P1. Building Integrated Photovoltaics > Conclusions 

• Insulation behind PV panels degrades power production slightly in three out of the four cell technologies tested. The fourth technology showed a very slight improvement in power output due to the insulation.
  
• BIPV energy production and demand reduction were insensitive to climate location. Maximum building peak demand reductions were in Riverside and were about 20% of the rated panel output. Other sites and systems were as low as 5%. Peak demand was set during the summer due to air conditioning loads.
  
• A vertical south-facing BIPV panel has a small effect on building or system peak demand. PV panels integrated into vertically mounted curtain wall products will not produce as much power as roof-mounted panels. This is primarily due to reduction of incident solar radiation on the panel due to its mounting angle. Shading from other buildings or objects, such as trees close to the building will also significantly reduce power output. Rooftop and/or parking lot shading structures provide a better match for reducing peak demand.
  
• Simple payback periods for all locations are from about 20 to 90 years. The cost of BIPV may be offset in California by utility or government rebate programs, but it is clear that vertically mounted curtain wall BIPV is expensive relative to other distributed power generation options. Rooftop and parking structure PV systems have better payback periods due to higher power production and coincidence in peak power production with peak cooling loads.

BIPV algorithms are now embedded in DOE 2.2, but the current version does not do shading analysis, which must be done manually. DOE 2.2 is a widely used hourly, whole-building energy simulation program.

• For new construction, vertical BIPV should be considered when the cost of the installed BIPV is less than the initially specified curtain wall material. This may be the situation for show case office buildings.
  
• For new construction and retrofit, BIPV in vertical curtain-walls may have public relations value. Although this may be an intangible benefit, it directly demonstrates the building owner's commitment to sustainable design.
  
• Curtain-wall mounted BIPV should be considered when installing a rooftop or parking lot system to take advantage of its public visibility. A rooftop system is usually hidden from public view. Adding curtain-wall mounted BIPV to a rooftop system project would likely lower the marginal installed costs and provide a public relations benefit.

Based on new data regarding the characteristics of California building stock and statewide energy use, the projected benefits of this project are updated as follows:

It is estimated that about 2.4 million square feet of new commercial construction will be added to the existing building stock between Years 2000 and 2015. Assuming that only 2% of this new construction adopts BIPV, about 48 million square feet of floor area would be included. Assuming a square footprint, about 7 million linear feet could be positioned toward the south. Further assume that only 25% is facing south or southwest and that of this 25%, that only 25% is truly unshaded all year. The net amount of suitable south facing linear feet is about 0.44 million feet. Assuming the an average building height of 21 feet, the total area suitable for BIPV is 9.2 million square feet. In a typical installation, about 20% of this area would be covered with BIPV.

Assuming average annual electrical production is 6 kWh per installed square-foot of BIPV and that there is no offsetting summer peak demand reduction from vertically mounted BIPV, the annual energy savings by 2015 would be 11 GWh.

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