Solar Technology: From PV to CSP

Learn About the Numerous Ways Solar Energy can be Harvested

The amount of sunlight that reaches the earth every day is truly staggering. An estimate from the US Department of Energy states that more energy from sunlight hits the earth in an hour than the entire world uses in a year. With such a vast amount of energy freely at hand, it simply makes sense to harness and use that potential to some benefit. The only question is how we go about collecting it. Since the first solar panel was made in 1954, a multitude of new methods have been created that effectively do the same thing: take in sunlight and use it to our benefit. Read below to learn about several different technologies that collect solar energy, and stay tuned for further advances.

Photovoltaic (PV): Monocrystalline & Polycrystalline

Photovoltaics was the first technology invented to turn sunlight into electricity. The process works by converting part of the electromagnetic spectrum from the sun into electricity through a photochemical process. Essentially, electrons within the solar cell (multiple solar cells are wired together to form a solar panel) are struck by sunlight and are forced to move. Once those moving electrons are directed to move in a certain path, you have electricity running through a circuit. 

Those fundamentals are true of both types of photovoltaics that exist now, and most other types of solar technologies on this list. The two types of PV technology are monocrystalline and polycrystalline. Both use a framework-like matrix of crystalline silicon with added chemical elements that are used to increase the efficiency of the cell. 

The difference between mono- and polycrystalline PV is essentially a matter of refinement. That is, monocrystalline are formed from an ingot of pure silicon while polycrystalline are formed from the fragments of many silicon crystals. Monocrystalline are thought of as slightly more desirable because of higher efficiencies and slicker aesthetics. The higher efficiency is achieved because the silicon ingot allows easier movement of electrons. Polycrystalline are not formed from a single ingot, so they are easier to manufacture, which makes them slightly cheaper. They are, however, less efficient for skipping that process. 

True South Solar exclusively sells monocrystalline panels for their higher efficiencies, as generating more electricity in a smaller area is crucial for many residential and commercial customers limited by space. 

BIPV (Building-Integrated Photovoltaics)

One technology that has been advancing in recent years is building-integrated photovoltaics. Traditional solar panels are installed on top of a building after construction is complete, but building-integrated seeks to go one step further by replacing things like traditional roofing tiles with photovoltaic materials that fulfill the role of solar panels while providing a protective coating from water and debris for the building. 

Studies have also been done to incorporate BIPV systems to areas other than the roof of a building. Exterior walls that receive plenty of sunlight might make more sense than a roof, or developers might choose to coat the windows of a skyscraper with a transparent panel in order to generate electricity. However, BIPV is still underdeveloped as a market, and as a result there are few commercial installers and the lack of a mass market means the price point for a BIPV system is high. As solar systems in general continue to catch on in popularity, those issues will likely be resolved eventually. 

Solar Hot Water

While the goal of most other solar technologies is to produce electricity, the purpose of a solar hot water system is simply to heat up the water that will be used inside a home or business. Rather than relying entirely on an additional fuel to heat the water inside a hot water tank, this system uses a panel-like instrument called a “collector” which exposes water to sunlight, thereby increasing its temperature. From there, the water circulates back down and runs through a copper coil within the tank and raises the temperature of the water inside, only to begin the process again. As a result, the water that is exposed to sunlight on the roof never actually comes out of the faucet. 

Additional controls are also installed to prevent the solar hot water system from circulating cold water through the tank, as might be the case during the winter or at night. A secondary system might also be included to pump hot water through the plumbing of the solar hot water system during freezing periods. Overall, solar hot water systems are a great idea for people with high water usage and good solar exposure throughout the year, with some systems providing as much as 90% of a user’s hot water. 

Passive Solar

Passive solar designs are unique on this list, for they generally do not involve any additional technologies to be installed or integrated into the building (hence the “passive” aspect). Passive solar utilizes the structure of the building and surrounding area to create ideal heating and cooling within living spaces. The two basic components of passive solar allow sunlight to enter the space during desirable times and be absorbed, distributed, and even stored for use during the night. In this way, an additional layer of insulation is effectively created that warms the building at night and cools it during the day. 

The system works by allowing sunlight to enter and warm the building. The heat from the sunlight is then collected by an absorber, which mitigates the amount of heat in the room. The thermal mass is located next to the absorber, but is not directly exposed to sunlight, and it further collects heat from the absorber and emits it later at night. Finally, a control element outside of the building is used to account for seasonal variations. This control is often simply a roof overhang that provides shade during the summer and gives access to sunlight during the winter, but trees or other obstacles could also be used. Passive solar systems don’t generally need any mechanical input, but certain systems may also benefit from manual or sensor-driven fans and vents. 

Thin-film solar

Thin-film panels are perhaps the forgotten younger sibling when compared to monocrystalline and polycrystalline solar panels. Thin-film is notably less efficient than either of the other two, but the manufacturing process is also much simpler and therefore cheaper. As a result, the market for thin-film panels is growing, especially as the efficiencies for this type continue to improve. Thin-film also experiences fewer losses in conversion efficiency from shade and high temperatures, in comparison to mono- and polycrystalline. Another potential application is their flexibility, which allows for them to be applied to places that traditional rigid-framed solar panels would be excluded from. Sharply curved roofs, walls, or other structures are good candidates for such systems. 

Unfortunately, the panels also degrade more quickly than either mono- or polycrystalline panels. Their low efficiency also means that scaling up requires more structural components for the same amount of electricity as a traditional panel to be generated. While thin-film solar has some issues in comparison, its low price point and wider applications make it a worthwhile technology when considering all your solar options. 

CSP (Concentrated Solar Power)

Unlike the other types of solar power on this list, concentrated solar power is a form that is not feasible for residential projects. With this type of solar installation, a large number of mirrors or lenses are used to focus sunlight onto a specific area that contains a working fluid which generates steam for a traditional power plant model of generating electricity. 

For enough effective heat to be created, the system has to be installed in an area with a high amount of direct sunlight. Exactly how the mirrors, lenses, or working fluid are placed and designed in relation to the heat collection area varies depending on four recognized methods. However, in each method the mirrors track the sun throughout the day to maximize solar exposure, and depending on the type of working fluid used the generated heat can effectively be stored for use during the night. As a result, CSP is one of the few methods of solar technology that is not reliant on battery technology and can actively compete with conventional coal- or gas-fired power plants. CSP is also notable for having the highest measured efficiencies for converting sunlight to electricity, with some systems reaching over 30% peak efficiency. 

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