The signs of change are present. In 2003, potato chip manufacturer Kettle Foods installed a 114-kw photovoltaic (PV) system at its Salem, OR, facility. The 616 roof-mounted panels produce approximately 120,000 kilowatt-hours (kwh) of electricity each year. The solar generated electricity meets approximately 5% of the facility’s annual demand. Kettle followed a different strategy with its new 73,000-sq-ft manufacturing facility opened in 2007 at Beloit, WI. The facility uses 18 wind turbines located on the roof to create 18 kw of electricity.
Also in 2003, Frito-Lay installed a thin-membrane flexible PV roof at its Torrance, CA, facility. The system generates approximately 119 kw of peak power or about 186,000 kwh of clean energy annually. More recently, the company installed a concentrated solar thermal system at its Modesto, CA, plant. The 2008 installation includes 54,000 sq ft of solar concentrator mirrors on five acres. The football field-sized farm of 192 solar collectors move with the position of the sun, focusing the heat into tubes of glass filled with water. That water is directed into the plant’s boiler system where it is converted into steam to heat the oil used to cook SunChips. By using steam in the manufacturing process, the facility significantly reduces its use of natural gas.
Wide scale adoption of PV as part of factory operations by other bakers and snack food producers will require careful evaluation. Bakers will want to know: What does PV do? How and where do I use it? How much does it cost? Are there operational benefits to PV?
SUNLIGHT ENERGY. There is energy in sunlight. Heat from the sun is obvious, and solar thermal systems are finding increasing use for delivering hot water for factory needs. Capturing the sun’s heat is a fairly simple process of circulating liquid through collectors and transferring heat energy to a factory’s boiler or hot water system. Conversion of sunlight to electricity is considerably more complex.
PV technology produces electricity from the electrons freed by the interaction of sunlight with certain semiconductor materials such as silicon. The electrons are collected to form a direct current (DC) of electricity. Solar cells are the basic building block of PV technology. Many cells may be wired together to produce a PV module, and many modules are linked to form a PV array.
PV systems produce power intermittently because they work only when the sun is shining. Consequently, PV cannot promise energy independence but is rather a component in a network of locally produced and gridsupplied electricity. This network is often referred to as a "grid tie" or "distributed power" system.
In a distributed network, when factory-installed PV modules produce excess power, the electricity is shared with other customers on the electric grid, and the building’s electric meter turns backward. Conversely, power is drawn from the grid when factory needs exceed supply, and the meter registers use.
The capital investment payback calculation begins by determining cost savings that come from producing a kwh at the factory vs. the cost of purchasing that kwh from the grid. These savings are stacked against the PV system cost to determine if the investment is justified. Beyond dollars and cents there are social, environmental and operational advantages. To determine if PV is right for your facility, a broad understanding of design, cost and operating factors is required.
SYSTEM COSTS. There is no "one size fits all" when it comes to PV. Establishing system cost requires that a location be selected for the installation, and the company must determine the type of PV technology most appropriate for the application, size the system and establish the installation plan.
For industrial applications both rooftop and ground installations can be considered, each with advantages and disadvantages. An advantage to roof mounting is that the land is already paid for, while ground installations may use valuable land and interfere with future plant expansions. Roof installations are more likely to be free of shading elements that reduce system performance. However, roof maintenance can be complicated by the presence of PV modules. Ease of installation generally favors groundmounted systems because they usually involve little site preparation or investment in foundations. However, roof mounted PV shades the structure from direct sun and tends to reduce heat build-up inside the facility, a feature particularly appealing to bakers.
When sizing the PV system consider these design issues: • Establish the square footage and dimensions of available roof or land area. For roof installations, be sure to consider conflicts with roof-mounted equipment and penetrations such as stacks. • Select a module orientation that produces the optimal system performance — more electricity is generated from a direct light angle — when the sun is perpendicular to the surface of the PV modules. • Avoid shade elements that cast shadows across modules. These can significantly reduce power output. • Check local zoning and building codes to determine if they restrict PV. • Establish building roof characteristics (e.g. standing seam, membrane, built-up gravel, etc.) to determine the most appropriate PV mounting system. • Make sure the building is structurally sound to handle the added load.
After identifying the install location and area, you need to specify the system. The objective is to choose a system that meets site and budget constraints. The two broad categories of PV products are building-integrated PV (BIPV) and rack-mounted PV modules.
BIPV products are incorporated directly into a building structure and include both rigid and flexible (thin film) technologies. Rigid products include building materials such as facade panels. BIPV roofing systems that combine lightweight rigid insulation, a gypsum fire barrier, a durable white single-ply roofing membrane, and thin-film photovoltaic membrane are growing in popularity.
Advantages of a BIPV membrane roof include ease of installation, lightweight, durability (warranties up to 20 years) and no roof penetrations. However, because BIPV membrane is not optimally angled to the sun, the amount of electricity produced is less than what can be achieved through rack-mounted modules. This may not be significant in terms of the payback calculation, and given that a building needs a roof, any revenue generated by the roof is a plus.
PV modules mounted on racks are a proven workhorse in the burgeoning industrial solar energy market. These modules are available in a wide variety of types, sizes and prices. Generally speaking, higher cost equals higher quality as measured in power output and durability. However, with the rapid introduction of new PV products, this axiom needs careful scrutiny when specifying system modules.
Likewise, there is a wide variety of PV module mounting systems available on the market. Careful consideration is needed in selecting the mounting system that aligns with the specifications of the module manufacturer, project budget and roof characteristics.
The three general types of mounting modules are fixed, single-axis tracking and dual-axis tracking mounts. • Fixed-mount systems are positioned at the best angle and orientation to maximize solar radiation, either for the entire year or for the time of year when power is most needed. Single-axis devices are a better option, tracking the sun but not adjusting for seasonal variations in solar inclination. A recent informal survey found that single-axis mounts are priced only slightly below dual-axis systems creating serious consideration of dual-axis payback.
• Dual-axis mounts track the sun across the sky keeping the module at a right angle to the sun thereby capturing the maximum amount of available solar radiation. Dual-axis systems are typically the most expensive of the three alternatives.
Other considerations in designing a PV system include sizing electrical equipment (inverters, service panels, disconnect) and system monitoring devices. Pricing a PV system is no different than pricing any plant equipment purchase such as a new oven or packaging line. Pricing consists of system component, installation, maintenance and financing costs.
HIDDEN SAVINGS. Final cost calculations need to consider offsets provided by incentive and tax credit programs, which offer significant cost-reduction opportunities for PV systems. Incentive programs have been successful in stimulating adoption of renewable energy systems for residential and industrial users and are expected to be a factor for years to come. The types and number of programs are too numerous to review here. A good starting point for assessing state-by-state incentives is the "Database of State Incentives for Renewables & Efficiency" (www.dsireusa.org) operated by North Carolina State University.
Professional services for designing, purchasing and installing PV and solar thermal systems are rapidly emerging as the industry takes hold. Caution should be taken before signing on with a firm. Make sure they are qualified and reputable. Preferred system integrators and distributors are those that have experience in designing industrial installations, offer knowledge on the variety of design alternatives and are aligned with qualified installers.
PAYBACK CALCULATION. The payback calculation balances the amount of energy that can be produced from the factory’s PV system, the cost of the system, the cost of electric power from the grid, and incentives and tax credit offsets. Numerous decision tools are available for evaluating the economics of PV systems, from simple to complex. A good online tool can be found at www.OnGrid.net.
With the system specifications set, the rated power output determined, and purchase and installation costs known, the task now is to determine how much electric power can be generated from this installation so the payback can be calculated.
The first step is to identify the solar radiation available at the plant’s location measured in terms of average kwh/m2 / day for an entire year using the plant’s latitude as an inclination factor (see "Annual Direct Normal Solar Radiation," Page 109). A rough estimate on location is sufficient for an initial order of magnitude calculation.
System power output is now a simple calculation involving the rated output in watts of the PV modules, available solar radiation at the factory location, efficiency factor of the system (approximately 75%) and system degradation (typically 0.5% per year).
The next step is to establish a current baseline cost for electric power by establishing the cost per kwh from the grid supplier. Keep in mind that rates often vary by time of year, time of week and time of day. Be sure to align power rates with the time the PV system will be producing power. Finally, as part of the baseline analysis, estimate power company rate increases over the life of the PV system.
Property value can also be brought into the payback calculation. Real estate professionals generally agree that well-designed and functioning PV systems increase the resale value of property when matched with comparable properties without PV.
Cash flow plays a role in investment decisions. A nice feature of PV is that beyond the initial investment, maintenance cost is low, usually involving only occasional cleaning. Most module manufacturers offer a warranty of 20 years or more, and industry experts predict PV systems to perform considerably longer.
There is one exception to the low maintenance cost argument. A large cost component in a PV system is the inverter. Most inverters are rated for 10 to 15 years of service and require replacement at that time. Unlike grid application inverters that stay in service continually, solar inverters take a beating because of the daily cycle of cold start to full. Installing heavyduty inverter equipment is probably money well spent.
A number of software products on the market ease the burden of managing a PV system. They allow remote monitoring with the ability to detect performance of the entire system and individual modules.
SUSTAINABILITY AND GREEN. Increasingly PV is being adopted as part of broader corporate sustainability portfolios. Sweeping the world is a wave of interest by corporations to be portrayed as green and sustainable. In some cases the green push is driven by companies wishing to avoid a label of environmentally unfriendly. Regardless of the motivation, PV is a tangible step in promoting a green culture.
PV is a visible statement of commitment to the environment and the reduction of CO2 emissions. Anecdotal evidence also points to higher worker productivity and lower turnover rates in factories that broadly adopt elements of green culture.
The ideal situation is to realize social and environmental benefits from a renewable energy installation and save money at the same time. The steps are defined for beginning that assessment.
Don Schjeldahl is vice-president and director at Austin Consulting, Cleveland, OH. He can be reached at firstname.lastname@example.org.