Safety Considerations for Photovoltaic Systems

Transcription

1 Pennsylvania Building Officials Conference & Pennsylvania Fire Code Officials State College, PA September 18, 2015 Safety Considerations for Photovoltaic Systems Ron Celentano of Celentano Energy Services (CES) also representing PASEIA/MSEIA Ron Celentano - Solar Industry Consultant Design; Project Oversight; Installation; Inspection; Technical Training & Support; Policy Issues; Interconnection/Net Metering, SRECs; Pres. Of Pennsylvania Solar Energy Industries Assoc.(PASEIA); VP of MSEIA ; CelentanoR@aol.com

2 Safety Considerations for Photovoltaic Systems About how in the dead of night solar panels can deliver quite a jolt. The importance of recalculating roof loads and capabilities start this discussion. Recognizing and using electrical disconnect mechanisms Will it hold it? Recognizing the unseen impacts of retrofit projects

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4 Cumulative Solar PV Installed in the World As of End of 2014 International Energy Agency s (IEA) Photovoltaic Power Systems Programme (PVPS)

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7 Solar PV Installed in the US 2014: 6,201 MW Installed

8 Solar PV Installed in the US Top 10 States Total (End of 2014): 18,280 MW Pennsylvania: ~ 220 MW by June, 2015

9 ~220 MW; 7850 Systems

10 Photovoltaic Applications Street Lighting Commercial Residential

11 Photovoltaic Applications Commercial Car Port

12 3 MW Project - Fairless Hills, PA Utility Scale SunTechnics / Conergy

13 Fixed Tilt vs. Tracking the Sun Fixed Tilt Array 2-Axis Tracking Array 1-Axis Tracking Array

14 Photovoltaic Applications-Building Integrated

15 Photovoltaic Applications-Building Integrated Solar Shingles

16 Photovoltaic Applications-Building Integrated

17 Applications-BIPV Solar Roofing Tiles Solar Roofing Systems (Philadelphia)

18 Applications-BIPV Solar Roofing Tiles Solar Roofing Systems (Corona, CA) Demo Project Solar Tile vs Conventional PV 30 Solar Roofing Tiles 450 W 9 BP Solar 350 Polycrystalline Modules 450 W

19 Applications-Building Integrated PV Glazing

20 Uni-Solar Peel & Stick 700 kw (Thin Film)

21 SolarSave Roofing Membranes

22 PV Systems PV Systems in SE PA in SE PA

23 PV Systems in SE PA

24 PV Systems in SE PA

25 PV Systems in SE PA

26 Photovoltaic (Solar Electric) Technologies Single Crystalline (Monocrystalline) Amorphous Silicon Polycrystalline (Multicrystalline)

27 Typical Crystalline Cell Module Solar Cell Solar Array Solar Panel or Module

28 Various Configurations (History)

29 PV Module Specs Rated Power (watts) Maximum Power Voltage (Vmp) Maximum Power Current (Imp) Open Circuit Voltage (Voc) Short Circuit Current (Isc)

30 Short Circuit Current Isc = 8.81 A Imp = 8.33 A Maximum Power Point (305 Vmp, Imp) 36.6 V 45.5 V

31 Weather Impacts on PV Performance Irradiance Current (amps) Temperature Voltage Power (Watts) = Volts x Amps Based on the NABCEP Study Guide

32 PV IV Curve (J.Wiles) Increased Isc Approximately 20% Rated Isc = 3.5 A Current Irradiance 1200 W/m 2 at 25 o C 1000 W/m 2 at 25 o C Standard Testing Temperature Decreased Isc Approximately 20% 800 W/m 2 at 25 o C Peak Pow er Points 10 VDC 16 VDC Voc = 21 VDC Battery Voltage Range Voltage 10/29/03 INSP-16

33 Irradiance and Temperature Readings Pyranometer or Radiometer Estimates Cell Temperature Temp. Factor = 1 + ((cell temp (C) 25 C) x Temp Coeff for Pmax Irradiance Meter Typically, Temp Coeff is about 0.5%/C; so above Temp Factor = 1.07

34 Checking Performance Nominal PV Capacity (STC) vs Actual Power Output Nominal Capacity or Rated Standard Testing Conditions (STC): watts/meter 2-25 o C Cell Temperature air mass Inverter output power = 2000 x 0.7 x 0.9 x x 0.97 x 0.94 = 1017 watts STC array power 700 W/m 2 factor (700/1000) Derating Factors These can be incorporated in PVWATTS simulations to estimated solar electric generation Mismatch & dust factor Array temperature factor Wiring efficiency factor Inverter efficiency factor Based on the NABCEP Study Guide

35 Grid-Tie PV Simple Line Diagram Interconnection through a backfeed breaker - NEC 2008, allows up to 120% rating of load center for both commercial and residential for; otherwise, needs to be a supply side connection or line side tap (for example, no more than a 7.68 kw inverter (40 Amp) should backfeed through a 200 Amp service load center, unless main breaker is downsized accordingly). MUST consider this for expanding PV system capacity.

36 Location of Solar PV Backfeed Breaker

37 Larger PV System with Line Side Connection Inverters DC Disconnect /Combiner Switch Inverter Combiner Panel (AC Disco) Utility Isolation Switch (AC Disco - Outside)

38 Another Large Residential System (BOS) DC Disconnect /Combiner Switches, Inverters, Inverter Combiner Panel (AC Disco), and Solar Generation Meter

39 More Examples of Balance of Systems

40 Battery Back Inverter A.K.A. Bi-Modal Inverter (DC Coupled System)

41 AC Coupled System w/ups Wiring Diagram

42 5.89 kw PV System; Only 4.35 kw Configured on Backup System mods w/ micro inverters; only 17 mods configued to back up PV system w/ 4.4 kw Magnum inverter and 200 Ahr battery capacity

43 Combiner Box, J-Box and DC Disconnect Configurations Fused Combiner Box For PV Source Circuits J-Box For Wire Transition (USE-2 to THWN-2) Inverter Integrated DC Disconnect

44 Combiner and DC Disconnect Configurations

45 Combiner and DC Disconnect Configurations

46 Combiner and DC Disconnect Configurations

47 Utility Isolation Switch in PA CB or pull-out type discos not acceptable Acceptable Utility Isolation Switch From the PUC Interconnection Regulations and found in all PA Utilities Interconnection Procedures: Small generator facilities shall be capable of being isolated from the EDC by means of a lockable, visiblebreak isolation device accessible by the EDC. Note: PPL waives this requirement for Level 1 (10 kw or less) systems

48 Micro-Inverters And DC Optimizers

49 Shading Impacts 2,798 Watts 2,358 Watts 15.7% less power production due to shading vs fully exposed modules

50 Watts output :01pm :07 AM 10:04 AM 11:02 AM 12:00 PM 12:57 PM 1:55 PM 2:52 PM Time of day 12:09pm

51 Electric Shock Risks Solar PV About how in the dead of night solar panels can deliver quite a jolt.. Recognizing and using electrical disconnect mechanisms

52 Electric Shock Risks Solar PV Firefighter Safety and Photovoltaic Installations Research Project Underwriters Laboratory, November 29, The research included experiments to develop empirical data for understanding the magnitude of these hazards and unsafe conditions, including the following: Assessment of PV power using a variety of light sources; Shock hazard due to severing of conductors and assessment of potential shock hazard from damaged PV modules and systems; Shock hazard due to the presence of water and PV power during suppression activities; and Shock hazard due to direct contact with energized components during firefighting operations, emergency disconnect and disruption techniques. Note: This and the next three slides show excerpts taken from an article in written by one of the authors of this study, Robert Backstrom

53 Electric Shock Risks Solar PV In order to aid firefighters understanding of the significance of the results of this project, hazards were quantified into four levels using milliampere (ma), the base metric unit for electric current. Safe levels are defined as 0-2 ma, perception levels are defined as ma, lock on levels are defined as ma, and electrocution can result at levels greater than 240 ma. Assessment with light sources Artificial light from fire trucks that used scene lighting during a nighttime fire event; Light from an exposure fire; and Light from a low ambient source, such as a full moon. The results of the experiment indicate that when illuminated by artificial light sources, such as fire department light trucks or an exposure fire, PV systems are capable of producing electrical power sufficient to cause a lock-on hazard.

54 Electric Shock Risks Solar PV Severing of conductors The results of the experiments indicate that a firefighter may be subjected to an electrical shock hazard due to damaged PV system components, as live electrical parts may become exposed. Some of this damage may occur during the fire or overhaul operations. Suppression techniques These experiments were conducted using different nozzles, water pressure, conductivity, voltages and distances. The electric shock hazard due to application of water is dependent on voltage, water conductivity, distance and spray pattern. The research found that slight adjustments in water stream during firefighting and distance impacted the risk of shock. 20 feet was a safe distance.

55 Electric Shock Risks Solar PV Effect of direct contact Results from the experiments indicate that severely damaged PV arrays are capable of producing hazardous conditions ranging from perception to electrocution. Damage to the array may result in the creation of new and unexpected circuit paths. These paths may include both array components (such as module frames, mounting racks and conduits) and building components (such as metal roofs, flashings and gutters). Emergency disconnect Turning off an array is not as simple as opening a disconnect switch. Depending on the individual system, there may be multiple circuits wired together to a common point, such as a combiner box. All circuits supplying power to this point must be interrupted to partially de-energize the system. As long as the array is illuminated, parts of the system will remain energized. Tarps or foam may be used to cover the modules in the array to block light. Tarps offer varying degrees of effectiveness to interrupt the generation of power from a PV array. The research did find that heavy, densely woven fabric and dark plastic films reduce the power from PV systems to near zero.

56 Resources for Municipalities and Code Officials This very popular course now reflects the National Electric Codes through 2014 and includes a new lesson on the International Fire Code, with building and fire safety information related to residential PV systems. The International Association of Electrical Inspectors continues to offer expertise and continuing education units for this course. A set of three self-directed online modules is aimed at supporting instructors interested in teaching solar content online. The modules teach users effective instructional strategies and implementation for online or hybrid instruction.

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58 Resources for Municipalities and Code Officials Solar America Board of Codes & Standards Expedited Permitting Guide reports/expedited-permit/index.html PennFuture Zoning and Permitting Guidebook Mayor s Office of Sustainability City of Philadelphia Guidebook for Solar Photovoltaic Projects in Philadelphia DVRPC Renewable Energy Ordinance Framework Solar PV Pending

59 DVRPC s Solar Ready II U.S. Dept. of Energy - SunShot Solar II Program The Delaware Valley Regional Planning Commission (DVRPC) is dedicated to uniting the region s elected officials, planning professionals, and the public with a common vision of making a great region even greater. DVRPC serves a region of nine counties: Bucks, Chester, Delaware, Montgomery, and Philadelphia in Pennsylvania; and Burlington, Camden, Gloucester, and Mercer in New Jersey. Promote best management practices for streamlined and standardized solar regulatory practices at the municipal level Solar Ready II will work with municipalities and stakeholders to: Identify existing conditions and barriers to solar photovoltaic (PV) adoption Develop and implement a plan to reduce soft costs of solar PV Provide free "light" technical assistance and training on solar PV best management practices

60 DVRPC Renewable Energy Ordinance Framework Solar PV Setbacks for PV

61 Setbacks for PV 2012 IFC

62 Setbacks for PV Alternate State of Oregon

63 Setbacks for PV Alternate State of Oregon

64 Structural Integrity Will it hold it? Recognizing the unseen impacts of retrofit projects

65 Wind Loading Roof Mounted Systems

66 Calculating Uplift Forces Uplift forces during windy conditions may reach 50 lbs/ft 2 or more. This would be considered velocity pressure based on high winds in a local region (for example, the velocity pressure of 12.5 lbs/sqft for eastern Montgomery County at 70 mph). By assuming a very high velocity pressure in the calculation inherently assumes a corresponding safety factor. Therefore, calculations should be done for lag-bolted roof mounted PV arrays to ensure they can withstand the withdrawal load; After calculating the withdrawal load, minimum lag bolt length can be determined, knowing its diameter and the type of wood its penetrating.

67 Calculating Uplift Forces Simple Example Assume: - Uplift force to be 40 lbs/ft 2 ; - 12 modules in array; each module = 10 ft 2 or 120 ft 2 for the array - 10 mounting feet lag bolted into Douglas Fir Determine uplift forces: - Module: 40 lbs of uplift per sq. ft. x 10 sq. ft. = 400 lbs - Array: 400 lbs x 12 modules = 4,800 lbs - Mounting Point: 4,800 lbs / 10 mounting feet = 480 lbs per mounting foot

68 Calculating Uplift Forces Lag Bolt Calculation Simple Example pounds uplift force per attachment point - Asphalt shingle roof - Douglas Fir roof framing - Assumed 5/16 diameter lag bolts are used How long do they need to be? Allowable withdrawal loads for lag screws in seasoned wood, pounds per inch of penetration of threaded part Source:

69 Calculating Uplift Forces Simple Example Lag Bolt Calculation - Minimum length of thread on a lag bolt that needs to penetrate the wood 480 lbs 274 lbs/inch = 1.75 inches - Assume combined thickness of mounting bracket, shingles, and roof membrane is ¾ inches; Minimum Lag Bolt Length = = 2.75 inches Also see: - Mounting and Mechanical Design NABCEP Study Guide V4.2 - Pitched-Roof PV Mounting SolarPro 3.2

70 Confirming the Strength of Residential Roof Structures for Solar Installations Sandia National Laboratories (Sandia) conducted a first-of-its-kind study to stress wood rooftop structures to failure. The research team used a series of tests to collect actual rooftop load capacity data and compare it to the perceived load-carrying capacity in building codes. Study results demonstrate that conservatism in the existing building code and the engineering analysis methodology significantly underestimates the actual loadcarrying capacity of residential roof structures. For all sample configurations evaluated, empirical testing revealed a greater ultimate capacity than the prescribed allowable capacity. On average, rafter based tests demonstrated a 330% excess load-bearing capacity, as compared to values computed in the National Design Standard, while composite action increased strength by as much as 74%.

71 Confirming the Strength of Residential Roof Structures for Solar Installations Empirically Derived Strength of Residential Roof Structures for Solar Installations SANDIA REPORT SAND Unlimited Release Printed December 2014 Structural Code Considerations for Solar Rooftop Installations SANDIA REPORT SAND Unlimited Release Printed December 2014 Reducing Soft Costs of Rooftop Solar Installations by Demonstrating Structural Strength (Summary)

72 Are structural engineering analyses a requirement for PV permits in your area? Are they required even on newer construction? Do you ever wonder whether this step is really necessary? The rooftop solar PV permitting process varies greatly, even between neighboring cities. Inconsistencies between jurisdictions can cause difficulties for solar installers who work across boundaries, adding sizable permitting costs and delays that may not be required in neighboring jurisdictions. To address this issue, Sandia National Laboratories conducted a series of tests funded by the U.S. Department of Energy's SunShot Initiative to evaluate the structural behavior of common residential roof structures. The effort involved a wide range of destructive tests on numerous scaled wood structures to produce and capture data on actual rooftop load capacity.

73 Proposed Inspection Guidelines Solar PV system inspection should include a checklist covering the following at a minimum: PV Arrays (Mechanical Attachment, Grounding, Conductors; Standards) Inverters - Grid-tied and Stand-alone (Standards) Overcurrent Protection (breakers / fuses) Electrical Connections Disconnects Charge Controllers & Batteries (if applicable) Grounding Conductors The above should be NEC compliant and meet any other required standard, such as IEEE, PJM and building codes

74 Inspection Issues COMPLY WITH National Electric Code (NEC) Tie up all wires onto PV array racks and/or frames, particularly on roof installations Use the proper type wire and wire size throughout the PV installation Always include a DC disconnect and AC disconnect in close proximity of the inverter In addition to grounding everything, include a direct ground between the inverter (grounding bar or terminal) and the grounding bar in the main service panel Use insulated bushings to protect wires when using metal fittings Properly ground metal conduit if it carries wire with a voltage 250 volts or higher Do not wire more than two PV strings of modules in parallel without including a properly sized fuse Properly label and mark all components; including NEC labeling for DC and AC disconnects

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80 Inspection Issues DC Fused Disconnect Fuses Must Be DC Rated AND With the Proper Voltage Limit (these are incorrect fuses since they are only rated at 125 VDC for a PV system over 300 VDC)

81 Inspection Issues Lower Rail Positioned Too High Underneath Modules: No More Than 25% of Module Should Overhang Over Rail

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83 Inspection Issues Grounding Bushing Required When Voltage is Above 250 and Metal Conduit is Attached to the Larger Knockout, Which Could Break Away From the Box (the metal conduit would then not be grounded).

84 Inspection Issues