Jan 11, 2010

Definitions of Solar Power Terms

You may have noticed a lot of technical terms being used in solar power technology descriptions and data sheets. Here’s a list of common phrases explained in simple language:

Rated Power or Maximum Power (Pmax)
The maximum power a solar panel can produce. This is at the optimum trade-off between voltage and current. Remember, this value will change depending on the type of solar cell and the technology used. Example below.

Maximum Power Voltage or Maximum Power Point Voltage (Vpm)
The voltage at which maximum power is produced by a solar panel; assumed value = 30.

Maximum Power Current or Maximum Power Point Current (Ipm)
The current at which maximum power is produced by a solar panel; assumed value = 5.

Since , Pmax = Vpm * Ipm;
Pmax = 30 * 5
Pmax = 150 watts.
Open Circuit Voltage (Voc)
The maximum possible voltage across the solar module (when current is zero).

Short Circuit Current (Isc)
The maximum possible current flowing through the solar panel (when resistance is zero, which is also when voltage is zero).

Temperature Coefficient (Pmax)
The change in power when the temperature changes

Temperature Coefficient (Voc)
The change in voltage when the temperature changes

Temperature Coefficient (Isc)
The change in current when the temperature changes

Normal Operating Cell Temperature (NOCT)
The temperature at which solar cells operate under standard operating conditions (SOC) or standard test conditions (STC), which are typically:
  • Insolence (aka, irradiance) of 0.8 kWh/m2 (calculate your insolence levels at Apricus)
  • Temperature: 20ºC temperature
  • Wind speed: 1 m/s.

Peak Tolerance Rating (PTC Rating)
The minimum warranted power that can be generated by a solar cell under practical conditions. Since SOC may be rare in the real world, the cells are tested under a practical setting by an independent body, such as the California Energy Commission.

Cell Efficiency or Module Efficiency
The energy conversion level of the solar cell or solar module.

Watts per Ft.2
Power generated by each square foot of the solar panel.

Maximum System Voltage
The maximum voltage that can be generated by linking more solar panels in a series to form a solar array.

Series Fuse Rating
The current reading at which the fuse will open and cause the circuit to break to protect the solar panel from damaging.

Warranted Tolerance (-/+)
The lowest possible power that the manufacturer guarantees when the panel is first operated. A 10% warranted tolerance on a 200 watt panel means it guarantees at least 180 watts when its removed from the box.