MySmartGrid Developer Wiki

This is an old revision of the document!

It's easy to confuse terms like power, energy and current, especially in the German language. This page is to document the definition of the terms.

Definitions

Current (Strom)

The unit for measuring current is Ampere (A), the symbol is I. Example: I = 5A
In our case, the current is what changes over time, since the voltage is fixed (230V).

Voltage / electric tension (Spannung)

The unit for measuring voltage is Volt (V), the symbol is U. Example: U = 230V
The power grid supplies either 400V between two line conductors (Außenleiter) or 230V between a line conductor and neutral.
- We assume, the voltage in the grid is fixed.

Power (Leistung)

Electric power is the rate at which electrical energy is transferred by an electric circuit.
The unit is Watt (W), the symbol is P. Example: P = 200W.
The Power is the product of current and voltage. P = U * I.

Electrical Energy (Energie)

Electrical Energy is the amount of work which can be performed by electricity.
The unit for measuring energy is kilowatthours (kWh), the symbol is E. Example: E = 23 kWh
The energy is calculated as follows: E equals the integral from t1 to t2 of u(t) * i(t) dt
The unit is kilowatt times hour (kWh). NOT kilowatt by hour (kW/h)!

Use of the terms

Since most of the project's participants don't have a background in electrical engineering, we need to use a language they can understand. Therefore we use terms from common language, which in some cases are not technically correct but will be understood.