BIPV – Building Integrated PhotovoltaicsOctober 2, 2012

What are Building Integrated Photovoltaics?

Building integrated photovoltaics (BIPV) are photovoltaic building materials that replace pieces of the building envelope. These photovoltaic materials are not necessarily traditional solar panels €“ they can range from photovoltaic glass to thin film cells laminated onto a roof. BIPV products demonstrate the desire of architects to harmoniously incorporate an energy system (and one that generally needs to have a direct line of sight toward the horizon) into the design of a building. The (as yet unattained) goal of BIPV is to bolster PV’s value proposition by reducing the cost of labor and building materials through consolidating active PV material and either roofing, cladding, or both.

The industry has seen a couple of interesting products over the years that have attempted to broker this diplomatic arrangement. We’ll look at a couple of them below.

 

The Module as Architectural Element

Adventurous architects and well-funded DIYers have long been integrating basic PV modules into carports and patio shades with varying degrees of success. Sanyo took the concept one step further by using glass for the module back sheet and even applying an extra active layer on the bottom of the cells to absorb reflected light. With this approach to integration, the designer is limited to an aesthetically pleasing, though costly field of traditional modules.

 

Stick-On laminates

Beginning in 2006, United Solar Ovonic made an amorphous silicon (a-Si), flexible module that could be stuck directly to the surface of a flat metal roof – either in the field or in a factory setting. While seemingly a great way to combine solar active material directly with the roofing surface, the polymer encased Unisolar product had to contend with a harsh combination of chemical fallout, UV rays, and temperatures that threatened to go way beyond the published Normally Operating Cell Temperature (NOCT) of 46 degrees Celsius. Unisolar offered a confidence-inspiring 20 year warrantee, but the company declared bankruptcy earlier this year.  In 2010, Global Solar presented their PowerFLEX stick-on module using Copper indium gallium selenide (CIGS) technology instead of a-Si. The CIGS module shares the form factor and installation flexibility of the Unisolar product, but should perform better in the high temperatures experienced while coupled to the hot roof surface.

 

Solar Shingles

Dow Solar shingles are the product of a $20 million grant from the U.S. Department of Energy to Dow Chemicals to develop BIPV. Dow€™s Powerhouse solar shingles are made in their Midland, Michigan factory using copper indium gallium selenide (CIGS) thin-film solar cells from Global Solar in Arizona. Solar shingles replace conventional asphalt shingles and are installed in the same fashion €“ with a hammer and a nail €“ so they will not require specialized labor. [1]

Dow does not disclose the efficiency of their solar shingles, but they should have efficiencies around 10%, similar to regular thin-film panels from Global Solar. However, a representative from Dow said on the phone that the efficiencies will vary depending on the budget because the shingles are custom made. This doesn’t sound encouraging and doesn’t imply that Dow has a dedicated production capacity for the product. However, the top sheet on the shingles is tempered glass, which indicates that the product may be of very high quality.

 

Solar Tiles

Solar tiles, by Solarcentury, are another emerging solar roofing option. The advantage of these tiles over the Dow shingles is that they have higher conversion efficiency because they use polycrystalline or monocrystalline silicon cells. A comparison between thin film and crystalline silicon can be found here. At Standard Test Conditions (STC), solar tiles have about 13% conversion efficiency. But, as with the Unisolar laminates and the shingles, operating temperature may be much higher than STC temperature.

 

PV Glazing

PV glazing is glass incorporated with solar cells. This glass can be used in the glazing of a building such as windows and skylights, and can be used to create mosaics. It blocks UV and infrared radiation, providing insulation for the building. PV glass is categorized by its solar cells €“ thin-film or crystalline. Semi-transparent PV glass has crystalline PV cells adhered to the surface. Its light transparency is, therefore, a function of the spacing between cells. Transparent PV glass, on the other hand, has varying layers of thin-film cells painted on the surface to control transparency. [2] The efficiency of CIGS PV glass at STC ranges between 9% and 13%. [3]  With glazing, the thermal gain issue may be less of a problem since there is generally some amount of free air behind the window or skylight for convection cooling to take place. On the other hand, windows are placed for reasons other than generating power (like looking at the neighbor’s new solar array) and might not be pointed in the best direction for PV power generation.

Solar Façade

Another BIPV option is to clad the façade of a building with solar cells.

Ferdinand-Braun-Institut für Höchstfrequenztechnik
The Ferdinand-Braun-Institut für Höchstfrequenztechnik building in the Adlershof borough of Berlin has a 39 kW façade made of copper indium selenide (CIS) thin-film solar cells. [4]


Co-operative Insurance Tower
The Co-operative Insurance Tower in Manchester, England has a solar façade of 579.5 kW made of 7,344Sharp 80 watt crystalline panels. [5]


The BIPV Balance of System (BOS)

Apart from the integrated solar modules, the remaining BIPV BOS is the same as a conventional PV system. Click here for a discussion of the pieces of a solar PV system. BIPV replaces conventional solar panels and racking and mounting systems, but still requires an inverter, charge controller and battery (off-grid), and a monitoring system.

Summary

Despite the advances in BIPV technology, BIPV still has glaring disadvantages. The efficiencies of thin-film BIPV modules are less than normal crystalline solar panels and BIPV costs more than normal crystalline solar panels due to emergent processes and lower factory capacities.  Tightly integrated BIPV systems with smaller form factors and no air space, such as the solar shingles, will heat up and lose efficiency because they lack sufficient ventilation for convection. There is also not much angular flexibility for the installation of BIPV other than designing the structure with solar collection as its primary design influence. In spite of these disadvantages, the desire to integrate PV active material into our buildings is understandably strong – and makes a lot of sense. The companies highlighted above are well-positioned to take advantage of dropping materials prices and emerging processes for further advancement of the technology.

COMPLIMENTS OF CIVIC S.