Archive for March, 2007

PhotoVoltaics: The Right (of) Way

Monday, March 26th, 2007

Over the last year, I’ve spent a lot of time lookng at PhotoVoltaic (PV) systems, certainly one of the hot areas in the Cleantech/Greentech investment boom currently underway. Much of the interest has been in rooftop PV systems, largely because of tax credits and incentives from utilities.

I really like the idea of distributed PV generation: it meshes with the afternoon peak power requirement, and can reduce the burden on transmission systems by voltage support and reduced thermal load in transformers and lines. Yet after visiting rooftop PV installations ranging from a few to 500 kw, I haven’t been able to work up a lot of enthusiasm for them.

Installation on existing roofs has problems such as

  • risk of penetrating the weather barrier, leading to structural deterioration
  • potential mismatch between the lifetime of the roof and the modules
  • interference with other rooftop requirements, such as HVAC and skylights
  • high NRE (non-recurring engineering) because each site and roof is different
  • high installation costs because the mounting needs to be adjusted for each rooftop
  • construction and maintenance (cleaning) health hazards (risk of fall). Standing on one rooftop, I asked the owner about cleaning. He replied that they come up twice a year and wash the panels with soap and water. Just what I want — somebody standing on a slippery roof (NOT!).

So I’ve came to the conclusion that PV needs to be installed either as building-integrated modules in new construction or on purpose-built structures, like parking lots. But I think the best place for PV is the right of way along our hundreds of thousands of miles of railroads and highways:

  • A production line can be created, where the same steps are repeated all along the right of way from the back of a truck or railcar:
    • Install a column
    • Run conduit along the columns
    • Install inverters every ‘x’ columns
    • Pull cable to inverters
    • Mount, orient, and wire the panels
    • wire the panels
  • Electricity is already available along roads for lighting, and along railroads for signaling, so it is straighforward to connect this PV generation to the grid.
  • Cleaning can also be done using a pressure washer from the back of the truck or railcar