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Solar Modules
  • Solar Modules (aka panels) – capture energy from sunlight and convert it to DC electricity

  • 72-cell modules are common for commercial/residential systems

  • Smaller 60-cell modules used for residential when space requires a smaller footprint

  • Thin film is used extensively in utility-scale solar farms

  • Mono- or Poly-crystalline cells, Mono-crystalline tend to be slightly more efficient/generate more watts per area

  • Modules are designed to withstand wind, hail, and snow

  • Bifacial modules can make use of light reflected onto the back face of the panel

  • Output degrades slowly over time, ~3% in year 1 and <0.5% each year thereafter – manufacturers warranty output for 25 years or longer

  • “Tier 1” designation designates financeable and “high quality” modules… but best indication is listing on California’s incentive-eligible website  


  • For best efficiency, modules will face south, although east- and west-facing modules will also produce electricity.  North-facing should be avoided

  • Residential / pitched roof systems are usually mounted on rails, with the modules at the same pitch or “tilt” as the roof.  Rails will be screwed to the roof framing, so care must be taken to flash and seal completely

  • Commercial / flat roof systems are typically mounted on “ballasted racking” which provides tilt for the modules of 10-15 degrees, and is held down by ballast blocks so there are no roof penetrations

  • The roof must be capable of supporting the additional load, and roofing should have a remaining lifetime of at least 25 years

  • Carport-mounting or ground-mounting on poles with racking is also common, but distances to the existing electrical system can affect installation costs

  • Motorized Tracking Systems can keep modules aimed more directly at the sun during each day and through the seasons, but add cost and complexity

  • Inverter(s) – convert DC electricity to AC for use by standard AC devices/equipment or to feed back into the grid for others to use.  Synchronizes AC voltages to match the grid.  Can be 1-phase or 3-phase.

  • Three common architectures: Central-, String-, and Micro-Inverter

    • Central inverters are lowest cost but also lower efficiency because shade or malfunction of one or two modules degrades the output of the entire array

    • String inverters act like multiple central inverters, each responsible for a subset or "string" of solar modules.  Shade or debris on a module affects the efficiency for that string rather than the entire array, and this added efficiency also adds a bit more cost.

    • Microinverter technology puts an inverter at each individual solar module, converting DC to AC right at the panel.  It is highly efficient but also carries the highest cost.

  • When an array of solar modules is likely to experience varied shading or soiling, as is often the case across a rooftop, a good compromise between efficiency and cost is to use power optimizers at the modules (like a microinverter) together with a simplified string inverter - this is the SolarEdge architecture. 

  • Inverters usually offer web-based monitoring

Battery Storage
  • Battery storage can be used to store excess solar production instead of selling it back to the grid, as well as to provide backup power in case of a utility power outage.  

  • Lead-acid batteries are the most-used technology for renewable energy battery storage.  Deep cycle lead-acid batteries provide reliable and affordable service for many years.  They are available in flooded or absorbent glass mat (AGM) types and are easy to maintain.  AGM versions offer up to 5X faster charging times, higher current densities and no required maintenance, for a modest cost premium.  Lead-acid batteries are 99% recyclable and are the most recycled product in North America.

  • Lithium-ion batteries are also available for renewable energy storage, and have the benefits of highest power density, lowest weight and no required maintenance.  However, their lifetime is shorter and cost significantly higher than lead-acid batteries, and special equipment and precautions must be taken to ensure safety and avoid potential overheating. Lithium-ion batteries are only partially recyclable and cannot be recycled into new batteries.​

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