Simply put, photovoltaic systems convert light into electricity, or “solar energy.” Simple concept, not so simple technology!
Current photovoltaic (PV) technologies use semiconductor materials also found in computers and other electronic equipment. Sunlight strikes the doped-semiconductor surface and releases electrons—producing electricity. Doped? What is this? Semiconductors are treated to allow them relay electrons.
Let’s suffice to say, the process is fairly involved, similar to that of computer chip manufacturing. An ingot cylinder of silicon is grown, cut into thin wafers (e.g., 0.3 mm), etched, and doped. This is not an inexpensive process, and individuals/homeowners cannot manufacture their own. When you read about building your own solar panel, well-intended self-help promoters still point out that the “solar cells” must be bought or recycled (off obsolete panels). The cells are where the expense lies, and at this time, the least expensive cells are being manufactured in China.
Under ideal conditions, each solitary 100 cm2 (e.g., 4” x 4”) solar cell produces only about 2 amps of electricity. Two amps is equivalent to 1 watt of electricity (0.5 usable voltage in crystalline-silicon solar cells). This is hardly enough electricity to power anything. So, the cells are interconnected within a sealed weatherproof package called a module.
A single solar module varies in size and rated output. A typical size may be 5′6″ x 3′3″ x 2″ and may have a maximum power output of 100 to 300 watts. During “optimal conditions” (e.g., clean panels in direct summer sunlight with no clouds in the Sahara dessert), a single panel may generate 6-hours of power with an optimal output of 250 watts in a 24-hour period an optimal output of 1,500 watts which will power a television for 5-hours, a refrigerator for 2 hours, or a clothes dryer for 20 minutes. Most northern states within the United States have an optimal 4-hours of direct sunlight per summer day for a total single panel output of 1,000 watts in a 24-hour period—when it is not raining or overcast during the daylight hours. This will power a refrigerator for 1 ½ hours, a computer for 4 hours, or a clothes dryer for 13 minutes. So, one panel does not a commercial power facility make.
Multiple connected panels form what is referred to as an array. When two panels are wired together in series, voltage (e.g., wattage output) doubles. When wired in parallel, current (e.g., voltage) doubles. To achieve the desired voltage and current, panels must be wired in series and in parallel until the optimal output is met. Each grouping is referred to as an array, and power facilities require multiple groups, or arrays in order to attain a desired capacity.
As of December 2011, the alleged largest completed photovoltaic power facility in the world is Huanghe Hydropower/Golmud Solar Park located in China. The facility alleges to cover over 1,482 acres and has a rated capacity of 200 MW. As the source of information, regarding this facility, is limited primarily to wikipedia which has coordinates (as the other top ten have), and the name alone implies a hybrid facility. The reference to “alleged” is in regards to my difficulty in confirming the existence of the a solar facility at the coordinates provided by wikipedia and lack of other substantiating information.
Completed in April 2012, the largest photovoltaic facility in the world became Charanka Solar Park which is located in north central India (Latitude: 24º N). The facility is located on 4,900 acres and has an installed capacity of 214 MW Still under construction, it has an anticipated capacity of 500 MW by 2014.
The largest photovoltaic power facility in North America is Sarnia Power Plant in the southern tip of Ontario, Canada (Latitude: 42º 56’N). It covers 240 acres of land, has a rated capacity of 80 MW, and has over 1.3 million modules. The tariff (e.g., wholesale) costis 44.3¢ CDN (45¢ USD) per kW-h, and it was developed by First Solar.
The largest photovoltaic power facility in the European Union is Montalto di Castro around Rome, Italy (Latitude: 42º 21’N). It covers 48 acres of land, has a rated capacity of 44 MW, and has over 78,720 modules. The cost per kW-h was undisclosed, and the panels were built by SunPower.
The largest photovoltaic power facility in the United States is Copper Mountain Solar Facility in Boulder City, Nevada (Latitude: 35º 47’N) in the U.S.A. It covers 380 acres of land, has a rated capacity of 48 MW, and has over 775,000 modules. The cost per kW-h was undisclosed, and the panels were built by First Solar.
Power production claims are based on “rated capacity,” not actual output. Rated is ability, and output is reality. Ability of the installed panels diverges from that of latitude and local conditions.
Of the sites discussed above, the Canadian Sarnia Facility has a higher rated capacity than that of the U.S.A. Copper Mountain Facility. Yet, based on published capacity factors, photovoltaic power produced in the Sarnia Facility (Latitude: 42º) is actually 11.2 MW, not the published rated capacity of 80 MW, and power produced in the Copper Mountain Facility (Latitude: 35º) is 12 MW, not 48 MW. Their capacity factors are 14 and 25 percent, respectively. Thus, although ranked higher for capacity, the Sarnia Plant, in reality, produces less power than the Copper Mountain Facility which is rated as a lesser producer. On the other hand, the best rating goes to India’s Charanda Solar Park (Latitude: 24º) which has the highest rated capacity and highest ability to produce–rated at 214 MW, actual 64 MW (capacity factor of 30 percent). So, boasting about higher capacity ratings is a red herring. Further scrutany is well advised.
Capacity is limited by access or lack of access to solar light. Given optimal conditions, season, and latitude, a commercial solar power facility has the potential to produce up to 6.9-hours of solar energy—under rarely attained, best case conditions. The range in the U.S.A. and Europe is actually 3 to 5 hours. Yet, most civilizations require 24-hours of electricity. Third world countries must limit their energy requirements and accommodate peak mid-day production times while descending into darkness at nighttime. This is not acceptable in industrial nations which require electricity 24/7. In the perfect world of solar energy dependence, is this possible?
Total reliance on photovoltaic power would require the number of panels either be increased 4 to 6 times (with no reserve for a rainy day), ideally 12 to 18 times (with a two day rainy day reserve) over that which is required during peak hours. If the total 24-hour energy requirement has already been accommodated for in the actual energy production, the number of panels would be increased 3 times in order to provide a two day reserve. A reserve of two days would hardly be adequate for extended periods of inclement weather or weeks of obscured skies from forest fires and/or volcanic ash. A total reliance on photovoltaic power during inevitable weather obstacles would, thus, require a monumental increase in the number of panels and land requirements. But wait! This is not the only obstacle.
Since sun does not shine 24/7, energy must be stored for those periods of time when there is no sun or when the sun is obscured. And batteries are the only means for storing electricity. Batteries are not only expensive, but they have a limited lifetime expectancy. How do we deal with this today?
Full circle, once again, brings us back to fossil fuels. Despite their claims, many of the existing photovoltaic facilities are actually hybrids, fossil fuel power facilities supported by photovoltaic power, or electricity generated by a photovoltaic power facility is feed to a grid that is supported mostly by fossil fuel power plants.
Yet, let us not stop here. Misinterpretation is a nasty, persistent sore. Are there not technological considerations on the horizon that could stem offer some hope? Let’s look at component materials, solar tracking systems, and prospects for the future.