What is solar sharing?

The system is called “solar sharing” (ソーラーシェアリング) in Japan. Who knows what expression will eventually take root in English. We’re talking about a new way of producing clean energy without compromising food production.

Dscn2432_3 How does it work?

Solar panels are installed on a frame about 3 meters above the ground, with wide spacing between panel rows. About three quarters of sunlight reach the ground and the remaining quarter reaches the panels. In this way, the same area is used simultaneously for both agriculture and power generation.

Picture: Solar sharing project of Ken Matsuoka in Tsukuba, Ibaraki prefecture, Japan.

This revolutionary idea is based on the fact that most plants don't need all sunshine they receive in an open field. Plants do need light for photosynthesis, but only to a certain point. Everything beyond this saturation point does not increase photosynthesis rate and can even be harmful (e.g. causing more evaporation and lack of moisture). Solar sharing takes advantage of this fact - panels use the excessive sunlight for power generation while crops are cultivated below them.

Solar sharing was invented by a Japanese Akira Nagashima in 2003 and today there are numerous trial projects all over Japan.

This blog aims to introduce these projects and everything related – from institutional background to on-site technological challenges.

Link to the inventor Akira Nagashima's project in Chiba prefecture (website is in Japanese):



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Power generation - performance report

Our solar sharing power plant has generated a lot of electricity since it started operation 5 months ago - precisely 22 952 kilowatt hours in the period from November 27, 22014 (start) to April 24, 2015 (today). That's not bad for an installed capacity of 40 kilowatts.

We use a monitoring service "Solar Monitor" that allows us to check real-time generation status online. Being able to check it anytime anywhere (that is, "anywhere with internet connection") is extremely convenient, and on sunny days it's also quite fun.
Picture below is Solar Monitor screen shot from today April 24, 2015, taken at 17:21. In the circle on the left you can see that the plant was still producing 2 kilowatts of power despite the late hour. That's one of the good things about days getting longer towards summer. From the screen you can see that today a total of 200.4 kWh was generated (for the record, it slightly increased to 201.9 kWh at the end of the day.)


For English explanation check an older screen shot below (click for enlargement):


By the way, the mechanism that allows us to change the panel angle (tilt) has been - as expected - a major contribution to performance.
I never noticed it before but the position of the sun on the sky is really different in winter and in summer. I do remember learning at elementary school that sun is low in winter and high in summer, but I never quite observed the sky to see how different "low" and "high" actually is. Until recently.
In terms of solar power generation, the position of sun has great implications. It means that while in winter you want to lean the panels into very steep tilt (as much as 60 degrees), in summer you want to put them in almost horizontal position (as little as 3 degrees). This greatly affects the amount of electricity produced.
Thanks to the panel adjustment mechanism, we're doing exactly this - optimizing the tilt every few days (or weeks) according to the seasonal height of the sun.
Graph below shows optimal angle of solar panels for each month of the year. The graph is for the location of Hachiouji (Western Tokyo), which is some 100 km from here, but it's the same Kanto region so the data roughly apply to our place as well (observation-confirmed). According to this graph, optimal tilt is 60 degrees in January, 34.5 degrees in March, 2.6 in June and 40.8 in October.


You can find the original graph here:

This was a quick performance report.

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Our solar power plant construction in 4 minutes

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Generation & selling electricity started!

Some awesome news: On November 27, 2014 ...

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(English) パネルの回転システムによって全354枚のパネルを一気に動か...

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«Panel rotating mechanism: From lever to winch