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Solar Energy

Imagine a building where the major components have photovoltaics embedded in the materials used in construction; the result being significant onsite production of solar power.

We're all familiar with solar panels on a building roof or a parking canopy. Solar panels have been the face of solar energy to date, although solar heat can provide energy as well. Integrating photovoltaics in a building is something completely different.

After decades of anticipation, the solar energy market has created a substantial and growing movement to integrate photovoltaics (PV) into buildings. This approach makes sense; solar energy within the building would generate power where it will be used and there is no need for any significant transmission or distribution infrastructure. This eliminates power losses and integrating solar power into buildings doesn't necessarily take up additional land or space.

Integrating solar cells into buildings focuses primarily on two aspects. One is the facade, which is essentially the exterior of the building. Facade systems include curtain walls (outer walls which are not structural), and spandrel panels (a wall between the head of a window and the sill of the window above in a buildings of two or more floors) and glazing. The use of integrated PV in the building skin replaces

conventional envelope materials, thus reducing the cost of the integrated PV

Figure 15.1 conventional envelope materials, thus reducing the cost of the integrated PV.

The second aspect of integrated building solar energy is the roofing system. This includes tiles, shingles, and standing seam products for steel roofs and skylights. For example there are now solar shingles which look like traditional asphalt roof shingles, and metal roofing with upwards of 16% efficiency.

Besides solar facades or roofs there are innovative products such as walkable PV floors, transparent or colored PV glass, outdoor benches, and tables. Even the development of solar-powered concrete is underway.

The integration of photovoltaic into buildings may have started with the research and development of solar panel windows as a solar collector; this is now a reality and is in the marketplace. Wiring is embedded in the window frame and can provide direct current (DC) or be connected to a central power inverter to convert the direct current from the solar window to alternating current (AC) that is then fed into the electric panel for the building. This technology shows tremendous potential. Some of the current versions of photovoltaic windows can transmit more than 70% of the visible light, similar to tinted glass windows already in use in commercial buildings. The power conversion for the initial design of the windows was low but has steadily improved. One research team calculated that even with 5% efficiency these windows can generate over 25% of the energy needs of a building. Besides energy generation, the windows could also reduce infrared radiation, thus reducing thermal loads and operational costs.

The Whole Building Design Guide (www.wbdg.org) states: "PV specialists and innovative designers in Europe, Japan, and the U.S. are now exploring creative ways of incorporating solar electricity into their work. A whole new vernacular of 'Solar Electric Architecture' is beginning to emerge.”

It's safe to say that integrating photovoltaics into buildings is innovative and will be disruptive for the traditional design and construction industry. However, if the approach provides beneficial results including lower energy and construction costs, greater utility, scalability, and creativity, building owners and contractors may see it as an opportunity and be attracted to its potential. Integrating photovoltaics into buildings will change the building design, with a clear priority of maximizing solar energy products and materials that can produce a substantial return on investment.

It is one thing to install a solar panel and quite another to construct a solar building. The design and construction of such a building will require some reeducation and training of engineers, architects and contractors, as well as possibly altering job responsibilities, trades, and skills. One would expect that substantial professional industry associations could assist in developing design guidelines and training.

Integrating solar into buildings makes sense for new construction where a building owner, architect, and engineer can design the integrated PV. This is referred to as building-integrated photovoltaics (BIPV). Existing buildings integrating photovoltaics are referred to as building-applied photovoltaics (BAPV) and are likely to be a more challenging undertaken. Ina new or existing building the architect, engineer, or contractor has to evaluate a proposed design related to solar access and identify potential use of photovoltaic systems.

Other aspects of designing photovoltaic into the building involve the building's location, its latitude, its structural aspects, nearby trees or buildings, shadowing, and average temperatures onsite. These factors must all be taken into account during the design stages where the goal is to achieve the highest possible value for the BIPV systems.

The majority of buildings using solar power are connected to a larger utility grid because the reality of using solar power for the entire building may not be possible. The building owner can operate the integrated solar power independently, but, connectivity with the grid provides a backup and could present an opportunity to sell power back to the utility. Both the building owner and the utility benefit with the grid being connected to BIPV. The on-site production of solar electricity typically coincides with the peak load times of the utility. The solar contribution reduces energy costs for the building owner while the exported solar electricity can help the utility grid during the time of its greatest demand.

The primary disadvantage of solar power is that it clearly cannot be created at night or during times of cloud cover. Solar panel energy output is maximized when the panel is directly facing the sun. This means that fixed locations have a reduced energy production when the sun is not at an optimal angle, unlike the solar farms that mount PV panels on towers that can track the sun to keep the panels at optimal angles throughout the day.

Solar cells convert about 20% of the sun's rays to electricity. While solar power can be a substantial initial investment, there is minimal maintenance, and after purchasing and installation it provides free energy. The

capital cost of solar power, batteries, and storage has continued to fall so that in many countries solar is cheaper than ordinary fossil fuel electricity from the grid

Figure 15.2 capital cost of solar power, batteries, and storage has continued to fall so that in many countries solar is cheaper than ordinary fossil fuel electricity from the grid. As the price of solar electricity continues to come down every year more and more countries will benefit from making the switch to solar when new capacity is added. The development of ultra-thin, lightweight, and highly flexible solar solutions is a key to the BIPV market.

China, Japan, and the United States have accounted for the majority of new solar energy capacity along with growth in Latin America, Africa, the Middle East and Europe, particularly Germany. In 2014 solar power accounted for more than 55% of new investment in renewable power and fuels. Industry analyst firm n-tech Research predicts the total market for building-integrated solar photovoltaic (BIPV) systems will grow from about $3 billion in 2015 to over $9 billion in 2019, then surge to $26 billion by 2022, as more truly integrated BIPV products emerge that are monolithi- cally integrated and multifunctional.

As the cost of solar goes down subsidies will likely disappear. Success of BIPV will provide opportunities and major changes, and create new BIPV businesses. Manufacturers and construction companies will likely partner. The Whole Building Design Guide (WBDG) has suggested a need for a solar

Figure 15.3

energy architect, but, a team of systems integrators, construction firms, installers, manufacturers, and contractors will be needed.

Interestingly, some researchers think the commercialization of BIPV should primarily emphasize aesthetics of the materials and products. Different colors of PV windows would allow some distinct and artistic features, though some may want the products to look more traditional (roof shingles.) Solar panels on the roof of an old building can be an eye sore, so the improved aesthetics of BIPV may increase acceptance of the technology. With the PV being embedded in the materials and products no one really notices the PV. Smart aspects of BIPV could be automation related to energy, system integration, and building energy management systems.

Some important issues related to BIPV include the development of building codes and specific standards. Also to be considered are economic incentives from local, state or federal governments, optimal system orientations, the service life of the products and materials, their durability and capability of withstanding the weathering process, cost, and performance.

The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined. Successful deployment of BIPV, combined with energy efficiency initiatives, can lead us to the goal of net zero buildings.

 
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