Superior Technology Integration Knowledge
Solar photovoltaic (PV) cells use sunlight to produce energy. All solar PV cells are made of materials called semiconductors that absorb photons when sunlight strikes the PV cell. The absorbed photons then knock electrons loose within the PV cells, allowing them to flow, which produces a current. Solar PV cells contain one or more electric field(s) that force the direction of electron flow. Placing metal contacts on the top and bottom of a PV cell harnesses this current so it can power external appliances, such as a calculator or pool pump.
On their own, solar PV cells produce a limited amount of energy, but when arranged and electrically connected and mounted on a supporting structure, the result is a solar PV panel that combines the electrical output of each solar PV cell, yielding a greater amount of energy production. The power, or wattage, that a solar cell or a panel of cells can produce is determined by measuring its current and voltage.
Three factors affect a solar panel’s performance:
There are many different types of solar PV panels on the market, and for every panel type there are even more manufacturers. The chemistry, construction, and performance vary greatly between panels.
For years, companies have sought ways to reduce manufacturing costs associated with traditional PV technologies. This search has resulted in several types of technologies over the course of the industry’s evolution.
The two most common types of solar panel technologies are rigid (mono- or polycrystalline) and flexible (thin film) .
Standard Test Conditions (STC)
To make an apples-to-apples comparison between the types of panels, standard test conditions (STC) have been defined. STC uses the same conditions for all panels: direct, incident sunlight at an intensity of 1000 watts per square meter (W/m²); a cell temperature of 25 °C (77 °F); and an air mass of 1.5 (air mass, or density, affects the amount of sunlight that reaches the Earth’s surface).
The operating temperature of a module is determined by the equilibrium between the heat produced in the PV module, the ambient operating temperature, and the ability of the panel to dissipate heat through its encapsulant materials.
As temperatures increase, stresses associated with thermal expansion also increase, thereby increasing the degradation rates of the PV module by a factor of about two for each 10 °C increase in temperature over its STC ratings. Why does this matter? Proper panel mounting is very important! The hotter a solar PV panel gets, the more negatively its output power is affected.
Using solar PV power reduces dependence on traditional means of generating power (grid power or fuel-driven generator). Other benefits of using solar power generation include:
- Quiet operation
- Small footprints
- Ease of use
- Low maintenance
Applications needing more power generation should consider using a high-efficiency, hybrid system.
Solar panels generate power anytime there is daylight, even on a cloudy day, making them a guaranteed power source. This makes them 100% effective, but not 100% efficient. The efficiency of solar panels is measured by how much solar irradiance a panel is able to convert to electricity. Single-junction solar cells are the most common solar cells. They typically convert anywhere from 10 to 20% of the sunlight received into electricity. By comparison, a record for solar cell efficiency of ~46%—using a four-junction concentrator-type cell—has been established by the National Renewable Energy Laboratory (NREL). It will be some time before this type of multi-junction solar cell technology is readily available.
Rigid Monocrystalline Solar Panels
Rigid monocrystalline is the first generation of solar PV panel technologies and is still the most efficient, setting the standard for other PV technologies; however, advancements in manufacturing technology have increased the efficiency of the multi- or polycrystalline panels to almost that of monocrystalline panels. While they are similar with efficiencies of 15 to 20%, monocrystalline panels are slightly more efficient in full sun, while multi- or polycrystalline panels deliver slightly higher output during periods of partial shade.
Flexible Solar Panels
Flexible solar panels are less efficient than their rigid cousins. Amorphous silicon cells can achieve an initial efficiency of 10%. Copper, indium, gallium, selenide (CIGS) cells with steel backing offer efficiency of up to 15%. CIGS panels are more efficient than amorphous silicon, but fare worse in low-light situations.
Life Expectancy and Overall Costs
Purchasing solar PV panels is the only direct cost associated with using them. Once you own them, the panels produce power for their rated life expectancy for free as long as there is sunlight. Invest in a panel that suits the intended application to withstand operating environmental challenges such as heat, inclement weather, and rough physical treatment.
When choosing or replacing a solar PV panel or array, the cost varies according to the type of panel. Rigid, silicon-based crystalline solar PV panels are widely considered to be the best technology available. However, this high quality corresponds with a higher price, making these panels the most expensive on the market.
Thin-film solar PV cells are less expensive to produce than silicon cells because they require fewer materials for construction. Because it takes very little material to make thin-film cells, this technology generates a lot of interest within the solar power industry.
Much like their rigid-panel cousins, thin-film PV technologies can produce power for many years. The lifespan of thin-film solar PV panels is limited by their physical construction. Many materials used in these panels, such as plastics and fabric, degrade with use and exposure to the elements.
In severe environments, a CIGS panel with a heavy-duty plastic or stainless-steel substrate usually lasts longer than an amorphous silicon panel of lighter-duty construction with the same power rating. Examine the physical construction of any flexible solar PV panel to ensure it suits the intended application.
Thin-film panels require more care and maintenance than rigid panel technologies. When buying, beware of cheaply produced thin-film panels. The PV technology may be well-crafted, but if the construction is poor, the panel may become unusable quickly.