small solar electric arrays
For small solar electric systems, the most common array design uses flat-plate
photovoltaic (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:
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
- No moving parts
- No need for extra equipment
- A lightweight structure
Solar arrays are designed to provide specified amounts of electricity under
certain conditions. The following factors are usually considered when determining
array energy performance:
The amount of electricity required may be defined by any one or a combination
of the following performance criteria:
- Characterization of solar cell electrical performance
- Determination of degradation factors related to array design and assembly
- Conversion of environmental considerations into solar cell operating
- Calculation of array power output capability
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 watt-hours (Wh),
or the power in watts supplied during an hour.
- 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%.
To ensure the consistency and quality of photovoltaic 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.
ENERGY AND POWER