SOLAR SHARING IN JAPAN: Opportunities and Experiences

Rene Castro Blog, Reports July 30, 2015

By: Slavka Batorova (GPSS Alumni)

Our most plentiful renewable source of energy is the sun. Technology that harnesses this power – solar photovoltaics (PV) – has experienced a rapid worldwide growth, but this growth also exposed its drawbacks and raised new challenges.

A major drawback of solar PV systems is their significant land use. Large scale PV facilities are installed directly on the ground, including farmland. Unsurprisingly, paving farmland with solar panels has drawn criticism for curtailing food production potential and destroying landscapes and biodiversity. Until recently, the prevalent mindset was that a piece of land can be used either for food or for energy production, but not for both. This mindset was overturned by the Japanese invention of “solar sharing”, which made it possible to produce food and renewable energy on the same land at the same time.

Although invented a decade ago, solar sharing went almost unnoticed until the Fukushima Daiichi nuclear disaster in March 2011. The disaster changed Japan’s energy policy and led to greater focus on renewable energy. Japanese government introduced a renewable energy feed-in tariff (FIT) scheme in July 2012, which made it mandatory for electric power companies to buy electricity from renewable sources at fixed prices for 10-20 years.

Solar sharing is based on the fact that most plants do not need all the sunshine they receive in an open field. Everything beyond the plant’s light saturation point does not increase photosynthesis rate and can even be harmful (e.g. causing lack of moisture). If crops do not need all the sunlight, why not use the excess for power generation?

The first one to combine this fact with solar power generation was Akira Nagashima. He proposed solar sharing in 2004, patented his invention and made the patent free for public use in 2005.

I graduated from Sustainability science master course in 2010, so I do have some academic background in topics like renewable energy. I remember discussing many interesting sustainability related topics in the class, but looking back now, I must admit they were quite abstract terms to me at the time.

Building a solar sharing power plant – which I believe is part of a sustainable solution to some old problems – was an opportunity to experience the practical side of my theoretical background. It was a chance to see the connection between the macro- and the micro-world, between a technology, a national policy and the everyday life.

Our power plant would not exist without Mr. Nagashima’s invention of solar sharing, but just as importantly, it wouldn’t exist without Japan’s feed-in tariff scheme which made solar sharing not just a nice thing to do, but also an attractive investment and source of income. So availability of the right technology and the right policy led to our personal decision to invest our time and money into this and not something else.

People often see national policies as something distant and unrelated to their everyday lives, but every policy is implemented through concrete actions of individuals. Under the big national policy of promoting renewables through feed-in tariff scheme, we took very small, specific steps like dealing with real estate agents when looking for suitable land, submitting and resubmitting application for FIT accreditation, negotiations with solar installation companies for whom solar sharing was as new as it was for me, bringing cold drinks to construction workers to help them survive in the summer heat, waiting for TEPCO to get things done. All these steps were full of compromises when we had to choose from available options rather than from ideal options, but in the end they sum up to a power plant of 40 kilowatts that will once be counted in some ‘abstract’ national statistics on renewable energy. Plus we have a nice place with chickens and sometimes goats where neighbors often stop by for a chat.

Screen Shot 2015-07-30 at 2.23.11 PMToday there are tens of solar sharing power plants in Japan. One of them is our power plant Oo in Tsukuba, Ibaraki prefecture. We (my husband Nobuo and I) built it last year and started raising free-range chickens under the panels this year. To the left is a photo of our chickens.



Why did we build a power plant?

I first learned about the concept of solar sharing in June 2013, when I visited a solar sharing project of Ken Matsuoka (in Tsukuba) who would later become – together with the inventor Mr. Nagashima – one of the pioneers of solar sharing. When I saw his plant, at that time under construction, I instantly became a fan. I realized that I just came across an epochal concept that could once change Japan’s agricultural and energy landscape.

I then visited the inventor Akira Nagashima at his trial site in Chiba prefecture and started English blog because there was no information on solar sharing in English at the time (today there are plenty of English articles). I gradually realized that rather than writing about others, I could build something myself. Nobuo, my husband, liked the idea as well, so we started together – the first step was finding suitable place – and our power plant Oo started producing electricity in November 2014. It will continue to sell electricity to TEPCO for the next 20 years. At an installed capacity of 40 kilowatts, it generates about 4500 – 5000 kilowatt hours of electricity per month, which is enough to cover demand of about 15-20 Japanese families.

In most solar sharing projects, the land under the panels is used to cultivate crops, but in our power plant we decided to raise free range chickens and sell eggs. Neither of us is a professional farmer so chickens are half for fun, half for business.

For more information check my blog:


So for me the lesson was that;

1) It is wise to be interested in government policies because they do have impact on our lives,

2) good policy makers make sure to go to the field and see how their policies are working with the “end-users”, because there are always things to improve.

Solar sharing power plant at Oo, Tsukuba, Japan. July 2015

Solar sharing power plant at Oo, Tsukuba, Japan. July 2015

How does it work?

Solar panels are installed on a frame about 3 meters above the ground. About two thirds of sunlight reaches the ground and the remaining one third hits the panels. Under the panels, crops can be cultivated or animals be raised. In this way, the same area is used simultaneously for both agriculture and electricity generation. Although the amount of electricity produced per square meter is lower in solar sharing than in ground-mounted installations, the fact that solar sharing unlocks vast areas of farmland for energy generation as a by-product of food production means a breakthrough increase in solar power potential.

Graph below shows that if solar sharing was installed on 20% of Japan’s farmland (with a shading rate of 25%), it could produce as much as 474.9 million megawatt hours of electricity annually. This is about 57 % of Japan’s total electricity demand in 2014.


Graph data sources: 

  1. 2014 Electricity Demand – The Federation of Electric Power Companies of Japan(FEPC)
  2. Cultivated acreage (data used to calculate solar sharing output): Ministry of Agriculture, Forestry and Fisheries (MAFF), Japan
  3. Solar power output and wind power output under feed-in tariff (FIT) scheme
  4.  Nuclear power – capacity and utilization rate (used to calculate hypothetical output) (All Japan’s nuclear reactors were shutdown at the time of writing this article). Japan Atomic Industrial Forum

※Calculation of hypothetical output is based on the capacity of 43 reactors classified “in operation” [operation suspended] as of July 15, 2015. Calculation takes into account a pre-Fukushima utilization rate of 70 % (February 2011). Current (July 2015) utilization rate of Japan’s nuclear power is 0 %.