Question

When will it become cost efficient over 10 years to install a PV system that will create a net positive effect for a 4 bedroom house?

Asked by benjamin
Austin, TX

assuming energy costs keep rising, that it is in a optimum location such as texas or arizona, and that we are pretty efficient and we use maybe 650kwh a month

Answer

Installing Photovoltaic panels (PV) to an existing home is not and will not be cost effective.

The reason is because standard construction techniques follows the path of least resistance and meet the minimum energy codes which will allow the home to pass inspection. 

Listed below are a few items explaining why existing homes will not be cost effective with PV panels: 

  • They leak air resulting in heat gain and loss
  • They have minimal to no thermal breaks in the façade which again result in heat gain and loss
  • The windows and placement of windows do not take natural day-lighting into account nor does it take heat gain due to solar radiation into account,
  • This is just to name a few items without getting into details.

Designing the home with energy consumption, production and efficiency as part of the program's requirement from the beginning has shown that PV panels can have a return on investment within 5-7 years or less.

  • For a successful project, the design team, made up of the owner, architect, mechanical and electrical engineers and general contractor, have to all be focused on the same goal....energy efficiency.
  • Any deviation from this goal in the form of a material change or construction means and method change without analyzing the affects on all systems intertwined, will result in less efficiency and extend return on investment.
  • The engineering and calculation must be done on paper prior to construction. Solar position and modeling must be performed, a high performance building envelope incorporated and finally energy consumption must be calculated for the worst case scenario.

With the calculated energy consumption values, the energy production by the PV system can then be designed in the most efficient configuration. The design must also use modern technology and ingenuity to reach the goal.

This in my opinion is the method for success - to succeed it will take time, educating the building trades and educating the public, before it’ll be the accepted standard of energy efficient design.

 

For more information:

Read "How much will it cost to get solar panels on our 2200 sq ft Dallas home? Will we be able to eliminate our energy bills?" a Q&A answered by Dennis Cheslik.

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