Solar panels are tilted at a 30-degree angle, facing southward, and mounted above ground to allow airflow for panel cooling. All of this helps maximize solar-panel efficiency.[/caption]
Solar panel, or more correctly solar cell, efficiency measures how much of the sun’s radiant energy that falls on the cell is converted into electrical energy. It is stated as a percentage. For example, a 15 percent efficiency rating means that of all the radiant energy that falls on a cell, 15 percent is converted into electricity. A cell’s efficiency is mainly determined by the type of technology it embodies.
For any given level of efficiency, the amount of electricity a cell will produce depends on two key factors: the panel’s angle of tilt toward the sun and the panel’s overall physical condition, including its cleanliness.
Solar Cell Technology
Not all solar cells are equal. Some are more efficient than others depending on the technology they incorporate. The most critical design factor is the material used in the cell to absorb or capture sunlight. Based on this criterion, solar cell technologies divide into two dominant streams – crystalline silicon (cSi) and thin film technologies. The crystalline silicon segment further divides into monocrystalline and polycrystalline cells. The thin film segment further splits according to the type of absorbent semiconductor used in the cell, the main types being amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium gallium selenide (CIGS).
Thin film technologies are so-called because they reduce the amount of absorbent material required to produce a solar cell. Although this reduces material cost, it may also decrease conversion efficiency. Thin film silicon cells are widely used in the solar power industry because of their low cost, flexibility in use, light weight and ease of integration compared to silicon cells. On the other hand, crystalline silicon cells generally have higher efficiency. Experts are divided as to which technology offers the best potential.
When solar cells first began to be developed during the 1950s and 1960s, their efficiency was very low, around 1 percent. By the time they started being produced on a commercial basis during the 1970s, their efficiency had climbed to 3 or 4 percent. Since those early years, better technology has greatly boosted efficiency. Today, cells used in solar panels installed at homes and offices typically have an efficiency ranging from 12 to 20 percent. The Department of Energy launched an initiative to reach 33-percent efficiency – called the “one third of the sun initiative” – and scientists and solar-power manufacturers have broken the 33-percent barrier, but these panels are not yet being manufactured.
Practical difference between different solar panel efficiencies
Higher efficiency solar panels aren’t necessarily better, they simply mean you’ll use less photovoltaic panels on your roof. You can either fit a larger solar system (measured in kw) on the same size roof using higher efficiency panels, or, you can use less solar panels in your solar-energy system if you’re concerned about roof space. For example, take a 10,000 sq ft rooftop space: utilizing highly efficient solar panels (ie. 18-19-percent efficient panels from SunPower) you could fit approximately 120 kilowatts on the roof. However, with a lower efficiency module (ie. 14-percent) you could only fit 100 kilowatts.
Other factors that affect solar-panel efficiency
Like all equipment, solar panels degrade over time through normal wear and tear. They are designed to provide an operating life of about 30 years, though during that period efficiency is not expected to degrade materially.
Even when new, the amount of electricity a panel produces can be significantly decreased if sunlight is prevented from striking its solar cells. This can occur if dirt and grime is allowed to accumulate on the panel’s protective glass sheets. These sheets should be regularly cleaned by hosing them down.
Inclination To The Sun
Solar panels used on commercial or government buildings are usually positioned on the roof. To maximize their exposure to sunlight, the panels face south in the northern hemisphere (and vice versa) and are angled at about 30 degrees to the earth’s surface. The pitch or tilt of a roof can also affect how much sun your photovoltaic panels will receive.
If a panel’s angle to the ground is fixed, its angle to the sun varies as the sun’s position in the sky changes during the day and from season to season. Research studies confirm that the amount of sunlight captured by a panel can be significantly boosted, by as much as 20 to 30 percent, if it is installed on racking system that tilts so that the panel’s angle to the sun is constantly optimized. These tilting racking systems are known as solar trackers, but they are not feasible for all installations.
While some panels are designed for hotter climates, most photovoltaic panels don’t like it hot (in fact, recent studies have begun to prove that snow and cold temperatures actually benefit solar-panel efficiency). Panels are typically installed a few inches above the rooftop, allowing them airflow to cool them down.
Shading on your rooftop can reduce the amount of sunlight your solar-panel system receives, which is why we conduct a shading analysis as part of our pre-installation process.