The average solar cell efficiency is thought to be between 12% and 22%. In 2007, a team lead by the University of Delaware, produced a record-breaking solar cell efficiency of 42.8% (the previous record was 40.7% efficiency). In 2015, it was reported that a team of researchers created the solar sunflower - with a crazily awesome efficiency of about 80%! The downside: cost.
The efficiency of solar panels is dependent on many factors:
Solar panel installations may produce only 1 kWh/m2/day, or they might produce as much as 8 kWh/m2/day or higher.
Keeping panels clean and free of dust and debris can help them to better absorb sunlight and produce more output. Likewise, you can help your solar panels by locating them in sunny areas that aren't shaded by trees, parked cars, buildings or other structures, since even a little bit of shading can dramatically decrease the cell's output.
Ideally, you would also want to tilt your panels to get the best exposure to the sun. Most homeowners just mount the panels in a fixed position, but there is a device known as a solar tracker that re-orients your solar panels as the sun moves across the sky. They add to the cost of a system, of course -- and they need to be properly maintained -- but they also help solar cells maximize output.
Many people are under the misconception that solar power is totally cost-free. It's true that the sun is free, but the energy produced by a photovoltaic system is not. It's not uncommon for a system to cost tens of thousands of dollars. The significant initial investment is a big reason that solar power is primarily being used in remote areas that do not have access to traditional power companies. The average homeowner simply doesn't have the extra funds to put into solar power, or is unwilling to make the high initial investment.
Over time, a solar powered system can pay for itself, however the initial price tag presents a steep hurdle for many homeowners. Optionally, and for a much smaller investment, homeowners could decide to use solar energy selectively within the home - for instance, the use of solar water heating, solar power air conditioning, or you can even heat your pool with solar power. If you're the handy type, you might decide to build your own solar panel for additional cost savings. On the positive side, solar panels often last 20 to 25 years or more.
That's not to say that solar power has to always be a large investment. Simple things like solar garden lights, Christmas lights, birdbaths and garden fountains are just a few examples of small things that can be run on solar power. On a slighter larger scale, recreational vehicles like boats can also be at least partially powered by solar.
Research is ongoing with strong beliefs that solar power will be more cost-effective in the near future, but also competitive with traditional power companies and more widely used in urban areas. As solar cell efficiency continues to improve, look for solar power to become a much more attractive and cost-effective energy alternative for both homeowners and businesses alike.