What is solar sharing?


Solar sharing is a new way of producing clean energy without compromising food production.

Solar sharing Power Plant Oo in Tsukuba, Japan.

How does it work?

Solar panels are installed on a frame about 3 meters above the ground. Rows of panels are widely spaced so that about one third of sunlight hits the panels and two thirds reach the ground. In this way, the same area can be used simultaneously for both agriculture (or other purposes, like picnics and barbecues) and power generation.

Power Plant Oo: barbecue.

Solar sharing 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 and can even be harmful (e.g. causing more evaporation and lack of moisture). In solar sharing, solar panels use the excessive sunlight for power generation while crops are cultivated below just as they would be anyway.

Solar sharing was invented in Japan by Mr. Akira Nagashima in 2003. Today there are many independent solar sharing projects all over Japan.

Our power plant Oo (pictures above and below) is one of them.

In our power plant, we combine electricity generation with raising free range chickens.

Power Plant Oo: hens.

How much energy can solar sharing produce?

*** You can skip this explanation and scroll down to see the graph.***

The best indicator to show the potential of a particular energy source is estimated annual energy production (年間可能発電電力量).

Annual energy production shows how much electricity the facility can produce (or did produce) over a given period of time. The measurement unit is watt hour (or kilowatt hour...).

Estimated annual energy production is calculated as:

installed capacity x capacity factor x 365 days x 24 hours

Installed capacity (設備容量)is the nameplate capacity of a facility. For example 1 solar panel at our power plant has a nameplate installed capacity ("maximum power at standard testing conditions") 115 watts. There are 354 panels in our power plant, so the installed capacity of the power plant is 115 x 354 = 40710 watts.

Capacity factor (設備利用率) is the ratio of the actual output over a period of time to the potential maximum output. If ten solar panels on your roof produced electricity only for six sunny hours on a day, their capacity factor for that day would be 25%  (6hours/24hours*100). (A bit simplified.)

Capacity factor differs for each type of energy. It is typically high and stable for nuclear and thermal plants – as much as 70 to 90 %, but lower for renewables because they depend on the availability of sun or wind or water.

Actual capacity factor of solar panel installations in Japan in 2012 (average of 12 months from April 2012 to March 2013) was 15%.

Taking into account this capacity factor, how  much energy could solar sharing installed on 20 % of Japan's farmland produce?

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. 
More than half of Japan's electricity demand could be covered without producing any waste and without curbing food production. That's quite some potential, isn't it. 

Click on graph for enlargement
Author: Slavka Batorova

Graph data sources:
*1  2014 Electricity Demand:
Source: The Federation of Electric Power Companies of Japan(FEPC)

*2 a  Cultivated acreage (data used to calculate solar sharing output):
Source Ministry of Agriculture, Forestry and Fisheries (MAFF), Japan

*2 b  In calculating the solar sharing potential, you need to know how much is the "installed capacity" (megawatts) per given area (1 hectare) at a given shading rate (25 % shading rate means that the size of panels is about quarter the size of the land below them.).  Solar sharing installed at about 25 % shading rate has installed capacity of 0.4 MW per 1 ha of land area. In other words, a solar sharing power plant of 40 kilowatts could be installed over a land of 1000m2 at a shading rate of about 25 %. So I used the factor of 0. 4 in calculating the  "Solar sharing on 20% of cultivated land" (green bar in graph). Actual shading rate in each solar sharing power plant is different. In power plant Oo, it's 33.7 %. Needless to say, at higher shading rate, installed capacity per given area will be higher.

*3  Solar power output and wind power output under feed-in tariff (FIT) scheme
Source: FIT scheme website

*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)
Source: 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 %.


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