Solar Panel Efficiency

Over the past 5 years, the price of solar panels has dropped dramatically while efficiency of solar arrays has increased significantly.

Yet, it appears that the renewable energy revolution continues to make life better and cleaner for many of us!  The University of Texas at Austin announced this month that one of its solar researchers has discovered a method to further double solar panel efficiency up to 60%!

Solar panel efficiency can be summarized as follows:  The term refers to the amount of solar energy that is converted to usable electricity after hitting a solar panel.  It does not need to be a bright, sunny day.  All you need is UV (ultraviolet) sunlight, filtered through clouds or even precipitation.  According to a recent article:

An issue with regular photovoltaic panels is that much of the energy delivered by sunlight results in the conversion of “hot” electrons, which are too high-energy to be converted to electricity in silicon and are instead lost as heat. University of Texas Chemistry professor Xiaoyang Zhu and his team discovered that an organic plastic semiconductor could double the number of electrons harvested out of one photon of sunlight.

Solar panel efficiency is currently about 30% for silicon photovoltaic (PV) solar cells.  But solar technology indicates that this figure can at least double, to reach 66% efficiency.

The importance of this discovery is the potential of reaching grid parity – the point at which the cost of purchasing solar electricity is less than the price of fossil-fuel based power.

Surprisingly, where you live has little to do with solar panel efficiency.  The primary impacts on solar output are from shading.  Solar panels that are shaded by trees, other vegetation or adjacent buildings are generally less able to produce electricity than those that are not shaded.  Even shade on a single panel can affect the overall performance of a solar array.  We recommend that you have a solar professional examine your property before purchasing or leasing solar panels to determine if and where solar panels should be located.

How solar panels work

Other components of a solar array can also affect the production of solar electricity.  Solar inverters convert the direct current that strikes a panel surface into alternating current, which is the power you tap via an electrical outlet.  The angle at which your panels are installed, and their placement on your rooftop, can also help maximize the amount of sunlight that hits the panels.

Improving overall energy efficiency within your home or building will help you save even more money with solar panels.  While solar electricity is free, there are limits to the amount that can be generated by a distributed generation system.  If you use more energy than you produce, you’ll draw on the grid (with a grid-tied system), increasing your power bill.

You can generate solar power even on a cloudy day because UV light is the primary factor required.  However, snow and ice can block sunlight from the solar panels, reducing their efficiency.  There are ways to remove snow on solar panels.  Other than that, minimal maintenance is required for a solar array over its lifetime.

In short, the things that affect how well solar panels work are largely within your control!

What is the expected performance of solar panels?

The performance of solar panels is pretty consistent over the decades they are expected to last, however.  Solar panel manufacturers and the solar industry in general expect the greatest decline in the first year: approximately 2-3%.  After that, a very small degradation rates of half a percent (0.5%) each year may occur.

Warranty information provided by solar manufacturers is helpful information to assess solar panel efficiency.  Solar output warranties use an industry standard of 90% output in the 10th year of usage.  By the 25th year, solar manufacturers guarantee at least 80% solar panel efficiency.

Warranties and guarantees, of course, are more conservative than the actual performance of solar panels.  Manufacturers are using a “worst case scenario” in predicting solar output declines over the years.

Actual solar panel efficiency of the installations on your property could be much higher.  Consider the fact that very little (if any) maintenance of solar panels is required.  This is because the panels do not include any moving parts, and they have been designed to withstand extreme weather conditions.

This means that an investment in solar power is probably even more sound than you’ll read in warranty information!

How do clouds affect solar panels?

For a definitive answer, the National Renewable Energy Laboratory (“NREL”) recently published a study after extensive research on the effect of cloud cover on solar power installations.  NREL is a national laboratory that is part of the U.S. Department of Energy‘s Office of Science and is the only federal laboratory fully vested in the research, development, commercialization and deployment of renewable energy and energy efficiency technologies.

The NREL’s study on how clouds affect solar panels is based on data collected over a year on the island of Oahu, Hawaii.  The purpose of its research is to determine where solar energy production may be compromised in a utility scale photovoltaic (PV system.

Although clouds may affect solar panels in a minimal way, solar power is still one of the cleanest, greenest forms of renewable energy.  The cost of solar energy has continued to fall over recent years, as well.  Yet, the reality is that cloud cover can reduce the efficiency of solar panels because their output reacts rapidly to changes in the intensity of sunlight.

Yet, solar technology continues to advance allowing greater amounts of energy to be collected from solar panels, even when its cloudy.  In fact, solar planners may be able to soon analyze the characteristics of cloud shadows, and reliably model, or predict output from, their individual systems over time.

For more information on the impact of clouds on solar panels, take a look at NREL’s Measurement and Instrumentation Data Center (MIDC) website.

How does heat affect solar panels?

Here we are in the “dog days” of summer.  Record temperatures over much of the U.S. might have some people wondering, how does heat affect solar panels?

The answer can be summarized in a single phrase:  less power.

As days get hotter – or in regions in which it is often warm – solar panels may experience a decrease in electric output.  In short, solar panel efficiency is negatively affected by heat.

This may be an ironic outcome, given that abundant sunshine generally means increased solar power generation.  But when comparing equivalent exposure to UV light, solar panels in cooler locations generate more power than their hot weather counterparts.  The difference is often made up by the greater numbers of sunny days in warm locations.  Or, if you live in a sunny, higher elevation climate, your solar panels may perform quite well, comparatively.

If you are scratching our head, be sure to talk to a solar engineer who can help you determine where to install solar panels, how many to use, and how much the cost will be.

Solar Pole Tracker uses GPS technology to increase solar panels efficiency

Now, solar panel efficiency is increased with the solar pole tracker.  This new technology helps optimize the amount of energy absorbed by solar panels by tracking the sun’s path across the sky during the day.  The solar pole tracker has been developed by Advanced Technology & Research Corp. with help of a $1.1 million grant last year from the Maryland Energy Administration.

The solar pole tracker is no ordinary heliotropic device.  It uses a GPS controller to help panels follow the sun throughout the day, increasing solar panel efficiency by up to 30%.  Now that the solar technology has been developed, the company is aiming to sell them to government agencies and private businesses.  Solar pole trackers could be affixed to light and utility fixtures to maximize solar powered lighting and signage.

At only $700-$1760, solar pole tracker devices will pay for themselves in 5 years or less, including renewable energy tax credits and net metering sales of extra electricity sold back into the grid.

Photonics can increase solar panel efficiency by 300%

Over the last few years, the cost of solar has dropped dramatically.  Now, there is news of a potential solar panel efficiency increase of 300%.  Researchers at HyperSolar have developed a film that can move certain light spectra to increase the conversion rate (and thus efficiency) of solar panels.

The solar technology, which uses photonics, also has the promise of further cutting the solar panel installation costs in half, from already reduced figures.  Developed in the U.S., cutting edge renewable energy tech like this is important to keep the country as an energy leader.

Demand for cheap and efficient solar panels is rising as installations are increasing worldwide.  Projections estimate that the 16 gigawatts of solar power that have already been installed globally will increase to 1,800 gigawatts over the next 2 decades!

Nanosolar products

Nanosolar recently announced that it will be selling and marketing its copper indium gallium selenide (CIGS) solar panels this year.  After intensive R&D, the company has reached 16.4% efficiency in the laboratory, closing in on the nearly 20% solar panel efficiency for a CIGS solar panel achieved by the publicly owned and operated National Renewable Energy Lab (NREL).

Nanosolar’s co-founder, Brian Sager, stated:

“The whole idea here is to buy multiple lines of manufacturing equipment and scale as the market demands. “We’re really only limited by market economics.”

Although details of the amount and type of product that will initially be sold by Nanosolar are unclear, most expect the CIGS solar panels it will sell will have 10-12% efficiency.

The world will be watching.  Many place their solar power “chips” on CIGS solar cells with respect to ultimate efficiency and inexpensive manufacturing.   While both CIGS and cadmium telluride have theoretical maximum efficiency in the range of 29-33%, CIGS is expected to ultimately prevail in the efficiency race.

With the new release of Nanosolar’s CIGS panels, competition will not be afoot between First Solar (selling panels with close to 11% efficiency and a cost of 87 cents per watt) and Miasole, which sells CIGS cells in the 10-11% efficiency range.

For a glimpse into the near future, here’s a short video showcasing Nanosolar’s roll-to-roll CIGS solar cells:

Ultra Thin Solar Cells

Recently, Boston College researchers observed the so-called “hot electron” effect in a solar cell for the first time, and then harvested the charges with ultra-thin solar cells.

What does this mean for you and for me?  The short answer is: improved solar panel efficiency.

Generally speaking, when UV light is captured in solar cells, it generates free electrons in a range of energy states. In order to capture the charges and convert them to renewable electricity, the electrons must reach the bottom of the conduction band.  In the past, one of the biggest hurdles has been the fact that  the highly energized “hot” electrons lose much of their energy to heat along the way.

You can see hot electrons in devices like semiconductors.  Yet, the high kinetic energy can cause the electrons, also known as “hot carriers,” to degrade a device. For years, researchers have theorized about the benefits of harnessing hot electrons for solar power through so-called “3rd generation” devices.

Thin Solar is In

Scientists are now using ultra-thing solar cells (less than 30 nanometers thick) in a mechanism that can extract hot electrons before they cool.  This may effectively open an “escape hatch” through which they typically don’t travel.

Professor of Physics Krzysztof Kempa used the analogy of trying to heat a swimming pool with a pot of boiling water:

Drop the pot into the center of the pool and there would be no change in temperature at the edge because the heat would dissipate en route. But drop the pot into a sink filled with cold water and the heat would likely raise the temperature in the smaller area.

He noted:

“We have shrunk the size of the solar cell by making it thin.  In doing so, we are bringing these hot electrons closer to the surface, so they can be collected more readily. These electrons have to be captured in less than a picosecond, which is less than one trillionth of a second.”

With ultra-thin solar cells, an overall increase in efficiency of 3% can be expected with absorbers 1/50th as thick as conventional cells!  The Boston College research team determined that the gains were the result of capturing hot electrons and an accompanying reduction in voltage-sapping heat. Currently, the film’s efficiency is limited by the negligible light collection of ultra-thin junctions. However, by combining the film with new light-trapping technology — such as nanowire structures –we  could significantly increase efficiency in an ultra-thin hot electron solar cell technology.

Will snow affect your solar panels?

I woke up this morning to the first snow of the winter season.  Only about 2 inches deep, but enough to cover the yard and streets with a calming white blanket.  The snow brings to mind one of the common concerns that people that own, or are considering, solar panels have.  Do the winter months affect the efficiency of solar panels?  What is the effect of snow on solar panels?

The good news is that, even if the weather outside is frightful, it can still be delightfully warm and lit inside your solar-powered home.  In fact, with the installation of solar panels on your home, you may be the only place in your neighborhood that retains power in a winter storm.  No need for a generator, either!  Don’t let this happen to you:

Truthfully, you will have to consider whether snow on solar panels is accumulating at a rate to slow or prevent their efficient operation.  Obviously, solar panels need to be exposed to sunlight in order to work.  Some sunshine can pass through an inch or two of snow, but more than that, and you may have to get up on the roof to clear away the snow from the solar panels.

Here are a few tips to deal with snow on solar panels, from actual homeowners:

1.  Tilt the panels enough so that snow and ice do not accumulate (I would guess this works for a light dusting or a few inches of snow, but not if you get a big storm).

2.  Toss a soft Nerf football at the panels to clear away a small patch – when the sun warms that area, the rest of the snow will melt away.

3.  Put rock salt around the solar panels to prevent freezing (some have noted that this may damage the panels).

4.  Get out a garden hose and spray away the snow from the solar panels.

5.  Use heat tape around the edges of the panels.

What do you think of these options?  Have you had to deal with snow on solar panels?  If you have any additional tips for removing snow from solar panels, please share them below!