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Photovoltaics

Photovoltaics or PV is a technology in which sunlight is converted into electrical power. It is best known as a method for generating power using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays, to convert energy from the sun into electricity. PV requires little to no maintenance, makes no pollution, and does not deplete materials. In some cases, it is possible to generate enough electricity from PV to power an entire building.

Contents

1.Definition                                                
2. Use/Application
    a. Established Techniques
    b. Emerging Trends

3. Use an Integrated Approach
4. Resources

5. Associated Strategies

6. Case Studies

PV Array

Photovoltaics or PV is a technology in which sunlight is converted into electrical power. It is best known as a method for generating power using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays, to convert energy from the sun into electricity. PV requires little to no maintenance, makes no pollution, and does not deplete materials. In some cases, it is possible to generate enough electricity from PV to power an entire building.

PV is made of semiconducting materials similar to those used in computer chips. There are two basic commercial PV module technologies available on the market today: thick crystal products and thin-film products.

Solar cells are typically combined into modules that hold about 40 cells; about 10 of these modules are mounted into a PV array. The arrays can be mounted at a fixed angle facing south or mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. PV is appropriate for small- and large-scale applications. PV arrays can be designed into a new structure or be retrofitted into existing buildings; in this case, they are usually fitted on top of the existing roof structure. Alternatively, an array can be located separately from the building but connected by cable to supply power for the building.

Thin-film solar cells use layers of semiconductor materials only a few micrometers thick. Thin-film technology has made it possible for solar cells to double as rooftop shingles, roof tiles, building façades, or skylight and atria glazing. The solar cell roof shingle offers the same protection and durability as ordinary asphalt shingles.

PV systems should be considered where energy-conscious design techniques have been employed first and equipment and systems have been carefully selected and specified. PV should be viewed in terms of life-cycle cost, and not just initial, first-cost, because the overall cost may be reduced by the avoided costs of the building materials (in the case of building-integrated photovoltaics) and labor they replace and the fact that solar energy is free (i.e., there are no fuel costs).

By serving as both building envelope material and power generator, building-integrated photovoltaics (BIPV) systems provide the following benefits:

·         Reduced materials and electricity costs

·         Reduced use of fossil fuels and emission of ozone-depleting gases

·         Added architectural interest to the building

PV systems either can be interfaced with the available utility grid or they may be designed as stand-alone, off-grid systems. When a building is at a considerable distance from the public electricity supply (or grid)—in remote or mountainous areas—PV may be the preferred possibility for generating electricity, or PV may be used with wind, diesel generators, and/or hydroelectric power. In such off-grid circumstances, batteries are usually used to store the electric power.

The benefits of power production at the point of use include

·         Savings to the utility in the losses associated with transmission and distribution

·         Savings to the consumer through lower electric bills because of peak shaving

·         Availability of power on-site when utility power is disrupted

A benefit of grid-tied BIPV systems is that the storage system is essentially free with a cooperative utility policy. It is also 100 percent efficient and unlimited in capacity. Building owners and the utility both benefit from grid-tied BIPV. The on-site production of solar electricity is typically greatest at or near the time of a building’s and the utility’s peak loads. The solar contribution reduces energy costs for the building owner, and the exported solar electricity helps support the utility grid during peak demand time. The benefit of stand-alone or off-grid systems is that the storage batteries provide power continuously, even at night.

Established Techniques

PV roofing system displaced traditional materials

Building-Integrated Photovoltaics System

A complete BIPV system includes:

·         The PV modules (which may be thin-film or crystalline, transparent, semitransparent, or opaque)

·         A charge controller to regulate the power into and out of the battery storage bank (in stand-alone systems)

·         A power storage system

·         Power conversion equipment, including an inverter to convert the PV modules’ DC output to AC, compatible with the utility grid

·         Backup power supplies such as diesel generators, and

·         Support and mounting hardware, wiring, and safety disconnects

Panels are usually mounted at an angle based on latitude, and often they are adjusted seasonally to meet the changing solar declination. Solar tracking can also be used to access even more perpendicular sunlight, raising the total energy output. PV modules usually have a 25-year warranty, but they should be fully functional even after 30–40 years.

Designing a Building-Integrated Photovoltaics System

CIS Tower, Manchester, UK,         includes a vertical PV facade

Design considerations for BIPV systems must include the following:

·         Building’s use and electrical loads

·         Site planning, building location, and orientation

·         Local climate and environment

·         Appropriate building and safety codes

·         Relevant utility issues and costs

PV may be integrated into many different assemblies within a building envelope, including:

·         The façade of a building, complementing or replacing traditional view or spandrel glass

·         Awnings and saw-tooth designs on a building façade, increasing access to direct sunlight while providing additional benefits such as passive shading

·         Roofing systems, providing a direct replacement for batten and seam metal roofing and traditional asphalt shingles

·         Skylight systems, providing both an economical use of PV and an exciting design feature

Emerging Trends

PV shingle

 The use of BIPV is growing worldwide. The manufacture of PV cells has also expanded dramatically in recent years. Total nominal “peak power” of installed solar PV arrays was around 3,700 MW as of the end of 2005, a 42 percent increase for the year, and most of this consisted of grid-connected applications.

Financial incentives, such as preferential feed-in tariffs for solar-generated electricity and net metering, have supported solar PV installations in many countries, including Germany, Japan, and the United States.

PV array Wellfleet Wildlife Sanctuary,     Massachussets

Solar panels will continue to come down in price as people use and buy more—as manufacturers increase production to meet demand, the cost and price are expected to drop in the years to come. In 2007, investors began offering free solar panel install-ation in return for a 25-year contract to purchase electricity at a fixed price, normally set at or below current electric rates. Prices are also dropping because of technological advances in manufacturing PV components.

The efficiency of solar cells continues to increase. A concentrator solar cell produced by Boeing-Spectrolab has recently achieved a world-record conversion efficiency of 40.7 percent. Increased power density of thin-film and crystalline solar cells is leading to efficiencies of near 20 percent. Although commercial production of high-efficiency solar cells exceeding 20 percent may not be imminent, the continued improvement of PV materials and technology means that it is only a few years away.

Net metering is an electricity policy for consumers who own generally small, renewable energy facilities, such as wind or solar power, that are tied to the utility grid. “Net,” in this context, is “what remains after deductions”—the deduction of any energy outflows from metered energy inflows. A system owner receives retail credit for at least a portion of the electricity generated. Forty U.S. states have some form of net metering in place.

Energy pay-back time—the time required to produce an amount of energy as great as what was consumed during production—is being researched and documented more carefully. For silicon technology, an energy pay-back of one year may be possible within a few years. Thin-film technologies now have energy pay-back times in the range of 1 to 1.5 years in some parts of the world.

Use an Integrated Approach

A new way of thinking must be adopted to meet the goal of reducing carbon emissions associated with buildings. Your solutions can begin by integrating four possible methods. None works alone, and they are not all relevant in considering every strategy. However, considering the following tactics is necessary:

·         Reduce the overall energy use in your building.

§         Photovoltaics should be considered after reducing energy needs and use in a building.

·         Specify energy-efficient equipment and technologies.

§         Specify equipment and technologies carefully to optimize the PV design.

·         Use renewable strategies and purchase green power.

§         Photovoltaics is a renewable technology that supports the reduction or elimination of energy produced by fossil fuels.

·         Educate building owners, operators, and occupants.

§         Help others learn about the benefits of photovoltaics and the relation to energy use in the building

·         Building-Integrated Photovoltaic Designs for Commercial and Institutional Structures: A Sourcebook for Architects

·         Energy Policy Act of 2005 (PDF 1.9 MB, 550 pages)

·         Federal Green Construction Guide for Specifiers 48 14 00 (13600) Solar Energy Electrical Power Generation Equipment

·         Incorporating PV in Buildings: A Gathering of Eagles

·         PV F-Chart—Provides analysis and rough sizing of both grid-connected and stand-alone PV systems

·         PVFORM—Offers simulation of grid-connected and stand-alone systems, including economic analysis; available from Sandia National Labs, Albuquerque

·         TRNSYS—Simulation system for renewable energy applications; originally for solar thermal, now has extensions for PV and wind

·         HOMER——Hybrid Optimization Model for Electric Renewables (HOMER) is a design-optimization model that determines the configuration, dispatch, and load-management strategy that minimizes life-cycle costs

Associated Strategies

All 50to50 strategies relate to each other in some way. However, we recommend that you consider investigating these selected 50to50 strategies to assist you in gaining a deeper understanding.

·         Active Solar Thermal Systems

·         Building Orientation

·         Daylighting

·         Life Cycle Assessment

·         Passive Solar Collection Opportunities

·         Renewable Energy Resources

·         Sun Shading

Case Studies

• Aldo Leopold Legacy Center
• Epicenter, Artists for Humanity
  

  Aldo Leopold Legacy Center
  Photo credit: The Kubala Washatko Architects,  
  Inc./Mark F. Heffron

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