Integrating Solar Electric Systems into Roofing Design

Using Building Integrated Photovoltaic (BIPV) Electrical Systems to reduce energy costs and contribute to a carbon neutral building design
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Sponsored by Johns Manville Corporation
Peter J. Arsenault, AIA, NCARB, LEED-AP with Brad Burdic, AIA

3.) BIPV Return on Investment: Most owners will eventually ask how long it will take to realize a return on their investment. Starting with the initial investment we can determine a simple or "straight line" return by dividing the final cost of the investment against the total annual return. Of course, no one expects the cost of purchased electricity to stay fixed. The good news is that the cost of the BIPV system is fixed - once it is in place, the installation cost is done. Therefore, by allowing an adjustment for increasing prices of electricity at an anticipated amount per year, the annual return is higher every year after the first year. Hence the time for the system to pay for itself is reduced.

It should not be overlooked that once the system has paid for itself in electricity output, then the owner gets to keep 100% of the returns for the remaining life of the system.

3.) BIPV Return on Investment

Initial Investment (from 1.) above)

/

Total Annual Return (from 2.) above)

=

Simple Return

x

Inflation adjustment

=

Adjusted Return

4.) Life cycle cost impacts: PV systems typically carry a 25-year warranty, but they could be fully functional even after 30years. Further, if they are integrated into roofing or other building systems, they may also extend the life of those other systems. Hence the long term impact and benefits are worth analyzing over the life of the system and the building.

Case Study Example


A retail store roof is a good example of being able to use thin film BIPV as part of the roofing system design.

A new construction retail store in California is used as an example to illustrate the economics of a specific BIPV installation.

Preliminary Assumptions:

Electric/Utility Assumptions:
Average Electricity Rate: $ .114/kWh
Electricity Inflation Rate: 6% annually

Facility/Roof Assumptions:
Facility Classification: Commercial/Retail
Available Roof/Installation Area: 41,500 SF
Roof Membrane/Material: Singly Ply thermal plastic polyolefin (TPO)

Tax/Financial Assumptions:
Federal Tax Classification: Commercial/Corporate
Federal Tax Bracket: 35%
Federal Investment Tax Credit: 30% of Installed Equipment Cost
Federal Accelerated Depreciation: 5-year Modified Accelerated Cost Recovery System (MACRS)
Utility 5-year PBI Rebate: $0.25/kWh monthly

PV System Summary:

System Size DC:

50 kW

Estimated First Year Energy Production:

74,743 kWh

PV Technology:

Thin Film Laminate on TPO Membrane

System Installation Elevation:

0 degrees (Flat on Roof)

System Installation Azimuth:

180 degrees (South)

Installation Environment:

Facility/Building Roof

Installation Method:

Heat Welded to TPO membrane

System Price:

$300,000.00

Utility 5-year Rebate

$92,499.12

Federal Investment Tax Credit

$ 90,000.00

Federal 5-year MACRS Depreciation

$ 89,250.00

Break Even Period

6 years

Internal Rate of Return (25 year period)

12.24%

Twenty-five year analysis of example BIPV system
Twenty-five year analysis of example BIPV system

Based on this example, the BIPV system will pay for itself after only 6 years and over the 25 year life of the system can be expected to generate in excess of $430,000 worth of energy. [see Figure 13]

Conclusion

Building Integrated Photovoltaic systems have developed and matured to become a viable option in many building situations today. Advances in technology, development of manufactured systems and flexibility in the installation of PV arrays make it possible for architects to design these systems successfully into the broader scheme of an overall building envelope. A growing number of installations demonstrate that it is very possible to put all of the parts of a system together to achieve the goals and objectives of a project including first year and long term affordability. The benefits of reduced energy costs, lower dependence on fossil fuels, and protection of building envelope components can now be realized by building owners as well as everyone else who seeks improvements in the natural environment.

Peter J. Arsenault, AIA, NCARB, LEED-AP is an architect and consultant focused on green and sustainable design based in Upstate New York.

Resources for additional information:

Johns Manville
www.specjm.com

Johns Manville has created JM E3co., the eco-leadershipâ„¢ company, to meet the needs of commercial roofing professionals in this new energy economy. The JM E3co. mission is to bring our considerable resources to:
· White, reflective "cool" roofing systems
· Green, vegetative roofing systems
· Solar solutions

 

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Originally published in November 2009

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