Hard Facts on PV Hardware
Hard Facts on PV Hardware
To achieve low life-cycle costs, all components of a solar home system must be of the highest quality. Moreover, users must be aware of the limitations of a particular system configuration to avoid disappointments. Rather than compromising in the area of components, it is wiser to specify a smaller, high-quality system that can support an extra module and extra lamps that can be added once the household can afford it.
PV Modules: The most reliable part of the system. However, photovoltaic modules should meet the so-called JRC 503 standard and at least a ten-year warranty should be offered. In countries where local production is protected by trade barriers, modules meeting these standards may be unavailable. In such cases, a ten-year warranty should be demanded.
Module support structure: Corrosion-free materials, such as galvanized or rust-free steel, or aluminum should be used.
Charge and load controller: This unit prevents system overload and overcharging. The controller design should include:
- a low-voltage disconnect,
- a high-voltage disconnect which should be temperature-compensated when needed,
- system safeguards to protect against reversed polarity connections in the DC circuits, lightning-induced surges, over-voltage transients, etc.
- a case or covering that shuts out insects and moisture while also protecting against extremes in temperature.
- battery charge indicator,
- support for additional modules to increase system capacity,
- a fail-safe mechanism that allows the user to restart it.
Ideally, solar home systems should use deep-cycle, lead acid batteries. These allow for deep discharge without seriously damaging or reducing the life of the battery. In a well-designed solar home system, such batteries can last up to five years.
Batteries should be sealed in a childproof case.
Lamps and ballasts: To maximize the lighting services provided by a system, fluorescent lighting should be used. However, a fluorescent lamp requires a well-designed ballast that ensures that the lamp will last for at least two years under normal operating conditions. Moreover, the ballast must not interfere with radio or TV reception. In some programs, the ballasts have been the most problematic component. Frequent switching, for instance, limits the life of the lamp. To minimize this problem, a warm-start ballast should be chosen.
As for fluorescent lamps, one must choose between the more efficient lamps (CFLs or linear lamps with preheated electrodes) and the less efficient, often locally produced linear lamps. In some areas, only less efficient lamps are available, and if the system is designed for quality lamps the users may face problems finding replacement lamps. If the user replaces the fluorescent luminaire with a simple incandescent bulb, additional system losses, and even dangerous overheating, could occur.
Where burning hours are very short (less than half an hour a day) and low light levels are acceptable, 1 to 2W incandescent lamps may be the best choice.
Luminaires: A well-designed luminaire with a reflector can cut power needs by almost half, as compared with most luminaires for PV systems that are available on the market. If diffusers are used, the luminaires must be sealed off tightly to prevent insects from getting in. This can, in turn, cause lamps to operate at temperatures higher than they were designed for (See also Not Cool to Be Hot, IAEEL 2/93)
Wiring, switches, and outlets: Preferably, switches and outlets should be rated for DC operation. All wiring should be stranded copper, dimensioned to keep voltage drops to less than five percent between the battery and the load. DC electricity has a polarity that must be maintained, and it is important that the insulation be properly color coded.
See also: Overview article on PV Lighting,
The Future Belongs to PVs, and
Selected Sources on PV Lighting.
Nils Borg
Source: Best Practices for Photovoltaic Household Programs, Asia Technical Department, World Bank. Top of page