How to Evaluate Solar Panel Electric Systems

Site

• 1

  Determine the solar resources for planned location of the unit. The system's design and the efficiency depends on the amount of sun the site receives.

• 2

  Examine the roof orientation. Place the panels in the proper position geographically, which ensures the maximum amount of seasonal and daily sunlight. For installation in the northern hemisphere, the best direction for the solar modules is true south. Place the panel 45 degrees east, which is west of true south, as an alternative to due south if necessary.This does not result in a large decrease in the system's efficiency.

• 3

  Consider the local weather conditions, such as cloudy mornings or foggy afternoons. These weather patterns influence the system's orientation and the amount of electricity the solar panels generate. Survey the site for objects that have the potential of blocking sunlight or shading the panels, including building trees or other obstructions.

• 4

  Have a licensed contractor assess the roof's condition and its remaining useful life. Consider the cost of making necessary repairs or replacing the roof before installing the system, as removing the PV system to remedy a defective roof in a year or two is costly. Find the best tilt or angle for the modules. On a flat roof, the solar modules take on the same angle as the roof. Factor the angle of a slope roof in the performance computations.

System Size

• 5

  Gather your electric statements for the last 12 months. Add the amount of kilowatt-hours (kWh) used each month and divide this figure by 12. This number provides the household's average kilowatt-hours usage per month.

• 6

  Divide the average monthly kilowatt-hours by 30 to get the average daily kWh. Decide what percentage of the average daily kWh the system must have the capacity to produce.

• 7

  Compute the roof area required for the solar panels. The Department of Energy website has tables and additional information for determining the appropriate roof area. Work with the supplier or installer to make accurate calculations for your project. For example, to generate 1000 watts from solar modules with an eight percent efficiency rating requires 150 square feet of space.

Components

• 8

  Compare the two key components for solar panel electric systems -- modules and DC/AC inverter. DC, or direct current, refers to the raw electricity produced by the panels. AC, or alternating current, denotes the type of electricity generated by the inverter, which powers standard household appliances.

• 9

  Evaluate the grade of the solar cells used for the panel --a,b,c or d. The highest rating of "a" means the cells meet higher standards and have less defects. Review the warranty for solar panels. A warranty of 25 years denotes a guarantee of the panel meeting a certain efficiency over the warranty period.

• 10

  Determine the efficiency rating of the inverter. The inverter's efficiency rating measures the amount of direct current electricity transformed into AC. An inverter with 97 percent efficiency means the system loses three percent of the direct current electricity during the conversion process.

• 11

  Check the inverter's startup voltage. The startup voltage determines how much of the day the system generates power. On a very cloudy day, an inverter with a startup capacity of 125 volts has a better chance of starting than an inverter with a180-volt requirement.