Sunday, October 20, 2013

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

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.