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Response to: "Integrated Photovoltaics: the next big thing for 2011?" March 8, 2011 By bedfordarchitect

BISD (Building Integrated Sustainable Design)

by Bill Caplan:
Wed March 9, 2011 3:03 pm

Perhaps not 2011 but there's a chance for 2012. We live in a world of tack-on technology,rarely taking full advantage of the opportunity for true interdisciplinary design from the start. As a result, there is tremendous inefficiency and waste, much of it in the name of Sustainable Design. The key to meaningful BIPV is forming a building's envelope in harmony with the environmental resource vectors emerging from a site. Integrated Photovoltaics in themselves do not create true sustainable design that necessarily improves carbon foot and makes economic sense. The design of a building's envelope must be generated so that its integration provides a substantive benefit, rather than a gratuitous gesture. With true unification of architecture, environmental resource vectors,envelope and program, perhaps it should more aptly designated BISD (Building Integrated Sustainable Design) which might define the way toward a new architectural idiom. This is the approach being promulgated at ShortList_0 Design Group LLC, and hopefully, one that will gain traction.

by Bill Caplan:
Thu Mar 10, 2011 1:46 pm

By "environmental resource vectors" we mean to encompass the full spectrum of resources that surround a building. They would include obtainable energy transmitted by radiation, conduction and convection; light; air to breathe; water to consume or utilize - whether in the form of solar rays, wind, fluid, gas or thermal mass; solar for direct electrical conversion or solar thermal, air flow for circulation and ventilation, thermal mass for heat and cooling, and even ambient light. My point is that when designing a new structure with true Building Integration, whether with PV cells or any other sustainable design eco-practice or technology, the shape and orientation of the envelope should be influenced by the vectors of these resources to maximize the value of the sustainable design features. Covering warehouses or parking lots with sustainable design technologies such as photovoltaic or solar thermal generation are clearly beneficial in open areas with good solar access. However, this is not always the case when retrofitting existing homes and small buildings in suburban or urban areas, where sustainable design technologies do not always provide a substantive value, especially when considering the carbon footprint of equipment production. Roof angle, orientation and shade factors for trees or other structures are rarely ideal. We are trying to address the future direction of architectural design in the conception stage, so that integration of sustainable technology is one with the design, and maximizes the harvest of surrounding energy resources ( ).

Response to WalkerARCHITECTS March 15 comment "We must underdstand the math."

by Bill Caplan:
Wed Mar 16, 2011 4:49 pm

Perhaps we are discussing two different topics:
1. "We must do everything we can, everywhere we can to rapidly reduce the carbon footprint of the body of our civilization."
2. Architecture across the built environment.

Topic 1. Rapidly reduce the carbon footprint:
We fully agree that the math mandates a focus on existing buildings. We also agree that "an affordable correction to each building" and that "Solar access, roof angles and so forth are not significant problems" on a significant numbers of tall buildings in urban areas. Targeting tall buildings in urban areas is generally a no-brainer where shadowing is not a problem, and is certainly a priority for focus. Affordable correction to each building is equally important, but the hitch is "to do it correctly", make it an "affordable correction to each building" and "reduce the carbon footprint effectively." The problem we need to address concerns small to midsize buildings. Pre-determining the operational effectiveness of small scale PV systems, their real output and thereby their true financial benefit and carbon footprint reduction, is a can of worms. Yes, by definition, installing a PV panel generates clean electrical power in place of carbon based consumption. If one ignores the financial cost, it always appears beneficial. But even this can be fallacious without considering the carbon footprint to fabricate the system components such as PV cells, panels, frames, hardware, inverters and hookup etc as wells as transportation and installation. For small systems, there is certainly a minimum system size and actual operating output necessary to significantly negate its own carbon footprint regardless of cost or generosity of the purchaser.

On small systems the math is often obscure, making it difficult for the average consumer to understand the real value of their intended investment. Manufacturer specification sheets and brochures often present the specs in a format that can be easily misunderstood, even by the technically savvy. With no standard presentation format it is difficult to compare systems. Regardless of indicated power rating, polycrystalline PVs typically lose up to 3% of their capability in the first few days of use, the initial burn-in. Then, output continues to degrade at approximately -1%/year, down 10% after 10 years, 20% after 20 years, etc. But there is more: temperature, dirt, interface and other considerations. Typical manufacturer published specs are determined under Standard Test Conditions (STC) at 25C (77F) and 1000W/m2 Solar Irradiance. However, actual solar cell onsite operating temperatures are typically near 50C (122F) when site ambient temperature is merely 20C (68F). A cell's power output degrades approximately 0.5%/degC. Operating at 50C reduces the output -12.5% from the STC value on the manufacturer's spec sheet which was tested at 25C. When the ambient temperature rises from 20C (68F) into the 30C to 35C (86F to 95F) range, the actual cell temperature rises significantly above 50C, potentially degrading specified output by 20% to 30%. The State of CA is already addressing this in their Guidelines for California's Solar Electric Incentive Programs (Senate Bill 1) 2nd Edition 12/2008 whereby they require Normal Operating Cell Temperature (NOCT) testing as well as onsite performance. Under NOCT criteria only 800W/m2 of Solar Irradiance is assumed as more representative actual average exposure. Therefore, a 200W PV panel (STC), after -3% from burn-in and under NOTC conditions of 800W/m2 at 50C, drops to a 136W rated output (200Wx.97x(800Wm2/1000W/m2)x87.5=136W). This does not include further reductions for airborne soot, dirt and bird droppings that can run -7%, system wiring and mismatch of -3% to -7%, and DC to AC Inverter loss typically -6%. Together these de-rate panel output to 112W, only 56% of the 200W listed. This is in week one. 10 years later it's down to 100W capability due to the -1%/yr aging.

None of these factors address the shading problem, which is less then obvious. Due to the way many manufacturers' connect individual solar cells on a single panel, shading just 2 or 3 individual cells can cause a large disproportionate drop in the panels output. A typical 60 cell panel may be divided with 3 strings of 20 cells each - the strings connected with bypass diodes. If only a few cells in the same string are heavily shaded, loss of power from the entire 20 cell string may occur - a major output reduction for the panel. Shade thrown from a relatively small object such as a roof vent, pipe or pole can cause significant output reductions as its shadow moves with the sun.

This brings us back to your points: "to do it correctly" and make it an "affordable correction to each building". It is not at all obvious that for small rooftop systems, the math is always done before procurement. I would postulate that a significant portion of installations do not produce the expected output, are not economically sound in anywhere near the expected payback time and worst of all, probably have a negative carbon impact when including the carbon footprint to manufacture, ship and install. This is one of the things we are researching at ShortList_0 Design Group as we seek methods to employ current sustainable technology to enable sustainable design with true sustainability.

Topic 2. Architecture across the built environment:
Without true building integration of sustainable technology such as PV, we risk littering the built environment from one shore to another - effectively distorting vernacular and period architecture with omnipresent tack-on products. This is not an architectural solution, it is an engineering one. The big problem here, as you so aptly point out, is with retrofitting existing buildings. This a lot tougher then designing new ones. Although we do not yet have good solutions for small building exterior architecture, better consumer education is needed to determine if real sustainability benefits can be achieved for a specific building with an external tack-on

To sum up, we seem to be on the same page: "We do need to do much better with both new projects and retrofit the existing built environment."

"We do of course have to do it correctly with each new building but the quantum reality" suggests a different target."
”Aerial photography of your city will convince you. Solar access, roof angles and so forth are not significant problems, we can do something with every building, even if it comes down to only changing the inhabitants energy conservation practices. We must do everything we can, everywhere we can to rapidly reduce the carbon footprint of the body of our civilization."
But for the sake both architecture and sustainability, we do have to do it correctly.
The complete discussion is available at
Bill Caplan