e-News #89: Shining Some Light on Photovoltaics

February 6, 2013
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What's on the horizon for this popular, renewable energy source?

Photovoltaic (PV) modules are among the most iconic of all building components. They make a visual statement of environmental consciousness and can substantially offset a building's use of finite resources, all while saving money on monthly utility bills. You may have seen PV systems appearing on roofs in your neighborhood or heard about how much PV prices have dropped. Is it time to consider PV for your own home or business? What's happening with solar technology and is now the right time to invest in PV?

Big Picture

In 2006, the California State Assembly passed the Global Warming Solutions Act (AB32) to reduce the state's greenhouse gas emissions to 1990 levels by 2020. The state's emission reduction goals require that all new residential homes will be zero net energy by 2020 and all new commercial buildings by 2030. Even with significant reductions in energy use, these goals cannot be achieved without on-site renewable energy. Photovoltaics (PV) are the most popular and most versatile building-applied renewable energy source. As a result, PV is expected to become a key component to achieving the goals set in the Global Warming Solutions Act.

Although PV is not required in current California Building Energy Code, Title 24 Part 6 (2008), roof designs will be required to be "solar-ready" beginning in 2014 and the technology has been considered for a future code update. Eventual inclusion in Title 24 may be encouraged by recent trends seen in the costs of PV systems.

A recent report by the Department of Energy's Lawrence Berkeley National Laboratory analyzed cost figures for 2011 and earlier and found installed PV prices decreasing. Historically, costs have fallen annually since 1998 for fixed PV installations, with more significant decreases in fixed and tracking PV installations since 2009. The median installed prices of projects funded through the California Solar Initiative have reduced by 3 to 7 percent relative to the systems installed in 2011.

Following this trend, the industry is on track to provide a more economically feasible renewable energy source for homeowners and small businesses that typically require a shorter return on investment. Although PV will not be required for new construction for some time, innovative systems and incentives are available for the trendsetters who are ready to invest in on-site renewable energy.

PV Technologies & Assessment

Several types of PV technologies are currently available for building applications including the traditional roof rack-mounted crystalline silicone systems and laminates made up of thin-film solar cells. Third- and fourth-generation solar technologies such as solar inks, dyes, and solar paints are still in their infancy. Other promising technologies - such as colored PV panels - are in development and expected to have residential and commercial building applications in the near future.

Flat plate systems are still the most common because of their durability, efficiency, and relatively low cost. They can be fixed or sun-tracking. Most residential applications are affixed directly onto the roof. Taking the roof's pitch as the slope of the system allows for easy installation, although there is an optimum angle for the PV installation according to the specific location on earth and it's relation to the sun.

Today, Internet users can easily assess the benefits of PV and learn what system type(s) may be most appropriate and effective for their use. In fact, resources such as simple modeling programs now are available online to help determine the PV array size, optimum angle, potential cost savings, and likely energy production of a photovoltaic system. Other online resources also include websites detailing rebate information, as well as tax incentives for PV installations.

Building Integrated Photovoltaics

Applied PV
Figure 1: An example of Building Applied Photovoltaics on a residential home.
Image courtesy of NREL.

Building Integrated (BIPV) or Building Applied (BAPV) Photovoltaic systems are considered second-generation technologies. What sets BIPV apart from its mounted system counterpart is the integrated nature of the product: BIPVs are embedded in the building's architecture, providing a source of renewable energy generation while serving as a component of the building's exterior. Solar cells can be integrated into roof tiles, façades & curtain walls, or embedded in glazing or skylights. BAPV are no different in terms of type of photovoltaics, only that they are added to a building as part of a retrofit instead of being installed as part of new building construction.

BIPV is gaining popularity over traditional rack-mounted systems for several reasons. They are lighter in weight which can ease the loads on structural systems, and can be applied to any surface of the building not just the roof or on unused land. In commercial applications, PV competes for roof space with mechanical equipment, green roofs, and cool roofs. Being able to generate electricity on other building surfaces increases the available capacity and alleviates the need to compete for valuable roof space. Designers can integrate BIPV into a building's design, making it serve a dual purpose as the building skin and as an energy generator. Since the systems serve a dual purpose, the higher first costs of BIPV can be shared between the two.

PV Cost Comparison
Figure 2: Comparison of residential rooftop prices for a rack-mounted PV Reference Case and three BIPV cases.
Courtesy of NREL.

The most common residential application of BIPV is roof tiles or shingles, which can be installed on a new home or when replacing a roof on an existing home. Homeowners are concerned with the aesthetics of their home solar project, and a key benefit of BIPV is that it can be seamlessly integrated into the surrounding asphalt or concrete shingles or clay tile. Secondly, homeowners are concerned with first costs and payback period. The National Renewable Energy Laboratory (NREL) released a report last year called "Building-Integrated Photovoltaics (BIPV) in the Residential Sector: An Analysis of Installed Rooftop System Prices" which compares three different systems: a rack-mounted crystalline system, verses two different thin-film technologies. The report looks at installation costs, module costs, building material cost offsets for traditional rack-mounted and BIPV installations. The comparison study represented in Figure ES-1 suggest that BIPV has the potential to achieve system prices that are about 10% lower than rack mounted PV system prices.

More opportunities exist for incorporating BIPV in commercial projects because of the size and type of building construction. Vertical curtain walls are the most used application, integrating the facade structure with solar cells. BIPV is also found in skylights, exterior light shelves, and overhangs - all being building components that have direct sun access. BIPV also is being integrated into parking canopies and shading devices, like the photo of the parking area shown in Figure 3. Integrated PV glazing systems are semi-transparent and appear either tinted or with a fritted pattern of solar cells allowing natural daylight to get through.

Integrated PV
Figure 3: An example of Building Integrated Photovoltaics in a parking area.
Image courtesy of NREL.

The negative side of BIPV is the low efficiency. Rack-mounted systems produce the most energy per square foot of solar array.  As shown in Table 1, the efficiencies of various thin film BIPVs are below the PV Reference Case, which is the typical rack mounted crystalline type. These values are typical across manufacturers and thin film processes. The flexibility that BIPV provides can overcome the efficiency barriers to using this type of photovoltaic system. With the increase in overall PV installations and decreasing costs, BIPV energy production efficiency certainly will improve over time. Efficiency is also improving in the distribution and conversion of power from DC (power current from solar collectors) to AC (current used in the electrical grid).

Table 1: Efficiency comparison of three BIPV cases and reference rack-mounted PV crystalline silicone system.  Courtesy of NREL.
ScenarioTechnologyFormEfficiencyModule Area (m2)
PV Refernce Case c-Si Rigid 14.5%  1.28
BIPV Derivative Case c-Si Rigid 13.8% 0.58
BIPV Thin-film Case 1 CIGS Rigid 11.2% 0.58
BIPV Thin-film Case 2 a-Si Flexible 5.8% 0.58

Technologies in Development

Since initial costs are the primary barrier to installing PV on homes and businesses, low-cost options will be essential for solar to become practical for use in all buildings. Much research has been conducted in printing solar cells, which may be one solution to the cost barrier. Energy production efficiencies of these technologies still are not comparable to rigid rack-mounted systems, although they are improving. Thin film solutions like dye-based panels, silicon nano-particles in screen printable ink, and printing solar cells on metal substrates are emerging as the latest solar innovations. If viable, these emerging energy-producing products soon could be integrated into furniture fabrics and window treatments, mixed in exterior paints, and potentially incorporated into nearly any part of a building.

Besides flexible applications of BIPV, research is being done to explore non-flat solar collectors, including rotating conical collectors which increase the efficiencies of PV significantly. This emerging technology would permit energy harvesting on a large scale to occur outside of wind and solar farms.

Project Spotlight

Completed in 2003, the Lillis Business Complex at the University of Oregon in Eugene, is home to one of the largest building-installed solar installations in the Northwest. Although the Lillis Business Complex is a 10-year old example of photovoltaic (PV) technology, it demonstrates a first-adopter application of PV.  The four-story building houses classrooms and lecture halls, faculty offices, undergraduate and graduate student services, study rooms, and a café. The project team worked closely with the general contractor, as well as university professors and students to collaborate on the project's energy systems. Students at the University had "identified sustainability as a key business strategy for companies of the future", and recommended the Lundquist College of Business building be a demonstration of sustainable solutions.

Ultimately, the building-integrated photovoltaics (BIPV) in the building's curtain wall make up just 13 percent of the building's total of 45 kW of PVs.  In reality they deliver even less because a tree largely shades half the wall. PV cells wired in series with a centralized inverter deliver only as much electricity as the least productive cell in each row, so shading a panel reduces its output more significantly than the tree's shadow alone might suggest. Most of the solar electricity at Lillis is generated by a large array of conventional panels mounted flat on the rooftop; all installed PV systems together supply about 10 percent of the building's predicted electricity demand.

The college's stated desire to incorporate sustainable design and technologies in the building's construction, as well as the efforts of the entire project team, resulted in the award of the U.S. Green Building Council's Leadership in Energy and Environment Design (LEED) Silver.

Incentives: Financing, Rebates, and Tax Credits

Typically the high initial costs of PV are a restrictive factor for a home or business owner. The cost from the equipment, installation, and any upgrades needed to make a PV installation ready for use add up quickly, making solar energy a cost-prohibitive renewable energy resource. As newer technologies develop through time and more people adopt renewable energy, the laws of economics imply that the costs will decrease. Until then, public utilities, energy commissions, and government entities have come together to incentivize solar installations in the form of rebates and tax credits.

Available Rebates and Incentives

In California, rebates and tax credits are only available for types of PV installations that are pre-approved by the California Solar Initiative (CSI). Regional program administrators for the utility companies distribute the available rebates, typically direct to the installing contractor so the customer gets a reduction in the upfront cost. Rebates are distributed in tiers, where early adopters receive the greatest incentives. The process starts by completing a free energy assessment to find ways to improve efficiency and conserve; such an assessment always should be the first step in any energy upgrade efforts. After making any changes discovered from the assessment, you are ready to select a contractor, identify appropriate PV equipment, and begin the installation process.

The California Solar Initiative (CSI)

For small business and residential customers who install systems less than 30 kW, the rebate is called the expected performance-based buy down (EPBB) and it is calculated in dollars/Watt of future performance based on system type, location, and shading, among other factors. The EPBB is paid in a one-time, up-front payment. Rebate availability is continuously updated on the Statewide Trigger Tracker on the Go Solar California website.

Larger commercial, government, or non-profit customers are better served by the Performance-Based Incentive (PBI) rebate program for systems over 30 kW. This program pays in cents per kWh based on the actual energy produced by the system. Monthly rebates under this program are paid out through 5 years, with rebate availability again updated on the Statewide Trigger Tracker.

Tax Incentives and Statewide Programs

In addition to rebates, there are one-time tax credits available for residential and commercial owners of solar installations. Starting in 2008, solar investment tax credits (ITC) were enacted and then were extended through the end of 2016. Currently, the credit value is up to 30 percent of the total system cost. It is important to note that the tax credit is only available for system owners, so if a PV system is installed but owned by someone else - such as a utility or other third-party - see if the owner is willing to pass along some of the tax savings. Other tax incentives like accelerated depreciation also are available, so check with your tax preparer to make sure you are taking advantage of all the incentives offered.

California Assembly Bill 811 made it possible for local governments to issue loans for energy efficiency and renewable energy systems. From this legislation, the CaliforniaFIRST partnership was born. The program allows eligible home and business owners in 14 counties and 126 cities to partake in low-interest loans, where payments are made annually with property taxes through 5 to 20 years depending on the expected useful life of the financed equipment. The loans are transferrable in the event of a sale of property.

In the some California regions, financing organizations and local governments are working together to offer these Property Assessed Clean Energy or PACE programs, which incentivize renewables and energy efficiency improvements through low-cost loans repaid as an additional property tax assessment. Visit PACE online for more information.

Training Highlights

California utilities offer outstanding educational opportunities that focus on the design, construction and operation of energy-efficient buildings. Listed here are a few of the many upcoming classes and events; for complete schedules, visit each utility's website.

Basics of Photovoltaic (PV) Systems for Grid-Tied Applications
February 13 (9:00 am to 4:30 pm)
PEC - San Francisco
register >

Introduction to Photovoltaic (PV) System Financing
February 28 (8:30 am to 4:30 pm)
PEC - San Francisco
register >


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e-News is published by Energy Design Resources (www.energydesignresources.com), an online resource center for information on energy efficiency design practices in California.

Savings By Design (www.savingsbydesign.com) offers design assistance and incentives to design teams and building owners in California to encourage high-performance nonresidential building design and construction.

Energy Design Resources and Savings By Design are funded by California utility customers and administered by Pacific Gas and Electric Company, Sacramento Municipal Utility District, San Diego Gas and Electric, Southern California Edison and Southern California Gas Company, under the auspices of the California Public Utilities Commission.


Download: EDR_eNews_089.pdf
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