Manual of basic techniques for a health laboratory - libdoc.who.int

2. Setting up a peripheral health laboratory 13— mains electricity supply— generators— solar energy supply system.Remote laboratories often have problems in ensuring a continuous supply of electricalpower and may need to generate electricity by using a local generator or asolar energy supply system.2.2.1 Sources of electricityGeneratorsElectrical energy can be provided by a fuel generator. It is possible to use the combustionengine of a motor car or a purpose-built generator. A purpose-built generatorproduces an alternating current of 110 volts (V) or 220V and can usually generatemore energy than a car engine. A car engine provides a direct current of 12V or24V, which can be fed into rechargeable batteries (see below).The type of current available will limit the selection of laboratory equipment; forexample, an instrument that requires direct current can be supplied with energy from:— batteries— a direct current network with a transformer— an alternating current network with a converter.The installation of a direct current network is simple and it is safe to operate.However, for instruments that require a low-voltage (6V, 12V or 24V) direct current,the high voltage produced from the direct current network must be convertedby means of a transformer. Alternatively, for instruments that require alternatingcurrent (110V, 220V or 240V), the direct current must be converted into alternatingcurrent by means of an inverter. Inverters are heavy and expensive and significantenergy losses occur in the conversion process. It is therefore preferable to use eitherdirect current or alternating current appliances, depending on your supply, andavoid the need for conversion.If no generator is available or if a mains power supply is accessible, but the electricalcurrent fluctuates or is prone to frequent breakdowns, a solar energy supplymay be preferable (see below).Solar energy supply systems (photovoltaic systems)A laboratory with a few instruments with low energy requirements can work with asmall energy supply. For laboratories located in remote areas, a solar energy supplysystem may be more suitable than a generator since there are no problems of fuelsupplies and it can be easily maintained.A solar energy supply system has three components:— solar panel(s)— an electronic charge regulator— batteries.Solar panelsTwo different types of solar panel are commercially available:— panels with cells of crystalline silicon— panels with cells of amorphous silicon.Amorphous silicon panels are less expensive, but produce solar energy less efficientlythan crystalline silicon panels.