Energy, Power, and Irradiance

Solar Basics

Solar panels work by turning sunlight into electricity. They do this using something called photovoltaic cells. Here's how it happens: Sunlight and Photons: The sun sends out energy in the form of light. This light has tiny particles called photons — minute packets of electromagnetic radiation. Solar Panels and Photovoltaic Cells: When photons hit a solar panel, they interact with photovoltaic (PV) cells in the panel. Energy Transfer to Electrons: The PV cells allow the photons to give their energy to electrons, which are subatomic particles inside the cells. Electric Current Creation: This energy knocks the electrons from their atoms and they start to flow. This movement of electrons is what creates an electric current, which is just another name for electricity.

There are also terms used to talk about the sunlight that reaches a surface: Irradiance: This is a measure of how much of the sun’s power (in the form of light) hits a certain area. It's like measuring how brightly the sun is shining on a particular spot. Insolation: Insolation is similar to irradiance, but it measures the total amount of solar energy that a place receives over a longer time, like a day or a year. Understanding these basic concepts can help you get a better idea of how solar panels work to convert sunlight into electricity that we can use.

⚡️Note: We typically measure energy in kilowatt-hours (kWh), and power (the rate at which energy is produced) in kilowatts (kW).

In solar, we usually define the size of a solar installation in terms of its power (in kW). Irradiance is typically reported in units of kilowatt-hours per square meter per day (kWh/m2 -d). The amount of irradiance hitting the surface of the earth is often quoted in terms of the number of hours of “full-sun” of solar energy. "Full-sun" is defined as 1 kW/m2.

How a PV System Produces Electricity

At the heart of a PV system is solar panels, which are made up of many solar cells. These cells are designed to capture photons, the basic units of sunlight. When photons strike a solar cell, they transfer their energy into electrons within the cell's material. This energy transfer excites the electrons, causing them to flow and generate an electric current.

This phenomenon, known as the photovoltaic effect, is the fundamental process through which solar panels convert sunlight into electrical energy.

Direct Current (DC) and Its Conversion

The electricity produced by solar panels is in the form of direct current (DC). In contrast, the standard form of electricity used in most homes and businesses is alternating current (AC). This difference necessitates a crucial component in the PV system: the inverter.

The Role of the Inverter

The inverter's job is to convert the DC electricity from the solar panels into AC electricity. This conversion is essential because AC is the compatible form of power for most modern electrical appliances and systems. It is also the form of electricity that is transported through the power grid.

Powering Homes and Businesses

Once converted to AC, the electricity can be used for a variety of purposes. It powers lights, appliances, electronics, and industrial equipment, functioning seamlessly with the electrical infrastructure of buildings. Additionally, any excess electricity generated by the PV system can be fed back into the grid, potentially earning credits for the system owner in regions where net metering policies are in place.

Components of a PV System

A simple PV system contains two basic types of components:

  • Solar Modules (Solar Panels):
  • Each module consists of multiple solar cells made from materials like silicon.
  • These cells convert sunlight directly into direct current (DC) electricity through the photovoltaic effect.
  • Inverters:
  • Inverters convert the DC electricity generated by the solar modules into alternating current (AC) electricity.
  • AC electricity is the standard form of power used and is compatible with the electrical grid.

Additional Essential Components

When we talk about solar photovoltaic (PV) systems, there's a term you'll often hear: "Balance of System" or BOS. This refers to all the parts of a solar PV system except for the solar panels themselves. Understanding BOS components is crucial for anyone involved in solar energy, as these elements are essential for the system's operation and efficiency. What Are BOS Components?

BOS components play various roles in a PV system, from converting energy to securing the panels. Here are some key examples: Inverters: These devices convert the direct current (DC) electricity produced by the solar panels into alternating current (AC) electricity, which is used in homes and businesses. Disconnects: These are safety devices that allow the solar system to be turned off, providing a safe way to disconnect the system from the power grid or the building for maintenance or in an emergency. Racking: This refers to the mounting systems that hold the solar panels in place, whether on a roof, on the ground, or on a tracking mechanism that follows the sun. Wiring: This includes all the electrical connections within the PV system, connecting solar panels to the inverter and then to the building's electrical system or the grid.

The Role of BOS Components

BOS components are vital for several reasons:

  • They ensure the safe operation and disconnection of the solar system
  • They are responsible for the effective conversion and distribution of the solar energy generated
  • They secure the solar panels, making sure they are correctly oriented and positioned for optimal energy production

Next up...

Factors Affecting PV System Efficiency