The term photovoltaic literally means light producing electricity. Turning photo (light) into voltaic (electrical current), is the basis of how solar panels work.
So, photovoltaic efficiency refers to how efficiently a solar cell or solar module produces electricity.
Photovoltaic efficiency describes the efficiency or conductivity of solar panels - the percentage of radiation (sun) energy that can be converted into electrical energy.
Currently, photovoltaic efficiency of silicon crystalline solar panel modules is up to 22%  - meaning those systems convert up to 22% of the sun's energy they're exposed to into useable electricity. Crystalline silicon was the first mainstream solar technology, and continues to be the most commonly used.
New technology silicon thin-film photovoltaic module efficiency is up to 8% . Although thin-film is less efficient, its advantages are that it's less bulky, has more applications, and is easier and cheaper to produce and install.
It's important to note that these records are for solar panel module efficiency (a circuit of multiple cells), not individual solar cells. Individual solar cell efficiency records are higher but less consistent.
Thin film solar panels are expected to become vastly more efficient as the solar and alternative energy race heats up. Alta Devices Inc have developed a thin-film solar cell that’s achieved 28.4% efficiency. It uses gallium arsenide (GaAs) as a conductor, rather than the traditional silicon based conductors. 
|Gallium arsenide crystalline (GaAs)||21%|
|GalnP/GaAs/GalnNAs Multijunction cell*||43%|
|* Figures rounded down to nearest percentage point.|
|** Multijunction data only available for individual cells - no module data available.|
Additional factors affect how much electricity a solar panel module will actually produce. Technical photovoltaic efficiency doesn't necessarily mean solar panel efficiency.
Angle and location also weigh in on the efficiency of solar panels. You'll need to figure out the optimal placement for your location to get maximum sun exposure hours.
In New Zealand, the north facing side of the house gets most sun exposure so New Zealanders install solar panels to face north, whereas solar panels in the United States generally face south.
Solar tracker technology is another development which increases overall solar panel efficiency.
As the sun moves, the panels change angle... boosting efficiency throughout the day.
Commercial solar farms like the Montalto di Castro solar park in Italy use sun tracking systems to maximize the amount of time that solar panels are exposed to the sun's radiation .
Similar systems are available for smaller scale private solar panels, however are less popular than static due to increased setup costs and maintenance.
Multijunction solar cells are another exciting new solar innovation. Individual solar cells (normally silicon) only react to a certain range of light depending on their molecular makeup - some silicon conducts and reacts to ultra-violet light, while other silicon reacts to infra-red light.
Multijunction solar cells combine layers of differently tuned silicon - so a single multijunction cell covers greater range of light and thus has a greater electricity production potential.
Concentrated solar is another technology increasing efficiency.
This involves using mirrors to concentrate sun radiation on a single cell. Concentrated solar exposure equals greater power production.
Other measurements to be aware of when researching solar power are photovoltaic capacity and watt hours.
Photovoltaic capacity refers to the maximum power output a solar panel module is designed to produce – if the solar module were exposed to constant and direct radiation.
Photovoltaic power capacity ranges from large solar farm installations, such as Montalto di Castro with a peak capacity of 24 mega watts , to small residential solar modules with a capacity of 180 watts.
It’s important to note that photovoltaic efficiency and capacity of solar panels are useful as indications only – they’re not measures of actual production.
Time of day, amount of sunshine or cloud, location, and numerous other factors will influence actual solar power production levels.
For these reasons, worldwide solar production is estimated to be around 25% of peak capacity levels.
Watt hours is arguably the most useful indication of a solar installation’s value as it can be directly compared to watt hours of electricity produced by traditional fossil fuel energy production or to how many watt hours a town or individual family uses.
Looking at watt hours presents a tangible cost comparison that solar panel efficiency doesn’t. The Montalto di Castro solar park for example produces around 40,000 mega watt hours (MWh) per year – enough to supply approximately 13,000 Italian houses .
Furthermore, by looking at expected watt hour generation, a cost per kWh figure can be calculated and compared.
 Green, M, A., Emery, K., Hishikawa, Y., Warta, W. (2011). Solar cell efficiency tables (version 37). Progress in Photovoltaics: Research and Applications, 19, 84-92.
 Jeanne Roberts. (2011). Alt Devices Inc. hits “sweet spot” in thin-film efficiency ratings. Energy Boom.
 SMA. (2011). Solar Park Montalto di Castro. SMA.
 Green, M, A., Emery, K., Hishikawa, Y., Warta, W., Dunlop, E, D. (2011). Solar cell efficiency tables (Version 38). Progress in Photovoltaics: Research and Applications, 19, 565-572.
 SunPower. Largest Solar Power Plant in Italy Completed. Retrieved from http://us.sunpowercorp.com/about/newsroom/press-releases/?relID=23297
Good Article > I am currently designing an Array to support 11+ PV Panels on a new Sustainable House in Napier New Zealand > Regards TAZman
Why arent we using solar power for everything? Huge uprnoft cost. Upwards of $25,000 for me, a single guy in an apartment, to install enough solar panels to completely power all my energy needs. Also, without improvements in energy storage, current batteries are also expensive and bulky to store the energy needed to run at night. Plug into the normal electric system and during the day you offset what you use, and possible put more in than you use, making the electric company pay you.
Thanks TAZ. Great to hear. Wow 11 panels is decent, how much power do you anticipate that'll generate?
If you ever feel like sharing some photos, they'd be most welcome on the site.
P.S. We're based in New Zealand also, in Christchurch.
Actually it is wonderful and eifecifnt! The city of Sevilie in Spain runs entirely on electric solar power. The reson for everyone not using solar power in the U.S was because of the Bush administration. Bush was big on oil and gas and didn't favor alternative fuel. As a result, solar power was not granted its potential. Although its available now, people don't understand its effectivness and benefits it provides.
I am considering strntiag a solar/wind energy business. I would like to know how many people would really consider installing solar panels and/or a wind generator on their home or business. If a complete system is too costly, would you consider a battery back-up system to run essential items in you home or business for when the power drops out? This would consist of 4-12 batteries, a couple of solar panels and/or a wind generator. This would operate items such as lights, well pump, refrigerator, radio or TV, telephones, and computers. Would you consider strntiag a small solar array (4-6 panels) and adding panels to it when you have extra money to spend on them?Please give me your feedback on what you think of GREEN energy and if you think it is the future or just a fad.Good answers so far. In response to f100_supersabre, A 4 battery system is not much. It all depends on what you will operate and how long. The more batteries the better. About the telephone, yes they are powered by the telephone line but businesses usually have multiple lines with a switching station that needs electricity to operate. Most homes now only have cordless phones which require electricity. If you keep a corded phone in your home this would be a non factor. When it comes to the size panels and wind generator that is relevant to your power consumption. What might be good for your house may be too big or too small for your neighbor.Keep the answers coming.
I am due to have a 4KW solar PV system installed next week. I spent yesterday with a renewable energy expert (for work, remote data communication). He told me that the "real" fall off in efficiency for solar panels is a 45% reduction in efficiency after six years. He also mentioned that this is widely known within the industry.
This would perhaps explain why the companies who quoted for my business were reluctant to discuss data collection in any great detail.
Needless to say, the first thing I will be doing will be setting up a data logging scheme.
Any comments gratefully received!!
I would like to ask if there are companies already producing silicone with 22% efficiency and Gallium Arsenide crystalline (GaAs) with 43% efficiency. Appreciate your confirmation and your providing us companies who are already manufacturing the mentioned item. We are in a renewal energy business and in the process of purchasing the items.
Appreciate to get your quick reply.
New Jersey Solar Installations set new single-month reorcd for installed solar capacity and number of installations for New Jersey Solar in June 2012. New Jersey has 10,086 solar energy array projects installed across New Jersey providing over 380 MW of installed capacity for New Jersey Solar Power. We ship solar panels and solar power kits to be installed all over New Jersey each year.
what the best wiring for sollar panel and Battery?
the sollar panel Characteristic is:Voc=40v Isc=4.6A number of panel=26 panel
AND Battery:12V 100A/h number of Battery=24 Battery
Battery wiring 24v beter or 48v?