Solar panels produce volts when exposed to the sun. But, that is only part of the equation. Panels also produce amps. In most cases, panels are rated in watts. Watts are the result of the number of volts multiplied by the number of amps.
Solar panels are rated by the work they can do measured in watts. Watts is a calculated value based on the volts and amps the panel produces. The calculations for evaluating the power ratings of a panel are quite easy.
Once you know the simple equations you can easily figure the power qualities of any panel.
Power Calculations ( Watts )
There is one basic equation employed in calculating the power factors of any electrical device, including solar panels. Based on what you know about the panel, the equation can be manipulated to calculate other values.
The base equation is:
V x I = P
- P = Power = Watts
- V = Volts
- I = Inductance = Amps = Current
- Volts of panel = 12.
- Current of panel in Amps = 5.0
- 12 Volts x 5 Amps = 60 watts.
Often the packaging of a panel will indicate the power rating and the volt rating. By modifying the equation you can calculate the current in amps.
The revised equation is :
P / V = I
- Watt rating of panel = 100.
- Volt rating of panel = 24.
- 100 watts / 24 volts = 4.16 amps.
By remembering this simple power equation, and doing a little math, you will be able to calculate the power values of any panel. These values come in handy when you need to determine if a panel will provide sufficient power for your project.
Solar panels produce Direct Current (DC) voltage. They can be built to provide nearly any DC voltage. The voltage of the panel is impacted by cell size, cell construction, number of cells, panel size, and panel wiring.
The result is panels from 0.5 volts to near 50 volts. Each volt range has a use. Not all voltages are appropriate for all applications.
Solar Panel Volt Ranges
- Micro or Mini = 0.5 – 5.0 volts.
- Small = 6.0 – 12.0 volts.
- Medium = 12.0 – 24 volts.
- Large = Over 24.0 volts.
These ranges are not official designations. They are general terms for panels at various power levels.
What Voltage is the Right Voltage?
Every electrical device requires a specific voltage to operate. Some devices are more particular than others. Electronic devices tend to need a specific voltage to operate properly.
Mechanical items, like motors, are usually more tolerant of voltage variations. It is advisable to stick as close to the voltage specified by the device manufacturer.
Too great a voltage variation can damage or destroy a sensitive device.
Voltage Variations Can Cause:
- Failure to operate.
- Poor operation.
- Overheat of device.
- Damage to device.
Micro and Mini Solar Panels
These panels are usually designed as substitutes for alkaline batteries. Therefore, they tend to produce voltages in multiples of 1.5 volts.
The size of these panels range from a few square inches to 30 or 40 square inches. Amp rating are usually in the milliamp ranges.
They are generally used for small electronic devices. The panels themselves do not have frames but are framed by the device they power. Power ratings do not usually exceed 2 watts.
Micro/Mini panels are used in devices like:
- Small portable radios.
- AAA, AA, C, D sized battery chargers.
- Small toys.
- Garden lights.
Panels in this group are used to drive larger electronic devices and small motorized devices. These panels are usually no larger than One Square Foot in size. Amp ratings are still quite small, usually not exceeding one amp.
These panels may come independently framed or framed within the device they power. Power ratings are around 5 watts.
Small panels are used for items like:
- Larger radios or Bluetooth Speakers .
- Small pond or fountain pumps.
- Car battery tenders.
- Security lights.
Panels in this range are what we envision domestic solar applications. They are up to 3 feet by 5 feet in size. Frames are aluminum.
Panels are generally mounted on roofs or pole-mounted arrays. Current ratings on these panels can approach ten amps. Power ratings rise as high as 250 watts.
Medium panels commonly supply power to:
- Grid tie homes.
- Off grid cabins and home.
- Well pumps.
- Utility and out buildings.
With the introduction of Maximum Power Point Tracking (MPPT) charge controllers, off-grid solar arrays were able to implement higher panel voltages.
Instead of the array being limited by the battery bank, the MPPT controller would step the higher voltage down to match the battery bank and increase current.
Large panels are now put out in excess of 30 volts and 300 watts of power. The size of these panels is nearly 4 feet by 6 feet.
Large panels can be used for:
- Larger grid tie systems.
- Large off grid homes.
- Industrial arrays.
Different Voltage Ratings on a Panel.
Every solar panel has three volt ratings. The nominal voltage is the circuit voltage the panel is designed for. The Volts at Maximum Power (Vmp) is the voltage the panel will produce under ideal conditions.
This value is essentially maximum working voltage of the panel. The third voltage value of a panel is the Volts at Open Circuit (Voc). This value is the amount of voltage the panel can produce under ideal conditions with no load.
To estimate different voltages:
- Nominal is circuit voltage = 12, 24, 48 volts
- Vmp voltage is Nominal + 45% of nominal.
- Voc voltage estimate is Nominal + 80% of nominal.
Current = Amps
The force known as current is expressed as amps. The amps produced by a solar panel are a function of the material used, the area of the panel, and the way the cells within the panel are wired.
Individual solar cells produce approximately 200 milliamps per square inch. Panel current can be increased by wiring cells in parallel rather than in series.
- Cell materials.
- Cell size.
- Number of cells.
- Cell connection pattern.
Amp production by solar panels ranges from a few milliamps in the micro and mini panel category to 10 amps from the large panels.
A device will only draw the current it requires. When choosing a panel, be sure the current produced is sufficient to operate the device. Using a panel that produces a lot more current than required is a waste of space and money.
Summary and References
Volts, amps, and watts are all factors we must consider when choosing a solar panel. Based on the requirements of your application, more volts may be more important than the current produced. In other cases, watts are all that matters.
Be sure you understand the power requirements of your situation before you choose a panel. A mistake can cost you time and money you would rather not spend.