How much electricity can solar sharing produce?

How much can solar sharing contribute to Japan’s energy self-sufficiency?

There are two basic indicators to describe the potential of an energy source:

1. Installed capacity

2. Estimated annual energy production

1. Installed capacity

Installed capacity (発電設備容量) is the maximum amount of

electricity that can be produced by a facility at a given time. It is measured
in watts （or kilowatts or megawatts...).

Example: If you install ten solar panels on your roof,

each panel with 100 watt nameplate capacity, then the installed capacity of
your roof-top solar plant will be 10 x 100 = 1000 watts, or 1kilowatt. Under perfect
conditions (full sunshine, the right angle), your panels can produce maximum of 1000 watts of
electricity.

If solar sharing was adopted on 15 % of

Japan’s farmland (4,549,000 ha in 2012) at a shading rate 25%, the total installed
capacity would be as much as 270 million kilowatts.

270 million kilowatts is a lot of electricity. It is
more than the peak demand in Japan in 2012 , which was about 156 million
kilowatts. Peak demand in today's Japan occurs on very hot summer days when
everyone turns on air-conditioning (Only In Hokkaido and Tohoku the peak demand occurs in winter due to heating).

As hot summer days are also sunny days when solar panels work at their maximum,  solar sharing could greatly contribute to energy supply in the summer peak demand.

Installed capacity, while an important indicator, can be a bit tricky though. No power plant generates electricity at maximum installed capacity all the time - either due to maintenance needs or lack of demand or - especially in case of renewables - because of the lack of “fuel”. The fuel for solar power is the sun. Solar panels on your roof produce nothing at night, and little
on cloudy days.

That's why we need the second indicator:

2. Estimated annual energy production

Annual energy production （年間可能発電電力量）shows
how much electricity over a given period of time the facility can actually
produce. The measurement unit is kilowatt hour.

Estimated annual energy production is calculated as:

installed capacity x capacity factor x 365 days x 24 hours

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 panels installed on 15% of Japan's farmland actually produce? The answer is: as much as 358 million megawatt hours of electricity yearly. This is about 40 % of Japan’s total electricity demand in 2012. Not so bad.

Who knows what Japan's energy infrastructure will look like in ten years. Solar sharing might be a vital part of it.

Project in Nishigoya, Tsukuba

Tsukuba is a city about 60 km northeast of Tokyo. One of the solar sharing pioneers Ken Matsuoka launched his project there in fall 2012.

He installed 579 solar panels on a metal frame over land area of about 1500m2.

The construction - from clearing the land and building metal frame to setting panels and cables, all based on Matsuoka's design and done DIY way - took him almost a year. Everything got ready in September 2013.

As of today October 14, 2013, the site is on a test
run. Actual selling of electricity to the grid is scheduled to start tomorrow – on October  15, 2013.

Matsuoka
will sell maximum of 49.9 kW to Tokyo Electric Power Company for the fixed
price of 42 JPY/kWh, guaranteed for 20 years.

Matsuoka also introduced manual tilting system to regulate the amount of light that can reach either the panels or the ground. He can now turn panels with a total weight of more than 8 tons using a single winch. Shading rate is 25.5 % (at panel tilt 0°). The purpose of tilting is not necessarily to maximize power generation output but quite the contrary, it can be used to provide more sunshine to crops when necessary, e.g. at critical growth stages like budding.

Matsuoka adjusting panel tilt:

Matsuoka is not a professional farmer but he does have experience growing his own food. He is now producing soybeans, tomatoes, eggplants and other crops for personal consumption under the panels. The site is registered as miscellaneous land - meaning Matsuoka has to pay higher taxes compared to agricultural land, but he has more freedom to choose how to use the land, what to grow and at what quantities. When we spoke last time, Matsuoka was envisioning a rice field on one part of the land, and a community garden on another. Both are great ideas because there are few on-site trials of growing rice under solar panels, and a community garden with many people coming and growing their vegetables just sounds good. Let's see what will eventually become reality.

The best thing about solar sharing is that building and running a power plant is not anymore something that only big power companies can do. Both technologically and financially, the hurdle is now low enough so that almost anyone can build their own small solar power plant and grow food below it. This will undoubtedly change our way of thinking about electricity.

Link to Ken Matsuoka's blog (Japanese):

http://gba03100.cocolog-nifty.com/tsukuba_ss/

History

Solar sharing was proposed in 2004 by Akira Nagashima, who turned his attention to the fact that most plants do not need all sunshine they receive in an open field. Plant photosynthesis depends on light – increased amount of light leads to higher photosynthesis rate – but only to a certain point. The amount of light beyond this saturation point not only doesn’t contribute to photosynthesis, but can even be harmful.

Based on this fact, Nagashima devised a system where solar panels use the excessive sunlight for energy generation while crops are cultivated below them. Nagashima applied for a patent in 2004 and made the technology freely available in 2005 (Patent publication No.
2005-277038).

Many trial projects have been launched since then, especially in the past two years. After the March 2011 East Japan earthquake and tsunami , followed by meltdowns at Fukushima Daiichi Nuclear Power Plant, Japan revised its energy policy and introduced feed-in tariff system to promote diffusion of renewable energy. Electric power companies now must buy
energy from renewable sources for fixed prices.

On March 31, 2013, Ministry of Agriculture, Forestry and Fisheries issued a guideline, acknowledging solar sharing system and setting rules for farmers who want to introduce it on land registered as agricultural. This was the first time that Japanese government recognized the already existing technology.

Why so revolutionary?

Why is solar sharing so revolutionary?

An oft-cited drawback of solar power generation is the requirement of a vast surface area. If solar panels are to produce the amount of electricity comparable with nuclear or thermal power
plants, the rooftops alone will not suffice. All over the world, low quality land as well as farmland has been used for large scale solar power development.

However, paving agricultural land with solar panels has drawn criticism for curtailing food production potential and destroying agro-ecological landscapes and biodiversity.

The prevalent mindset has been that on one piece of land we can have either agriculture or solar panels, but not both. Solar sharing, in which solar panels are installed above the field with crops,
overturns this mindset.

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.

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):

http://www.d3.dion.ne.jp/~higashi9/sola1.htm