- Solar Electricity Definition: Solar electricity is produced by sunlight hitting photovoltaic cells, generating power.
- Photovoltaic Effect: Solar energy electrical engineering relies on the photovoltaic effect, where sunlight creates electricity in semiconductor materials.
- Structure of Solar Cells: A solar cell consists of a thin n-type layer on top of a thicker p-type layer, with a depletion region at their junction.
- Charge Separation: Sunlight causes electrons to move to the n-layer and holes to the p-layer, creating a potential difference.
- Applications of Solar Electricity: Solar power is ideal for remote locations and moderate power needs, though it is less practical for high-power equipment.
Solar Electricity
When photovoltaic solar cells absorb sunlight, they generate direct-current solar electricity. A complete PV system may also include modules, mounting, wiring, protection, an inverter, metering and optional batteries.
How Solar Electricity Is Generated
Generation of electricity from solar energy uses the photo voltaic effect. In a conventional crystalline-silicon cell, a semiconductor p n junction creates a built-in electric field that separates light-generated charge carriers. One traditional architecture uses a thin n type semiconductor emitter above a much thicker p-type silicon base. Layer thicknesses depend on the cell design, so this is an example rather than a universal structure.
The lower p type semiconductor layer acts as the absorber and base in this example. Fixed ionised dopants form a depletion region and built-in potential at the junction.
Sunlight is absorbed across the active silicon, not only at the p n junction. A photon with energy equal to or greater than the band gap can excite a valence electron in the semiconductor into the conduction band, leaving a hole. Carriers generated outside the depletion region can contribute when they reach the junction before recombining.
The junction field drives electrons towards the n-type side and holes towards the p-type side. Selective contacts collect the separated carriers. With the external circuit open, charge separation creates a potential difference between the terminals.
When a load is connected, electrons travel through the external circuit and deliver power before returning to recombine with holes. Silicon is widely used, but other semiconductor materials and junction structures can produce the same photovoltaic function.
An individual photo voltaic cell produces limited voltage and current. Cells are connected in series and parallel to form modules, and modules are connected into arrays sized for the required power and energy. Output changes with irradiance, spectrum, cell temperature, orientation, shading and electrical losses. Cloud cover reduces irradiance and output. Moonlight is normally far too weak to provide useful power from a standard PV system.
Applications of Solar Electricity
Solar electric power systems range from small stand-alone supplies to rooftop arrays, microgrids and utility-scale plants. Site design should account for solar resource, shading, orientation, structural limits, grid connection, energy demand and local economics. Solar electricity can reduce purchased energy, serve remote loads or supply a grid when the system is designed and approved for that purpose.
Examples: A stand-alone solar light, telecommunications site, water pump or remote building can be economical where extending the utility line is costly. Batteries can shift daytime generation to night and support loads during poor weather. A grid-connected array without suitable storage and an island-capable inverter normally does not supply backup power during a grid outage. Mobile systems can serve camping, field work, boats and recreational vehicles when the array, charge controller, battery, inverter and wiring are sized for the load.
PV is not inherently restricted to low-power appliances. Properly designed rooftop, commercial and utility systems can supply high-power loads or large annual energy demand. Feasibility depends on available area, structural and electrical constraints, load timing, grid rules, tariffs, equipment cost and maintenance. Resistive heaters, air conditioners, washing machines and power tools can run from solar electricity when the PV, inverter and any storage can meet their starting and operating power. Efficiency and load management reduce the required system size. Surplus exports require a compliant grid connection and an agreement with the local electricity provider. Solar electricity can serve systems of many sizes when the design matches the load.
It can also charge batteries in caravans, recreational vehicles and boats, but the charging system must protect the battery and match the vehicle’s other charging sources.
