Harness the Sun

News Flash: The sun is hot. there's renewed and widespread attention being paid to it as a legitimate home energy source—and this time that interest might stick. A perfect storm of factors has come together to keep solar solutions on the front burner, including record crude oil prices, federal tax and local utility incentives, mainstream appreciation of global warming and green building, and smarter use of new technology that combines efficiency, low maintenance, easy installation, and aesthetics to achieve a faster return on investment for both builders and homeowners.

Forget those rural, off -the-grid homes of the 1970s and replace them with modern master planned communities in California and infill custom homes in Orlando, Fla. They are among the estimated 25,000 (and growing) homes that actively employ solar in some way. Toss aside bulky, metal-framed arrays in favor of sleek tiles or black panels that not only weave better into a roof form but also require a fraction of its square footage. Sprinkle in some passive heating and cooling solutions, daylighting options, and solar-powered path lights, and the sun's future in home energy looks bright.

Having quietly but effectively cut its teeth in the commercial sector, as well as making some stealthy moves among eco-minded consumers, the solar power industry—encompassing both solar thermal and photovoltaics (PV)—made itself ready for when rank-and-file housing finally came calling. And thanks to green building, new homes are better designed and built to optimize those systems and take advantage of passive solar benefits, as well—almost regardless of location or climate conditions.

Sure, there are some limitations, rules of thumb regarding optimum orientations and exposure, and caveats to effectively integrating solar. Chief among them is that its premium cost against retail utility rates still requires tax credits and rebates to boost its return on investment.

But solar today is quickly becoming a smart hedge against ever-rising electricity and natural gas bills. At some point in the near future—some say within the next decade—solar systems will run even with utility rates, without incentives. “We can already show savings on total aggregate housing costs over the length of a 30-year mortgage,” says Bob Reedy, director of the solar energy division of the Florida Solar Energy Council in Cocoa, Fla. “A solar hot water system might add to the loan amount, but the energy costs for that house will decrease and continue to do so,” he adds. Utility rates are expected to increase as they historically have, especially when grid power suppliers start applying variable rates for peak and non-peak use for homes, as they often already do for nonresidential buildings.

Consider what's coming together among the various solar solutions—and how builders can and are legitimately offering them to homeowners:

Aesthetics and Technology. Thanks to advances in solar technology, especially PV, you have to look a little closer to see a rooftop array these days. “We all remember the '70s and those battleships sticking out of the roof at odd angles,” Reedy says, recalling one major sticking point to solar's market acceptance in the past.

Today, a PV panel might look more like a skylight, a slightly darker section of an asphalt comp roof, or even more stealthily concealed within the channels of a standing-seam metal scheme, all the while collecting and converting more of the sun's light into electricity. “It's a fundamentally different technology and design,” compared with even recent semiconductor solar electric engineering, much less that of a generation ago, says Bill Kelly, general manager of the new-homes division of SunPower, a PV supplier in San Jose, Calif.

IN HOT WATER:Solar thermal is the term for using the heat energy of the sun to directly warm air or (primarily) water for distribution through the house using a heat exchanger. Though somewhat more cumbersome, evacuated tube technology (shown)—in which water or air is run through a tight array of dual-glass cylinders to collect and transfer the heat—can heat up to 100 gallons of water per day, cut hot water bills by half or more, and reduce a home's overall energy consumption by up to 30 percent. When combined with a tankless, on-demand water heater system (also serving as an on-grid backup), the energy (and water) savings are even higher.

The company's sun tile and solar panel products, for instance, have all of the electrical wiring on the back of the unit, leaving a full face to the sun to draw as much sunlight as possible. The design allows SunPower to increase the thickness of the wires (and thus their capacity) without impacting the design or efficiency of the solar cells. A mirror on the inside of the back panel also reflects and captures sunlight that sneaks through the face.

That efficiency allows SunPower and its contemporaries to work toward delivering truly built-in products, including panels and tiles that fit into a conventional pitched roof finish in smaller or split configurations that ease aesthetic concerns while extending PV's effectiveness in a wider variety of geographic locations and climate conditions. “Solar is possible in virtually any climate,” says Dana Bres, a research engineer for HUD's Partnership for Advancing Technology in Housing (PATH) in Washington, debunking the common myth that solar only works in the desert.

PASSIVE AGGRESSIVE:The most common passive solar heating strategy is direct, in which the sun's heat is allowed into the house through well-placed, south-facing windows to warm a thermal mass, such as a brick fireplace and/or tile floor over a concrete slab. Those thermal stores slowly release the heat to help maintain comfortable indoor temperatures once the sun's out of range. Today's advanced window technologies can be fashioned as passive solar conduits in applications such as clerestory windows (shown) to enable solar gain without losing that heat through the insulated glass. Passive solutions are, of course, nonmechanical, meaning they are quiet and require no maintenance—save a good spring cleaning.

That perception was further eroded when the NAHB Research Center tested PV-equipped homes in New York and Arizona to compare the electricity generated by a 2kw system. The East Coast homes conjured about a third less energy than their desert counterparts, but still enough to off set peak rates in the summer months. “With an intelligent design and a thoughtful process, you can put it anywhere,” says Bres. And have it look good … or at least not bad.

Cost Efficiencies. The day when the costs to install solar hot water and photovoltaics run even with utility rates is on the horizon but is not quite here yet. In the meantime, federal tax credits of up to $2,000 for qualified systems and utility rebates up to $4.50 per watt, mandated by state energy legislation to encourage alternative and energy-efficient use (see www.dsireusa.org for a state-by-state listing of incentives), help offset the premium up-front expense of adding solar.

The cost, while declining, is still steep. Current estimates run about $7,000 to $10,000 per kilowatt (1,000 watts), with most residential systems in the 2kw to 5kw range to effectively supplement the power grid. With federal tax credits and incentives, however, the cost of a 2kw system might drop by a third.

Assuming a peak-hour electric rate of $0.22 per kilowatt-hour (kwh) and an annual average of five hours of sunlight per day, a $9,000 system (after applying the tax credits and rebates) would pay for itself in about 11 years—assuming the utility rate stays constant. “We're already seeing peak-use and time-of-day rates in the high 30s,” says Reedy. “At that point, you're making money with PV.”

Other factors and strategies are also at work to reduce costs. Not only are manufacturing processes and materials use becoming more efficient, says Bres, but also builders are learning that PV is not an all-or-nothing proposition. “The goal should not be to pick up the entire [electrical] load of the house,” says Bres, but instead to design systems that offset peak loads (and rates, which, coincidentally, occur when the sun is highest in the sky, beating down on the solar panels) and take advantage of net metering.

BUILT-IN EFFICIENCY:Solar electric or photovoltaic (PV) systems convert the sun's heat energy into electricity. A system of wires behind the roof-mounted panels carries direct current (DC) power to an inverter, which converts it to alternating current (AC), which is then run through the service panel (and ideally tied to the meter) to serve the home's electrical needs. Where allowed or offered, surplus energy can be sold or credited back to the utility, a process called net metering. Advanced technology has enabled so-called “built-in photovoltaics,” a strategy that better integrates the panels or tiles into the roof finish (shown), and may be accomplished as the roofing material is being made. Installing the system then occurs as the rest of the roof is being placed by the roofing sub and connected by the electrician, saving labor costs and cycle time. Today's latest PV arrays require about 100 square feet of roof area per kilowatt, and a 2kw to 3kw system typically provides an adequate hedge against peak-rate electricity, if not offsetting the power grid entirely.

Which means remaining on the grid, a far cry from the goal in the 1970s. Simply, net metering allows surplus electricity generated by a PV array to be “sold” or credited and sent back to the utility, in essence spinning the meter backward, usually during peak hours, when rates are at their highest and the panels are collecting and converting the most energy.

When grid power is required (such as at night, when use and rates are at their lowest), those energy credits kick in. The home owners are only charged for electricity when their use of grid power exceeds what their solar system can generate. To date, 42 states offer net metering.

While a “net zero” electricity goal—in which credits and grid-power use balance over the course of a year, resulting in a zeroed-out electric bill—has been achieved, it can be a difficult and delicate calculation. “You can strive for it, but the homeowners' lifestyle is a wild card,” says Kelly. “We recommend sizing a system to save 40 percent to 60 percent of the owner's electric bill, rather than oversizing for net zero.”

LIGHT FANTASTIC:As any architect will tell you, daylight is essential to indoor comfort. The more surfaces drawing natural light, the better. Thankfully, today's high-performance windows and skylights, as well as translucent panels, glass blocks, and solar tubes for more private or internal areas, can be specified to block unwanted solar heat gain, reduce thermal transfer to R-values approaching those of a solid wall, and cut glare (the latter also helped by placing glass on multiple surfaces in a given room). Thus, windows, glass doors, and skylights can actually contribute to the home's overall energy efficiency while partially offsetting energy consumption for artificial light. These features, of course, should be Energy Star–qualified, and appliances should employ efficient compact fluorescent lightbulbs to reduce their energy use.

Further offsetting up-front costs, or at least making them more palatable to builders and home buyers, is the fact that solar thermal and PV have few, if any, moving parts to break. While they may require a trained installer (a network of which is evolving), they are almost self-contained systems bolted to the roof frame and fed into the subpanel or water heater. To further assuage homeowner fears of and responsibility for maintaining a system, suppliers, including SunPower, offer remote monitoring and troubleshooting services. By all accounts, though, solar thermal and, especially, PV systems have proven to be low maintenance and reliable, with warranties ranging from 10 to 25 years.

But we've been here before, to some degree. What's to keep solar from again being a flash in the panel, as it has shown to ebb and flow in consumer and housing industry consciousness since the 1970s? “This time, it's an economic driver instead of a regulatory or social driver,” says Reedy. “In the end, it's all about money, and now we can show it's a good investment.”

Solar energy solutions don't operate in a vacuum. To be truly effective, they must be part of a comprehensive commitment to reducing a home's energy needs. “The goal is not to replicate or replace the utility, but to conserve energy in a responsible manner,” says HUD's Dana Bres. That means designing and building a high-performance house first, one that lowers its energy demand as far as possible—including passive solar techniques (see “Passive Aggressive,” above), before adding solar thermal or PV to the mix. “At that point, you're talking about a 1kw to 3kw system to offset a total load of 5kw to 7kw,” Bres says. “That's achievable and reasonable.”

Active solar technology is continually evolving to further dig its heels into the building industry, make the most out of the sun, and improve its aesthetics. One such advancement is the Heliotube from Soliant Energy in Pasadena, Calif., which employs concentrator design for its PV panels. Each panel (similar in size and shape to a conventional flat-panel PV) features an array of self-powered tubes and lenses that turn to track the sun's path across the sky, optimizing sunlight to the solar cells. To reduce its premium cost compared even with PV, much less retail utility rates, Soliant eschews expensive silicon for a triple-junction, high-efficiency mirror material, which also boosts the system's efficiency. The downside? Chiefly that concentrator technology is bulkier than flat-panel PV. As a result, Soliant plans to launch its product in the commercial building sector first, likely in 2009, where rooftops are either flat or relatively unseen. A move into residential may follow a year or more later, depending on Soliant's success and continued consumer acceptance of and demand for solar solutions.

PV PATH:You can't walk through a Home Depot without tripping over a section's worth of photovoltaic-powered landscape lights and matching lampposts, so feed the consumer consciousness they've instilled by installing them in a spec home. Not only are they relatively inexpensive to buy and install (no wires required), but they resonate with buyers—and save energy by not only going off the grid to mark a path, illuminate a driveway, or uplight a shrub, but also by operating automatically and efficiently instead of relying on the owners to switch them off at bedtime.