Solar Rooftop Systems: system Design Considerations

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There are two general types of electrical designs for PV power systems for homes; systems that interact with the utility power grid and have no battery backup capability; and systems that interact and include battery backup as well. A grid connected solar rooftop system does not have battery back up.  This type of system only operates when the utility is available. Since utility outages are rare, this system will normally provide the greatest amount of bill savings to the customer per dollar of investment. However, in the event of an outage, the system is designed to shut down until utility power is

Typical System Components:

  1. PV Array
    : A PV Array is made up of PV modules, which are environmentally-sealed collections of PV Cells—the devices that convert sunlight to electricity. The most common PV module that is 5-to-25 square feet in size and weighs about 3-4 lbs./ft2 . Often sets of four or more smaller modules are framed or
    attached together by struts in what is called a panel. This panel is typically around 20-35 square feet in area for ease of handling on a roof. This allows some assembly and wiring functions to be done on the ground if called for by the installation instructions.
  2. balance of system equipment (BOS)
    BOS includes mounting systems and wiring systems used to integrate the solar modules into the structural and electrical systems of the home. The wiring systems include disconnects for the dc and ac sides of the inverter, ground-fault protection, and overcurrent protection for the solar modules. Most systems include a combiner board of some kind since most modules require fusing for each module source circuit. Some inverters include this fusing and combining function within the inverter enclosure.
  3. Dc-ac inverter This is the device that takes the dc power from the PV array and converts it into standard ac power used by the house appliances.
  4. metering: This includes meters to provide indication of system performance. Some meters can indicate home
    energy usage.\
  5.  other components : utility switch (depending on local utility)

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