July 11, 2008
Appeared in Building Design & Construction
There are many ways to be green, but three energy-related technologies stand out for their potential to positively impact the planet. As prices for oil, natural gas, and electricity spiral ever upward, it is crucial for Building Teams to focus on these alternative sources. This article gives an introduction to wind, solar, and geothermal power, explaining how they affect the building market as well as project planning and construction.
BIPV: Building-Integrated Photovoltaics
Considered one of the most promising renewable technologies, photovoltaics offer great potential to harness and utilize a cosmic source of free energy. Of course, there's no such thing as a free lunch, and the building and construction industry would still like to see first costs continue to come down for mounted solar arrays and building-integrated photovoltaics (BIPV). Still, recent technological improvements and applications have been impressive in terms of energy produced and building function and aesthetics.
“The solar PV market has seen considerable growth in the past few years, most recently with a record cell production of approximately 2,500 megawatts in 2006, and tremendous excitement in the investment community,” says veteran green designer and consultant, Jerry Yudelson, P.E., LEED AP, principal of Yudelson Associates, Tucson, Ariz.
PVs have many advantages. They require no fuel, give off no emissions, have no moving parts, and require little maintenance. In addition, Yudelson notes:
- Solar cells can easily be seen on buildings, so observers immediately identify the facility as a green building.
- PVs can help earn LEED points for energy efficiency and renewable energy.
- In addition to government and utility rebates and incentives, projects can sometimes qualify for tax benefits and accelerated depreciation.
- Some BIPV systems offer architectural and aesthetic appeal.
- Large PV projects often attract public and media attention.
While power plants and stand-alone PV arrays account for a large percentage of power generated, building-integrated PVs are showing a lot of promise. “BIPV is really the best and most economical way to utilize photovoltaics,” says Gregory Kiss, principal, Kiss + Cathcart Architects, a Brooklyn-based firm specializing in solar design. “Not only does it generate electricity, but it serves an additional purpose by replacing a conventional building material. For example, a BIPV façade can be equal to the cost of a high-end, non-BIPV façade.”
Furthermore, many BIPV materials and assemblies offer thermal insulation and shading. The most popular setting for the cells is to mount them on the roof, whether as integrated roof panels, insulated roof glazing, or a canopy. In recent years, however, Building Teams have introduced more louvers, opaque cladding, and insulated façade applications.
Although BIPVs can bring value to a building, Steven Eich, PE, LEED AP, and vice president at Environmental Systems Design, Chicago, points out that due to the way they are integrated into the building, energy output efficiency is lower than for conventional ground- or roof-mounted angled arrays. Eich, whose firm recently completed a PV curtain wall project for the North Exelon Pavilion at Millennium Park in downtown Chicago, explains: “In comparison to a PV system optimized for energy production, BIPV systems generally generate less energy. This is because BIPV modules must conform to the building structure, which likely is not as optimally oriented as a PV system should be. For instance, BIPV modules placed as spandrel panels in a building's façade will be de-rated approximately 50%, in comparison to an optimally situated PV module.”
In working out the dollars and cents for a prospective BIPV project, it's important to take into account several factors. First, the modules themselves generally account for about half the total system costs, while the inverter (the device that converts the electricity from DC to AC), the PV array support structures, electrical cabling, equipment, and installation make up the rest.
However, installation costs can vary significantly, according to Denis Lenardic, a PV consultant based in Slovenia who maintains the website www.pvresources.com. “When costs for site preparation, laying a foundation, system design and engineering, permitting, and assembly and installation labor are higher, total installation costs are higher also.” Lenardic estimates operations and maintenance expenses ranging between 0.02 and 0.1 cents/kWh, with an anticipated system life span of about 30 years. Although manufacturers typically offer 25-year warranties, some say that PVs can last up to 40 years.
“PVs, in general, tend to produce power for much longer than their warranty life,” claims associate principal Shaun Landman, PE, LEED AP, and engineer Taylor Keep, LEED AP, both with Arup, San Francisco. “They can be operated maintenance-free and are highly dependable and effective, aside from inverter replacement every 10 to 12 years.”
However, designers should be aware that BIPV systems do have a slow degradation of efficiency and will lose a small percentage of their output every year, according to Kiss.
Taking an overall look at the PV market, Yudelson has observed reductions in first cost. “Costs have come down, from about $10 per watt, peak, a few years ago to about $6 per watt, peak, in 2006, for reasonably sized systems of over 20 kW.” Even so, Eich has seen first cost derail potential projects. “Unfortunately, because of their expense, these systems are likely the first to be cut when project scope must be reduced to meet the budget.” Landman and Keep add that “custom system design is no longer required for BIPV in many situations, but cost is still very prohibitive, unless the project calls for an 'iconic' feature.”
At the same time, government and utility incentives can go a long way toward making qualifying projects economically viable. (For a detailed map of various state incentives, visit www.dsireusa.org.) One such incentive is called “net-metering,” which has been mandated by legislatures and public utility commissions in a number of states. Net-metering requires utilities to pay and charge equal rates regardless of which way the electricity flows. Consequently, if a PV installation is producing more electricity than a building can use, the facility can earn money selling the power back to the grid.
In the absence of incentives, however, it may be more difficult to get approval for a PV project, says Yudelson. “There is little economic justification for photovoltaics as an add-on energy supply system for public projects [which receive no tax benefits] or for private projects where there are no utility credits or low peak-period power rates,” he notes.
Crystalline Silicon and Thin Film
Another economic factor currently affecting the PV market is a global shortage of polysilicon, which is used to manufacture crystalline silicon PV modules. Although an alternative, thin-film modules, don't rely on silicon and potentially offer a lower cost per square foot, crystalline silicon is superior to thin-film modules in efficiency and electrical production per square foot.
“The real catalyst for the BIPV market will be the improvement of the cost-efficiency ratio of thin-film PV,” says Alok Bhargava, a senior analyst with Greentech Media, a Cambridge, Mass.-based market research and consulting firm. “As thin film achieves commercial scale production and higher operational conversion efficiencies, it will drive down the cost.” Ultimately, as Bhargava writes in a recent report, “Building Integrated Photovoltaics (BIPV): Market Outlook 2008 and Beyond,” http://www.greentechmedia.com/reports/research-report-intelligence-bipv.html, “When thin-film BIPV becomes cheaper than crystalline silicon BIPV, we expect the BIPV market to see considerable growth.”
Along these lines, other market researchers also foresee thin-film modules, which currently account for about 10% of the market, as gradually capturing a larger share. A recent report from BCC Research Analysis, Wellesley, Mass., forecasts that by 2013, thin-film modules will account for close to 19% of the market, while silicon-based PV products will decline from 89% in 2007 to 79% of the market in that time period. Economists at iSuppli, an electronics market analyst based in El Segundo, Calif., see thin film capturing 20% of the PV market share by 2010.
Overall, BCC Research Analysis projects that the global PV market will be worth more than $32 billion by 2012, growing annually at about 15%. The firm iSuppli more modestly predicts about $22 billion in 2012. Yet another analyst, New York-based Lux Research, anticipates growing pains in its “Solar State of the Market Q1 2008: The End of the Beginning,” http://www.luxresearchinc.com/press/RELEASE_Solar_state_of_the_market_Q1_2008.pdf.
In designing and specifying a building-integrated PV system, a number of factors must be taken into consideration to make them efficient and cost effective, notably climate and Building Team coordination.
Contrary to popular opinion, PVs actually work better in cold weather than in hot weather. “This is because photovoltaics are electronic devices and generate electricity from light, not heat, and like most electronic devices, photovoltaics operate more efficiently at cooler temperatures,” according to ABS Energy Research, a market analyst based in London, in a report (http://www.absenergyresearch.com/cmsfiles/reports/Solar-Photovoltaics-Report-2007.pdf) “In temperate climates, photovoltaics generate less energy in the winter than in the summer, but this is due to the shorter days, lower sun angles, and greater cloud cover, not the cooler temperatures.”
Architect Gregory Kiss explains further: “Ambient temperature needs to be taken into account, as some PV cell types are sensitive to high temperatures, especially for curtain wall applications that aren't well ventilated, and therefore are not a good choice for hot climates.”
In addition to temperature, Eich identifies insolation as significantly impacting BIPV energy production. Insolation is the measure of solar radiation received for a specific geographic area over a specific amount of time. For a given project geography, insolation can be determined by referring to the National Renewable Energy Laboratory's U.S. insolation charts (http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/).
Building Team role. Although strong Building Team coordination is important for any project, this is particularly the case with BIPV as it is a relatively new technology. In addition, costs of customization can escalate very quickly, so it's ideal to design the system as early as possible in the project cycle, making sure to consult with key specialists, manufacturers, and suppliers, advises Kiss.
ESD's Eich adds: “It is critical for all design team members to be made aware of the system as early as possible [so they can] understand the potential impact of a PV system on their area of design.” This includes architectural, mechanical, electrical, structural, façade, and other specialists. Landman and Keep state, “Due to the extra complexity in design, construction, and maintenance, it is more difficult to obtain an accurate life cycle cost analysis, and this needs to be an essential part of any PV feasibility study.”
When it comes to installation, notes Greentech Media's Bhargava, a high degree of precision is required in placing and orienting the panels to maximize light exposure while still providing accessibility for maintenance, coordinating the panels and inverters for optimal electrical production, and preserving the integrity of mounting structures.
Says Kiss, “Design-wise, it's important to optimize the dimensions and the electrical system layout for economy of installation, operational efficiency, and service.”
Down the Line
Technology development for the solar power market is moving along at a healthy clip. One recent start-up company is developing a product designed to achieve power generation at a costs of about 5 cents per kWh, which would make it competitive with conventional energy generation. And continued thin-film product development is moving in the direction of making the product more efficient and cost competitive. In fact, according to Landman and Keep, a new thin film product now being marketed for PV power plant installations claims a relatively low cost of 99 cents per watt.
Overall, Kiss looks with an optimistic eye toward the future. “There are enormous things that can be done. I'm looking forward to BIPV becoming more accessible and more customized, and more elegant types of electrical connectors designed with more aesthetics in mind.”
GEOTHERMAL HEAT PUMP SYSTEMS
As an established and proven source of renewable energy, geothermal building technologies, in particular heat-pump systems, are promoted by green building advocates the world over. The U.S. Environmental Protection Agency (EPA) credits geothermal heat pumps with providing the best life cycle cost payback, the lowest CO emissions, and the lowest overall environmental impact, as compared to all other heating/cooling systems.
Now that the cost of natural gas and oil has shot up so significantly, geothermal has become an even more serious consideration for building projects, say many building experts.
“The volatility of these utilities has led many building owners to seek a more stable form of energy, cost-wise, to heat and cool their facilities,” says Thomas Carson, P.E., manager of mechanical engineering with the A/E firm Schemmer, based in Omaha, Neb. “Geothermal is also riding a wave of notoriety due to the mainstream push to become green.”
Geothermal technologies essentially use the relatively constant temperatures within the earth's crust to heat buildings in the winter and cool them in summer. Heat pumps and other techniques, such as excavating and building below ground, allow building owners to draw out the stored energy for practical uses. The heating and cooling power is essentially free; all one has to do is tap into it. According to Matt Ebejer, P.E., vice president and healthcare market focus leader for Syska Hennessy Group, Los Angeles, using geothermal systems confers the following benefits:
- Reduced loads on the building's electrical system.
- Reduction of natural gas service to a building.
- Elimination of costly boiler and chiller equipment and rooms.
- Decreased need for rooftop equipment and related screening and structure to handle the equipment.
- Free domestic hot water, as a geothermal waste product, when the system is in the cooling mode.
Furthermore, the overall positive holistic impact of geothermal systems on the entire building can be significant. This can include occupant health benefits, reduced life cycle costs, and overall programmatic efficiencies—although these factors have yet to be fully documented and quantified.
“To date we have not been able to get a full grasp of the actual cost difference [of using geothermal systems] as they pertain to the complete building,” says Don Penn, P.E., a certified geothermal designer (CGD) and president of Image Engineering Group in Grapevine, Texas. For example, the building envelope, structural systems, electrical load requirements, and square footage reductions have never been evaluated. “Studies typically just include one mechanical system in comparison to one or more other choices, not a holistic evaluation,” says Penn.
Getting in the Loop
As noted, the brilliance of geothermal systems is in their ability to harness and convey the earth's constant temperature.
“Quite simply, geothermal systems take heat from the earth, transfer that heat to a refrigerant, and then distribute the heat into the structure with a forced-air or hydronic system,” explains J. Ramon, a contractor with Geothermal Design Associates, Fort Wayne, Ind. “In cooling, geothermal systems take heat from the structure, transfer the heat to the refrigerant, then transfer the heat back to the water or loop fluid.” In order to anchor the geothermal system to the earth, three different systems can be employed:
- Open-loop systems pump well water to the geothermal unit, where heat is either taken from it for heating purposes or put back into it for cooling.
- Closed-loop systems circulate a water/anti-freeze solution inside underground polyethylene piping and then absorb or reject heat into the surrounding earth.
- Water loops operate using water from a nearby pond or lake; ocean or bay water can also be used in some cases.
“Pond or lake loops may indeed be the best system available,” says Ramon. “They have the benefit of low installation costs in addition to the benefits of a closed loop. Also, pond and lake loops typically have more mild operating temperatures.”
The main benefit of closed-loop systems is that they require very little maintenance. However, due to excavation costs, they tend to be more expensive to install than open-loop types. “Typically, in certain parts of the country, such as the Midwest, loop systems are installed in a horizontal configuration, but in other parts of the country, where digging is more difficult or expensive, vertical loops are used,” Ramon clarifies. Vertical loops may be excavated or drilled.
Before determining whether a specific site is suitable for geothermal, a test bore must be performed. “What's more important than the geographic region or climate is the soil composition beneath the ground,” says Carson. “Ground types that provide good conduction of heat from the wells are best suited for geothermal, whereas ground that is rocky and difficult to drill is generally a poor candidate.”
New Developments in Earth Energy
Even though the key to the effectiveness of geothermal technology is its field infrastructure, this is generally a pricey first-cost item that often knocks heat pumps right out of the project budget. However, a few new system concepts are making the front-end work more affordable.
“Until about a year ago, a typical stand field consisted of six-inch bores ranging from 150 feet to 350 feet deep,” says Syska Hennessy's Ebejer. “Each bore would be provided with a one-inch U-tube pipe and could only provide from 1 to 2 tons of heating or cooling.” Now, a new pipe created for geothermal applications has been shown to work well with four-inch bores, yielding 3-5 tons of cooling per bore. This new pipe promises to reduce installation costs by about a third.
“Another development is that manufacturers are producing equipment that is substantially more energy efficient than conventional systems,” says Image Engineering Group's Penn. “The best chiller/air-handler pump system uses about 1.1 kilowatts per ton, whereas the new hi-efficiency geothermal equipment is ranging from 0.65 to 0.70 kW per ton.”
Many industry observers and green design practitioners would like to see more resources pumped into geothermal R&D. Fortunately, a number of government and academic research projects are also improving the technology. The U.S. Department of Energy, for example, is supporting numerous ongoing national laboratory research programs studying enhanced geothermal system development, as well as component-level improvements to downhole diagnostics, evaporative cooling, mixed binary working fluids, and corrosion-resistant coatings .
Tonya Boyd, assistant director of the Geo-Heat Center at the Oregon Institute of Technology in Klamath Falls, reports that her group is “looking at different ways of installing the loops in horizontal systems, like using horizontal boring systems, instead of digging trenches, and combining geothermal and solar thermal systems in northern climates where the heat in the ground is replenished by the solar thermal in the summer along with the cooling cycle of the geothermal system.”
The U.S. Leads the Way
The United States is among the most active countries in terms of direct-use geothermal applications and overall installed capacity. The majority of U.S. geothermal activity has been in the West, particularly in Nevada and California, where geothermal power generation provides around 6% of each state's energy demand.
Federal tax incentives passed into law in 2005 under EPAct 2005, plus the newly legislated Renewable Portfolio Standards in a number of western states, are driving growth of geothermal development. According to the U.S. Geothermal Energy Association, 61 large new geothermal projects were under way as of 2006.
Not surprisingly, many say there is considerably more untapped potential for geothermal. According to a recent Massachusetts Institute of Technology study, current system types could yield millions of gigawatts of geothermal energy, providing 10% of U.S. energy needs by 2050, if sufficient resources were invested in development.
“In spite of its enormous potential, the geothermal option for the United States has been largely ignored. In the short term, R&D funding levels and government policies and incentives have not favored growth of the U.S. geothermal capacity,” states the DOE-sponsored MIT report, “The Future of Geothermal Energy,” http://www1.eere.energy.gov/geothermal/future_geothermal.html.
Although it has a long way to go before being signed into law, the National Geothermal Initiative Act of 2007, now in Senate committee, could potentially ease things in the right direction. The bill seeks to invest $75 million in geothermal technology development this year, and $110 million per year, from 2009 to 2013. The bill also aims to expand geothermal energy production from a handful of western states to at least 25 states nationwide.
Obstacles and Opportunities
Besides a need for additional funding and development, life cycle benefits often need to be prioritized over first costs for geothermal projects to be viable.
“We see the geothermal systems being more applicable in institutional-type facilities, 40- to 50-year buildings, where the owner is savvy about long-term life cycle costs,” says Penn, whose firm Image Engineering Group has designed more than 150 geothermal systems for K-12 school districts in Texas. Facilities designed for “the developer market where the buildings are for an investment to turn over in a few years, where first cost prevails, typically are not good candidates,” he adds.
Also built into that first cost are such expenses as permitting and inspection fees, and the hard-to-predict value of drilling, especially in cases where a few drilling firms have a monopoly on a particular local market. At the same time, Carson points out, “The number of specialty well-drilling contractors has grown in the past five years, and this has brought down the cost of drilling new well fields.”
Building designers and contractors also complain that even without discussing first cost, they experience resistance from owners, developers, and even local officials simply because these parties lack understanding about the benefits of geothermal technology and how it works. Some see this stumbling block even when working with some MEP engineers and financial institutions.
One other challenge comes from environmentalists: Though interested in the energy profile of the systems, they are concerned about the invasiveness of geothermal installations and operations. Do underground wells pose a significant threat to soils and the ecosystem generally? Ebejer notes that closed-loop systems have been shown not to affect the groundwater, and the EPA considers geothermal systems to be environmentally safe.
“After the borehole is drilled and the loops placed in the hole, the borehole is grouted to provide sanitary protection for a water supply by preventing leakage downward along the borehole,” adds the Oregon Institute of Technology's Boyd. “Also, the grouting protects water-bearing formations by preventing the migration of water between aquifers, and will preserve the hydraulic characteristics of artesian formations and prevent leakage upward along the borehole.”
Carson does acknowledge that geothermal technology isn't environmentally perfect, mainly because a small percentage of food-grade propylene glycol circulates through the pipes to prevent freezing. Yet the cradle-to-cradle analysis—overall reduced carbon footprint, no added emissions, reduced energy use—makes a strong environmental case for geothermal.
In addition to the environmental and energy-saving advantages, geothermal development also helps stimulate local economic activity, as opposed to purchasing energy from outside utilities or overseas suppliers. Although increased financial incentives and R&D will be necessary to more fully realize geothermal's potential, many are optimistic. “I foresee geothermal use greatly increasing in the next few years,” predicts Ebejer. “As the cost of fossil fuels increases, an inexpensive source will be required, and geothermal offers that.”
Wind power for buildings
Wind is another environmentally friendly and cost-effective way to generate power. Wind energy is plentiful, renewable, and clean, and it can reduce greenhouse gas emissions by replacing conventional electricity. By the end of last year, wind-powered generators had a worldwide capacity of about 94 gigawatts—a mere 1% of the world's electricity. But the supply of wind power has grown fivefold since the year 2000.
Since the 1980s, the modern wind turbine has been used for electricity generation of small facilities in conjunction with battery storage in remote areas. Grid-connected turbines in the 1-10 kW range can power entire light commercial structures and use grid energy storage to save power for peak use. Users of small-scale turbines who are off the grid must adapt to intermittent power or opt to use batteries, diesel, or photovoltaic diesel systems to supplement their turbines.
A consistent 10-12 mile per hour wind is ideal for using wind turbines. In urban, industrial, and commercial locations, where it is difficult to sustain a consistent amount of wind energy, smaller systems may still be used to run low-power equipment, such as parking meters or wireless Internet routers.
There are surprisingly few limitations on wind power in zoning codes and local laws on the use of wind power in urban areas, other than those related to height. One common obstacle, however, is local opposition to erecting wind turbines, says Preston Koerner, a lawyer, environmentalist, and creator of the online journal Jetson Green (www.jetsongreen.com). Residents are often concerned about cost, noise, or installation disturbances of wind turbines, which tend to be minimal as compared to other project types. Koerner remains optimistic, however: “It's an innovation space,” he says. “A lot of money is going into clean technology right now, and we need it.”
Koerner and other experts point to a number of successful large-scale applications of commercial wind power outside the U.S., most notably the World Trade Center tower in Bahrain. New, state-of-the-art buildings in planning or under construction that will use wind power include the Pearl River tower in China, Core Tower in Florida, and the Clean Technology Tower in Chicago. Houston's Discovery Tower will feature its own rooftop wind farm. With these developments, industry experts believe, the United States alone is poised to provide 20% of the world's electrical grid by wind alone.