## How to Design a Solar PV System 101: The Basic Terms

Want a basic technical understanding of solar PV project terminology? Read on…

If you’re an experienced installer, none of this information will be new to you. If you’re new to solar, it will be helpful. But keep in mind, we’ll be skimming the surface.

We’re going to begin with the basic terms. This is very important for design because you need to understand the concepts before you start applying real numbers to a design. It will also help with sales because it will help you explain some basic concepts to curious customers.

Performing high-quality and efficient site visits is absolutely critical to the success of profitable solar projects, especially residential projects. You need to be able to capture all of the information you need to quote the system correctly, design the project, and tell the installation crew what to expect. An efficient site visit process will lead to smooth operations and profitable jobs while a complex or disorganized process can lead to unprofitable jobs and a lot of confusion.

Power

Power is an AMOUNT of energy. It’s the measurement of energy, measured in kilowatts (kW). Power is measured in an instant. Most of the sizing done in solar PV design (conductors, inverters, fuses, etc.) is based on how much power will be passing through a specific component of the system. Because power is measured in an instant, it can vary widely over time and from minute to minute.

Power (watts) = current (Amps) X voltage (volts)

Energy

Energy is the is the actual work done by power. It is measure in kilowatt-hours (kWh). Consumers pay for kWh. It’s a measure of power over time.

Power (kW) X Time (hours) = Energy (kWh)

Current

Electricity is the flow of negatively charged electrons. The current is the amount of negatively charged electrons in a specific part of a circuit.

Many people find it useful to use a water analogy when discussing electrical terms. In the water example, it’s useful to think of a dam with a pipe at the bottom where water can flow out. The amount of water that can pass through a slice of the pipe, in other words the area of the cross-section of the pipe, is analogous to electric current.

Voltage

Voltage is a measure of the force or pressure of the electric current in a circuit. It’s measured in volts. Electrons of the same material WANT to be homogeneous, i.e. they want to be evenly spread out. Thus, if one area has less electrons then another, the electrons will move in an attempt to equalize. This flow is what created a voltage potential and causes electrons to move.

To use the water example again, if the size of the pipe at the bottom of a dam is a measure of current, the height of the dam is a measure of voltage. Higher water behind the dam creates more pressure.

Resistance

Electrical resistance is the resistance of the flow of electricity through a conductor. It does not reduce the current flow of electrons (how many electrons there are in the circuit), but it does reduce the voltage (how fast they’re going). It is measured in ohms.

Voltage Drop (volts) = Current (amps) X Resistance (ohms)

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