Balance of System (BOS). Electrical and structural components, aside from the major components make up the Balance of System. Mounting rack for solar panels, housing of the batteries, pole and all inter-wiring are examples of the BOS for an off grid solar lighting unit. Quality of these parts is important to the overall life of the system. Aesthetics are also dependant on the parts and pieces selected to integrate the major components into a single package. Currently available systems range from very basic raw parts and pieces to architecturally attractive forms.

 

Choosing the Right Luminaire

Identify the lighting needs. With the cost of solar lighting systems ranging widely depending on size, it is best to identify how much light is really needed for an application. In addition to the quantity of light, the amount of hours the system must provide a specific light level each night has a big impact on system size and, therefore, cost. Review the use of your project site; will there be pedestrian activity all hours of the night, or only until a certain time? If lighting can be dimmed or turned off after that time the size and cost of the system will decrease. If security is a concern and illuminance must be maintained at a high level from dusk until dawn the system size and cost may increase significantly. Attention to these considerations when specifying solar lighting will ensure that the owner of the system pays for only the performance that the project will require.

 In 1997 the Commission Internationale de l'Eclairage (CIE) defined lighting zones that would typically have different lighting requirements. The IESNA and LEED rating system have both adopted this method of classifying a project site into one of four zones. Environmental Zones E1 − E4 provide descriptions of each zone and recommended maximum illuminance levels for each.

Environmental Zone E1, for example, is described as an area that is intrinsically dark, such as a park or residential area where controlling light pollution is a high priority. Areas classified as E1 will allow lower maximum illuminance levels compared to a project site classified as an environmental zone E2, E3, E4. Environmental Zone E4 allows the highest maximum illuminance levels and is described as areas of high ambient brightness such as an urban environment or areas experiencing high levels of nighttime activity (Source: IESNA − RP-33-99 Lighting for the Exterior Environment).

Recommended illuminance levels, uniformity levels and other important lighting criteria are published by the Illuminating Engineering Society of North America. This is a good basis for selecting illuminance levels if no lighting criteria are specified by the local municipality or project.