Solid State Relays
Conventional, electromechanical relays use a hold-on coil which must be permanently energized. This energy must be provided by the battery or the generator through fuel. The efficiency factors of the generator and motor must be taken into consideration.
A diesel motor has an efficiency factor of approximately 40 %. The generator has an efficiency factor of approximately 50 %. This leads to a loss of approximately 80 % of the energy provided in the diesel fuel (overall efficiency factor 40 % x 50 % = 20 %) which is transformed into electrical power. This makes it worth-while to optimise even the smallest electrical loads.
For switching elements, it means the holding current and power loss via the internal resistance should be as small as possible. These requirements can only be met with a different technology: solid state relays. These relays do not have any moving parts or electrical switching contacts. They also have a longer life-span compared with electro-mechanical relays because of the low internal resistance of only 1 mOhm and they are also subjected to significantly less temperature changes. All this requires much lower switching energy. Typically, the holding current of an electro-mechanical relay is 30 mA to up to 200 mA. A solid state relay, by contrast, only requires a control current of 10 mA.
When replacing five electromechanical relays with solid state relays you can save almost 1 A of energy. This corresponds to approximately 0.3 g CO₂/km. If CO₂ values exceed the limit, this emission would correspond to a penalty of € 28.50, € 5.70 per relay. Five solid state relays correspond only to 0.015 g CO₂/km. The potential savings when using solid state relays are tremendous.