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Solar energy installations around the world are growing exponentially as solar power becomes cheaper and more reliable.  It is now cost effective in most countries to convert a home to full energy self sufficiency through the use of a solar panel system, connected to the grid.


So what is Solar Power and how does it work?



You've probably seen calculators with solar cells -- devices that never need batteries and in some cases, don't even have an off button. As long as there's enough light, they seem to work forever. You may also have seen larger solar panels, perhaps on emergency road signs, call boxes, buoys and even in parking lots to power the lights.

Although these larger panels aren't as common as solar-powered calculators, they're out there and not that hard to spot if you know where to look. In fact, photovoltaics -- which were once used almost exclusively in space, powering satellites' electrical systems as far back as 1958 -- are being used more and more in less exotic ways. The technology continues to pop up in new devices all the time, from sunglasses to electric vehicle charging stations.

The hope for a "solar revolution" has been floating around for decades -- the idea that one day we'll all use free electricity fro­m the sun. This is a seductive promise, because on a bright, sunny day, the sun's rays give off approximately 1,000 watts of energy per square meter of the planet's surface. If we could collect all of that energy, we could easily power our homes and offices for free.



Photovoltaic Cells: Converting Photons to Electrons

­­The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity. A module is a group of cells connected electrically and packaged into a frame (more commonly known as a solar panel), which can then be grouped into larger solar arrays, like the one operating at Nellis Air Force Base in Nevada.

­Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely.

PV cells also all have one or more electric field that acts to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off for external use, say, to power a calculator. This current, together with the cell's voltage (which is a result of its built-in electric field or fields), defines the power (or wattage) that the solar cell can produce.

That's the basic process, but there's really much more to it. On the next page, let's take a deeper look into one example of a PV cell: the single-crystal silicon cell.



How Silicon Makes a Solar Cell

Silicon has some special chemical properties, especially in its crystalline form. An atom of sili­con has 14 electrons, arranged in three different shells. The first two shells -- which hold two and eight electrons respectively -- are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell.

The only problem is that pure crystalline silicon is a poor conductor of electricity because none of its electrons are free to move about, unlike the electrons in more optimum conductors like copper. To address this issue, the silicon in a solar cell has impurities -- other atoms purposefully mixed in with the silicon atoms -- which changes the way things work a bit. We usually think of impurities as something undesirable, but in this case, our cell wouldn't work without them. Consider silicon with an atom of phosphorous here and there, maybe one for every million silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. It doesn't form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.

When energy is added to pure silicon, in the form of heat for example, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons, called free carriers, then wander randomly around the crystalline lattice looking for another hole to fall into and carrying an electrical current. However, there are so few of them in pure silicon, that they aren't very useful.

But our impure silicon with phosphorous atoms mixed in is a different story. It takes a lot less energy to knock loose one of our "extra" phosphorous electrons because they aren't tied up in a bond with any neighboring atoms. As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon. The process of adding impurities on purpose is called doping, and when doped with phosphorous, the resulting silicon is called N-type ("n" for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon.

The other part of a typical solar cell is doped with the element boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type ("p" for positive) has free openings and carries the opposite (positive) charge.


Anatomy of a Solar Cell

B­efore now, our two separate pieces of silicon were electrically neutral; the interesting part begins when you put them together. That's because without an electric field, the cell wouldn't work; the field forms when the N-type and P-type silicon come into contact. Suddenly, the free electrons on the N side see all the openings on the P side, and there's a mad rush to fill them. Do all the free electrons fill all the free holes? No. If they did, then the whole arrangement wouldn't be very useful. However, right at the junction, they do mix and form something of a barrier, making it harder and harder for electrons on the N side to cross over to the P side. Eventually, equilibrium is reached, and we have an electric field separating the two sides.

This electric field acts as a diode, allowing (and even pushing) electrons to flow from the P side to the N side, but not the other way around. It's like a hill -- electrons can easily go down the hill (to the N side), but can't climb it (to the P side).

When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs. Each photon with enough energy will normally free exactly one electron, resulting in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the N side and the hole to the P side. This causes further disruption of electrical neutrality, and if we provide an external current path, electrons will flow through the path to the P side to unite with holes that the electric field sent there, doing work for us alo­ng the way. The electron flow provides the current, and the cell's electric field causes a voltage. With both current and voltage, we have power, which is the product of the two.

There are a few more components left before we can really use our cell. Silicon happens to be a very shiny material, which can send photons bouncing away before they've done their job, so

an antireflective coating is applied to reduce those losses. The final step is to install something that will protect the cell from the elements -- often a glass cover plate. PV modules are generally made by connecting several individual cells together to achieve useful levels of voltage and current, and putting them in a sturdy frame complete with positive and negative terminals.

How much sunlight energy does our PV cell absorb? Unfortunately, probably not an awful lot. In 2006, for example, most solar panels only reached efficiency levels of about 12 to 18 percent. The most cutting-edge solar panel system that year finally muscled its way over the industry's long-standing 40 percent barrier in solar efficiency -- achieving 40.7 percent [source: U.S. Department of Energy]. So why is it such a challenge to make the most of a sunny day?




Energy Loss in a Solar Cell

Visible light is only part of the electromagnetic spectrum. Electromagnetic rad­iation is not monochromatic -- it's made up of a range of different wavelengths, and therefore energy levels. (See How Light Works for a good discussion of the electromagnetic spectrum.)

­Light can be separated into different wavelengths, which we can see in the form of a rainbow. Since the light that hits our cell has photons of a wide range of energies, it turns out that some of them won't have enough energy to alter an electron-hole pair. They'll simply pass through the cell as if it were transparent. Still other photons have too much energy. Only a certain amount of energy, measured in electron volts (eV) and defined by our cell material (about 1.1 eV for crystalline silicon), is required to knock an electron loose. We call this the band gap energy of a material. If a photon has more energy than the required amount, then the extra energy is lost. (That is, unless a photon has twice the required energy, and can create more than one electron-hole pair, but this effect is not significant.) These two effects alone can account for the loss of about 70 percent of the radiation energy incident on our cell.

Why can't we choose a material with a really low band gap, so we can use more of the photons? Unfortunately, our band gap also determines the strength (voltage) of our electric field, and if it's too low, then what we make up in extra current (by absorbing more photons), we lose by having a small voltage. Remember that power is voltage times current. The optimal band gap, balancing these two effects, is around 1.4 eV for a cell made from a single material.

We have other losses as well. Our electrons have to flow from one side of the cell to the other through an external circuit. We can cover the bottom with a metal, allowing for good conduction, but if we completely cover the top, then photons can't get through the opaque conductor and we lose all of our current (in some cells, transparent conductors are used on the top surface, but not in all). If we put our contacts only at the sides of our cell, then the electrons have to travel an extremely long distance to reach the contacts. Remember, silicon is a semiconductor -- it's not nearly as good as a metal for transporting current. Its internal resistance (called series resistance) is fairly high, and high resistance means high losses. To minimize these losses, cells are typically covered by a metallic contact grid that shortens the distance that electrons have to travel while covering only a small part of the cell surface. Even so, some photons are blocked by the grid, which can't be too small or else its own resistance will be too high.




Solar-powering a House

Wh­at would you have to do to power your house with solar energy? Although it's not as simple as just slapping some modules on your roof, it's not extremely difficult to do, either.

First of all, not every roof has the correct orientation or angle of inclination to take full advantage of the sun's energy. Non-tracking PV systems in the Northern Hemisphere should ideally point toward true south, although orientations that face in more easterly and westerly directions can work too, albeit by sacrificing varying degrees of efficiency. Solar panels should also be inclined at an angle as close to the area's latitude as possible to absorb the maximum amount of energy year-round. A different orientation and/or inclination could be used if you want to maximize energy production for the morning or afternoon, and/or the summer or winter. Of course, the modules should never be shaded by nearby trees or buildings, no matter the time of day or the time of year. In a PV module, if even just one of its cells is shaded, power production can be significantly reduced.

If you have a house with an unshaded, southward-facing roof, you need to decide what size system you need. This is complicated by the facts that your electricity production depends on the weather, which is never completely predictable, and that your electricity demand will also vary. Luckily, these hurdles are fairly easy to clear. Meteorological data gives average monthly sunlight levels for different geographical areas. This takes into account rainfall and cloudy days, as well as altitude, humidity and other more subtle factors. You should design for the worst month, so that you'll have enough electricity year-round. With that data and your average household demand (your utility bill conveniently lets you know how much energy you use every month), there are simple methods you can use to determine just how many PV modules you'll need. You'll also need to decide on a system voltage, which you can control by deciding how many modules to wire in series.

Solving Solar Power Issues

The thought of living at the whim of the weatherman probably doesn't thrill most people, but three main options can ensure you still have power even if the sun isn't cooperating. If you want to live completely off the grid, but don't trust your PV panels to supply all the electricity you'll need in a pinch, you can use a backup generator when solar supplies run low. The second stand-alone system involves energy storage in the form of batteries. Unfortunately, batteries can add a lot of cost and maintenance to a PV system, but it's currently a necessity if you want to be completely independent.

The alternative is to connect your house to the utility grid, buying power when you need it and selling it back when you produce more than you use. This way, the utility acts as a practically infinite storage system. Keep in mind though, government regulations vary depending on location and are subject to change. Your local utility company may or may not be required to participate, and the buyback price can vary greatly. You'll also probably need special equipment to make sure the power you're looking to sell the utility company is compatible with their own. Safety is an issue as well. The utility has to make sure that if there's a power outage in your neighborhood, your PV system won't continue to feed electricity into power lines that a lineman will think are dead. This is a dangerous situation called islanding, but it can be avoided with an anti-islanding inverter -- something we'll get to on the next page.

If you decide to use batteries instead, keep in mind that they'll have to be maintained, and then replaced after a certain number of years. Most solar panels tend to last about 30 years (and improved longevity is certainly one research goal), but batteries just don't have that kind of useful life [source: National Renewable Energy Laboratory]. Batteries in PV systems can also be very dangerous because of the energy they store and the acidic electrolytes they contain, so you'll need a well-ventilated, nonmetallic enclosure for them.

Although several different kinds of batteries are commonly used, the one characteristic they should all have in common is that they are deep-cycle batteries. Unlike your car battery, which is a shallow-cycle battery, deep-cycle batteries can discharge more of their stored energy while still maintaining long life. Car batteries discharge a large current for a very short time -- to start your car -- and are then immediately recharged as you drive. PV batteries generally have to discharge a smaller current for a longer period of time (such as at night or during a power outage), while being charged during the day. The most commonly used deep-cycle batteries are lead-acid batteries (both sealed and vented) and nickel-cadmium batteries, both of which have various pros and cons.



Finishing Your Solar Power Setup

The use of batteries requires the installation of another component called a charge controller. Batteries last a lot longer if they aren't overcharged or drained too much. That's what a charge controller does. Once the batteries are fully charged, the charge controller doesn't let current from the PV modules continue to flow into them. Similarly, once the batteries have been drained to a certain predetermined level, controlled by measuring battery voltage, many charge controllers will not allow more current to be drained from the batteries until they have been recharged. The use of a charge controller is essential for long battery life.

The other problem besides energy storage is that the electricity generated by your solar panels, and extracted from your batteries if you choose to use them, is not in the form that's supplied by your utility or used by the electrical appliances in your house. The electricity generated by a solar system is direct current, so you'll need an inverter to convert it into alternating current. And like we discussed on the last page, apart from switching DC to AC, some inverters are also designed to protect against islanding if your system is hooked up to the power grid.

Most large inverters will allow you to automatically control how your system works. Some PV modules, called AC modules, actually have an inverter already built into each module, eliminating the need for a large, central inverter, and simplifying wiring issues.

Throw in the mounting hardware, wiring, junction boxes, grounding equipment, overcurrent protection, DC and AC disconnects and other accessories, and you have yourself a system. You must follow electrical codes (there's a section in the National Electrical Code just for PV), and it's highly recommended that a licensed electrician who has experience with PV systems do the installation. Once installed, a PV system requires very little maintenance (especially if no batteries are used), and will provide electricity cleanly and quietly for 20 years or more.


Developments in Solar Cell Technology

We've talked a lot about how a typical PV system operates, but issues concerning cost-effectiveness (which we'll get into more on the next page) have spurred endless research efforts aimed at developing and fine-tuning new ways to make solar power increasingly competitive with traditional energy sources.

For example, single-crystal silicon isn't the only material used in PV cells. Polycrystalline silicon is used in an attempt to cut man­ufacturing costs, although the resulting cells aren't as efficient as single crystal silicon. Second-generation solar cell technology consists of what's known as thin-film solar cells. While they also tend to sacrifice some efficiency, they're simpler and cheaper to produce -- and they become more efficient all the time. Thin-film solar cells can be made from a variety of materials, including amorphous silicon (which has no crystalline structure), gallium arsenide, copper indium diselenide and cadmium telluride.

Another strategy for increasing efficiency is to use two or more layers of different materials with different band gaps. Remember that depending on the substance, photons of varying energies are absorbed. So by stacking higher band gap material on the surface to absorb high-energy photons (while allowing lower-energy photons to be absorbed by the lower band gap material beneath), much higher efficiencies can result. Such cells, called multi-junction cells, can have more than one electric field.

Concentrating photovoltaic technology is another promising field of development. Instead of simply collecting and converting a portion of whatever sunlight just happens to shine down and be converted into electricity, concentrating PV systems use the addition of optical equipment like lenses and mirrors to focus greater amounts of solar energy onto highly efficient solar cells. Although these systems are generally pricier to manufacture, they have a number of advantages over conventional solar panel setups and encourage further research and development efforts.

All these different versions of solar cell technology have companies dreaming up applications and products that run the gamut, from solar powered planes and space-based power stations to more everyday items like PV-powered curtains, clothes and laptop cases. Not even the miniature world of nanoparticles is being left out, and researchers are even exploring the potential for organically produced solar cells.

But if photovoltaics are such a wonderful source of free energy, then why doesn't the whole world run on solar power?


Solar Power Costs

Some people have a flawed concept of solar energy. While it's true that sunlight is free, the electricity generated by PV systems is not. There are lots of factors involved in determining whether installing a PV system is worth the price.

First, there's the question of where you reside. People living in sunny parts of the world start out with a greater advantage than those settled in less sun-drenched locations, since their PV systems are generally able to generate more electricity. The cost of utilities in an area should be factored in on top of that. Electricity rates vary greatly from place to place, so someone living farther north may still want to consider going solar if their rates are particularly high.

Next, there's the installation cost; as you probably noticed from our discussion of a household PV system, quite a bit of hardware is needed. As of 2009, a residential solar panel setup averaged somewhere between $8 and $10 per watt to install [source: National Renewable Energy Laboratory]. The larger the system, the less it typically costs per watt. It's also important to remember that many solar power systems don't completely cover the electricity load 100 percent of the time. Chances are, you'll still have a power bill, although it'll certainly be lower than if there were no solar panels in place.

Despite the sticker price, there are several potential ways to defray the cost of a PV system for both residents and corporations willing to upgrade and go solar. These can come in the form of federal and state tax incentives, utility company rebates and other financing opportunities. Plus, depending on how large the solar panel setup is -- and how well it performs -- it could help pay itself off faster by creating the occasional surplus of power. Finally, it's also important to factor in home value estimates. Installing a PV system is expected to add thousands of dollars to the value of a home.

Right now, solar power still has some difficulty competing with the utilities, but costs are coming down as research improves the technology. Advocates are confident that PV will one day be cost-effective in urban areas as well as remote ones. Part of the problem is that manufacturing needs to be done on a large scale to reduce costs as much as possible. That kind of demand for PV, however, won't exist until prices fall to competitive levels. It's a catch-22. Even so, as demand and module efficiencies rise constantly, prices fall, and the world becomes increasingly aware of the environmental concerns associated with conventional power sources, it's likely photovoltaics will have a promising future.


How Solar Thermal Power Works



Most of us don't think much about where our electricity comes from, only that it's available and plentiful. Electricity generated by burning fossil fuels such as coal, oil and natural gas, emits carbon dioxide, nitrogen oxides and sulfur oxides -- gases scientists believe contribute to climate change. Solar thermal (heat) energy is a carbon-free, renewable alternative to the power we generate with fossil fuels like coal and gas. This isn't a thing of the future, either. Between 1984 and 1991, the United States built nine such plants in California's Mojave Desert, and today they continue to provide a combined capacity of 354 megawatts annually, power used in 500,000 Californian homes [source: Hutchinson]. Reliable power, at that. In 2008 when six days of peak demand buckled the power grid and brought electricity outages in California, those solar thermal plants continued to produce at 110 percent capacity [source: Kanellos].

Wondering where the technology's been since then? In the 1990s when prices of natural gas dropped, so did interest in solar thermal power. Today, though, the technology is poised for a comeback. It's estimated by the U.S. National Renewable Energy Laboratories that solar thermal power could provide hundreds of gigawatts of electricity, equal to more than 10 percent of demand in the United States [source: LaMonica].

Shake the image of solar panels from your head -- that kind of demand is going to require power plants. There are two main ways of generating energy from the sun. Photovoltaic (PV) and concentrating solar thermal (CST), also known as concentrating solar power (CSP) technologies.

PV converts sunlight directly into electricity. These solar cells are usually found powering devices such as watches, sunglasses and backpacks, as well as providing power in remote areas.

Solar thermal technology is large-scale by comparison. One big difference from PV is that solar thermal power plants generate electricity indirectly. Heat from the sun's rays is collected and used to heat a fluid. The steam produced from the heated fluid powers a generator that produces electricity. It's similar to the way fossil fuel-burning power plants work except the steam is produced by the collected heat rather than from the combustion of fossil fuels.


Solar Thermal Systems



There are two types of solar thermal systems: passive and active. A passive system requires no equipment, like when heat builds up inside your car when it's left parked in the sun. An active system requires some way to absorb and collect solar radiation and then store it.

Solar thermal power plants are active systems, and while there are a few types, there are a few basic similarities: Mirrors reflect and concentrate sunlight, and receivers collect that solar energy and convert it into heat energy. A generator can then be used to produce electricity from this heat energy.

The most common type of solar thermal power plants, including those plants in California 's Mojave Desert , use a parabolic trough design to collect the sun's radiation. These collectors are known as linear concentrator systems, and the largest are able to generate 80 megawatts of electricity [source: U.S. Department of Energy]. They are shaped like a half-pipe you'd see used for snowboarding or skateboarding, and have linear, parabolic-shaped reflectors covered with more than 900,000 mirrors that are north-south aligned and able to pivot to follow the sun as it moves east to west during the day. Because of its shape, this type of plant can reach operating temperatures of about 750 degrees F (400 degrees C), concentrating the sun's rays at 30 to 100 times their normal intensity onto heat-transfer-fluid or water/steam filled pipes [source: Energy Information Administration]. The hot fluid is used to produce steam, and the steam then spins a turbine that powers a generator to make electricity.

While parabolic trough designs can run at full power as solar energy plants, they're more often used as a solar and fossil fuel hybrid, adding fossil fuel capability as backup.

Solar power tower systems are another type of solar thermal system. Power towers rely on thousands of heliostats, which are large, flat sun-tracking mirrors, to focus and concentrate the sun's radiation onto a single tower-mounted receiver. Like parabolic troughs, heat-transfer fluid or water/steam is heated in the receiver (power towers, though, are able to concentrate the sun's energy as much as 1,500 times), eventually converted to steam and used to produce electricity with a turbine and generator.



Power tower designs are still in development but could one day be realized as grid-connected power plants producing about 200 megawatts of electricity per tower.

A third system is the solar dish/engine. Compared to the parabolic trough and power towers, dish systems are small producers (about 3 to 25 kilowatts). There are two main components: the solar concentrator (the dish) and the power conversion unit (the engine/generator). The dish is pointed at and tracks the sun and collects solar energy; it's able to concentrate that energy by about 2,000 times. A thermal receiver, a series of tubes filled with a cooling fluid (such as hydrogen or helium), sits between the dish and the engine. It absorbs the concentrated solar energy from the dish, converts it to heat and sends that heat to the engine where it becomes electricity.


Solar Thermal Heat

Solar thermal systems are a promising renewable energy solution -- the sun is an abundant resource. Except when it's nighttime. Or when the sun is blocked by cloud cover. Thermal energy storage (TES) systems are high-pressure liquid storage tanks used along with a solar thermal system to allow plants to bank several hours of potential electricity. Off-peak storage is a critical component to the effectiveness of solar thermal power plants.

Three primary TES technologies have been tested since the 1980s when the first solar thermal power plants were constructed: a two-tank direct system, a two-tank indirect system and a single-tank thermocline system.

In a two-tank direct system, solar thermal energy is stored right in the same heat-transfer fluid that collected it. The fluid is divided into two tanks, one tank storing it at a low temperature and the other at a high temperature. Fluid stored in the low temperature tank runs through the power plant's solar collector where it's reheated and sent to the high temperature tank. Fluid stored at a high temperature is sent through a heat exchanger that produces steam, which is then used to produce electricity in the generator. And once it's been through the heat exchanger, the fluid then returns to the low temperature tank.

A two-tank indirect system functions basically the same as the direct system except it works with different types of heat-transfer fluids, usually those that are expensive or not intended for use as storage fluid. To overcome this, indirect systems pass low temperature fluids through an additional heat exchanger.

Unlike the two-tank systems, the single-tank thermocline system stores thermal energy as a solid, usually silica sand. Inside the single tank, parts of the solid are kept at low to high temperatures, in a temperature gradient, depending on the flow of fluid. For storage purposes, hot heat-transfer fluid flows into the top of the tank and cools as it travels downward, exiting as a low temperature liquid. To generate steam and produce electricity, the process is reversed.

Solar thermal systems that use mineral oil or molten salt as the heat-transfer medium are prime for TES, but unfortunately without further research, systems that run on water/steam aren't able to store thermal energy. Other advancements in heat-transfer fluids include research into alternative fluids, using phase-change materials and novel thermal storage concepts all in an effort to reduce storage costs and improve performance and efficiency.


Solar Thermal Chimneys

Just as solar thermal greenhouses are a way to apply solar thermal technologies to an everyday need, solar thermal chimneys, or thermal chimneys, also capitalize on thermal mass materials. Thermal chimneys are passive solar ventilation systems, which means they are nonmechanical. Examples of mechanical ventilation include whole-house ventilation that uses fans and ducts to exhaust stale air and supply fresh air. Through convective cooling principles, thermal chimneys allow cool air in while pushing hot air from the inside out. Designed based on the fact that hot air rises, they reduce unwanted heat during the day and exchange interior (warm) air for exterior (cool) air.

Thermal chimneys are typically made of a black, hollow thermal mass with an opening at the top for hot air to exhaust. Inlet openings are smaller than exhaust outlets and are placed at low to medium height in a room. When hot air rises, it escapes through the exterior exhaust outlet, either to the outside or into an open stairwell or atria. As this happens, an updraft pulls cool air in through the inlets.

In the face of global warming, rising fuel costs and an ever-growing demand for energy, energy needs are expected to increase by nearly the equivalent of 335 million barrels of oil per day, mostly for electricity [source: Meisen]. Whether big or small, on or off the grid, one of the great things about solar thermal power is that it exists right now, no waiting. By concentrating solar energy with reflective materials and converting it into electricity, modern solar thermal power plants, if adopted today as an indispensable part of energy generation, may be capable of sourcing electricity to more than 100 million people in the next 20 years [source: Brakmann]. All from one big renewable resource: the sun.


Solar’s Future According to Intersolar: 100 GW per Year - In 2013!  This has doubled installed capacity Worldwide in last 2 1/2 years!

Intersolar Founder and CEO Markus Elsaesser on the state of solar.

Herman K. Trabish: July 16, 2013



Few people have a better view of the solar industry or have been more astute at predicting where it would go than Intersolar founder and CEO Markus Elsaesser. He talked to GTM about his perspective and solar's future last week at Intersolar North America 2013 in San Francisco .

Elsaesser first brought his successful international event to San Francisco in 2008, just as the U.S. solar industry was starting to take off. Then he took Intersolar to India when that country only had 20 megawatts of grid-connected solar, but had just instituted a target of 20,000 megawatts by 2022.

Two years later, he founded Intersolar China just before solar’s unprecedented expansion there. And this year, Intersolar opened in Sao Paulo , Brazil , just as the international industry has begun looking to Latin America.

The only time his timing was off was at the beginning. He founded the first Intersolar in 1991, when he was still a college student. “There was almost no industry or market, just the vision that renewables would someday play a role in the energy supply,” Elsaesser said. German lawmaker and solar advocate “Hermann Scheer was a speaker at the first conference and really inspired me. He was a visionary. The feed-in tariff he helped design and put in place created the international market.”

But that market didn’t take off until 2001, when, thanks to its feed-in tariff, Germany took over the global market. “There was so much demand for exhibitor space we had to move to Munich in 2008. About the same time, we decided to start the U.S. show in San Francisco .”

The decision to create a new Intersolar is based on the local market and local policies, Elsaesser explained. But he often sees indications that those things will happen before anybody else seems to perceive them.

Just before India introduced its 20,000-megawatt target, Elsaesser said, India ’s energy minister came to Intersolar in Munich . “He was more interested in wind and biomass than in solar at the time and was only scheduled to stay for two hours. He stayed for three days. India is now a gigawatt-scale market.”

In 2010, Elsaesser met with Saudi Arabia ’s electricity and commerce ministers in Riyadh . Then, he said, “they sent a representative to our show in Munich . After that, Saudi Arabia set a goal to implement 48 gigawatts of solar.”

Like India in 2009, Brazil now has only 20 megawatts of installed grid-connected capacity. “But we had our conference in August, and they introduced net metering and had it in place by the end of the year,” Elsaesser said. There were 200 attendees at the one-day conference and no exhibits.

“We introduced the feed-in tariff and addressed things like tax issues and regulatory barriers and introduced the idea of an industry association. At the next Intersolar Brazil, we will have exhibitors.”



Charting the Fall of Solar Prices

It's taken 60 years, but solar is tantalizingly close to beating fossil fuels on price.






The prices of solar cells are falling rapidly, and will keep doing so for the next few years. The big questions revolve around the rate of the price declines. And the panels themselves aren't the only place where cost reductions will be found. America has very high "soft costs" -- installation, permitting, marketing etc. Whittling down these expenses will help, too.

Solar is taking off at a breakneck pace (admittedly from a tiny base). Stephen Lacey at Greentech Media provides the striking figures illustrating the exponential growth of solar photovoltaics (PV) in the past few years:

It took nearly four decades to install 50 gigawatts of PV capacity worldwide. But in the last 2 ½ years, the industry jumped from 50 gigawatts of PV capacity to just over 100 gigawatts. At the same time, global module prices have fallen 62 percent since January 2011. Even more amazingly, the solar industry is on track to install another 100 gigawatts worldwide by 2015 -- nearly doubling solar capacity in the next 2 1/2 years.




Even though prices of modules -- the solar panel itself -- have plummeted in the last few years, a report from the Department of Energy's Lawrence Berkeley National Laboratory reveals that other costs haven't been so easy to bring down:

Non-module costs -- such as inverters, mounting hardware, and the various non-hardware or "soft" costs -- have also fallen over the long-term but have remained relatively flat in recent years. As a result, they now represent a sizable fraction of the total installed price of PV systems.

So, Greentech Media analyst Shyam Mehta cautions that panels getting cheaper actually might not bring down total prices by much:

[There is] the issue of exactly how meaningful a reduction of around $0.20 per watt in module prices (from $0.62 per watt at the end of 2012 to $0.42 per watt in 2017) is in the overall context of [solar] economics. Assuming an installed cost of $2.25 per watt for a utility-scale system in the U.S. right now, our base-case forecast implies a system cost reduction of less than 10 percent...It's not exactly a game-changer.

David Roberts at Grist suggests that reducing the soft costs that are staying stubbornly high in the U.S. will be a key part of driving solar forward:

When it comes to accelerating the wide deployment and falling costs of clean energy, market innovation is every bit as important as technological innovation. Even if PV technology remains static (which of course won't happen), enormous savings could be had simply through market building -- helping markets with high soft costs match the performance of those with low soft costs.


Much of the soft costs holding back solar are related to regulation. In the New York Times, David Crane and Robert F. Kennedy criticize the amount of red tape in the U.S. and advise America to learn something from Germany 's solar success:

In Germany , where sensible federal rules have fast-tracked and streamlined the permit process, the costs are considerably lower. It can take as little as eight days to license and install a solar system on a house in Germany . In the United States , depending on your state, the average ranges from 120 to 180 days.

John Farrell, at the Institute for Local Self-Reliance, considers the size of this disparity all the more reason to be convinced that U.S. solar will keep getting cheaper:

Is it too ambitious to assume the price of solar continues to fall by 7% per year? On the contrary, if the cost of solar continues at that pace, it will take the U.S. until 2025 -- 13 years! -- to match today's cost of solar in Germany . Can anyone honestly claim we'll remain so far behind for so long?





If solar prices do continue to fall quickly, the technology will come ever closer to its moment of glory: (hazily defined, so-called) grid parity. This is when solar can really be called "cheap" -- grid parity comes when solar is less expensive than fossil fuels, even without subsidies. (That fossil fuels receive several types of subsidies, in particular a free pass for carbon dioxide emissions remains a sore spot for solar advocates in the debate about subsidies.) Ambrose Evans-Pritchard at the Telegraph describes the steady march towards this tipping point:

"The US Energy Department expects the cost of solar power to fall by 75pc between 2010 and 2020. By then average costs will have dropped to the $1 per watt for big solar farms, $1.25 for offices and $1.50 for homes, achieving the Holy Grail of grid parity with new coal and gas plants without further need for subsidies...The race is on: somebody, somewhere, is soon going to deliver grid parity with a clarity that silences all critics. Then we can all forget about subsidies for solar, and tax it instead, a future cash cow."

The belief that solar costs will keep falling is by no means universal, but the potential prospect has many energy analysts excited. This is not the 1970s with its brief boom in solar hot water and heating tech. Solar electricity prices have declined dramatically, and could be genuinely cheap in sunny climates in the not-too-distant future.


Lawrence Berkeley National Labs: Solar Costs Continue To Fall



Meanwhile, costs keep falling simply as a consequence of market developments. Lawrence Berkeley National Labs (LBNL) recently released their report summarizing the trends in installed costs of solar installations from 1998 to 2012.  They looked at over 92,000 installations over the past two years, and found that the cost dynamics continue to move strongly downward.

Some of the main findings:

Installations in the U.S. more than quadrupled from 2009 to 2012, going from 7,000 megawatts to 31,000.

Costs continue to fall at a healthy clip, with the most recent year-over-year declines of 14% for systems less than 10 kilowatts (kW), 13% for systems in the 10 – 100 kW range, and 6% for systems larger than 100 kW.  Median installed prices were $5.3, $4.9, and $4.6 per watt respectively. LBNL attributes these declining U.S. prices mainly to falling module prices, which accounted for 80% of the total price drop.

The trend in 2013 appears to be continuing.  The initial data available from the California Solar Initiative shows prices falling by 10-15% in the first six months of this year.

LBNL did note that the module prices appeared to be stabilizing in 2013, but the report also commented that experience from other countries suggests the price declines can and will continue.  The median installed price of small residential PV systems last year (without tax) was $2.6 in Germany (fully half the price in the U.S. ), $3.1 in Australia , and $3.1 per watt in Italy .

Many of these additional gains will come about as a result of reductions in soft costs, as permitting becomes streamlined, and companies develop more efficient customer acquisition and financing tools.

Meanwhile, Deutsche bank’s most recent report – released this month – suggests that within 18 months, 75% of the world’s market will be sustainable for solar (no subsidies needed) as costs continue to fall.  The Bank estimates levelized costs of solar at 10-20 cents per kilowatt-hour, and noted that power purchase agreements in the U.S. were being signed in the range of 9 cents.  So while we have seen a rapid increase in the amount of solar installed to date, it appears as if this is just the beginning.





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