When talking about efficiency in solar panels I think it's really important that people understand that the term 'efficiency' used for appliances and 'efficiency' used for a power source like solar panels is completely different. Efficiency in appliances like your washing machine measures difference in energy input versus the useful output of an appliance. The efficiency percentage for solar panels is how much sunlight hitting a panel is turned into power that we can use. When you hear solar panels are now reaching 20% efficiency it is actually really good news.
Currently the average efficiency rating for solar panels are around 15%, which has come a long way from 2% in 1954. Now let's compare this to a car that burns gasoline at an efficiency of around 15-25% or a coal power plant which is 33%. For some people the efficiency rate of 20% still sounds low, but I don't think it should put you off.
Efficiency for solar power is calculated in terms of the area size of the solar panel, and quite often the more efficient a solar panel is the more expensive it is. A 1m2 solar panel might be 15% efficient and another 1m2 panel might be 30%, but it is likely that the 30% efficient panel is more than twice the price. Therefore you might decide to go with 2 of the 1m2 solar panels to save you money, if you have the room on your roof.
On the 3rd of September 2013, CSun, a Chinese solar cell and panel manufacturer announced that their new generation of mono-crystalline solar panels are 20.26% conversion efficient and have received certification from the Fraunhofer Institute for Solar Energy Sytems (ISE) in Europe. The company plans to start mass-producing these new panels by the end of the year. CSun states that these panels offer "outstanding cost advantage and space reduction".
Sunpower, a solar panel manufacturer based in California has already won the 20% solar panel efficiency battle, but the price has been too expensive for the panels to taken up by the market. It is only the Chinese companies that can really make a difference to the solar power market.
Hopefully the price on these CSun panels will make solar power more appealing to a wider audience if they can produce more power at a lower cost.