In a two-part series, Chris Kneeland, NABCEP – Solar PV, project engineer in RTM’s Milwaukee office, shares his solar energy expertise. Part one provided an overview of photovoltaics basics and part two dives into photovoltaics panel design and structure.
Photovoltaics Panel Design & Structure
A basic PV cell only produces a small amount of electrical power, so many PV cells must be connected to result in more usable energy. Typical panels have 60-72 cells and 400 watts can be achieved with a 72-cell module.
The typical solar panel is made up of:
- Photovoltaic cells
- A transparent top surface (usually glass)
- A rear surface made from a thin polymer sheet to prevent water and gases from entering
- An encapsulant to hold the top surface, rear surface and solar cells together (usually thin sheets of ethyl vinyl acetate)
- An outer frame (usually aluminum)
Photovoltaic systems are classified in two major categories: grid-connected (or utility-interactive) systems or stand-alone systems. Grid-connected systems operate in connection with the electric utility grid, while stand-alone systems operate independently from the grid and usually rely on batteries for storage of energy for use at night. Stand-alone systems are very expensive and the batteries normally need replacement every five to 10 years.
PV systems operate like other electrical power generating systems, but they often require specialized equipment to conduct, control, convert, distribute and store energy. These components may include: DC-AC power inverters, battery banks, system and battery charge controllers, auxiliary energy sources, or balance of system hardware.
Photovoltaic modules and arrays create an output of direct-current (DC) electricity. Inverters are required to change the DC from the panels to alternating current (AC) for consumer use. There are two types of inverters: micro-inverters and central (or string) inverters. Micro-inverters mount to each panel while a central inverter covers a string or combined strings of solar panels to create AC. Since micro-inverters optimize power at the panel level, they are best for residential and small-scale commercial projects where one or more panels may be shaded or installed on different planes.
A standard residential application will use around 10 to 20 photovoltaic panels to power a home, but a large-scale industrial application requires a much more powerful system. For industrial use, many solar panels are interconnected to create a solar array. Solar arrays can then be combined together, by the dozens or even hundreds, to form a photovoltaic system. PV systems for industrial facilities require large open spaces – such as flat roofs or parking lots – as, in general, the larger surface area a PV module or array covers, the more electricity will be produced. The systems should face south or southwest and have little to no shade from trees, equipment or buildings to optimize power production.
In addition to the overall energy renewable savings realized by using a PV system, another benefit for using solar energy in industrial applications is that it can allow for “peak shaving” to reduce utility penalties during peak demand.
Speak with Chris Kneeland to learn more about photovoltaics including general costs, length of time for payback and warrantees: 414.273.1432.