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

14 Manual of basic techniques for a health laboratorySolar panels must be installed so that they are exposed to direct light, since shadereduces the efficiency of energy production. They should be inclined at an angle of15°. The underside of the panel must be freely ventilated. The minimum distanceof the underside of the panel from the surface of the supporting construction mustbe more than 5cm to avoid heating of the panel, which would reduce the efficiencyof energy production.Electronic charge regulatorsA charge regulator controls the charging and discharging of the batteries automatically.When the battery voltage falls below a threshold value during discharge, thelaboratory instrument will be disconnected from the battery. On the other hand, ifthe voltage increases above a threshold value (e.g. when the battery is recharged),the solar panel will be disconnected from the battery. A good charge regulatoradapts the maximal voltage of the battery to the change in the temperature of theambient environment. This prevents the loss of water in the battery by evaporation.It is important to keep a spare charge regulator in stock in case of breakdown. Thecharge regulator chosen should be stable under tropical conditions. It is advisableto choose a charge regulator with an integrated digital display that allows the batterycharge to be monitored easily.BatteriesLead batteriesSolar energy systems require rechargeable batteries, which may be either lead ornickel–cadmium (Ni–Cd) batteries. Lead batteries are preferred and many typesare available commercially (see Table 2.1). High-efficiency batteries have practicaladvantages, although they are more expensive than normal batteries.When purchasing batteries choose 12V batteries with the highest capacity (1000ampere-hours (Ah)).Several types of maintenance-free lead batteries are commercially available, butthey are expensive and less efficient than those that require maintenance. The developmentof this type of battery is still in progress; it has not been thoroughlytested in tropical climates. Therefore, the maintenance-free batteries are not recommended.Transport of lead batteriesLead batteries should be emptied before being transported. It is important to rememberthat if lead batteries are to be transported by air they must be empty ofelectrolyte solution, which should be replaced on arrival at the destination.Table 2.1 Specifications for batteries used for solar power supplySpecificationType of batteryNickel–cadmium Lead–calcium Lead–calcium Lead–calciumantimony (2%) antimony (6%)Type of electrolyte liquid liquid liquid liquidMaximum discharge 100% 80% 80% 50%Discharge during normal operation 20% 20% 20% 20%Voltage/cell 1.2 V 2 V 2 V 2 VSelf-discharge rate high low medium lowTopping up required minimal infrequent frequent infrequentCapital costs high mid-range mid-range lowSuitability for photovoltaic use highly highly recommended notrecommended recommended recommended