about 3.3 metres above the ground. This allowed farm workers and agricultural equipment to operate below them.

The panels’ angles were adjusted manually every month. This helped them receive more sunlight for electricity generation.

Key Findings of the Study

Solar Panels Reduced Rice Yield

Rice grown beneath the panels produced an average of about 6.5 tonnes per hectare.

Rice in the open control field produced approximately 8.5 tonnes per hectare.

Therefore, the agrivoltaic field recorded around 23% less rice.

The main reason was reduced sunlight. Solar panels created partial shade over the plants. Rice needs sunlight for photosynthesis, growth and grain formation.

The shaded plants also produced less biomass. They developed fewer panicles. Panicles are the flowering structures that carry rice grains.

These effects directly reduced the final harvest.

Rainfall and Weather Also Influenced Production

The yield difference was not exactly the same every year.

Losses were more noticeable during wetter growing seasons. This suggests that rainfall, cloud cover and panel shade may interact.

Cloudy weather already reduces the amount of available sunlight. Additional shade from solar panels can further limit photosynthesis.

The six-year duration was therefore important. A one-year experiment could have produced misleading results because weather changes from season to season.

Long-term observation gave researchers a clearer understanding of the system.

Solar Panels Changed the Field’s Microclimate

The panels did more than block sunlight. They also changed conditions around the plants.

The maximum daytime air temperature beneath the panels was approximately 0.8°C lower than in the open field.

Minimum temperatures were broadly similar in both areas.

This cooling effect could become useful in regions facing extreme heat. However, its benefits depend on the crop, local climate and season.

Too much shade can reduce growth. Carefully managed shade may protect some crops from heat stress and excessive water loss.

Changes in Rice Quality

The experiment also found changes in grain quality.

Rice grown under the panels had:

• More chalky grains
• A lower percentage of whole grains after milling
• Higher protein content
• Higher amylose content

Chalky grains contain opaque white areas. They can break more easily during milling. This may reduce their commercial value.

Protein and amylose influence the texture and cooking quality of rice. Higher amylose generally produces firmer and less sticky cooked rice.

Therefore, agrivoltaic farming can affect both the amount of rice harvested and the quality of the final product.

How Less Rice Produced More Overall Value

The most notable finding came from the economic assessment.

If researchers had considered only crop production, the conventional field would have performed better. It produced more rice.

However, the agrivoltaic field produced two valuable outputs:

Rice + Solar electricity

When the value of both outputs was combined, the study estimated that the agrivoltaic system generated a gross return about 14 times that of the rice-only comparison.

This does not mean every farmer will earn 14 times more after installing solar panels.

The result was based on the conditions and assumptions of this particular experiment. Actual returns may depend on:

• Installation costs
• Electricity prices
• Government incentives
• Maintenance expenses
• Panel efficiency
• Crop yield
• Weather conditions
• Loan and financing costs
• Grid connectivity
• Local land-use regulations

Gross return is also different from net profit. Gross return measures total value before all expenses are deducted.

Meaning of “Don’t Put All Your Eggs in One Basket”

The proverb means that depending on only one source can be risky.

Traditional rice farmers mainly depend on their harvest. Poor weather, pests, diseases or falling market prices can reduce their earnings.

Agrivoltaics adds another source of value. Even if crop production declines slightly, electricity generation may provide additional revenue.

The approach can be explained through a simple formula:

Food production + Renewable energy = Diversified farm output

However, diversification must be properly designed. Installing too many panels could create excessive shade and severely reduce food production.

Why Agrivoltaics Matters for Japan

Japan has limited flat land. It must balance several competing needs, including agriculture, housing, industry and renewable-energy infrastructure.

Agrivoltaics could help the country expand solar power without completely removing productive farmland from cultivation.

The system may offer several benefits:

• Better use of limited land
• Additional income for farmers
• Local production of renewable electricity
• Reduced dependence on fossil fuels
• Lower daytime temperatures under panels
• Greater economic resilience in rural areas
• Support for Japan’s climate and energy goals

It may also encourage younger people and businesses to invest in farming by creating new revenue opportunities.

Challenges of Combining Solar Power and Farming

Agrivoltaic farming is not suitable for every field or crop.

Major challenges include:

Reduced sunlight

Too much shade can lower photosynthesis, plant growth and crop yield.

High installation costs

Elevated solar structures can be more expensive than ordinary ground-mounted solar farms.

Farm machinery access

Panels and supporting poles must be placed carefully so that tractors and other machines can move safely.

Crop-quality changes

Partial shade may affect grain appearance, protein levels, texture and milling quality.

Maintenance requirements

Panels, electrical equipment and supporting structures require regular inspection.

Weather risks

Strong winds, storms and heavy snowfall can damage elevated installations.

Complex income calculations

A high gross return does not always mean a high net profit. Equipment, financing and maintenance costs must be considered.

What Can Improve Agrivoltaic Rice Farming?

The Japanese experiment shows that panel design is extremely important.

Future systems could reduce crop losses through:

• Wider spacing between panels
• Adjustable panel angles
• Higher panel structures
• Shade-tolerant rice varieties
• Improved planting density
• Better fertilizer management
• Weather-based panel adjustment
• Semi-transparent solar panels
• Sensors and automated monitoring
• Artificial intelligence for managing sunlight distribution

Panels could be tilted to give crops more sunlight during important growth stages. They could then be repositioned to generate more electricity after the harvest.

Can This Model Work in India?

The findings are relevant to India because the country is expanding solar power while protecting agricultural production.

Agrivoltaics may be useful in areas with strong sunlight and reliable grid access. It could provide farmers with an additional income stream.

However, Japanese findings cannot be applied directly to every Indian rice field.

India has different crop varieties, temperatures, monsoon patterns, irrigation systems and farm sizes. Local trials would be required before large-scale adoption.

Pilot projects should examine:

• Effects on Indian rice varieties
• Performance during the monsoon
• Water use and evaporation
• Costs for small and marginal farmers
• Access to agricultural machinery
• Electricity-purchase arrangements
• Long-term soil and crop health
• Net income after all expenses

Why the Six-Year Study Is Important

Many agricultural experiments last for only one or two seasons. This trial continued from 2018 to 2023.

The longer duration allowed researchers to study different rainfall and temperature conditions.

It revealed a consistent trade-off. Solar-panel shade reduced rice productivity. Yet electricity generation substantially increased the total value produced from the land.

The findings provide useful evidence for farmers, policymakers, solar developers and agricultural researchers.

Key Takeaways

• The experiment was conducted in Chikusei, Ibaraki Prefecture, Japan.
• It ran for six growing seasons from 2018 to 2023.
• Solar panels covered about 27% of the agrivoltaic field.
• Rice yield under the panels averaged about 6.5 tonnes per hectare.
• The open field produced about 8.5 tonnes per hectare.
• Rice yield under the panels was around 23% lower.
• Maximum daytime temperature fell by approximately 0.8°C.
• Shading affected rice growth and grain quality.
• The field produced both rice and solar electricity.
• The estimated gross return was around 14 times higher than the rice-only comparison.
• The figure represents gross return under specific study conditions, not guaranteed profit for every farm.

Conclusion

The Japanese experiment presents a practical example of sharing farmland between food and energy production.

Solar panels reduced rice yield because they limited sunlight. They also affected grain quality and plant development.

At the same time, the panels generated electricity. This gave the field a second and potentially valuable output.

The study does not prove that solar panels should be installed over every rice farm. It shows that well-designed agrivoltaic systems can help diversify agricultural income and use land more efficiently.

The central lesson is simple. The future of farming may not always require choosing between crops and clean energy. With careful planning, the same land could produce both.

That is the modern agricultural meaning of “Don’t put all your eggs in one basket.” Study in Field Crops Research