Photovoltaic units simply explained: Watts to kWp, Ah to Wh, and the difference between amperes & volts

In the world of solar energy, users often encounter terms like watts, kWp, Ah, Wh, amperes, and volts. These units are essential for correctly understanding power, capacity, and energy consumption. This article explains the conversions step by step and offers practical tools such as calculators and tables.

Converting watts to kWp

Converting watts (W) to kilowatt-peak (kWp) is simple: divide the watt number by 1000, as 1 kWp corresponds to exactly 1000 watts. For a typical balcony power plant with 800 watts, this means: 800 watts = 0.8 kWp. This solar unit calculator formula helps to quickly evaluate the nominal power of solar modules. The meaning of kWp lies in the peak power under standard test conditions (STC), ideal for planning photovoltaic systems.

Converting Ah to Wh

Ampere-hours (Ah) indicate the charge amount of a battery, while watt-hours (Wh) indicate the usable energy. The Ah to Wh formula is: Wh = Ah × Volts (V). For 100 Ah and 12 V, the result is 100 Ah × 12 V = 1200 Wh. Converting Ah to Wh is crucial because storage batteries are often specified only in Ah, but consumers are billed in Wh or kWh. This allows for fair comparison of different batteries, regardless of their voltage.

Why convert storage batteries from Ah to Wh?
Ah alone is deceptive because voltage is missing – a 100 Ah battery at 12 V delivers twice as much energy as at 6 V. Wh shows the actual runtime for devices like refrigerators or routers. In solar systems, this optimizes self-consumption and avoids misinvestments.

Amperes and volts: The difference

Amperes (A) measure the current flow, comparable to the amount of water per second in a river. Volts (V) represent the voltage, like the water pressure that drives the current. Amperes multiplied by volts result in watts (W): P = U × I (Power = Voltage × Current). With the water metaphor: Amperes (flow rate) × Volts (pressure) = Watts (energy transfer). This fundamental principle explains why solar calculators consider volts and amperes.

Conversion table: Practical solar unit calculator

Here is a clear table for quick conversions. Save or screenshot it for your planning.

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Capacity (Ah)	12 V (Wh)	24 V (Wh)	48 V (Wh)
50 Ah	600 Wh	1200 Wh	2400 Wh
100 Ah	1200 Wh	2400 Wh	4800 Wh
200 Ah	2400 Wh	4800 Wh