What are some important considerations in choosing PV lighting?
Amount of solar irradiance
Solar irradiance for photovoltaic (PV) power is affected by location, weather, time of year, and surrounding structures. The solar radiation received by the earth's atmosphere is 1367 watts per square meter (Messenger and Ventre 2004), but this amount is reduced when the solar radiation passes through the air mass. Solar radiation is the radiant energy emitted by the sun. The term "solar irradiance" refers to the amount of radiant flux incident on any surface, including buildings. The solar irradiance is lower at sea level, for example, than it is on a mountain top. It is also generally true that the farther away a location is from the equator, the lower the solar irradiance will be available at ground level. In summer, solar irradiance is available longer than in winter. Weather also affects the amount of solar irradiance. Cloud cover, for example, will reduce solar irradiance. Finally, solar irradiance may be blocked by buildings, trees, or snow and dirt on the PV panels (see "How does solar radiation vary by location?").
Aesthetic and structural concerns
Some of the components in PV lighting systems, such as the PV panels, tend to be large and awkward. Structural support and wind load should be considered to ensure that the PV panel does not pose a safety hazard to people. A smaller PV panel may reduce both aesthetic and structural concerns but will limit the power capacity of the PV panel.
Cost vs. performance
Cost is an important factor in any investment. From the end-user's point of view, PV lighting systems include more components and therefore are more expensive to purchase than traditional, grid-powered lighting systems. However, in areas where electricity from the grid is not accessible, extending the power lines is often prohibitively expensive. For example, it would be economically ineffective to extend a power line to a remote mountain area only for powering luminaires at a campground's parking lot. In these types of remote locations PV power may be a good alternative for providing lighting at night.
The performance of a PV lighting system is related to the quality of its components. Generally, the higher the quality, the more expensive the system. Technologies associated with PV lighting are not fully mature (at time of publication), and some components may not be reliable even if they are expensive. These costs and risks have often pushed PV lighting out of consideration for use in a wide variety of lighting applications. However, the increasing desire for energy independence and the rising cost of energy may change this situation in the future. By carefully matching PV lighting to appropriate applications, PV lighting may find its way to more lighting markets and thereby reduce both the costs and risks associated with these systems (see "How does the cost of PV lighting systems compare to grid-powered lighting systems?").