Here is a summary of the monthly performance of our power plant from December 2014 (the first full month of operation) until June 2015.
The best performing month so far was May with 6231 kWh of electricity produced, and the worst month was February with 4460 kWh. An average Japanese household consumes about 300 kWh of electricity a month, so our power plant produced enough electricity for 14 households in its weakest month (February) and for 20 households in the strongest month (May).
But some months have more days than others. When we take that into account and calculate average amount of electricity generated per day in a given month, we'll find out that the worst month in fact was not February (28 days) but April (30 days) - an average of 148.8 kWh was generated a day. The best month remains May with average daily performance of 201 kWh. See the graph below:
The size of our power plant is 40.71 kW in terms of installed capacity of solar panels (354 panels x 0.115 kW), and 38.5 kW in terms of maximum capacity of inverters (7 inverters x 5.5 kW).
The question I am interested in is: How many kilowatt hours of electricity does each 1 kW of installed capacity generate per year?
As our power plant has been in operation for only seven months, I don't have a twelve months worth of statistics yet. But if I assume that the same trend will continue for the next four months, I can extrapolate data from the seven months introduced above.
This multiplied by 12 months gives us a prediction for yearly performance.
5003 x 12 = 60037 kWh/year
When we divide this yearly performance (prediction) by the installed capacity 40.71 kW, we'll find out that 1474 kWh of power will be produced annually per 1 kW of installed capacity.
60037 kWh / 40.71 kW = 1474.76 kWh
This is very good result.
Actual performance depends on many factors so it's hard to make simple comparisons, but just for reference, Japanese makers of solar power systems such as Sharp, Panasonic and Toshiba estimate annual energy production per 1 kW of their products somewhere between 1000 and 1200 kWh. (Source: Eco-hatsu {in Japanese}). In the light of that, our power plant's estimate of 1474 kWh per 1 kW of installed capacity per year is an excellent outcome.
So why is it important to push performance to the maximum?
Of course on the individual level there is financial incentive - for me, each kilowatt hour produced means a few more yens earned. But it's important from the global perspective as well: Solar power systems take a lot of energy to manufacture and install, and they have to "pay" this energy back. The more energy our power plant produces, the shorter is its energy payback time, and the higher is its net energy gain.
Of course on the individual level there is financial incentive - for me, each kilowatt hour produced means a few more yens earned. But it's important from the global perspective as well: Solar power systems take a lot of energy to manufacture and install, and they have to "pay" this energy back. The more energy our power plant produces, the shorter is its energy payback time, and the higher is its net energy gain.
Energy payback time is the time it takes a solar power system to generate the same amount
of energy that was used for its manufacture and installation. So how long is that time? On average, it's "between six months to two years, depending on the location/solar irradiation and the technology," according to this 2012 article from the Center for Life Cycle Analysis at Columbia University. That's already quite short. But it can always be shorter.
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