Demystifying photovotaic

Solar photovoltaic (PV) technology converts the sun’s energy into electrical energy. It’s renewable and a nonpolluting source of energy.

There are two types of PV system: grid-tied systems (which use the power company’s grid to store electrical energy—most common) and standalone systems (which require batteries to store electrical energy, used in cabins & remote applications—more complicated and expensive).

Grid-tied System Components

· Solar PV panels convert the sun’s energy to direct-current (DC) electrical energy. PV panels are made from semiconductors. The photovoltaic effect was discovered by Edmund Becquerel in 1839, but was popularized by the work of NASA. Three basic types of PV are single-crystal (highest output, but most expensive), polycrystalline (most common), and thin film. The higher the sun’s intensity, the higher the output power of the panels. Panels are connected in series and/or parallel to give the desired system voltage and power.

· An inverter converts DC to pure sine-wave alternating current (AC) as most electrical load in the United States is AC.

· Racks hold the panels together on the roof or on the ground. Typical systems are rack-mounted, tracking systems, stand-off, and building-integrated.

· BOS (balance of system) consists of wires, fuses, junction boxes, lightning arrestors, ground wires, etc. In other words, anything that is not panels, inverter, and rack.

Standalone System Components

Standalone system components: same as grid-tied systems. In addition, there are batteries (storage of the DC energy) and a charge controller (controls charging of the batteries).

Phases of a Solar Project

1. Site assessment phase: This will determine if a site has adequate sunlight for a solar PV system. A solar pathfinder is used to determine the year-round shading of a particular site. The area of available space will determine the maximum size of the system. Twelve months of electrical bills are analyzed to determine electrical needs of a site. Focus on Energy will provide a 50-percent grant for the cost of the site assessment. The site assessment phase may point out recommendations to reduce electrical needs, such as replacing incandescent light bulbs with compact fluorescent light bulbs, or installing high-efficiency appliances, better insulation, or resetting the thermostat. Reducing the energy consumption could mean a smaller PV system would be required.

2. System selection phase: The solar installer and customer go through the goal and expectations for the solar PV system. The size of the PV system is determined by the available space for the panels on the roof, the budget, the amount of available sunlight for the area, and the amount of electricity to be produced. The minimum size for a system to be grid-tied is 1.5 kilowatts (kW) for We Energies customers; maximum size is the power used at the site (obtained from the 12-month average electrical bill). Typically a system size will fall between the minimum of 1.5kW and 4-5kW (an average household).

Once the solar PV size is determined, the solar panels and inverters are selected by the solar installer. There are different ways the solar panels can be installed, all dependent on roof type and condition. The solar installer might recommend rack-mounted panels, pole-mounted panels, ballasted mounts, etc., depending on the situation.

3. Incentive phase: Once a system has been decided, the solar installer will apply for a incentives. Focus on Energy covers 30 percent of the total cost of the project. The federal incentive is $2,000. We Energies’ “Cash-Back” is based on the size of the system. Overall incentives will be about 40 percent of the total cost of the system. The grant application process usually takes about 30 days.

4. Build phase: A city permit must be pulled before work can begin. Solar PV systems may require different trades: solar technology, electrical, and roofing. The solar installer will submit a plan, electrical schematics, and component specifications to the city for the proposed system, and pull a permit. Once permits are done, the actual installation can take place.

5. Commissioning phase: The system going live is also called commissioning. The solar installer, a master electrician, We Energies, and a city inspector will go over the system to ensure every component is installed appropriately before connecting the system to the grid. A bidirectional utility meter may be installed if there is not one already onsite. Some installations may require a second utility meter.

The current payback of a typical solar PV grid-tied system is around seven to 12 years.

Swee Sim owns Future Green, 2352 S. Kinnickinnic Ave., with his wife Lisa Sim. (414) 294-4300 or futuregreen.net. Future Green is consulting with Bella’s Fat Cat regarding site assessment and solar photovoltaic installation.

Resources

Energy estimation by location (PV Watts): rredc.nrel.gov/solar/codes_algs/PVWATTS/version1/US/Wisconsin

Incentives: dsireusa.org

Focus on Energy: focusonenergy.com/renewable

MREA: the-mrea.org

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