Photovoltaic solar power is the technical term for solar panels that convert sunlight directly into electricity. This is in contrast to techniques that capture solar energy in other ways, or for different uses. Other techniques include hot water heating1 , interior temperature control2 , and concentrated heat for electricity production. If you are interested in electricity production based on solar heat, see our article on Solar Thermal Power.
A photovoltaic (PV) solar panel produces an amount of electricity proportional to the type and intensity of light hitting the surface. Generally only one side of the panel is capable of producing power, so if you turn it to face away from the light source, it will not produce little to no power. Not all solar panels are created equal. Different designs have advantages and disadvantages. We won’t go into too much detail with regards to different types of panels. An in-depth article on the subject can be found at Wikipedia: Solar cell.
Solar PV panels are a form of renewable energy. They have tremendous potential for energy production because they draw directly on the light from the sun. Most renewable forms of energy are based on solar light and heat. In the case of wind or hydro power for instance, it is the sun that drives both the wind and water cycle. Solar PV has the advantage of being a direct conversion of light into electrical energy. In theory, there is more than enough available energy in the sun’s light striking the earth to provide all of the power that humanity currently uses. This is the case even if only a tiny fraction of the land area of the earth were covered in solar panels.
Solar PV has been advancing steadily for decades. In the 1970’s it cost tens of thousands of dollars to buy one watt of solar cells. The cost has dropped to only a few dollars per watt today. Solar PV is edging closer to being cost-competitive with classical forms of electricity production such as coal, nuclear and hydro. In terms of cost, wind power and solar thermal power are two renewable energy resources that are slightly ahead of solar PV.
Things to consider
Power production from solar PV depends on direct sunlight. For maximal power, the panel should be tilted so that it faces directly at the sun at all times during the daytime hours. There are automated computer systems that can do this rather easily in conjunction with electronic motors. A cheaper alternative is to simply install the panel facing the direction that it will absorb the maximal sunlight. In the northern hemisphere of the earth (north of the equator), this means that the panel will usually be angled to face south and upwards at an angle approximately equal to the latitude of its geographical location. In the southern hemisphere, the panel would be facing north.
The number of sunny hours can vary greatly depending on location and season. Using something like this solar atlas for the United States can give you a general idea of where the sunniest areas are. To get a better idea of seasonal variation, one would use a more specific solar calculator tool such as this one, again for the United States. These information tools amalgamate several different pieces of information, including average cloud cover.
Solar PV installations can take up a fairly large area. One square meter of solar panel, in ideal conditions, will be hit with about 1000 watts per meter squared of light from the sun. The efficiencies of panels can vary between 6% and 42% depending on type and quality3 . So this means that the panel will produce between 60 and 420 watts of power. If built, one million such panels would take up minimally 1km2 and likely around 2-3 km2. This area would produce between 60 and 420 megawatts of electricity, in times of perfectly clear sunshine. This rough estimate should give you an idea of the space usage for large installations.
People have considered the idea that by distributing solar PV production around the planet in the sunniest regions, we could power the entire planet. In short: this is possible, but not feasible. Yet. It may be feasible someday, but there are some critical problems with this approach today.
Building that many solar PV panels would currently be prohibitively expensive. There are less costly alternatives available, even among renewable energy sources. These less costly forms of power are thus regarded as a more feasible solution.
Also, it would be extremely expensive to build the infrastructure necessary to transmit the electricity to where it is needed. Heavy-duty transmission lines crossing hundreds of kilometers can easily cost billions of dollars. This cost rapidly becomes unmanageable when we consider a global network being powered by the sunniest places in the world.
Solar PV power is not dispatchable. That is, it cannot be turned on at will. If the sun isn’t shining, you won’t get power from a solar PV installation. For a deeper look at why dispatchable power sources are necessary, see our article on reliable power. You may also be curious about what forms of renewable energy are dispatchable.
This is not to say that solar PV is useless. Just because something cannot power the entire world power grid does not mean it is useless. Despite what power industry lobbyists might say, there is no single power source that is cost-effective in every area of the world. Different areas have different resources. This includes natural resources such as coal, uranium, rivers, wind, and sunshine. However it can also include human and knowledge-based resources that are necessary for implementing a power system. It makes sense to tailor power systems to their locale in terms of the resources that are naturally available, and what the local populace desires and is capable of.
It is also worth noting at this point that simply because solar PV is not dispatchable does not mean that it cannot contribute meaningfully to the power grid. Similarly intermittent sources such as wind power are being integrated successfully with power grids all over the world. More imagination than simply ‘turn it on and leave it on’ is necessary, but we can make intermittent sources work well in a power grid. One such technique for doing so is illustrated in our article about leveraging hydro to use wind.
Peak production at peak demand
In those places in the world where it gets very sunny, it also tends to get very hot. If these places happen to be wealthy, they also tend to employ air conditioning. Air conditioning uses a very large amount of energy, and generally it comes from the electricity grid. Solar PV energy is naturally at its best on a hot, clear, sunny day. This coincides well with the times of great electricity demand due to air conditioning. This natural load-matching characteristic can make solar PV quite valuable. The grid operators will find it necessary to fire up fewer peak-matching units. Peak-matching units are often fired by natural gas, and are quite expensive to operate. What most people don’t know is that baseload electricity is generally much less costly to produce than peak-matching electricity. Both baseload and peak-matching power sources are necessary to operate a functioning power grid.
Build at any scale
Photovoltaic technology can provide power at almost any scale. We can use it for a big chunk of our power grid, but we can also use it to run a calculator. Economies of scale dictate that we can provide more bang for the buck at large scales. However, with PV this is mainly due to bulk ordering of panels, management, maintenance, and grid connection costs. The actual panels themselves don’t really get much cheaper per watt at the large scales. The same panel might be used in a huge multi megawatt array or on top of a house. The amount of power this panel would produce is not affected by the size of the total installation. The power output is defined entirely by the amount of direct incident sunlight.
Solar thermal electricity production does not have this ability. In order to function reasonably well it needs to be at a fairly large scale. These are facts that apply to all forms of thermal power plants. The primary reason is design constraints on the feasible and economic construction of steam turbines to convert the heat into power. These systems work better with large temperature differences between their hot units and cooling units. Large temperature differences generally mean relatively large power generation units. Heat engines also tend to work more efficiently when built at a relatively large scale. Wind power is one of the few other energy forms that can be built at almost any scale.
Solar PV panels are modular. That is, they can be built at a certain effective size and then placed side-by-side. Two identical solar panels that are placed near each other should will together produce almost exactly twice as much electricity as only one of them can alone. This is an important fact because it allows us to use large numbers of PV panels to build any size of power installation that we want. Being able to combine modules to fit any scale is closely related to being able to build anywhere. Being able to draw on the energy of sunlight almost anywhere can be a huge advantage in solar PV’s favour.
Build almost anywhere
One of the major uses of solar PV is off-grid. That is, not connected to a centralized power grid. This is because it can be cheaper to build a PV setup in remote areas rather than pay for an expensive transmission line to connect them. This sort of development can make a lot of sense for applications such as livestock water pumps.
Solar panels may be useful when you need to deploy electrical power to do some sort of work far from civilization. Coupled with a battery system they can provide steady power. For example, this can be useful for equipment such as repeater transmitters. These are units that are placed in remote areas to ‘repeat’ transmissions that they receive. They effectively extend the range of other transmitters, and allow land-based radio systems to reliably reach across a larger area4 .
It is not cost-effective to set up a coal-fired engine of some sort as a livestock pump far from civilization. For one thing, such a system requires fuel, and would require refueling on some timescale. Wind power can be deployed at almost every scale, but at a small scale it can be about as costly as solar PV. Also, we may be looking to get power to places that get little to no wind. Hydroelectric power can also be built at many scales, but it requires a local flow of water.
As mentioned earlier, solar PV power is intermittent. It is not necessarily there when you need it. This limits its usefulness for the grid unless it is combined with systems for energy storage. Additionally solar power could be paired with dispatchable backup systems such as hydro or natural gas.
The sun might not shine a lot in the places we need the power most, such as our big cities. As mentioned above, the infrastructure for transporting electricity can be quite expensive to build. This adds to the difficulty of using solar PV electricity in places with relatively little sunshine.
Also, solar PV has less value for those places that have higher energy usage in the winter than summer. Locations at a higher latitude generally has fewer hours of sunshine during their winters, which limits the output of solar PV. In places with a winter peak, solar PV has limited usefulness for meeting peak demand. It is interesting to note that in some places there is both a winter peak and a summer peak. Where very large amounts of electricity are used on both the coldest and the hottest days of the year.
It is also interesting to note that this has not stopped Germany from building the most solar PV of any nation. Their solar resource is relatively poor, but they have forged ahead with its development. They lead the world in this area5 .
Some people don’t like the look of solar panels. They think that solar panels take away from the natural beauty of the land, or of a building. This is related to the ‘not in my back yard’ resistance to several forms of renewable energy development, including wind power.
The authors of this article disagree on all accounts. We find that solar panels are quite aesthetically pleasing compared to most other forms of power. Think of smoke stacks, cooling towers, strip mining, and coal fly ash landfills. Solar panels can be aesthetically pleasing on their own, or can be integrated into nice-looking rooftop units.
Aesthetics goes beyond looks for us as well. We believe that a solar PV installation is contributing to a better world. The technology isn’t perfect yet, but it is maturing at a rapid pace mostly due to the fact that it is seeing broad-based political support in nations who are looking to make their energy systems renewable. Without support during these development phases, solar PV would not be advancing as quickly as it is. It has the potential to be one of our best electricity sources, and every installation built today contributes to the development of that potential.
Damage to arable land
Just as with many types of human land development, in developing land for a ‘solar farm’, there will be some environmental impact. Some of this is unavoidable, and some is done for cost-cutting or simply convenience.
One controversial action in solar farm development is the removal of foliage from the land, and chemical treatment so that new plants will not grow. This is done because plants can interfere withthe maintenance of equipment and eventually shade the solar panels. This so called practice of ‘salting the earth’ is believed by some to run counter to the overall environmental message of solar power.
Modern installations around the world have achieved very low costs per installed watt compared to the numbers we have seen for solar in the past. Solar PV is still more expensive than the mainstream forms of power, but it is advancing very quickly. The following are a number of information sources that seem to indicate that solar electricity is much closer to being competitive than most people believe.
A project is underway in California to install 250 MW of solar photovoltaics at a cost of about $3.50 per installed watt6 . This was estimated to be equivalent to about 20 ¢/kWh. This is a very low price for solar PV, and is a demonstration of the tremendous progress solar PV has made in the last few decades.
In China, a bid came through to build a 10MW solar PV plant at a cost of 10 ¢/kWh7 . The companies who placed the bid have already completed several large projects around the world. The reduced cost bid seems to be primarily due to the thin film low silicon panels that have been developed8 .
It should be kept in mind that these are the lowest cost estimates that we have uncovered in our investigation of solar PV power. Despite this, we believe they are worth discussing in the sense of what solar PV may very soon be capable of in a broader sense. A cost of 10 ¢/kWh is regarded as a major tipping-point in the electricity industry. At that cost, solar PV would be competing intensely with even the most cost-effective (baseload) forms of electricity generation today.
Additionally, even at costs between 10 and 20 ¢/kWh, solar PV would be extremely desirable in some areas of the world. Due to its natural tendency toproduce during peak demand times, solar PV contributes to peak-matching power generation rather than baseload. Peak-matching electricity generation is generally significantly more expensive than baseload. Natural gas peak-matching power generation is estimated at between 10 and 34 ¢/kWh depending on location, subsidies, and technology ((Wikipedia: Cost of electricity by source)). It is clear that solar PV is becoming more and more competitive with peak power generating units. In the next decade we may see a tipping point where solar PV becomes less expensive than natural gas in areas that have a summer peak. That is, the most electricity that they use is on the hottest days of the year.
In conclusion, solar PV demonstrates great potential for development in certain geographic locations. This potential is evident today in sunny areas of places like China, Spain and California. In the near future, the development of solar PV is very likely to accelerate due to ongoing improvements that are dramatically reducing its cost. Solar PV is no longer a ‘pie in the sky’ power source. Its potential is being realized around the world at a tremendous rate.
- Wikipedia: Solar water heating [↩]
- Wikipedia: Solar thermal energy: Heating, cooling, and ventilation. Accessed October 10th, 2010. [↩]
- University of Delaware team sets solar cell record. University of Delaware Daily. [↩]
- Wikipedia: Radio repeater [↩]
- Wikipedia: Solar Power In Germany [↩]
- First Solar announces two solar projects with Southern California Edison. Semiconductor Today. [↩]
- 10 cents/kwh, world’s cheapest solar energy? China.org.cn [↩]
- China’s New Focus on Solar. Renewable Energy World. [↩]