Monday, February 12, 2018

Basics of Solar Panels: Terminology

For part 2 of my series on solar panels, I give definitions of basic terminology.



Aside from being an excellent Australian rock band, AC (Alternating Current) and DC (Direct current) are methods of delivering electrical current.

AC (Alternating Current) means that the current switches direction back and forth.

DC (Direct Current) means that it flows in one direction between the positive (+) and negative (-) poles.

Electrical power is often expressed as (Voltage) (Current type). For example, household power is usually 120 volts AC, whereas automotive systems are usually 12 volts DC.

As a useful note, Amps x Volts = Watts.

The ampere, or amp, is a unit of electrical current.

Amp Hours are an Amp of Power (unit) over an Hour (time) at a specific voltage. If I have 10 amp hours at 12 volts, I can draw 1 amp for 10 hours, or I can draw 20 amps for ½ hour.

If you need to convert amp hours, remember that Amps x Volts = Watts, so 10 Amps at 12 volts = 120 watts, and 1 Amp at 120 volts is also equal to 120 watts.

Because of this, I prefer to convert things to amp hours.

A measurement of electrical force. The most common voltages for solar panels are 12 volt (most automotive systems) and 120 volt (United states wall voltage). Mostly needed (for this) in order to convert other units

Wattage is a measurement for electrical power. It is often the easiest way to establish a constant electrical draw amount, even when discussing radically different voltage amounts.

Watt hours are a watt of power over an hour of time. This can be useful as a measure of power draw. If you have 100 watt hours of storage, you have 100 watts of power for 1 hour, or 50 watts of power for 2 hours, or 10 watts of power for 10 hours, etc.

Hertz (Hz)
Cycles per second. Usually used to refer to AC power, which in the US runs at 60 back/forth cycles a second. When talking about solar power, this is mostly used when dealing with inverters (see below).

A measure of electrical resistance. The higher the ohms, the harder it is to get power through to something else. A device with high resistance will typically cause inefficiency.


Mono/Poly Crystalline

A type of solar cell.

Solar panels made up of Monocrystalline cells are more expensive, but more efficient. They tend to have a black color.

Polycrystalline are less expensive, but less efficient. They tend to have a blue color.

Solar Cell
A single Photo Voltaic cell. Several of these together form a panel.

PV (Photovoltaic)
The most common type of solar cells. They generate electrical energy from sunshine.

Charge Controller
A device that interfaces between a charge source (in this case a solar panel) and a battery, allowing the battery to charge. These come in several styles, such as Pulse Width Modulation, On/Off, and Maximum Power Point Tracking.

Charge controllers are not usually 100% efficient, so looking at the efficiency rating can make a big difference.

Some charge controllers include something called a DC-DC converter. This is used to change the DC voltage to another voltage.



A battery is a device to store electrical energy. They come in several chemistries, such as:
  • Lead Acid, the most common. This is the type of battery that cars use.
  • Lithium Ion aka Li-ion. These are usually laptop and cell phone batteries. 
  • Nickel Cadmium aka NiCad. Mainly used in older power tools. 
There are also several types of battery, such as:
  • Deep Cycle, meant to be used when you will frequently discharge the battery, such as during off-grid living. 
  • Absorbed Glass Mat aka AGM, aka Gel Type. A type of battery designed to be a good mix of power density and durability, it will not spill if it is tipped over making it a good choice for a vehicle.
Several extensive articles can be written just about batteries, and I recommend that anyone serious about solar power do more research into them.

Battery Cell
The smallest individual part of a battery. When one of them goes bad, the entire battery dies.

It can also be important to know the number of cells and voltage per cell in a battery, in order to determine the total voltage.

An inverter converts electricity from DC power to AC power. The most common inverters convert 12 volts DC to 120 volts AC.

Inverters come in several types, such as
  • Pure sine wave: The most expensive, but the least harsh on electronics and other equipment.
  • Modified sine wave: Most inverters are like this.
  • Square sine wave: Only a few very, very inexpensive inverters are like this. They typically have trouble running anything electronic, or with complex electronic circuits.
Inverters are rated in watts, in order to provide a constant measure between voltages. They are rated in continuous power (you can draw this much power constantly, and it should not cause any problems) and peak power (you can go up to this amount briefly, but if you keep drawing this, it can cause damage to the inverter).

If an inverter is rated at 120 watts, that means that it can convert 10 Amps at 12 volts DC (a car battery) to 1 Amp at 120 volts AC.

This is a general term for being self reliant in power production. For example, if I own an off-grid cabin, then it is probably not hooked up to city power, and I may have a solar panel array or a generator.

Off-grid can also be used to refer to things like having your own heating, sewer, or other utilities. It may also be used to refer to producing your own food and/or fuel.

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