Solar Power

Harnessing the power of the sun.

There are several kinds of solar techniques that are currently available. However, each of them is based on quite different concepts and science and each has its unique advantages. Generally speaking, non-concentrated photovoltaic solar panels (PV) and concentrated solar power (CSP) are the two most mature technologies.

Solar Thermoelectricity
Solar thermoelectricity uses parabolic disc technology to capture thermal energy basted on the thermoelectric effect. Electricity is produced through a concentrator thermoelectric generator (CTEG) A thermoelectric device is divided into two (2) parts IT produces energy by converting differences in temperatures in the two parts into volts using a semi-conductor
Advantages
*A simple system that can be deployed on roof tops.
*Able to work in harsh environments.
*Quiet in operation.
*Capable of virtually endless shelf life.
*The thermoelectric part has simple structure without any moving parts.
*Extremely reliable.
*Driven by low grade heat energy.
Drawbacks
*The efficiency of the thermoelectric materials is still very low, the recently achieved figure of merit is only 1.3~2.0.
*Like most of the other solar technologies with concentration requirements, this system 10 is unable to collect diffuse irradiation and must rely  on direct radiation only.
*In order to have sufficient output, high temperatures are needed to make it work efficiently (~200o C based on Carnot or thermal efficiency), which lead to higher concentration ratio of the collector (10~100 suns) and more precise tracking systems. Higher concentration collector will increase capital cost and maintenance cost.
*Thermoelectric material like Bismuth telluride is toxic and expensive.
*Cooling systems are required to decrease the temperature of the cold side in order to increase to total efficiency.

Dye Sensitized Solar Cell (DSSC)

A dye-sensitized solar cell (DSSC, DSC or DYSC) is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photo electrochemical system.
Advantages

*DSSCs use low-cost materials; are simple to manufacture, and are technically attractive.
*DSSCs can be replacements for existing technologies in “low density” applications like rooftop solar collectors, where mechanical reliability and light weight of the glass-less collector are important factors.
*The process of injecting an electron directly into the TiO2 is qualitatively different to that occurring in a traditional cell, where the electron is “promoted” within the original crystal. In theory, given low rates of production, the high-energy electron in the silicon could re-combine with its own hole and generate less volume of current.8
*As a result of these favorable “differential kinetics” (the reaction rate), DSSCs work even in low-light conditions, allowing them to work under cloudy skies and non-direct sunlight when traditional designs would suffer a “cutout” at some lower limit of illumination, when charge carrier mobility is low and recombination becomes a major issue. The cutoff is so low that this technology is being considered for indoor use, collecting energy for small devices from the lights in the house.
*Common semiconductor systems suffer noticeable decreases in efficiency as the cells heat up internally. DSSCs are normally built with only a thin layer of conductive plastic on the front layer, allowing them to radiate away heat much easier, and therefore operate at lower internal temperatures.

Drawbacks
*Current efficiency is still relatively low compare with traditional semiconductor solar cells.
*Dyes will degrade when exposed to ultraviolet radiation that limits the lifetime and stability of the cells adding a barrier layer will increase the cost and may lower the efficiency.
*Generally, DSSC technology uses liquid electrolyte that has temperature stability problems. At low temperatures, the electrolyte can freeze, stopping power production and potentially leading to physical damage. Higher temperatures cause the liquid to expand, making sealing the panels a serious problem.
*The electrolyte solution contains volatile organic solvents and must be carefully sealed. This, along with the fact that the solvents permeate plastics, precludes large-scale outdoor application and integration into flexible structures.
*Although the dye is highly efficient at converting absorbed photons into free electrons in the TiO2, only photons absorbed by the dye will produce electric current. The rate of photon absorption depends on the absorption spectrum of the sensitized TiO2 layer and upon the solar flux spectrum. The overlap between these two spectra determines the maximum possible photocurrent. Typically, dye molecules have poorer absorption in the red part of the spectrum compared to silicon, which means that fewer of the photons in sunlight can be used for electrical current generation. These factors limit the current generated by a DSSC; for example, a traditional silicon-based solar cell offers about 35 mili-ampere per square centimeter (mA/cm2), whereas current DSSCs offer about 20 mA/cm.

Concentrated Photovoltaic (CPV)
Concentrated photovoltaic technology uses optics, such as lenses to concentrate a large amount of sunlight onto a small area of solar photovoltaic materials to generate electricity.
CPV systems are categorized according to the amount of solar concentration, measured in suns (the square of the magnification).
Advantages
*Despite the energy lost during the concentrating process, CPV can achieve the highest efficiency among all kinds of solar technologies.
*Unlike traditional, more conventional flat panel systems, CPV systems are often much less expensive to produce, because of the reduced use of        semi-conductor material compared with flat-plate silicon. This reduces risk for the investor and allows more rapid adjustment of plans based on changing markets.

Drawbacks
*Like most concentration systems, CPV is unable to collect diffuse irradiation… Some researchers suggest equipping the CPV unit with a tracking system. However CPV can collected more energy than non-concentrated PV techniques due to superior performance during morning and late afternoon time. Although the energy consumption by a tracking system is minimal, the moving parts of the tracking system make it less reliable and increases both manufacturing and maintenance costs.
*Even a small cloud may drop the production to zero. Unlike concentrated solar power, the storage system that can mitigate this problem above is expensive since it is much easier to store heat than electric energy. This kind of instability will not be preferable when connected to the grid.
*For HCPV, the price for the multi-junction cell can be 100 times more expensive than a silicon cell of the same size. This means that the concentration ratio must 100 times higher in order to make the system more economic than silicon panels. However, such a high ratio of concentration will lead to greater requirements of tracking system and cooling systems. These will further increase the capital cost of the whole system.

CPVs are developing and improving in every few months. Compared with the traditional photovoltaic panel techniques, CPVs are better suited to solar farm rather than rooftop use.
Like other solar technologies, CPVs have both advantages and drawbacks. Theoretically, CPVs can achieve a lower cost

Photovoltaic Solar Panels (PV)

Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material.
Crystalline Silicon
The majority of PV modules (85 percent to 90 percent of the global annual market) are based on wafer-based crystalline-Si. The manufacturing of c-Si modules typically involves growing ingots of silicon, slicing the ingots into wafers to make solar cells, electrically interconnecting the cells, and encapsulating the strings of cells to form a module. Modules currently use silicon in one of two main forms: single- sc-Si or mc-Si. Current commercial single sc-Si modules have higher conversion efficiency about 14 to 20 percent. Their efficiency is expected to increase to 23 percent by 2020 and 25 percent in the longer term.
Thin Films
Thin films are made by depositing extremely thin layers of photosensitive materials in the micrometer (μm) range on a low-cost backing, such as glass, stainless steel or plastic. The first generation of thin film solar cell produced was a-Si. To reach higher efficiencies, thin amorphous and microcrystalline silicon cells have been combined with thin hybrid silicon cells. With II-VI semiconductor compounds, other thin film technologies have been developed, including cadmium telluride (CdTe) and copper-indium-gallium-diselenide (CIGS).
The main advantages of thin films are their relatively low consumption of raw materials; high automation and production efficiency; ease of building integration and improved appearance; good performance at high ambient temperature; and reduced sensitivity to overheating. The current drawbacks are lower efficiency and the industry’s limited experience with lifetime performances. For utility production, thin film technologies will require more land than crystalline silicon technologies in order to reach the same capacity due to their lower efficiency. So, land availability and cost must be taken into consideration when thin film technology is considered.

Despite the optimistic prediction of photovoltaic industry, this technology has disadvantages that will need more effort to solve: Solar electricity is still more expensive than most other forms of small-scale alternative energy production. Without governments mandating feed-in tariffs for green solar energy, solar PV is in less affordable to homeowners than solar hot water or solar space heating. Solar electricity is not produced at night and is greatly reduced in cloudy conditions. Therefore, a storage or complementary power system is required. Solar electricity production depends on the limited power density of the location’s insolation.

Performance and price range of different PV technologies

The best way to compare the value of two solar cells is to measure the dollars/watt ratio. The current best deals on solar cells is about $4.30 per watt. For a 50 watt solar panel, your total cost will be about $215. Keep this in mind when assessing the cost and purchasing solar cells and panels.
Newer panels may or may not be more cost effective for you, if you have ample mounting space for your solar panel, size shouldn’t be a problem, so if you find that you are able to use more primitive technology for a cheaper dollar/watt price, go with it.
Concentrated Solar Power (CSP)

Concentrated solar power systems use mirrors or lenses to concentrate a large area of sunlight, or solar thermal energy, onto a small area. Electrical power is produced when the concentrated light is converted to heat which drives a heat engine (usually a steam turbine) connected to an electrical power generator.
Advantages
*The working fluid can achieve higher temperatures in a concentrator system when compared to a flat-plate system of the same solar energy collecting surface. This means that a higher thermodynamic efficiency can be achieved base on Carnot Efficiency discussed above.20
*The thermal efficiency is greater because of the small heat loss area relative to the receiver area.21
*Reflecting surfaces require less material and are structurally simpler than flat panel collectors (FPC). For a concentrating collector, the cost per unit area of the solar collecting surface is therefore less than that of a FPC.
*Owing to the relatively small area of receiver per unit of collected solar energy, selective surface treatment and vacuum insolation techniques are used to reduce heat losses and improve the collector efficiency are economically viable.
Drawbacks
*Concentrator systems collect little diffuse radiation depending on the concentration ratio.
*Some form of tracking system is required so as to enable the collector to follow the sun.
*Solar reflecting surfaces may lose their reflectance with time and may require periodic cleaning and refurbishing.
*In relatively cloudless areas, the concentrating collector may capture more radiation per unit of aperture area than a FPC. It will be more preferable to adopt concentrating collectors in arid or semi-arid area.

Comparison between PV and CSP

When discussing CSP one should consider more than just the power towers, as there are only a few that are in operation. More common are parabolic trough solar thermal power plants, which are less harmful to birds. Parabolic trough systems are often applied in hybrid systems paired with conventional power plants. The conventional part of the plant provides power throughout the night, and the solar energy is added to the total capacity during the day.
But when it comes to producing electricity from the sun, solar PV panels are also contributing in PV power plants. The debate of whether CSP or PV power plants will prevail has been argued for several years. When looking at current and future price levels CSP has—and will have—the highest leveled cost of electricity (LCOE; €/kWh). Due to large price reductions in PV over the last few years the LCOE of PV is about half the cost of CSP, and will remain so until 2030.
Unlike PV—besides pricing—CSP faces many other challenges focused around water for cooling CSP; the speed at which a PV plant can be built compared to CSP; and PV’s proven technology. When it comes to financing, these factors may push investors more towards PV than to CSP.
However, one of the key benefits of choosing CSP over PV is be that CSP plants can more easily provide ancillary services and provide dispatch-able power on-demand using long-term storage. Combining these features in a hybrid power plant could make CSP competitive with PV in the future.