Making the Connection—Key Issues in Connecting A

MAKING THE CONNECTION

Key Issues in Connecting a Photovoltaic System to the Utility Grid WE’VE COME A LONG WAY Connecting residential or small com- a builder, code expert, utility engi- mercial photovoltaic (PV) systems neer, regulator, legislator, or private to an existing utility grid has come citizen. If not properly addressed, a long way in recent years. Experts any one of these crucial issues could within the PV industry have solved hinder or halt the installation of a many earlier problems, bringing us PV system. to the point today where we know As we discuss the relevant issues how to install, operate, and maintain under the two main categories of PV systems safely and conveniently. code issues and utility issues, But governments, communities, and remember the bottom line: many utilities who are not yet familiar with former technical obstacles to using PV systems have legitimate concerns PV systems no longer exist, and that we must address through educa- critical problems raised in the past tion and support. are being successfully resolved. This brochure will help you understand the issues that surround PV interconnections, whether you are

CODE ISSUES Building Codes has been steady during the last several years. We now see commercial Local building authorities rely on products designed for building nationally developed building codes systems—such as PV roofing that delineate required safe-building materials and PV curtain wall practices. Building inspectors are products—that are included in concerned with the proper construc- construction plans. In addition, tion of safe buildings. Of primary the mounting of systems on flat interest is ensuring that a PV system roofs has been greatly simplified. or structure has been installed correctly. For example, the system must be fastened according to approved design drawings so that it Solar Depot, Inc./PIX04479 won't cause the roof to leak or be blown off the roof, leading to serious structural damage. Before embarking on a PV installation project, the appropriate code officials Solutions—The development of should be consulted to ensure com- innovative building-integrated PV pliance with all local codes. systems that meet building codes

1 Local Covenants Electrical Codes Some communities may adopt restric- The National Electrical Code (NEC), tions, primarily for aesthetic reasons, published by the National Fire that make it difficult or impossible Protection Association, is designed to install PV modules. If visual to prevent electrical shock and fire aspects are not properly addressed, hazards associated with electrical community representatives are not systems. Some utility-interconnected likely to look favorably on the wide- PV systems operate at direct-current spread use of PV within their (dc) voltages exceeding 200 volts community. If a community has before being inverted to standard a particularly restrictive covenant alternating-current (ac) voltage. with respect to solar systems, it may Direct-current systems are not as be necessary common, and their safe operation to meet with requires “dc rated” hardware. the covenants board to Solutions—In 1984, PV systems NREL/PIX05777 explain the achieved the status of a special planned instal- equipment article in Article 690 lation and of the NEC. Article 690 carefully address spe- spells out requirements for making cific concerns. PV systems compliant with the NEC. A guide for recommended practices Solutions— based on the NEC provides practical Increasingly, information on designing and instal- U.S. commu- ling safe, reliable, code-compliant nities are being PV systems (see PV Power Systems, designed with NEC: Suggested Practices, SAND96- allowances for solar energy written 2797). Only within the last few into the established covenants. The years have fully code-compliant city of Davis, in northern California, systems been available. However, is a model community that has many systems that comply with the pioneered these types of covenants. code have operated safely for more As more examples of model cove- than 10 years. PV system installers nants become widely publicized, must understand the Article 690 the public will be more open to requirements, and local code institutionalizing these measures in authorities unfamiliar with PV their communities. Well-prepared systems must be educated. materials, such as a sketch of a proposed installation or a photo- Representatives from the solar energy graph of a similar installation, industry have actively guided the can help allay the concerns of a revisions of NEC Article 690 for covenants board. many years. The most recent 1999 version will be released in late summer 1998.

2 The NEC requires that all As another example of improved equipment be listed by a products, the ac PV module is a recognized listing agency— recent innovation that converts for example, Underwriters dc power to standard ac before it Laboratories. Several PV leaves the module, which eliminates inverters are now listed, the need for high-voltage dc wiring

Solar Associates/PIX04472 Design making it possible to and allows for PV systems as small install a fully code-compli- as 100 watts. ant PV system acceptable to most code authorities.

UTILITY ISSUES Power Quality Solutions—Any electronic appliance, such as a PV inverter, that is FCC Power quality “noise” is any electrical Class B compliant means that it has energy that interferes with other passed the required tests to meet the electrical appliances operated by the FCC regulations for high-frequency customer and neighbors on the same electronic noise. The Institute of transformer. The Federal Communi- Electrical and Electronic Engineers cations Commission (FCC) is con- (IEEE) also has power-quality stan- cerned with power-quality noise that dards, such as IEEE 519, Recom- affects communications. Utility com- mended Practices and Requirements panies are also concerned because for Harmonic Control in Electrical they seek to provide high- quality service to their customers. In particular, utilities care about such issues as harmonic distortion, power factor, and flicker. For a home, power is delivered at 120/240 volts ac at 60 Gretz, Warren NREL/PIX04167 cycles per second. Any electric service not at that rating can interfere with the proper operation of some appliances. A PV inverter that con- Power Systems. The Underwriters verts dc power from PV modules Laboratories standard for listing into usable ac power for a house a PV inverter includes testing for can also inject noise. If a utility power quality so that listed PV customer’s power-quality problem inverters will conform to applicable is traced to a PV inverter, the utility requirements. can shut down the PV equipment until the issue is resolved.

3 Metering Agreements can easily wipe out any economic benefit a small PV system could Metering agreements directly affect provide a homeowner. Most utilities the bottom-line economics of the PV require special metering to measure system. For example, special meter- power flowing in both directions— ing and additional metering charges into the house and into the grid. Many utilities impose additional charges on utility-interconnected The ABCs of Net Metering PV systems, including “standby” Under federal law, utilities must allow independent power producers to intercon- charges or higher “minimum nect with the utility grid and must purchase monthly” charges. any excess electricity they generate. Many And for the states have gone beyond the minimum excess electricity requirements of the federal law by allowing generated, utilities “net metering” for customers with PV normally pay the systems. Where available, the customer customer a wholesale is billed only for the “net” electricity rate, rather than the purchased from the utility over the much higher retail rate. entire billing period—that is, the difference between the electricity Solutions—Some utili- coming from the utility grid and the ties have established Available electricity generated by the PV system. If the “net” amount is posi- metering and accounting Not available tive, the customer pays the utility at the retail rate on the net kilowatt- arrangements that make grid- Z8-B317505 hours of energy used. If the “net” amount is negative, the customer either connected PV systems more is credited on the next bill for the excess electricity, or is paid for the excess economical. For example, some electricity at the wholesale rate. states have adopted net-metering Dual metering is an alternative, where customers or their utility purchase and policies (see box) that allow utility install two non-reversing meters that measure electrical flow in each direction. customers to use their PV genera- This adds significant expense to installing a PV system. Homeowners pay for tion to offset retail purchases over all the electricity from the utility at the retail rate—not just the net amount. an entire billing period, or over an And the utility only pays them the much lower wholesale rate on the electricity entire year. Net metering improves fed back to the utility. the economics of PV generation by allowing customers to capture the Faced with the alternative between net metering and the traditional dual-meter- retail value of electricity for most or ing approach, many states, utility commissions, and utilities have opted for net all of their PV generation. In addi- metering because it is less expensive for all involved. Some opponents believe it tion, some utilities offer time-of-day imposes financial burdens on utilities or their non-participating customers. pricing, which results in higher Studies have shown that the quantity of PV relative to the size of the utility's prices during “peak” daytime hours revenues is minimal—even without considering reduced costs of meter hard- and lower prices during “off-peak” ware, interconnection, meter reading, and billing. These studies do not include nighttime hours. Time-of-day pricing the issue of peak-shaving capability or the environmental, distribution, and can provide substantial bill savings fuel-diversity benefits provided by distributed, small-scale, renewable-energy to customers with PV systems—by systems. Nevertheless, to address utility concerns about potential financial allowing them to reduce their elec- burdens, laws limit the number of installations within any single utility service tricity use during peak hours, or in territory. Currently, net metering is available in 23 states to certain customers some cases, to sell back any excess and technologies—including residential PV system owners. electricity they generate at higher

4 peak rates. The better the match Solutions—National standards on between the electrical output of the protection, safety, and operation reli- PV system and the time of highest ability are now available for utilities prices, the more effective the system and PV system manufacturers. The will be in reducing utility bills. standards that utilities adopt for safety, reliability, and interconnection usually come from the IEEE. In 1988, IEEE Oak Ridge National Lab./PIX03205 Safety and Reliability and the American National Standards Utilities must ensure the safe and Institute released Standard 929-1988, reliable operation of the entire utility IEEE Recommended Practice for Utility grid for employees and the public. Interface of Residential and Inter- Traditionally, utility system safety mediate Photovoltaic Systems, which issues have been the most significant addresses the basic issues of equip- obstacles to installing PV systems. ment protection, safety, and allow- Most utilities have no experience able limits for power quality. For with generating systems smaller equipment protection and safety, than 50 kilowatts, except for small for example, it covers the ranges gasoline generators. Because such over which inverters are allowed to generators have been a safety concern operate. With valuable participation for linemen nationwide, utilities are by utilities, IEEE 929-1988 is being understandably wary of small power extensively revised to address utility How Interconnection systems, regardless of type. However, issues surrounding the safe and reli- Became an Issue PV inverters are significantly differ- able interconnection and operation ent from small gasoline generators of PV systems. Until the final draft The Public Utilities Regulatory because they have very sophisticated of IEEE 929 is released, the existing Policy Act of 1978 (PURPA) automatic safety controls that rival IEEE 929-1988 serves as a sound requires utilities to buy power those used for large generating units. standard for utility interconnection. from owners of PV systems and other independent producers of electricity. An approved, utility- grade inverter converts the dc FOR MORE INFORMATION, CONTACT: power from PV modules into ac power. This power must exactly Christy Herig Produced for the match the voltage and frequency National Renewable Energy Laboratory U.S. Department of Energy National Center for Photovoltaics 1000 Independence Ave., S.W. of the electricity flowing in the 1617 Cole Blvd. Washington, D.C. 20585 utility line and meet safety and Golden, CO 80401 by the National Renewable Energy power-quality requirements. (303) 384-6546 • (303) 384-6490 (fax) Laboratory, a DOE national laboratory. Safety switches in the inverter e-mail: [email protected] automatically disconnect the PV DOE/GO-10098-523 Source: Bill Brooks (North Carolina Solar system from the line if there is a June 1998 problem with the utility power, Center), Connecting Photovoltaics to the so that utility repair personnel Utility Grid: A Non-Technical Guide to PV Interconnection Issues, June 1997. will not be shocked by electricity flowing from the PV array into Cover photographs: left—Bill Eager/ what they expected to be a PIX00568; right—Ascension Technology, “dead” utility line. Inc./PIX04478; power lines—Warren Printed with a renewable-source ink on paper containing at least 50% wastepaper, Gretz, NREL/PIX00001. including 20% postconsumer waste.