Current x Resistance = Volts
I x R = V
Voltage is equal to current multiplied by resistance. This calculation is known as Ohm’s Law. As with power calculations, you can express this calculation indifferent ways. If you know volts and current, you can calculate resistance. If you know volts and resistance, you can calculate current:
Volts/Resistance = Current
V/R = I
Volts/Current = Resistance
V/I = R
Power
Volts x Current = Power
V x I = P
Power is measured in watts. It equals volts times current. A 9-volt circuit with a4-amp current equals 36 watts of power (9 x 4 = 36).Based on this calculation, we can also work out voltage if we know power andcurrent, and current if we know voltage and power:
Power/Current = Volts
P/I = V
Example: A 36-watt motor with a 4-amp current is running at 9 volts.
36 watts/4 amps = 9 volts
Current = Power/Volts
I = P/V
Example: a 36-watt motor with a 9-volt supply requires a 4-amp current.
36 watts/9 volts = 4 amps
Power (watts) is also equal to the square of the current multiplied by theresistance:
Current² x Resistance = Power
I² x R = P
Energy
Power x time = energy
Energy is a measurement of power over time. It shows how much power is used, or generated, by a device, typically over a period of an hour. In electrical systems, it is measured in watt-hours (Wh) and kilowatt-hours (kWh).A device that uses 50 watts of power, has an energy demand of 50Wh per hour.
A solar panel that can generate 50 watts of power per hour, has an energy creation potential of 50Wh per hour. However, because solar energy generation is so variable, based on temperature, weather conditions, the time of day and so on, a new watt-peak (Wp) rating is now used specifically for solar systems.
A watt-peak rating shows how much power can be generated by a solar panel at its peak rating. It has been introduced to highlight the fact that the amount of energy a solar panel can generate is variable and to remind consumers that a solar panel rated at 50 watts is not going to be producing 50 watt-hours of energy every single hour of every single day.
Direct Current and Alternating Current
Two types of current can flow through an electrical circuit.
Direct Current is a constant charge flowing in one direction, moving from the high voltage(positive) power source to the low voltage (negative) power source. Batteries and solar panels both work on direct currents.
An alternating current is a stream of charges that reverse direction very rapidly. The current switches directions several times each second. This cycle of switching directions is called frequency and is measured in Hertz (Hz). The faster this cycle of switching, the higher the frequency. Grid electricity works on AC power. AC power in Europe cycles around 50 times a second (50 Hz), whilstin the United States, AC power cycles 60 times a second (60 Hz).