Health & Safety Issues Associated with Solar Photovoltaic (PV)

Transcription

1 Health & Safety Issues Associated with Solar Photovoltaic (PV) Presented To: Presented By: MOEMA ASM Michigan Occupational Health Conference Detroit, MI October 18, 2014 Thomas W. Neelands, CEM Sr. Project Manager NOVA Consultants, Inc. NOVA Consultants, Inc Novi Road, Suite 300 Novi, Michigan (248) FAX (248) Professional Engineering, Environmental, and Energy Services 1

2 Purpose To provide a basic understanding and means to mitigate worker health and safety risks associated with commercial solar photovoltaic (PV) arrays. Note: The benefits of solar photovoltaic (PV) outweigh the barriers. Solar PV installations are highly reliable, they require little maintenance, there is minimal operating cost, and they are a sustainable source of safe, reliable, and environmentally clean power. 2

3 Solar PV Growth 3

4 Major Components and Operations DC Source Circuit DC Output Circuit AC Power AC Power Racking PV Solar Modules Combiner Boxes Inverter(s) AC Service Disconnect Meter Common components of PV solar arrays: Racking supports the PV modules and wireways Solar PV modules combined in series to increase the DC voltage Combiner boxes parallel DC source circuits to increase current Inverter parallel DC output circuits to increase current and convert to AC power AC disconnect isolates the inverter & solar array from the facility / utility grid. CT cabinet and generation meter monitors AC power generation Utility grid or facility substation distributes AC power 4

5 Common Types of PV Solar Arrays Ground Mount - Fixed Ground Mount Fixed Ballast Ground Mount - Trackers Carport 5

6 Common Types of PV Solar Arrays Residential - Roof Commercial - Roof Integrated Roof Shingles 6

7 Health & Safety Risks DC Source Circuit DC Output Circuit AC Power AC Power Racking PV Solar Modules Combiner Boxes Inverter(s) AC Service Disconnect Meter PV solar modules generate power when exposed to a light source Broken or cracked PV solar modules 12 to 13 modules make a DC source circuit that generates up to 550 VDC. Interrupted grounding systems 7

8 Health & Safety Risks DC Source Circuit DC Output Circuit AC Power AC Power Racking PV Solar Modules Combiner Boxes Inverter(s) AC Service Disconnect Meter Tripping hazards terrain and conduit runs Power available from either direction solar array (load side of AC disconnect) and utility grid (line side of AC disconnects) Solar PV systems on roof tops access and potential arcing Back-feed from DC strings due to common bus Emergency response to catastrophic failure - fire 8

9 Safe by Design - Roof Top Array Layout Minimum 6 ft. to edge of roof Straight and sufficient number of walkways Clear access to heat and smoke vents; HVAC units, substations, skylights, and other roof devices 9

10 Roof Top Array Wire Management Fire hazards associated with arcing type faults of DC circuits. Mitigate: Ensure good wire management design and installation. Ensure proper system grounding Utilize Arc-Fault Circuit protection 10

11 Safe by Design Wire Management NEC 2011 Code: Arc-Fault Circuit Protection (Direct Current) To mitigate fire initiation hazards associated with arcing type faults occurring in dc source circuits and dc output circuits, NEC requires arc-fault circuit protection for PV systems. Good wire management. Good wire management. Arc-Fault Detecting Combiner Box 11

12 Safe by Design Wire Management NEC 2011 Code: (E)(1) DC Circuits Beneath Roofs Wiring methods shall not be installed within 10 of the roof decking or sheathing except where directly below the roof surface covered by PV modules and associated equipment. The 10 requirement is to prevent accidental damage from saws used by fire fighters for roof ventilation during a structure fire. 12

13 Trained Personnel - DC Power Backfeed (Look both ways) Red = Energized Module to Combiner Box Multiple fused DC Strings to a common bus bar in the CB Combiner Box w/ Disc Combiner Box to Inverter Fused DC homerun from each CB to the inverter Inverter Equipped with a common bus bar Module Row A DC Source Fuse DC Output Module Row B Fuse AC Power Module Row C 13

14 Example DC Power Backfeed (Look both ways) Red = Energized Module to Combiner Box Multiple fused DC Strings to a common bus bar in the CB Combiner Box w/ Disc Combiner Box to Inverter Fused DC homerun from each CB to the inverter Inverter Equipped with a common bus bar Module Row A DC Source Fuse Open CB Disc DC Output Module Row B Fuse AC Power Module Row C 14

15 Example DC Power Backfeed (Look both ways) Red = Energized Module to Combiner Box Multiple fused DC Strings to a common bus bar in the CB Combiner Box w/ Disc Combiner Box to Inverter Fused DC homerun from each CB to the inverter Inverter Equipped with a common bus bar Module Row A DC Source Fuse Open CB Disc DC Output Module Row B Fuse Shutdown Inverter and OPEN DC and AC disconnect AC Power Module Row C 15

16 Example DC Power Backfeed (Look both ways) Red = Energized Module to Combiner Box Multiple fused DC Strings to a common bus bar in the CB Combiner Box w/ Disc Combiner Box to Inverter Fused DC homerun from each CB to the inverter Inverter Equipped with a common bus bar Module Row A DC Source Fuse Open CB Disc DC Output Module Row B Open CB Disc Fuse Shutdown Inverter and OPEN DC and AC disconnect AC Power Module Row C Open CB Disc 16

17 Safe by Training Catastrophic Failure During a fire the PV array can quickly degrade exposing hazardous chemicals to direct flame and become dissipated in the smoke. 17

18 Inhalation Hazards Due to Fire Boron No heath effects to humans or the environment Cadmium Telluride A known carcinogen, the primary route of exposure is inhalation Gallium Arsenide The heath effects have not been studied, it is considered highly toxic and carcinogenic Phosphorus The fumes are considered highly toxic. 18

19 Recommended Practice Fire fighters to wear Self-Contained Breathing Apparatus (SCBA) and full protective clothing 19

20 Mitigating Health & Safety Risks Strategy Safe by Design Design for safety Follow standards and regulations Design for : Safe construction Safe oper. & maintenance Safe emergency response Qualified Contractor Common Construction Utilize Site Safety Plan Provide contractor safety aware Utilize a construction plan Review the design w/ foreman Robust commissioning process Start-up and test Common Design Process Defined scope Standards NFPA 70 Structural analysis Quality Checks Design reviews Construction plan Common Start-up Safe project execution Approved final inspections Safe system start-up Safe system operation Safe system maintenance 20

21 Mitigating Health and Safety Issues Common Design - Quality Checks Perform structural analysis. Assess roof structure Perform geotechnical analysis Design structures for wind and snow loads Ensure proper wire ampacity and fuse sizes, taking into considerations module type, DC circuit configuration, potential cold temperature Ensure all metallic parts are grounded properly Design wireway / conduit runs and ground cover to avoid trip hazards 21

22 Mitigating Health and Safety Issues Common Design - Quality Checks Design wireways to properly support DC circuits and connectors and avoid contact with the roof or metallic frames to avoid damaging the insulation. Design roof arrays - Ensuring safe roof access Provide safe clearance from roof s edge Provide straight walkways / aisles Ensure safe space around heat and smoke vents and sky lights Ensure assess to all roof devices requiring O&M Utilize arc fault detecting devices for roof mounts and/or when DC circuits enter a building. Review design with safety minded professional 22

23 Mitigating Health and Safety Issues Common Construction Practices Communicate the site safety plan, with project specific requirements Personal Protective Equipment (PPE) Right tool for the task Right equipment for the task DC electrical refresher training Site specific requirements roof clearance, confined space, other Execute a construction plan Sequence of installation ground wire before DC circuits On-going documented quality checks, ensuring compliance with the design and specifications. Work as though all wires and connections are energized 23

24 Mitigating Health and Safety Issues Common Construction Practices Execute and document detailed commissioning of the system DC string voltage and polarity Grounding conductivity Inverter start-up and anti-island test Current test on DC circuits Infrared scanned image of modules, connectors, combiner boxes, etc Provide continuous safety awareness, especially DC power safety 24

25 Safe by Design or Not? 25

26 Safe by Construction Plan or Not? 26

27 Safe by O&M Plan or Not? 27

28 Conclusion Use a competent firm to design, procure, and construct solar PV arrays. Authorities Having Jurisdiction need a common process for permitting new, green technology; including ordinances, permit process, and trained inspectors to help ensure safe installations. Electricians should have refresher safety training of DC power Ground maintenance personnel need safety awareness training of solar PV systems. Fire departments need emergency response process to isolate solar PV systems and the understanding of potential chemical releases. 28

29 Conclusion The benefits of solar PV outweigh the barriers, as illustrated by the increased growth of solar PV installations. Thank you. Contact Information: Tom Neelands NOVA Consultants, Inc Novi Rd. Suite 300 Novi, MI (248)