This week on Ask Dr. Kaye, we’re going to take a look at one of the most promising renewable energy sources - solar power. The sun’s energy is everywhere, and nearly limitless. On an average bright sunny day, solar radiation provides ~ 1,000 watts of energy per square meter (about 10 square feet). Of course this figure varies with atmospheric conditions, weather, latitude, and other factors - but that is a TON of energy. And it’s free, and nearly everywhere. Renewable Energy – Spotlight on Solar Power | Unofficial Networks

Renewable Energy - Spotlight on Solar Power

Renewable Energy - Spotlight on Solar Power

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Renewable Energy - Spotlight on Solar Power

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Solar Array in the Alpes de Haute Provence region of France.

This week on Ask Dr. Kaye, we’re going to take a look at one of the most promising renewable energy sources – solar power. The sun’s energy is everywhere, and nearly limitless. On an average bright sunny day, solar radiation provides ~ 1,000 watts of energy per square meter (about 10 square feet). Of course this figure varies with atmospheric conditions, weather, latitude, and other factors – but that is a TON of energy. And it’s free, and nearly everywhere.

If that is the case, then why aren’t there giant arrays of solar panels everywhere, powering all of humanity’s electrical needs? Unfortunately, converting that abundant, free energy into electricity in a safe, reliable, and efficient manner is still slightly beyond our grasp. In recent times, however, we are making great headway towards that goal.

How Does It Work?

Solar radiation is converted into electricity inside of photovoltaic cells. “Photo” means “light” and “voltaic” refers to the ability to generate electricity – thus photovoltaic cells create electricity from light. When wired together, photovoltaic cells (aka “PV”) become a module. Modules wired together are then called an array, which is colloquially referred to as a “solar panel.”

PV cells generate electricity through the photovoltaic effect, which occurs when certain materials absorb photons of light energy and release electrons. These electrons are harnessed and then used to generate a current of electricity.

Cartoon showing flow of electrons in a solar photovoltaic cell. From Sandia Labs, USDE.

Solar technology is much older than you might think. French physicist Edmund Bequerel first noticed the PV effect in 1839, but wasn’t until 1905 when the genius Albert Einstein  investigated the physics of light and its potential to generate electric currents, work which later won him the Nobel Prize in physics. Bell Labs developed the first photovoltaic module in 1954.

At the heart of a solar panel lies a carefully selected package of materials specifically chosen for their ability to produce electricity via the photovoltaic effect. Silicon is the most prevalent semiconducting material inside a solar panel. When photons hit the silicon wafers, electrons are knocked loose from each silicon atom, and they are forced by an electric field to rush through the solar panel to the other side, where they are collected and used to generate a direct current.

Pure silicon is an inefficient conductor of electricity, so different materials are added to it in a process called “doping” to enhance performance, much like the actions of Floyd Landis in the Tour de France.  Common doping materials in solar panels include phosphorous, which makes “n-type” silicon, and boron, which makes “p-type” silicon. The N-type is negative, having an excess of electrons, whereas the P-type is positive, as it has holes for the electrons to fill.

Silicon atom, from the US Dept. of Energy.

When you place these two doped sheets of silicon together and bombard them with energy in the form of photons in sunlight, electrons are knocked loose and flow from the negative side to the positive side, creating a current that then makes a voltage.

There’s more to solar panels than two layers of doped silicon, however. Silicon happens to be extremely reflective, which is not a good property when you are making a device that needs to suck in as much light as possible. To combat this, an anti-reflective coating is added to glass that forms the top cover of the panel. Further refinement is needed to get past another basic physical property – the different wavelengths of the individual components of sunlight.

Solar panels must also include materials that overcome a hindrance in photon absorption at different wavelengths of light – or what is known as band gap energy. Each wavelength of light has it’s own characteristic energy level, and solar panels include sheets of materials such as gallium arsenide and aluminum gallium arsenide that filter out the wavelengths and differentially absorb their photons at different depths in the panel section to facilitate maximum free electron generation within the silicon. Even with the best of materials, however, modern production-grade solar farms still display limited efficiency due to this inhibition.

A functioning solar panel electricity generation system must also include a means of storing the electricity generated from the panels, and making it usable by our electrical grid (or your house). Power is typically stored in batteries, and then released to a device that turns the direct current (like that in your car) into alternating current (like that in your house). This is typically achieved via a device called an inverter. Some solar installations sell excess electricity back to power grids, and draw from them only when they need power (i.e. at night).

Where Is it Successfully in Use?

Solar technology is truly everywhere, although the highest-efficiency installations tend to be located in places where there is abundant sunshine year–round, such as Australia, the West -Central US, and Germany.

The largest solar farm in the world is found in China – the Huanghe Hydropower Golmud Solar Park, which generates up to 200MW of electricity.  The second largest is the Ukraine’s Petrovo Solar Park (180MW), and the Sarnia facility in Canada (97MW). Australia is currently building three large solar power plants in the rage of 180 MW to 150 MW.  The largest installation in the USA is found on Nellis Air Force Base, a 70,000 panel installation that can generate up to 14MW.

Solar panel arrays at the Golmud Solar Park in China, from LDK Investor's Group.

Smaller solar panel arrays are in use on rooftops around the world. Not only do people lower their electricity bills by installing solar on their rooftops, they can even potentially make money by selling electricity back to the grid in times of high production. Some people even use passive solar power to heat hot water for showering, which saves electricity. 

Do Ski Areas Use Solar?

Many ski areas have adapted solar technology with great success. Here in California, we enjoy hundreds of days a year of sunshine and some of our resorts have installed solar panels, but they are mostly used for outreach and marketing purposes. As of 2010, there were two ski areas in the world with ski lifts that are entirely solar powered – the Westendorf resort in Austria, and the Tenna resort in Switzerland.

Tenna is a farming village with a population of 112 – and given what they accomplished, 80 of them must be either geniuses or really crafty engineers. In order to make their new t-bars 100% solar powered, they needed far more space for solar panels than they had available on the rooftops of the lift terminals. To solve this problem, they designed a suspension cable system that placed a network of smaller panels up the stringline of the T-bar cables.

Solar powered ski lift at Tenna, Switzerland. From Discovery.com.

Here in the US, Aspen leads the solar charge among ski areas, with about 170 kW of solar energy production capacity on their ski patrol headquarters, the Little Nell hotel, an employee housing building, and one array out on their golf course clubhouse (and on their golf carts!) In fact, the electrical utility in Aspen is on track to become the first carbon-neutral utility by 2015.

The Future of Solar Power

Earlier I briefly touched upon the inefficiency of modern solar panels due to the limitations of silicon as a semiconductor, light wavelength band gap, and the inability of available technology to deal with those main issues. What is the current state-of-the-art in modern research and technology – what is being done on the cutting edge of solar research right now?

Last year, MIT researcher Dr. Daniel Nocera created a solar power-producing artificial “leaf” out of silicon and inexpensive metal elements. Nocera’s man-made leaf mimics the natural process of photosynthesis by allowing light photons to split water molecules into component hydrogen and oxygen atoms, which generate small amounts of electricity in cells woven into it’s structure. The MIT team received $4million in ARPA-E funds to try to bring this product to market in the next few years – watch out for solar panel leaves in a leafy city near you.

Another promising front in the solar panel efficiency battle is the use of quantum materials. Earlier we discussed how photons hit doped silicon and cause it to give off an electron. Imagine if this process could be enhanced further by including materials that caused the silicon to dump two or more electrons instead of just one? Scientists from the National Renewable Energy Laboratory did just that – they developed “quantum dots” that turned the energy typically lost in heat production into usable electricity generation in prototype solar panels, a process called “Multiple Excitation Generation.” If this technology matures, it could revolutionize the solar industry.

These exciting technologies are two examples of cutting-edge solar power research. Follow these links to read more about others, such as solar windows, organic solar cells, and a different kind of quantum dot cells.

I asked DJ and avid backcountry skier Aaron Pope, who is the Manager of Sustainability Programs at the California Academy of Sciences Museum in San Franscisco, to give us his take on the importance of developing new solar technology.

“Modernizing our energy economy will take collective effort and rapid scientific advancement. As you can see, there are some really innovative technologies emerging these days. The next few years should see an explosion in new solar products coming to market, making power from the sun a more efficient, affordable solution. It’s actually already a quite a bargain, once you factor in the hidden costs of burning fossil fuels. We should also focus on efficiency and conservation measures, the cheapest and cleanest solution of all.”

Take a look at the map of the US, Germany, and Spain – a great deal of our country is already ripe with solar energy generation potential. When technology advances to the point where quantuum materials and synthetic nanotechnology can bring us cost-effective solar solutions, we will be ready. And our economy will be more than ready for the jobs needed to build modern solar plants, if we manage to keep them in our country by investing in education needed to train our workers to build these third-geenration solar panels.

Imagine a Squaw Valley entirely off the grid – Headwall and KT spinning on storm days powered entirely by stored up sunlight banked during our abundant days of sunshine. It’s not a stretch to think that with a seemingly “never-ending-week-after-week-of-nothing-but-sun”  season like we have had in 2012, if this tchnology was in place,  our lifts could be solar powered for the following decade. If it ever snows again, that is.

Solar power generation potential in the US, Germany, and Spain, from the SEIA.

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