The strong rays of the sun beat down on the earth, transmitting heat and light energy. Some of the light energy can be converted directly into electricity using semiconductors made of silicon and other materials.

Bell Laboratories in the United States was the first to develop solar cells using silicon semiconductors. That was in 1954. At the time, electric conversion efficiency was low—only several percent. But in the 1970s the solar cell conversion rate rose to 15%, making them practical for use. Solar cells being developed today have a conversion efficiency rate of almost 20%.

The amount of electric energy available from the sun's rays is said to be about 1 kW for every square meter of sunlit surface. This means that a solar cell with a surface area of one square meter and an efficiency rate of 20% can generate 200 watts of electricity. Boosting the conversion rate higher reduces the per-unit cost of generating the electricity, producing more power without requiring more space for the solar panels.

In 2002, the world's total production of solar cells was about 520,000 kW (production is measured by the number of kilowatts the cells can generate). Japanese production came to 48.9% of that amount, or 255,000 kW, making Japan the world's top manufacturer of solar cells. This indicates the dependability of the country's semiconductor technology and the strength of the efforts taken by Japanese companies to develop new solar electric products in pursuit of higher conversion efficiencies and thinner solar cells.