Solar 101: How Solar Really Works
Solar photovoltaic systems, often called solar PV for short, are made up of a number of components, the biggest and most important being the solar panels, solar inverters, mounting platforms and cabling infrastructure. Combined, these components harness radiant light from the sun, convert it into electricity and transmit it into homes and businesses to power electrical devices, like lights and appliances, and provide heating and cooling via the electrical currents they create. Here is a general overview of how solar PV systems work.
The solar panels themselves are perhaps the most well-known of all the system components, since they're the most visible part of the package, often perched atop homes and businesses roofs. Solar panels are also considered the life blood of a solar power system, because solar panels actually capture the sun's radiation, thereby initiating the entire process of converting sunlight into an electrical current. The job of solar panels is to essentially create the electrical current.
Solar panels can come in all shapes and sizes, but are typically comprised of a grouping of solar cells that are wired together and encapsulated by a glass casing that protects the equipment against the elements. Solar cells are essentially made up of semiconducting materials - often silicon - that are sandwiched together between positive and negative charges. When sunlight hits a cell, the photons within the sunlight knock electrons free from the semiconducting material. This starts the flow of electricity. Then, conductive plates made of metal on the sides of the cells gather the electrons and transfer them through wires. At this point, these electrons can flow just like any electrical current.
While there are a number of factors that determine the electrical output of a solar power system, the number of solar cells and overall size of the solar panel array, are the major determinants in how much electricity can be generated from a solar system. The more solar cells and larger the solar panel array is, the more electricity can be generated. They type of solar cells will also impact the efficiency with which a solar panel generates energy. Generally speaking, monocrystalline silicon is the most efficient material to use in solar cells. Polycrystalline silicon and thin film cells are also commonly used and are less expensive than monocrystalline.
Solar PV systems would be worthless without solar inverters - as such, many consider solar inverters the "brains" of the entire system. The way they work is, once radiant sunlight is converted into electricity, solar inverters transform the electrical current from direct current (DC) power to alternating current (AC), so it can actually be used in various applications.
This step is necessary, because solar panels cannot create AC power on their own and in the United States, most electrical devices run on DC power. In a DC system, the electrical current flows in one direction. By contrast, AC power is a bit more complex, moving in both directions, backwards and forwards.
Since the U.S. grid system actually works on AC power, solar inverters have the ability to convert electrical converts back and forth between DC power (used to power devices in the home) and AC power (to put electricity back onto the grid).
Typically, solar inverters are about 95% efficient, so they only lose about 5% of the electricity during the conversion process.
There are three general types of solar inverters:
- Stand-alone inverters are those that do not need to be plugged in to an electrical device. Instead, they draw their charge from a battery powered by the solar PV system itself. These are often a good choice for non-grid tied systems.
Grid-tied inverters are compatible with the utility grid. They're designed to shut down automatically in a black out situation due to safety concerns. As such, grid-tied inverters cannot provide backup power during an outage situation.
Battery backup inverters also draw energy from a battery, but what is unique about them is they're designed to export excess energy back to the utility grid. In this way, they can supply AC currents during utility outages.
Cables and Wires
Next, a series of cabling infrastructure is necessary to actually bring the converted power into homes and business. In essence, the solar cable is an wire that interconnects all parts of the solar PV system.
Cabling networks can vary, but typically are designed to be UV and weather resistant and capable of dealing with extreme fluctuations in temperature (both heat and cold), since one common factor for these system is that they're used outdoors. The most common type of cabling used is a DC voltage of 1.8 kV and a temperature range from - 40 degrees Celsius to 90 degrees Celsius.
Another important feature of the solar cable is that it must be insulated well enough to withstand the thermal and mechanical loads. To achieve this, most solar cables use plastic that are cross-linked using electron beams. This protects against the weather elements, including the sun's radiation and humidity that would otherwise erode the system over time.
Finally, the mounting system is the skeleton of the solar power system. Mounting systems are the platforms upon which solar arrays reside. Most commonly, home and business owners mount their solar systems on top of their roofs so that they can gain greater access to direct sunlight. However, mounting systems can also be built on the ground or on other erected structures, like a pole.
Solar mounting systems must be installed according to local building codes. However, generally speaking, rooftop PV arrays are generally mounted parallel to the surface of the roof with just a few inches of space between the system and roof. Arrays are mounted at angles that enable them to optimize sunlight capture - i.e. closest to a 90 degree angle with the sun.
Ground mounted systems are typically used by utility companies to generate larger amounts of electricity to be deployed onto the grid. Ground based mounting systems include pole mounts, foundation mounts and ballasted footing mounts to secure the arrays firmly to the ground. In some cases, ground mounted systems are designed to provide some type of shade, such as a patio cover or even a parking garage cover.