Solar lexicon
Frequently used terms in solar technology - simply explained
Note: The following definitions of terms are for general guidance and information purposes only. No liability is assumed for the accuracy, completeness and up-to-dateness of the content. It does not constitute legal or technical advice.
1. volt (V) - voltage ("pressure")
The voltage describes the "force" with which the current flows through the cables.
Comparison: If electricity is like water, the voltage corresponds to the water pressure in the pipe.
2. ampere (A) - current ("quantity")
Indicates how much current is actually flowing.
Comparison: The amount of water that flows through a pipe per second.
3. watt (W) - power
Watt is the product of voltage (volt) and current (ampere):
Watt = Volt × Ampere
It shows how much energy is supplied or consumed per second.
4. watt hours (Wh) / kilowatt hours (kWh) - energy
The amount of energy results from the power multiplied by the time:
Wh = Watt × Zeit
It shows how much energy has been stored or consumed.
Example: 1,000 Wh = An appliance with an output of 1,000 W runs for one hour.
What do volts and ampere-hours (Ah) mean?
For example, if you see a battery with the specification: 12 V - 100 Ah, then that means:
- Volt (V) indicates the voltage level for which the battery is intended - e.g. for a 12 V inverter.
- Ampere hours (Ah) show how much current the battery can supply over a certain period of time.
1. calculate energy content (Wh or kWh)
Formula: Wh = V × Ah
Example: 12 V × 100 Ah = 1,200 Wh = 1.2 kWh
👉 This is the total amount of energy that the battery can supply when it is fully discharged.
2. which devices can you connect?
- The voltage must match the device - a 12 V device will not work with 48 V!
- The capacity (Ah) indicates how long your device can be operated.
Example: You have a 100 W device at 12 V.
- Current requirement: 100 W ÷ 12 V = 8.33 A
- Running time: 100 Ah ÷ 8.33 A ≈ 12 hours
3. how many batteries do you need?
Example: You want 5 kWh of storage at 48 V.
Calculation: 5,000 Wh ÷ 48 V = 104.17 Ah
Solutions:
- z.e.g. two 48 V / 100 Ah batteries in parallel
- or four 12 V / 100 Ah batteries in series (results in 48 V)
Other important factors
- Depth of discharge (DoD): Batteries are often only discharged to approx. 80 %.
- Efficiency: Charging/discharging losses are approx. 5-10 %.
- Cycle stability: Indicates how often you can discharge and recharge the battery.
Conclusion
You can use volts (V) and ampere hours (Ah):
- Calculate the stored energy(Wh / kWh)
- Estimate the runtime of your devices
- Plan the battery to fit into your system
- Ensure the correct voltage level