Tuesday, October 7, 2008

Photovoltaics are Smaller, More Efficient, Less Expensive, and Better-Looking Than Ever

By Rich Binsacca - Source: BUILDING PRODUCTS Magazine - Publication date: 2008-09-15

Harnessing the sun's abundant energy for electricity and hot water has been a noble effort for decades, hampered not only by economics but also by residential aesthetics. During the last few years, though, system manufacturers and solar energy experts have introduced solar electric, or photovoltaic (PV), solutions to meet the public's demand for both curb appeal and better control of their energy costs.

Modules and arrays designed to fit in with various roofing finishes are all the rage, if not yet the norm. Even better, the solar cell technology within them collects and converts more of the sun's energy into usable electricity, thus reducing the overall size of the arrays to effectively (if partially) offset more of what's coming into the house from the local utility grid.

That evolution has enabled mainstream builders, including the nation's largest, D.R. Horton, to offer PV as an option, or perhaps even a standard feature, in some of their new homes.

And, truly, roof-mounted, grid-connected PV systems are easy to get through approvals, install, and maintain. They've undergone extensive third-party testing, certification, and code approvals; require maybe an extra day's work for a roofer, electrician, or solar sub (though lead times to order and receive the modules need to be respected); and rarely cause trouble for the homeowner.

In addition, the ever-falling costs of today's photovoltaics, especially of systems that can be sized smaller thanks to high-performance building practices and to offset peak electricity usage (instead of replace the utility grid altogether), can be amortized over a 30-year mortgage, reducing return on investment to a pretty attractive per-month calculation.

And don't forget federal tax credits, utility rebates, and other incentives that directly or indirectly reduce costs even further.

But let's not get too far ahead of ourselves. Integrating solar energy is actually, and ideally, the last step in achieving sustainable and resource-efficient housing. "Solar only gets you so far," says Scott Kramer, forward planner for Scottsdale, Ariz.-based Meritage Homes. "Most of the [energy] efficiency we achieve in our homes comes from other features. Solar is the icing on the cake."

The PV Process

If providing solar is in your future as a builder, the process begins all the way back on the boards, with a land plan and set of models that ensure homes in the community have adequate exposure and orientation to the sun.

That discipline is easiest to follow when there's a big empty parcel, but hardly impossible with an infill or scattered-lot opportunity.

For Encore, a 45-unit, single-family, two-parcel infill project nearing sold-out status in Vacaville, Calif., Meritage Homes easily accommodated PV. "We were able to orient the streets and place the houses in accordance with the approved plat to maximize the exposure to the sun," says Kramer.

Meritage also leveraged a handful of existing house plans in its portfolio for Encore, rather than designing a new or specific set of models to suit the 2.3-kWh roof-mounted PV systems offered as standard on all 45 homes. Simply, the builder thoughtfully placed the 2,080- to 3,714-square-foot units within the land plan to achieve the best orientation and exposure for a PV system--while also meeting objectives for a varied streetscape and other marketing and sales considerations.

To achieve adequate exposure and output, a typical residential system usually requires about 100 square feet of clear surface area per kilowatt of PV capacity. The system should be able to satisfy about one-half to three-quarters of the home's electricity demand. For most single-family homes, that's between 1 and 3 kWh.

The array should face due south at an angle that matches the location's latitude to enable at least six hours of daylight to hit the panels year-round. That being said, some solar experts say a 15- to 20-degree variation east or west from due south won't significantly degrade the system's effectiveness. A slightly southwesterly exposure, in fact, might perform better during peak-use hours, when solar's value really shines.

Regardless of where you build, in heating or cooling climates, the key is to make sure the panels aren't shaded and intruded upon by vent pipes and other penetrations through the roof structure, the latter of which might require some adjustments on the mechanical plan and upfront consultation.

"Builders have to start thinking of the roof as prime real estate," says JoEllyn Newcomb, general manager of Independent Power Systems in Boulder, Colo., a residential PV designer and installer. "Think of the roof as a potential power plant."

Added Value

That's an important distinction to remember in the grand scheme of an energy and environmental message to home buyers: Photovoltaic panels produce energy; the only energy they save, per se, is the electricity they offset from the power grid.

Conservation, by contrast, comes from smart building products and practices. A better-built home may allow a smaller--and thus less expensive --PV array to offset most of what the grid provides, but even then, the system carves only a small slice of the green pie.

For instance, Warmington Homes gained only six extra points within a local green building rating system for the standard, 2-kWh-per-unit PV system at Vantage, a 76-unit townhouse condominium project in Palo Alto, Calif.

The real return for Warmington has been an enviable sales pace at Vantage that has even allowed two price increases amid the deep discounts and other sales incentives that competing projects are offering. "It's helped us achieve our sales goals and reliable absorption, no question," says sales manager Debi Garlick.

Kramer has seen similar results at Encore, with one sale a week. And he reports that offering homeowners the ability to monitor their energy use and PV-system offset of the grid power inspires them to conserve energy even more. Some Encore buyers have received monthly electric bills in the single digits, less than 10% of what they would likely pay for a code-minimum house without PV.

Encore's electrical-use cost offsets average in the 70% range, aligned with what PV gurus promote as a reasonable and attainable peak-performance (ideal conditions) goal with a 2- to 4-kWh system. Not only does that size of a system significantly lower a homeowner's utility cost burden, but a builder's investment as well.

The industry-average cost per installed kilowatt of PV is about $10,000, perhaps less for more capacity and multiple-unit systems. Various rebates, tax credits, net metering, and other financial incentives to both builders and home buyers might cut that expense in half or more. At that scale and with those incentives, a PV system becomes more financially attractive, it's cost more easily recouped in an accelerated home sales pace, if not a higher sales price under current market conditions.

Buyers also may appreciate knowing that solar-powered homes are hot on the resale market, as well. The National Appraisal Institute estimates that an annual energy-cost savings of $800 achieved with a PV system equates to perhaps a $16,000 or 20% bump in property value, a distinct market advantage.

But that window is closing. PV shipments to the residential sector have risen substantially every year since 2003, specifically 28% in 2006, the latest figures available from the Energy Information Administration. The combined factors of ever-rising energy costs; federal, state, and local incentives and mandates for green building (and PV, specifically); and built-in system designs that render the panels nearly unnoticeable signal continued growth.

"The way these homes are built is the way of the future," says Kramer of the comprehensive approach Meritage took with Encore, including PV. "You might as well get ahead of the curve."

Rich Binsacca is a freelance writer in Boise, Idaho.

How It Works
Residential photovoltaic (PV) systems consist of silicon-based, semiconductor-material solar cells that combine to create modules or panels, which are then ganged on the roof or on the ground as arrays to collect the sun's energy. The layered design of the cells and panels, the precise components of which vary among manufacturers, collects as much solar energy as possible, even on cloudy days and in occasional shade. That being said, the ideal placement and orientation of any solar array is on a large, south-facing surface, preferably a roof, that is unencumbered by shade trees, roof penetrations, or other objects. Whether the weather is hot or cold is immaterial, though the seasonal location of the sun's path does impact the amount of light to capture. Ideally, the array is angled to the location's latitude to capture solar energy at its most intense level. Fewer daylight hours in winter result in proportionately less power generation.

While traditional rack-mounted systems still prevail, the latest evolution of solar cell technology features built-in panels that visually integrate into the roof finish and slope. Dimensional panels and tiles are designed to look like and replace roof shingles, standing-seam metal, or concrete roofing products to improve their aesthetic acceptance.

PV panels and their component parts have no moving parts and emit no pollutants in their operation. Standard electrical wires transmit the energy they collect as a direct current (DC) to a centralized inverter. The latest PV systems average about a 12% conversion ratio between the sunlight that hits the panels and the amount of energy they can collect, though conversion rates are rising--and panel sizes shrinking--as solar cell technology evolves. The inverter converts the DC power collected to alternating current (AC) power--usable electricity for most household needs--a process that itself sacrifices another 15% of the energy collected. The AC power is then sent to the load center, from which it is either distributed through the house or sent back to the utility as energy credits to be used later, a process called net metering.

In the past, a common--if idealistic--goal was to achieve a "net zero" electricity balance, in which a residential PV array and battery storage system generates all of a home's electricity needs, thus rendering utility-grid power supplemental or unnecessary. Today, primarily to keep installation costs in check and maintain the reliability of an always-on utility power source, most residential PV systems are scaled to offset the peak-use times and rates of grid-provided power, usually in the mid-afternoon to early evening hours, and hopefully generate some energy credits to further reduce utility bills.



U.S. Dept of Energy, Solar Energies Technology Program: Provides a separate section for builders about integrating solar into their projects, including links to state-offered incentives and cost estimating tools.www1.eere.energy.gov/solar/pv_builders.html

National Renewable Energy Laboratory (NREL) Renewable Resources Data Center: Includes data, models, tools, and links for integrating solar. www.nrel.gov/rredc/solar_resource.html

American Solar Energy Society: Provides a wealth of information about integrating solar, upcoming events, news, links to state and local chapters, and other resources. www.ases.org

The Solar Energy Industries Association: In addition to being a legislative advocacy group, the SEIA provides information about PV/solar systems integration, news, events, and data, among other resources. www.seia.org

Southface: A non-profit entity, Southface provides builders with tips for planning for, sizing, and installing a residential PV system, as well as costs and payback. www.southface.org/solar/solar-roadmap/residential/residential_pv_options.htm

Database for State Incentives for Renewable Energy: Refer to this Web site for a comprehensive list of incentives in your state, and check with your utility provider for additional incentives. www.dsireusa.org

Selling Solar

Whether making a pitch internally to offer PV as an optional or a standard feature or selling it to buyers, consider the following points in solar's favor:

  • Higher property and resale value
  • Reduces grid-provided electricity and cost, especially peak-use times and rates (usually midday, when PV is operating at peak performance)
  • Hedges against future price increases for traditional energy sources
  • Cost premium partially offset by utility rebates, tax credits, net metering, and quality building practices
  • Taps an unlimited, pollutant-free energy source
  • Reduces the demand for more and upgraded or expanded energy-producing facilities and distribution conduits
  • Can be easily pre-wired for future installation and accommodates expansion
  • Offsets or mitigates carbon emissions
Global Solar

Global Solar

Global Solar. PowerFlex Solar Strings offer a pre-connected format for the company's flexible Copper Indium Gallium diSelenide (CIGS) cells, allowing manufacturers of solar products and modules (i.e., the end products installed on houses) to more easily fit thin-film cells into their manufacturing processes. The CIGS cells are made on a bendable substrate, the company explains, making it more adaptable in shape and size and thereby allowing for new and innovative designs. 520.546.6313. www.globalsolar.com.



Sharp. Poly-crystalline modules feature a textured solar cell surface that increases light absorption and improves efficiency, while a bypass diode minimizes the power drops under shady conditions. The module achieves an STC maximum power rating of 187 W and a 12.7% conversion efficiency, and is designed for the company's solar racking system. Sharp's OnEnergy system offers custom designs and delivers a complete package of all components and fasteners. 800.765.2706. www.sharpusa.com/solar.



SunPower. SunTile roof tiles and solar panels provide a built-in look for various roof finishes. The tile product suits S-shape and flat tile profiles; each panel measures 17 by 59 inches and achieves an STC power rating of 63 W. Panel-designed products integrate with various roof finishes, measuring 61.39 by 31.42 inches and achieving an STC maximum power rating of 210 W and a conversion efficiency of 16.9% per panel. The company's solar cell technology delivers up to 50% more power than conventional cells and converts up to 22% of available sunlight into electricity. Both systems are available with optional online monitoring service. 877.787.6527. www.sunpowercorp.com.



Kyocera. A trio of KD Series solar modules uses a larger and more powerful solar cell to deliver a higher output per module and achieve an STC maximum power rating of 135 to 205 W, depending on the model, says the firm. The MyGen Grid-tie Photovoltaic Power System offers a complete package of modules, inverter, wire and lightning protection, and mounting and mechanical support that hastens installation and meets most code and utility requirements. 800.223.9580. www.kyocerasolar.com.

Evergreen Solar

Evergreen Solar

Evergreen Solar. ES-Series poly-crystalline solar panels feature String Ribbon wafer technology. The panel's design consists of 108 poly-crystalline silicon solar cells, anti-reflective tempered solar glass, EVA encapsulant, polymer backskin, and a double-walled anodized aluminum frame. Each panel measures 371/2 by 61.8 inches and weighs 40.1 pounds. Three panel options achieve an STC maximum power rating of 180 to 195 W; multiple mounting options enable installation versatility. 508.357.2221. www.evergreensolar.com.

Ready Solar

Ready Solar

Ready Solar. The Solar in a Box system is a factory-assembled, 2-kW standardized solution for residential applications. Each racking system accommodates a PV module measuring 10 by 6 feet to deliver 0.5 kWh of electricity. The turnkey solution (including modules from one of several manufacturers) consists of panels, an inverter, mounting system and hardware, and roof jacks and flashing. The homeowner can monitor the system's performance online, and battery backup is available as an optional upgrade. 877.817.3239.www.readysolar.com.

Luma Resources

Luma Resources

Luma Resources. This residential roof-mounted solar kit, invented by a roofing contractor, uses thin-film PV technology and consists of 60 solar shingles, a DC-AC inverter, and all flashing and fastening components. Each interlocking shingle measures 51.125 by 15.625 inches and achieves an STC maximum power rating of 31 W. The system is designed to integrate with common horizontal roof shingle layouts. 888.733.5862.www.lumaresources.com.



EcoTechnologies. PVL-136 FlexLight is a flexible, lightweight, laminate PV panel that adheres directly to the roof finish without nullifying the roof's warranty. The panel's laminated design captures the complete solar spectrum more efficiently than traditional systems, says the manufacturer, to produce more electricity per watt; the top layer minimizes power loss when the panel is shaded. Each panel measures 216 by 151/2 inches, achieves an STC maximum power rating of 136 W, and is code-approved for use in Miami-Dade County, Fla. 888.522.3626. www.ecotechnousa.com.



Sanyo. HIT Series photovoltaic panels for residential, grid-connected systems feature a proprietary hybrid of single crystalline silicon surrounded by ultra-thin, amorphous silicon layers to reach greater cell and module efficiencies. Panels measure 51.2 by 35.2 inches, achieve an STC maximum power rating of 180 to 205 W, and boast conversion efficiencies up to 17.4%. Bifacial models also generate electricity from ambient light that has passed through the panel or is reflected off surrounding surfaces. 469.362.5645. www.us.sanyo.com/solar.