Solar power and solar panels

The basic PV or solar cell (for example: Goal Zero Nomad 20 ) typically produces only a small amount of power. To produce more power, solar cells (about 40) can be interconnected to form panels or modules. PV modules range in output from 10 to 300 Watts. If more power is needed, several modules can be installed on a building or at ground-level in a rack to form a PV array.

In addition to solar cells, a typical PV module or solar panel consists of these components:

• A transparent top surface, usually glass
• An encapsulant -- usually thin sheets of ethyl vinyl acetate that hold together the top surface, solar cells, and rear surface
• A rear layer -- a thin polymer sheet, typically Tedlar, that prevents the ingress of water and gases
• A frame around the outer edge, typically aluminum.

Energy performance ratings for PV modules include the following:

• Peak Watt -- Measures the maximum power of a module under laboratory conditions of relatively high light level, favorable air mass, and low cell temperature. These conditions are not typical in the real world.
• Normal operating cell temperature -- Measures a module's nominal operating cell temperature after the module first equilibrates with a specified ambient temperature. It results in a lower Watt value than the peak-Watt rating, but it is probably more realistic.
• AMPM Standard -- Measures the performance of a solar module under more realistic operating conditions. It considers the whole day rather than "peak" sunshine hours, based on the description of a standard solar global-average day (or a practical global average) in terms of light levels, ambient temperature, and air mass.

Home Solar Electric System Arrays

For home solar electric systems, the most common array design uses flat-plate PV modules or panels. These panels can either be fixed in place or allowed to track the movement of the sun.

The simplest PV array consists of flat-plate PV modules in a fixed position. These are some advantages of fixed arrays:

• No moving parts
• No need for extra equipment
• A lightweight structure.

These features make them suitable for many locations, including most residential roofs. Because the panels are fixed in place, their orientation to the sun is usually at an angle that is less than optimal. Therefore, less energy per unit area of array is collected compared with that from a tracking array. This drawback, however, must be balanced against the higher cost of the tracking system.

Energy Performance

Solar arrays are designed to provide specified amounts of electricity under certain conditions. The following factors are usually considered when determining array energy performance:

• Characterization of solar cell electrical performance
• Determination of degradation factors related to array design and assembly
• Conversion of environmental considerations into solar cell operating temperatures
• Calculation of array power output capability.

The amount of electricity required may be defined by any one or a combination of the following performance criteria:

• Power output -- power (Watts) available at the power regulator, specified either as peak power or average power produced during one day.
• Energy output -- the amount of energy (Watt-hour or Wh) produced during a certain period of time. The parameters are output per unit of array area (Wh/m²), output per unit of array mass (Wh/kg), and output per unit of array cost (Wh/$).
• Conversion efficiency -- defined as "energy output from array" ÷ "energy input from sun" × 100%.

This last parameter is often given as a power efficiency, equal to "power output from array" ÷ "power input from sun" × 100%. Power is typically given in units of Watts (W), and energy is typically in units of Wh, or the power in Watts supplied during an hour.

To ensure the consistency and quality of PV systems and increase consumer confidence in system performance, various groups -- such as the Institute of Electrical and Electronics Engineers (IEEE), the International Electrotechnical Commission (IEC), and the American Society for Testing and Materials (ASTM) -- are working on standards and performance criteria for PV systems.

Home Solar Electric Components

A typical home solar electric system consists of these components:

• Solar cells
• Modules or panels (which consist of solar cells)
• Arrays (which consist of modules)
• Balance-of-system parts.

The balance-of-system equipment required depends on whether the system is a stand-alone system, connected to the electric grid, or a hybrid system. Balance-of-system equipment can include:

• Mounting racks and hardware for the panels
• Wiring for electrical connections
• Power conditioning equipment, such as an inverter
• Batteries for electricity storage (optional)
• Stand-by gasoline electric generator.