Solar Electric Panels: Overview

All solar electric panels should have durable connectors on the module. The connectors should be sturdy, and the method of attaching the wire should be simple, yet provide a secure connection. Most modules have sealed junction boxes to protect the connections. Field testing experience shows that PV cells and connections between cells within the module laminate rarely fail. Most problems occur in the module junction box where the interconnections between modules are made. These can often be repaired in the field without replacing the module. Before buying a solar electric panel, look at the junction box and see if it is easy to make the connections. Are the terminals rugged and is there a place to connect bypass diodes? Is the junction box of good quality?

A switch or circuit breaker as part of a combiner box should be installed to isolate the PV array during maintenance. This same recommendation applies to the battery circuit so another switch or circuit breaker is required. Also circuit breakers are normally installed to isolate each load. Fuses are used to protect any current carrying conductor. Fuses and cables in the array circuit should be sized to carry the maximum current that could be produced by short-term "cloud focusing" of the sunlight--up to 1.5 times the short circuit current at 1,000 w/m² irradiance. Slow-blow fuses or PV breakers are recommended. Only fuses rated for dc current should be used. (Auto-motive fuses should not be used.) All metal in a solar panel array should be grounded to help protect the array against lightning surges, and as an added safety feature for personnel working on the system. The negative conductor on most solar electric systems is also grounded to the same grounding electrode used for the equipment ground. Other disconnect and grounding requirements are given in the National Electrical Code® (NEC). This code is intended to ensure that safe, durable solar electric systems are installed.

Orientation

Drawing illustrates the path of the sun over varying season. Remember when selecting a site for your solar panels to a pick a spot that is clear of shade from a minimum of 10AM to 2PM from December 21st (for locations north of the equator). Even a limb from a deciduous tress will substantially reduce your array's power output.

A solar electric panel array can be mounted at a fixed angle from the horizontal or on a sun-tracking mechanism. The preferred azimuth for arrays in the northern hemisphere is true south. The decrease in energy production for off-south arrays roughly follows a cosine function, so if the azimuth of the array is kept to ±20° of true south, annual energy production is not reduced significantly. Some arrays are sited west of south to skew the production toward an afternoon peak load demand. For most locations, a tilt angle near the latitude angle will provide the most energy over a full year. Tilt angles of latitude ±15° will skew energy production toward winter or summer, respectively. For solar data for selected sites, click here (this data doesn't include the optimization of tracking data - just the average, high and lows for panels oriented at the same angle as the latitude of major US cities).