a.u.c. 351 august 19, 2011 photovoltaic (solar panel ... · of photovoltaic electric systems is...

A.U.C. 351 August 19, 2011

PHOTOVOLTAIC (SOLAR PANEL) ELECTRICAL SYSTEMS

1

1. INTRODUCTION

1.1 Prompted by environmental concerns and the rising costs of fuel and electricity, the use of photovoltaic electric systems is becoming more prevalent throughout the City of New York, as well as the rest of the nation. Many experts in the field of solar photovoltaic (PV) electric systems agree there are many dangers that firefighters are exposed to when encountering these installations during fire operations.

2. INFORMATION

2.1 Both residential and commercial solar photovoltaic systems operate on the same principle and both pose similar dangers, the greatest hazard of which is direct current (DC) shock. The residential system generally is smaller and may contain fewer safety features than the larger commercial system.

2.2 Most photovoltaics are made primarily of silicon, the second most abundant element in the earth’s crust, and the same semiconductor material used for computers. Silicon materials (monocrystalline silicon, polycrystalline silicon, microcrystalline silicon, and amorphous silicon) as well as “thin-film” semiconductors (cadmium telluride, gallium-arsenide, and copper indium diselenide) used in this technology exhibit a property known as the “photoelectric effect” that causes them to absorb photons of light and release electrons. These electrons are then harnessed and an electric current results that can be used as electricity. PV systems can still produce electricity on cloudy days, but not as much as they do on sunny days. PV systems do not produce electricity at night.

2.3 The basic PV or solar cell produces only a small amount of power (1-2 watts). To produce more power, solar cells (about 40) can be interconnected to form modules (panels). PV modules range in output from 10 to 300 watts. If more power is needed, several modules can be installed to form a PV array. About 20 to 30 PV modules typically will provide enough power for a household.

3. PHOTOVOLTAIC COMPONENTS

3.1 Cell (Figure 1)

The photovoltaic cell is the device that converts the sun’s light energy into electricity by means of the photovoltaic effect. The cells convert solar energy into direct current electricity. They are typically 12-20% efficient. It is the fundamental component of a PV energy system.

AUC 351 August 19, 2011 PHOTOVOLTAIC ELECTRICAL SYSTEMS

2

3.2 Module (Figure 1)

A module (solar panel) is an interconnected assembly of photovoltaic cells. The cells are arranged in a grid-like pattern on the surface of the module. Most modules are rigid, but there are some that are flexible composed of “thin-film” cells. A typical PV module consists of a protective weatherproof enclosure for the cells and electric wiring needed to connect the module with the rest of the system. Sealed junction (combiner) boxes containing fuses or circuit breakers protect the connections.

3.3 Array (Figure 1)

The modules in a PV array are normally first connected in series to obtain the correct voltage for the system (residential system outputs of 600 volts are common); individual leads are then connected in parallel to allow the system to add more current (amperage). Photovoltaic arrays are typically measured by the peak electrical power they produce, in watts, kilowatts, or megawatts. Most PV arrays use an inverter to convert the DC power produced into alternating current (AC) that can tie into existing infrastructure to power lights and other electrical loads.

4. PHOTOVOLTAIC SYSTEMS

4.1 Stand-alone (Off-grid) (Figure 2)

Stand-alone PV systems operate independent of the utility grid. These type systems are comprised of PV arrays, a charge controller and storage batteries to supply power to DC loads. If the system has to supply AC power, an inverter is required. Many stand-alone inverters also incorporate charge controllers that energize and regulate battery output as well as control the input from the PV array. Storage batteries (Figure 3) are needed due to the intermittent nature of sunshine. The batteries store some of the electricity generated by the PV panels, so that when sunshine is insufficient or at night, the system can still supply power. The system can also be enhanced by a diesel generator or wind turbine to supply peak demands. Stand-alone systems generally provide 12 or 24 volts DC. An inverter will convert this voltage to 220 volts AC.

4.2 On-grid (Figure 4)

On-grid connected systems utilize grid-tie inverters that are integrated with the public utility. These type inverters synchronize the solar energy from the photovoltaic array that it converts from DC to AC to the primary electrical panel of the building. The power may then be used by loads within the building or it may flow out to the utility. Grid-tie inverters can feed energy back into the distribution network because they contain special circuitry to precisely match the voltage and frequency of the public distribution system. For safety reasons, grid-tie inverters should shut off automatically and cease operation during a blackout situation to eliminate the hazard of back-feeding into a fault and creating a hazardous condition for utility workers coming into contact with electric lines while working to restore power in an emergency. Batteries may also be used for these type systems to store power where the consumer wants to have electricity in the event of a blackout.


3

5. ROOF INSTALLATIONS

5.1 Stand-mounted (Figure 5)

Stand-mounts are bulky and constructed with a grid-like system of supports (aluminum or steel) that are affixed directly to roof joists using metal hardware. Non-penetrating ballast (concrete block) trays are an alternative stand-mount option. Stand-mounted equipment is also known as a universal mounting because it can be installed both on rooftops as well as on the ground. Stand-mount systems atop roofs must be installed to withstand wind loads. They are typically used with larger solar panel systems.

5.2 Flush-mounted (Figure 6)

Flush-mounted PV arrays are achieved by placing a metal end bracket on each side of the module and elevating it just several inches from the surface to allow for cooling air circulation. The bracket is then attached to the roof. They are commonly used with small solar arrays and on peaked roofs because the structural design cannot support large ones.

5.3 Integrated design (Figure 7 & 7A)

Integrated PV arrays serve as a structural element (roof, wall, canopy or skylight). It thereby reduces concentrations of added weight and avoids penetrations required for mountings and wiring. It also reduces the vulnerability of the equipment to high winds. The photovoltaic shingle, made to look like conventional asphalt shingles, is one such technology. The development of “thin-film” photovoltaics has also led to the increased use of integrated design. Integrated, as well as flush-mounted arrays, may be difficult or impossible to detect during nighttime hours.

6. OPERATIONS

6.1 Incidents involving PV systems will require firefighters to make adjustments similar to those made with other types of electrical equipment. When a PV array covers a large portion of the roof it leaves little room for members to maneuver and operate. Firefighters must avoid walking on modules since this can expose them to electric shock. Additionally, firefighters must never cut any wires associated with a PV array. Energized PV components submerged on a roof retaining water is yet another potential life-threatening shock hazard. If feasible, tactical operations should be performed away from all PV components. Shutting off power at the main electrical panel, does not ensure that all power to the building has been removed. This holds true for opening PV disconnect (isolation) switches which can be located: on the roof, next to the main electrical panel, adjacent to the inverter, nearby the charge controller, in the battery bank area, and outside the building.

When exposed to sunlight, PV arrays will continue to generate electricity and energize conduit and components up to the inverter. The use of rooftop disconnects should not be relied upon since they are mainly installed in order to perform maintenance on the system. Shut-off electrical power to the inverter to ensure power does not enter the building from the PV array conduit, batteries, or back-up generator. Be aware that inverters do have capacitors which store energy.

Rev. 09/17/19


4

The energy within the capacitors, however, will discharge soon after the power to the inverter is disconnected. An additional electrical shock hazard exists for PV systems that have battery back-up power. Batteries maintain electric current day or night regardless of system isolation efforts. (Figure 8)

6.2 Once installed, there is no easy way to remove PV modules, and doing so would be extremely dangerous. Additionally, PV system conduit on the roof contains energized wiring posing a serious shock hazard to firefighters performing vertical ventilation. At fires, the restriction of ventilation will result in a more punishing interior operation. The opening/removal of skylights and scuttles as well as horizontal ventilation should be the prime focus of ladder company operations. All ventilation must be coordinated by members both inside and outside the building in order to avoid the dangers of backdraft and flashover.

6.3 Firefighters discovering PV arrays at fires and emergencies should immediately notify their Company Officer and the IC for subsequent relay to all operating members. They should also inform the IC if the PV system is involved in fire and if it is going to negatively impact vertical ventilation operations.

For top floor/cockloft fires in non-fireproof buildings where fire is beneath the PV array, roof venting operations, including the use power saws, may not be possible. Cutting the roof must be limited to areas that are clear of PV arrays and other components, while constantly evaluating whether the venting operation will pull the fire into uninvolved areas of the building. Ladder company efforts inside the building should be directed toward opening ceilings to define the boundaries of the fire. Care must be taken to avoid compromising PV conduit and components inside attic, cockloft and wall spaces with hand tools. PV system conduit and wiring can also be installed in closets and garages. Ventilation fans can facilitate smoke and heat removal from the top floor once the fire has been extinguished. The Incident Commander (IC) should delay overhaul until there is confirmation that that the PV system has been shutdown.

6.4 Using water on energized PV system components is a decision that should only be made by the IC after careful size-up. If decided upon to use water as an extinguishing agent, Engine company officers should position hoselines to cut off fire extension and push the fire back toward the main fire area. Hose streams should not be applied directly onto energized PV system components. A fog nozzle, utilized from a distance, and set at a 30 degree spray pattern is recommended to prevent electric current from travelling upstream towards members operating hoselines. Straight steams or foam should not be used since they are excellent conductors.

6.5 When the weight of the PV array is placed directly on the roof beams, another concern should be the added load. Under heavy fire conditions where exposed roof beams lose their strength, early roof collapse should be anticipated. Depending upon the mounting option selected, size of array, and type of materials used, photovoltaic systems can add thousands of pounds to the roof surface. Additionally, flush-mounted arrays may be subjected to both uplift and down-force wind loadings.


5

6.6 Fires involving PV systems should be extinguished with the same care as any other type of electrical equipment. De-energize all of the PV components along with any other utility supplied electrical power serving the building. Members should wear full PPE, and utilize the appropriate extinguishing method commensurate with the size and magnitude of the fire. It may prove difficult or dangerous to attempt to remove all burning or smoldering materials from under or around PV modules without subjecting members to electrical shock. The removal of modules by firefighters is NOT an option. The utility company and the licensed solar power installer/electrician (if contact information is available) should be requested to respond through the dispatcher. Incipient fires can be extinguished using Class C (dry chemical) portable fire extinguishers. Advanced fires, may dictate the limited use of water in a fog pattern from a safe distance. Avoid standing in areas where pooling water is located.

6.7 During normal charging operations, batteries emit both hydrogen and hydrogen sulfide gas which are both highly flammable. Spark producing equipment could cause an explosion should an explosive atmosphere exist. Spilled electrolyte (sulfuric acid) from lead acid batteries will release toxic fumes during evaporation. Sulfuric acid is not inherently flammable but it can cause and support a fire by reacting with other chemicals and liberating enough heat to ignite ordinary combustibles. The release of oxygen by sulfuric acid can also feed a fire. Sulfuric acid will dissolve many metals, releasing flammable hydrogen. Heat generated during this chemical reaction can ignite the hydrogen, creating an explosive environment.

Lithium ion batteries contain flammable liquid electrolyte that may vent and ignite when subjected to mechanical damage or high temperatures. Lithium batteries may burn rapidly and ignite nearby combustibles. Batteries involved in fire generate explosive, flammable, toxic and corrosive gases. Full PPE and respiratory protection is mandatory. The use of dry chemical or foam extinguishing agents has proven to be effective on battery fires. The IC may have to suspend interior operations to test for hazardous conditions. Special calling to the scene SOC companies with specific protective clothing and monitoring equipment may be required to safely help mitigate the operation.

7. SAFETY AND HEALTH CONCERNS

PV panels produce DC power. If sunlight strikes them, they will produce electricity.Unless there is a disconnect switch on the PV array itself, the wires running from thearray to the power distribution system should always be considered live.

Even though the electrical power from the utility grid can be disconnected at the maindistribution panel, electrical energy is still present as long as the PV array is connected.

All PV modules are not alike. Different modules will produce different levels of voltage.

Utilizing disconnects ahead of or after the inverter still does not eliminate the electriccurrent coming from the PV array.

Combiner boxes should not be opened by firefighters in an attempt to shutdown the PV array.

The amount of sunlight that photovoltaic arrays are exposed to directly influences theirpower output. Time of year, time of day, and climatic conditions all affect the amountelectrical energy being produced.


6

PV systems do not produce electricity at night. However, lightning flashes occurring atnight can energize the PV System.

Beware of redundant power (battery, generator, wind turbine, etc.) equipment installed to“kick-in” when the photovoltaic arrays are isolated and are not producing electrical energy.

Don’t attempt to breach PV arrays with hand or power tools. A firefighter cutting into aphotovoltaic array can be electrocuted.

Top floor and attic fire and overhaul operations must be supervised and controlled toavoid breaching through roofing material and penetrating PV modules.

Auxiliary lighting equipment and apparatus headlights are not powerful enough togenerate dangerous voltage from a PV array.

Battery banks store solar-generated electricity. Avoid disconnecting or cutting the wiresthat connect the batteries to each other or to the system in an attempt to disable thembecause of the arcing that could occur. Metal tools should be kept away from batteryterminals. Even with the PV system disconnected from the batteries, the batteriesthemselves still have the potential for electrical shock.

Firefighting and emergency operations at roof level can accidentally cause damage to PVequipment and wiring under the best of conditions. This situation can create hiddenelectrical shock hazards to unsuspecting members.

All members who operate on the roof must be aware of the increased tripping and fallhazard. Additionally, PV modules are slippery when wet. Firefighters under dark andsmoky conditions may be unable to see them.

Photovoltaic systems with its combination of plastics, metals, fiberglass, and chemicalswhich degrade during a fire are a legitimate health concern. The products of combustionof these materials are emitted into the atmosphere. Firefighters should wear full PPEincluding SCBA.

PV systems contain metal framing and stands, brackets, anchor bolts, nuts, cables, wires,junction boxes, etc. Many of these exposed components have sharp edges that can injurefirefighters.

If a PV system is compromised, arcing could occur and cause burn injuries.

PV signage/labels required by codes denoting components may be missing or removeddue to negligence or vandalism.

On buildings with sloped roofs, PV arrays will generally be installed on the South andWest facing sides.

The ability of PV arrays to trap snow and debris will add more weight to the roof. This inconjunction with the PV system’s inherent dead load will increase the possibility of roofcollapse.

Members on the roof must avoid positioning themselves between PV arrays and escaperoutes. Emergency egress points should be determined early.

A Safety Officer should be assigned to the roof to oversee operations when firefightersare working in close proximity to a PV system.


7

8. ADDITIONAL CONSIDERATIONS

8.1 Strategy and tactics must be flexible due to the presence of PV systems and the inability of firefighters to de-energize all of the electrical equipment. The possibility, during daytime hours, of energized conductors within conduit is always present. Therefore, it is extremely important for firefighters to locate all electrical conduits leading away from PV arrays prior to performing such tasks as extinguishment, ventilation, and overhaul.

8.2 When electrical shutdown is required, request the response of the appropriate utility company for their expertise and to enhance the overall safety of the operation. Also, consider calling the PV installers, whose contact number information is often found on key component equipment.

8.3 Company officers on BISP or other outside activities finding a hazardous condition relative to a PV system installation that is imminently perilous to members or occupants due to size, location, arrangement, defects, or lack of maintenance should be instructed to request the response of the administrative Battalion Chief. If warranted after an examination, the Chief should notify the dispatcher to have a Department of Buildings representative respond.

8.4 Buildings with PV systems necessitate that they be entered into CIDS. Transmitted Data should include but not limited to the following:

PV ARRAY ON ROOF

LIMITED ROOF OPERATIONS

PV DISCONNECTS LOCATED AT

BATTERY STORAGE SYSTEM LOCATED AT

BACKUP GENERATOR LOCATED AT

INSTALLER CONTACT NUMBER

9. SUMMARY

9.1 All electrical features of a PV array should be treated as energized. Photovoltaics are not like conventional electrical equipment. They do not “turn off” by the flip of a switch. PV system voltage, even at low amperages, is extremely dangerous. Breaking a PV module or compromising wiring leading from the array to an inverter can expose members to an electrical shock. When operating at buildings with PV systems, members should follow standard operating procedures with awareness of potential exposure to live electrical components. This knowledge must guide strategy and tactics to ensure a safe and successful operation.


8

Figure 1 Photovoltaic components

Figure 2 Stand-alone (Off-grid)


9

Figure 3 Storage batteries

Figure 4 On-grid connected system


10

Figure 5 Stand-mounted flat roof PV array

Figure 6 Flush-mounted peaked roof PV array


11

Figure 7 Integrated wall PV design

Figure 7A Flat roof PV design

PV array

Rev. 09/17/19


12

Figure 8

Combiner Box

DC Shut-off

Inverter

AC Shut-off

Rev. 09/17/19

a.u.c. 351 august 19, 2011 photovoltaic (solar panel ... · of photovoltaic electric systems is...

Documents