Solar power has great potential, but in 2008 supplied less than 0.02% of the world's total energy supply. There are many competing technologies, including 14 types of photovoltaic cells, such as thin film, monocrystalline silicon, polycrystalline silicon, and amorphous cells, as well as multiple types of concentrating solar power. It is too early to know which technology will become dominant.
Since the mid-1990s, leadership in the PV sector has shifted from the US to Japan and Europe. Between 1992 and 1994, Japan increased R&D funding, established net metering guidelines, and introduced a subsidy program to encourage the installation of residential PV systems. As a result, PV installations in the country climbed from 31.2 MW in 1994 to 318 MW in 1999, and worldwide production growth increased to 30% in the late 1990s.
Germany became the leading PV market worldwide since revising its Feed-in tariff system as part of the Renewable Energy Sources Act. Installed PV capacity has risen from 100 MW in 2000 to approximately 4,150 MW at the end of 2007. After 2007, Spain became the largest PV market after adopting a similar feed-in tariff structure in 2004, installing almost half of the photovoltaics (45%) in the world, in 2008, while France, Italy, South Korea and the US have seen rapid growth recently due to various incentive programs and local market conditions. Recent Studies have shown that the global PV market is forecast to exceed 16 GW in the year 2010.The power output of domestic photovoltaic devices is usually described in kilowatt-peak (kWp) units, as most are from 1 to 10 kW.
A significant problem with solar power is the capital installation cost, although cost has been decreasing due to the learning curve.Developing countries in particular may not have the funds to build solar power plants, although small solar applications are now replacing other sources in the developing world.
The U.S. Energy Information Administration calculates that, all-told, electricity from a Solar PV plants costs 4 times that of conventional coal. Bloomberg New Energy Finance in March 2011, put the 2010 cost of solar panels at $1.80 per watt, but estimated that the price would decline to $1.50 per watt by the end of 2011.