Generators

Depending on the community and its needs, generators can be an excellent option as an energy source for the water purification system. In recent years generators have improved dramatically in many areas including higher efficiency, better emission values and lower noise level. The main types of generators are gasoline, diesel and natural gas powered generators.

Gasoline
Gasoline generators are readily available at acceptable cost and they use the most accessible fuel. However the price of gasoline has been quite high as of late and there are size restrictions. Also, many of these small generators are air cooled, preventing heat recovery from the jacket (see below).

Diesel
Diesel generators are very fuel-efficient. They do not require frequent maintenance and are designed to function for long hours continuously. If used in cold weather, diesel generators have problems starting due to the thickening of the fuel. Heaters in the oil pump and/or in the fuel supply system will solve this problem, should it exist.

Natural Gas
Natural gas is the cleanest fuel compared to diesel and gasoline. Natural gas also causes less engine buildup which leads to a longer lifetime. The availability of natural gas is an issue in rural communities with little infrastructure.

Heat Recovery
Considering that only a maximum 35% of the fuel's combustive energy will be converted to electrical power and that the balance will be rejected by the combustion engine via its cooling jacket, the exhaust pipe and by radiation, it often makes economic and environmental sense to recover most of the heat from the cooling jacket and occasionally some more from the exhaust pipe. The heat is recovered by means of a closed water loop, which produces hot water in a secondary loop via indirect heat exchange. For hybrid systems the following combinations are possible.

Water Purification	Electric Power Use	Hot Water Use
Membrane Filtration	Filtration System Pumps Ozonator or UV Lamp Optional: Lighting Refrigeration Communication	Space Heating Hot Water Supply for Communal Facilities
MSF Evaporation	MSF System Pumps Optional: Lighting Refrigeration Communication	MSF Heating Optional: Space Heating Hot Water Supply for Communal Facilities
MVR Evaporation	MVR Compressor Drive MVR System Pumps Optional: Lighting Refrigeration Communication	MVR Make-Up Heat MVR Supplemental Evaporation Optional: Space Heating Hot Water Supply for Communal Facilities

The generator size needs to be chosen such that at a minimum the primary objective of powering the water purification system is accomplished. Depending on need, the generator can be chosen to be larger to cover secondary requirements such as lighting, etc.

In case of the MSF, the primary reason to install a generator would be to satisfy needs in the area of lighting and other domestic electrical use first and then as a bonus, use the reject heat to operate a MSF system for the production of potable water, if that is needed and if there is no better use for the generator's reject heat.

Conversely, a generator may be sized for heating and powering a MSF with a specific potable water production rate. The excess electric power then can be used for other domestic or commercial electrical purposes, assuming there is sufficient opportunity for consumption.

Such hybrid systems produce both potable water and electric power at acceptable cost, while operating a generator exclusively for producing electric power is expensive in terms of cost per kWh produced.