# MySmartGrid Developer Wiki

### Site Tools

terms

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.

• We won't discriminate between current and power (Strom und Leistung). We will use the term current consistently, and don't talk about power. However what we actually mean is power, so the unit is Watt (W) or Kilowatt (kW).
• Yes, this will make every electrical engineer scream in agony (including me ). But we need to keep in mind that people talk about “Strom” and mean “Leistung”.
• We know the law of conservation of energy. So we are aware, that the term “consumption of energy (Stromverbrauch)” is wrong. The law tells us, that the amount of energy does not change. Instead there is a change of the form of the energy. For example from electrical to heat or motion. 