J.29 6980_37 Maintenance of Solar Photovoltaic System.pdf

Distribution: IS0A (Web Release Only) Initiated By: AJW-223/17X

This Maintenance Technical Handbook (MTHB) provides the necessary guidance to be used in conjunction with information available in manufacturer’s technical reference books and other handbooks, for the proper maintenance of the Solar Photovoltaic System (SVS). It also provides information on special methods and techniques that will enable maintenance personnel to achieve optimum performance from the equipment.

This document requires actions by the Airway Transportation System Specialist (ATSS) at operational facilities with Facility, Service, and Equipment Profile (FSEP) equipment: CLEAN (Web Release Only).

Field offices must keep accurate FSEP records, per Order 6000.5E, Facility, Service, and Equipment Profile (FSEP) and address information for distribution of directives. To update FSEP, utilize your FSEP contact available at this link:

https://employees.faa.gov/org/linebusiness/ato/operations/technical_operations/ajw1/ajw1b/fsep/.

To update addresses, utilize your Regional Name and Address Coordinator contact available at this link:

https://ksn2.faa.gov/arc/aml/Home/lcssportal/LCSSPortalDocuments/NameAndAddressPOCList.pdf

FAA Technical Performance Record (TPR) Workbooks will be provided by automated TPR or eTPR based on FSEP records to record required system parameters directly into the National Logging Network (NLN). For DoD sites TPR forms may be electronically downloaded at https://www.adx.faa.gov/portal/group/non-dod/tprs to record system parameters.

The National Periodic Maintenance/Certification Scheduling (PMS) database is maintained by the Office of Primary Responsibility (OPR). The release of this document notifies the field of an update to the Remote Monitoring and Logging System (RMLS) National PMS database. An RMLS Task Glossary Report will be available on the Technical Library with this MTHB under associated files for cross referencing the Task Number to the Chapter 4 paragraph in approximately five working days after release of this MTHB.

Users are encouraged to submit recommendations for improvements to 9-AMC-AJW141TechDocServices@faa.gov.

James D. Linney Director, Operations Support

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL AVIATION ADMINISTRATION

Air Traffic Organization Policy

ORDER

JO 6980.37

Effective Date:

01/12/2021

Implementation Date:

07/15/2021

SUBJ: Maintenance of Solar Photovoltaic System https://employees.faa.gov/org/linebusiness/ato/operations/technical_operations/ajw1/ajw1b/fsep/ https://ksn2.faa.gov/arc/aml/Home/lcssportal/LCSSPortalDocuments/NameAndAddressPOCList.pdf https://www.adx.faa.gov/portal/group/non-dod/tprs mailto:9-AMC-AJW141TechDocServices@faa.gov

RECORD OF CHANGES DOCUMENT NO. Order JO 6980.37

CHANGE TO

BASIC

SUPPLEMENTS

OPTIONAL CHANGE TO

BASIC

SUPPLEMENTS

OPTIONAL

MM DD YY MM DD YY

An electronic copy of the current Record of Changes (ROC) is available for download and print at https://nas.amc.faa.gov/phoenix/views/technicalDocument.xhtml?view=roc&num=6980.37&pre=H

FAA Form 6000-25 (10/12) Electronic Adobe Version https://nas.amc.faa.gov/phoenix/views/technicalDocument.xhtml?view=roc&num=6980.37&pre=H

01/12/2021 JO 6980.37

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Table of Contents Paragraph Page

Purpose ........................................................................................................................1-1 Audience ......................................................................................................................1-1 Where Can I Find This Order? ......................................................................................1-1 Cancellation .................................................................................................................1-1 Explanation of Policy Changes .....................................................................................1-1 Certification ..................................................................................................................1-2 Aircraft Accidents .........................................................................................................1-2 Maintenance Procedure ...............................................................................................1-2 Risks ............................................................................................................................1-2 Implementation Date ....................................................................................................1-3 Related Publications .....................................................................................................1-3

Purpose or Function .....................................................................................................2-1 Description ...................................................................................................................2-1 Theory ..........................................................................................................................2-3

2-4. Types of PV Panels ......................................................................................................2-4 2-5. Panel Mounting ............................................................................................................2-4 2-6. Solar Cell Efficiency ......................................................................................................2-5

Grounding ....................................................................................................................2-5 Grounding and Lightning Protection .............................................................................2-6 Grounding is Required by the National Electrical Code® (NEC) ...................................2-6 PV Array Wiring ............................................................................................................2-6 Effects of System Design on Panel Efficiency ...............................................................2-7 Blocking and By-Pass Diodes in Solar Panels ..............................................................2-7 Basic Requirements for a Solar System .......................................................................2-8 Solar Charge Controllers ............................................................................................ 2-10

3-1. General ........................................................................................................................3-1 Section 1. Photovoltaic System (Generic)

3-2. Photovoltaic Array Components. ..................................................................................3-1 3-3. Inverter DC to AC volts. ................................................................................................3-1 3-4. Tracker (if used to generate 5% more electricity) ..........................................................3-2 3-5. PV System Power Output .............................................................................................3-2 3-6. Charge Controller (if used) ...........................................................................................3-2 3-7. Battery (deep cycle) 12V Charge controller Setting ......................................................3-2 3-8. System Efficiency .........................................................................................................3-3 iv

Table of Contents (Continued) Paragraph Page

General ....................................................................................................................... 4-1 FAA Form 6000 Series and eTPR Workbooks ..............................................................4-1

Section 1. Performance Checks

Section 2. Other Maintenance Tasks

Section 3. Condition Based Maintenance Tasks 4-6. As Required..................................................................................................................4-4

General ....................................................................................................................... 5-1 General Remote Maintenance Monitoring (RMM) .........................................................5-1

Section 1. Performance Checks 5-3. Perform visual inspection..............................................................................................5-1

Tighten all loose nuts and bolts ....................................................................................5-1 Check connections .......................................................................................................5-1 Check shading of the solar array ..................................................................................5-1 Inspect Combination Box(es) ........................................................................................5-2 Disconnect switches .....................................................................................................5-2 Check the Inverter ........................................................................................................5-2 Take the following precautions before doing performance checks ................................5-2 Checking Voltage and Current Levels ..........................................................................5-3

Section 2. Other Maintenance Tasks 5-12. Testing the Charge Controller and Inverter ...................................................................5-4

Section 3. Special Maintenance Procedures Visiting Sites with Photovoltaic Arrays ..........................................................................5-5

5-14. Cleaning the Solar Array(s) ..........................................................................................5-5 Checking for Infestations ..............................................................................................5-5 Electrical System Checks .............................................................................................5-5 Solar Inverter and Charge Controller Checks ...............................................................5-5 Check All Labels and Their Locations for Correctness ..................................................5-5 thru 5.30. Reserved ......................................................................................................5-5

Section 4. Troubleshooting Procedures

System Troubleshooting ...............................................................................................5-5 v

Table of Contents (Continued) Paragraph Page

Solar Energy Facts .......................................................................................................6-1 Photovoltaic Panel Rating.............................................................................................6-1

6-3. How to calculate the annual solar energy output of a photovoltaic system ....................6-2 Factors Influencing Insolation .......................................................................................6-2 Conditions that influence how much solar energy a particular site gets during the day .6-3

6-6. Maximum Power Point (MPP) and Rated Power of Solar (PV) Panel ...........................6-5 Standard Test Conditions (STC) for Specifying Solar Panel .........................................6-6 Normal Operating Cell Temperature (NOCT) Ratings ...................................................6-6 Solar Panel Output Specifications I-V Curve.................................................................6-6 Solar / PV Cell I-V Curve ..............................................................................................6-6 Solar Panel I-V Characteristic Curves for Series and Parallel Connections ..................6-8 SolarEdge P300 Power Optimizer ................................................................................6-8 Solar Power Panel Array Performance Parameters, Definitions, and Graphs ...............6-9 PV System Electrical Design Common Problem Areas ............................................... 6-10 Required Information for Permit .................................................................................. 6-10 Site Diagram............................................................................................................... 6-10 National Electrical Code (NEC) .................................................................................. 6-10 Electrical System Grounding ...................................................................................... 6-11 Sun Trackers .............................................................................................................. 6-11 vi

List of Illustrations

Figure Page

Figure 2-1. Basic Diagram of a Solar Photovoltaic System...................................................... 2-1 Figure 2-2. Construction of a Typical Solar Cell ...................................................................... 2-3 Figure 2-3. Solar Cells and Modules in a Solar Panel ............................................................. 2-3 Figure 2-4. Battery Charged by Two Solar Panels .................................................................. 2-8 Figure 2-5. A Simple Solar System ......................................................................................... 2-8 Figure 2-6. Solar System with Controller ................................................................................. 2-9 Figure 2-7. Solar System with Controller and Inverter ............................................................. 2-9 Figure 2-8. Typical Grid Connected PV System with Battery Storage ................................... 2-10 Figure 5-1. Fluke 374 True-RMS AC/DC Clamp Meter and Extech SP505 Solar Power Meter, with Solar Wrenches and Unlocking Tool ............................................................. 5-3 Figure 6-1. Example of “Standard Sun” Irradiation on a Solar Photovoltaic Array .................... 6-1 Figure 6-2. Map of PV Solar Radiation .................................................................................... 6-3 Figure 6-3. Sunlight Hours per Day Zone Map ........................................................................ 6-3 Figure 6-4. Example of an I-V Curve and Rating of a 12V Solar Panel .................................... 6-5 Figure 6-5. Rated Output for Solar Panels at Different Light Intensities (W/m2) ...................... 6-6 Figure 6-6. SI-V Typical Silicon PV Cell Characteristics (Under Normal Conditions) .............. 6-7 Figure 6-7. Solar Panel I-V Characteristic Curves (Typical)..................................................... 6-8

List of Tables

Table Page

Table 6-1. System Sizing Based on Sun Hours ...................................................................... 6-4

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General Information and Requirements

Purpose. This Maintenance Technical Handbook (MTHB) provides guidance and prescribes technical standards, tolerances, and procedures applicable to the maintenance and inspection of Solar Photovoltaic Systems. It also provides information on special methods and techniques, which will enable maintenance personnel to achieve optimum performance from the equipment. This information augments information available in manufacturer’s Technical reference material, Technical Instruction Books (TIB), other MTHBs, and complements the latest edition of Order 6000.15, General Maintenance Handbook for National Airspace System (NAS) Facilities.

Audience. This MTHB requires actions by the Airway Transportation System Specialist (ATSS) at operational facilities with solar arrays and Facility, Service, and Equipment Profile (FSEP) equipment: CLEAN.

Where Can I Find This Order?

FAA Personnel. For electronic copies, FAA personnel can use one of the following websites to locate this order.

On the Technical Library website at:

https://nas.amc.faa.gov/phoenix/views/technicalLibrary.xhtml.

On the Directives website at:

https://employees.faa.gov/tools_resources/orders_notices/.

From the My FAA website, select “Tools and Resources” then select 'Orders and Notices'.

On the National Airspace Systems (NAS) Document Distribution Application (DDA) at https://nas.amc.faa.gov/nasdda/.

The ATSS and all administrative personnel must subscribe to the Auto- Notifications Services for electronic library release notifications at https://technet.faa.gov/. This document can be printed for local use as required.

Department of Defense (DoD).

All DoD customers must register for an Aeronautical Data Exchange (ADX) website account at https://www.adx.faa.gov. When registering, the user must request access to the NAS Engineering tab of the application. The FAA does not distribute hard copies to DoD customers. For problems accessing the ADX website contact 9-ACT-ADX-PM@faa.gov.

For DoD customers who have questions related to this Maintenance Handbook, contact Power Operations Engineering Team, Critical Power Distribution System (CPDS), at

(405) 954-4635.

Cancellation. Not applicable.

Explanation of Policy Changes. This MTHB implements Configuration Control Decision (CCD) No. N37603, Maintenance of Solar Photovoltaic System (SVS).

https://nas.amc.faa.gov/phoenix/views/technicalLibrary.xhtml https://employees.faa.gov/tools_resources/orders_notices/ https://nas.amc.faa.gov/nasdda/ https://technet.faa.gov/ https://www.adx.faa.gov/ mailto:9-ACT-ADX-PM@faa.gov

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Certification. Refer to Order 6000.15, for general guidance on the certification of systems, subsystems, and equipment. As stand-alone power systems, Solar Photovoltaic systems do not require certification.

Aircraft Accidents. When aircraft accidents or incidents occur, Air Traffic Organization (ATO) Technical Operations personnel are responsible, when requested by the Technical Operations Aircraft Accident Representative (TOAAR) through the appropriate control center, to evaluate and document the technical performance of the facilities which may have been involved (for some facilities, it may also be necessary to remove them from service, and to conduct flight inspections). This requires that facility operational data be obtained and recorded in the maintenance log or eTPR, if eTPR workbooks are available, and/or on a generic 6000-8, Technical Performance Record form where no eTPR workbooks are available. These records are official documents, and may be used by an aircraft accident investigation board in the determination of facility operational status at the time of the accident. Refer to the latest edition of Order 8020.16, Air Traffic Organization Aircraft Accident and Incident Notification, Investigation, and Reporting, for detailed guidance on requirements and activities following an aircraft accident/incident.

Maintenance Procedure.

Order 6000.15, this MTHB, the applicable equipment TIB, and other applicable handbooks are consulted and used together by the maintenance technician in all duties and activities for the maintenance of the Solar Photovoltaic System. These documents are collectively as the single official source of maintenance policy and direction authorized by Technical Operations Services. References located in the appropriate paragraphs of this handbook entitled Chapter 3, Standards and Tolerances, Chapter 4, Maintenance Requirements, and Chapter 5, Maintenance Procedures, indicate to the user whether this handbook and/or the equipment TIB must be consulted for a particular standard, key inspection element or performance parameter, performance check, maintenance task, or maintenance procedure.

Refer to Order 6000.15, for shutdown coordination and scheduling policy.

Risks.

Operational. In compliance with the latest edition of Order JO 6000.50, National Airspace System (NAS) Integrated Risk Management, specialists should assess local system configuration and maintenance actions using the information, instructions or procedures delivered with this MTHB for Operational Risk Management (ORM) to the NAS. No known operational risks were identified during the evaluation of the content of this MTHB.

Safety. In compliance with the latest editions of Orders 1100.161, Air Traffic Safety Oversight, and JO 1000.37, ATO Safety Management System, local safety assessment is required when conducting the maintenance and operations activities contained in this MTHB. A National Safety Risk Management (SRM) Report for this MTHB is available at https://nas.amc.faa.gov/phoenix/views/technicalDocument.xhtml?&file=6980_37_mthb_srmrpt.pdf.

http://nas.amc.faa.gov/phoenix/views/technicalDocument.xhtml?&file=6980_37_mthb_srmrpt.pdf

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Security. In compliance with the latest edition of Order 1370.121, FAA Information Security and Privacy Program and Policy, the FAA must ensure that security controls are implemented and commensurate with the risk and magnitude of the harm that would result from the loss, misuse, denial of service, unauthorized access, or modification of Federal information assets. No known security risks were identified during the evaluation of the content of this

MTHB.

Implementation Date. This MTHB must be implemented by 07/15/2021. All facilities nationwide must comply with these changes by the implementation date. The changes may be implemented any time after the effective date, but must be implemented by the implementation date. If the implementation date occurs during a completed task interval window, then follow the new guidance for the certification or maintenance task(s) at the next regularly scheduled interval.

Related Publications. The following related publications are referenced throughout this handbook.

Note: The nature of this directive requires reference to numerous publications.

To avoid frequent revision, for the purpose of changing references to the latest issue, personnel shall consider all references as the most recent edition.

Order 6000.5E, Facility, Service, and Equipment Profile (FSEP).

Order 6000.15, General Maintenance Handbook for National Airspace System (NAS) Facilities.

Order JO 6000.50, National Airspace System (NAS) Integrated Risk Management.

Order JO 1000.37, ATO Safety Management System.

Order 1100.161, Air Traffic Safety Oversight.

Order 1370.121, FAA Information Security and Privacy Program and Policy.

Order 3900.19, FAA Occupational Safety and Health.

Order JO 6950.22A, Maintenance of Electrical Power Cables.

Order JO 6980.25, Maintenance of Batteries for Standby Power.

Order 8020.16, Air Traffic Organization Aircraft Accident and Incident Notification, Investigation, and Reporting.

Article 690 of the National Electrical Code (NEC).

CCD No. N37603, Maintenance of Solar Photovoltaic System.

FAA-STD-019, Lightning and Surge Protection.

Various Equipment Manufacturers’ Commercial off the Shelf (COTS) Publications.

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Technical Characteristics

Purpose or Function. The Solar Photovoltaic (PV) system generates direct current (dc), free, clean, low maintenance, and environmentally friendly power which is available in two ways:

(1) Standby power to charge the battery string alone or in combination with DCBUS standby power; and 2) Grid connected power to reduce utility energy consumption. In National Airway System (NAS) remote sites with no electric grid power available, dc provides primary power.

Use of an Inverter converts dc power to alternating current (ac) power as needed. This maintenance technical handbook is limited to the non-grid application of Solar Power.

Description.

Basics of Solar Electricity. Figure 2-1 shows a basic solar PV system diagram. The sun shines on photovoltaic modules in an array that produces dc voltage and current. A charge controller regulates the voltage and current as it travels into batteries where it is stored for use when needed. DC appliances run off energy straight from the batteries. For ac appliances, an inverter converts dc power to ac power. AC energy is either consumed on site, or delivered back into the utility grid with a grid connection.

Figure 2-1. Basic Diagram of a Solar Photovoltaic System

PV Systems are classified based on their functional use, equipment configuration, and equipment connections with other power sources. Typically a system will be used either “utility inter-tied” (grid-tied), or “stand-alone” (off-grid). Off-grid systems typically have battery backup.

PV System Components. A PV system consists of the following components.

PV Array. A PV Array consists of PV modules, which are environmentally sealed collections of PV Cells that convert sunlight to electricity. The module size depends on number of PV cells used. A commonly used PV module with 72 cells, 300 watts, 72” X 39” size weighs about 50 lbs. A module with 60 cells, 250 watts, 64.5” X 39” weighs about 40 lbs. Physical size and weight are important factors in PV system design.

PV String. Modules/panels wired in series make a string to develop 12V, 24V, 36V, or 48V dc power systems. All panels must match in specifications and current ratings to wire modules in series. The lowest rated panel limits the current. Several strings connected in parallel increase output current of the PV array.

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Battery Charge Controller. A battery backup system utilizes a controller for off-grid applications, to remain operational on loss of utility feed. The controller maintains the battery backup system. Make sure the charge controller has a low voltage disconnect. The Key Features of a Battery Charge Controller are:

• Multistage charging of battery bank.

Changes the amount of power sent to the batteries based on its charge level, for healthier batteries.

• Reverse current protection.

Stops the solar panels from draining the batteries at night when there is no power coming from the panels.

• Low voltage disconnect.

Turns OFF attached load on low battery and turns it back ON once the battery is charged.

• Display.

May show voltage of battery bank, state of charge, amps coming in from solar panel.

Batteries. The batteries provide backup power when the main power is unavailable. Battery size should meet facility power requirements. A solar power system application requires deep Cycle batteries. These batteries can discharge heavily and still keep operating in a partial state of charge. The battery capacity depends on temperature, so a Battery Temperature Sensor is an important part of a solar power system. The Temperature Sensor significantly enhances proper battery charging.

DC-AC inverter. Inverter input takes dc power from the PV array and converts it into standard ac power output used by the facility. Array power output must match inverter capability. For a grid-tied system, the inverter synchronizes PV generated power with the utility.

It has sensing capability to protect the system during commercial power outages or lack of sunlight. The inverter connects to the AC power load through a disconnect switch.

Combination Box. Each PV string output feeds into a combination box through individual fuses and blocking diodes to combine into one pair of dc power wiring. The output is then fed to battery charges through a disconnect switch. This integrates the solar modules into the structural and electrical systems of the facility. The wiring systems include disconnects for the DC and AC sides of the inverter, ground-fault protection, and overcurrent protection for the solar modules (figure 2-8).

Metering. Metering components include meters that provide an indication of system performance. Some meters can indicate facility energy usage.

PV System Selection and Sizing. The first step in designing a PV system is to decide whether to install a system that connects to the local utility grid, or a remote system that functions without a utility connection. The amount of shade-free area available from roughly 9 a.m. to 3 p.m. for mounting the PV array must also be determined.

Most power modules have a peak output around 12 Watts per square foot of module area. For every 100 square feet area, a PV array of 1200 peak Watts output can be installed. The amount of roof area available helps an estimate of the total potential array output. For safety consideration, ensure there is enough room around the PV array to work near it safely.

Cost of the System. Using a cost of $8 to $10/Watt of the array’s peak output to install a PV system provides a preliminary assessment between available funds and array size.

The Underwriters Laboratory (UL) uses safety and performance standards specific to the equipment type and issues a listing for models that pass the safety and performance tests.

Install modules that have a UL 1703 listing.

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Theory. A solar panel contains several cells. Each solar cell (figure 2-2), consists of two wafers of “doped” silicon (p-type and n-type) in contact to form a junction, with each wafer having an electrical connection. Each cell, although very thin, measures approximately 100 mm across, and may produce up to 0.7 volt.

Several Solar Cells are wired together and protected from the weather to create a panel;

sometimes referred to as a module. A 24 Volt (nominal) panel may contain 72 Solar Cells wired in series within it, giving its maximum power a voltage of approximately 0.4 x 72 = 28.8 volts.

These cells sit on a tough backing plate while the grid of electrical connections lies above and below the cells. Electrical connecting strips go from the bottom of one cell to the top of the next, connecting the cells in series. Over this is a non-reflective layer to increase light absorption, because silicon is naturally reflective.

Finally, on top is a layer of tough glass, and the whole structure is usually mounted within an aluminum frame to seal it against the weather.

Figure 2-2. Construction of a Typical Solar Cell

Figure 2-3 shows a solar panel or module formed by combining several cells. These solar panels are then electrically connected to form an Array.

Each cell within the array is 0.5V, 8A. Modules should tilt up at least 10 degrees to avoid pooling rainwater, which can cause dirt build-up on the array. Solar modules can be damaged by 1” size hail at 51 mph, even when the panels meet standards ASTM E1038-10, UL 1703, and IEC 61215. A maximum load test certification is required.

Figure 2-3. Solar Cells and Modules in a Solar Panel

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Types of PV Panels. There are three basic types of PV modules, all of which use silicon material.

Monocrystalline cells. These cells are cut from a single crystal of silicon. They are effectively a slice from a crystal and are smooth textured in appearance. Monocrystalline cells are the most efficient and the most expensive to produce. They are also rigid and mounted in a rigid frame to protect them.

Polycrystalline (or Multi-crystalline cells). Polycrystalline cells are effectively a slice cut from a block of silicon consisting of a large number of crystals. They have a speckled reflective appearance. These cells are slightly less efficient and less expensive than monocrystalline cells mounted in a rigid frame.

Amorphous cells. These are manufactured by placing a thin film of amorphous (non-crystalline) silicon onto a wide choice of surfaces. These are the least efficient and least expensive to produce of the three types. Due to the amorphous nature of the thin layer it is flexible and if manufactured on a flexible surface, the whole solar panel can be flexible.

The power output of amorphous solar cells reduces over time, particularly during the first few months, after which they are stable. The quoted output of an amorphous panel should be that produced after stabilization.

Panel Mounting. Solar panels are large flat objects that can fall due to high wind, so they need to be firmly secured. Proper selection of an installation location is very important for maximizing power delivery.

Mounting Direction. Solar panels in the northern hemisphere should face due south.

In the southern hemisphere, they should face due north. This may vary slightly if hills, high trees, or other obstacles block the sun at end of the day. It is important to avoid shading from trees, hills, buildings, or other objects that may block the sun any hour of the day.

Mounting Angle to Horizontal. Generally, the angle of the panels to horizontal should be the same as the latitude in spring and autumn; 15 degrees less in summer; and 15 degrees more in winter. For best performance, mount panels to allow their angle change at least 4 times per year if possible. For fixed mounting, use the same angle as latitude. It is best to vary this based on which part of the year provides the best performance.

Structural Materials for Mounting. Galvanized angle steel is usually appropriate for mounting PV panels. There is a slight possibility of corrosion occurring between the aluminum (the normal material used for the frame of the panel itself) and zinc used in galvanizing.

However, in most outdoor situations that are reasonably dry, this should not be a problem.

System Expansion. If possible, the method of mounting solar panels should allow the addition of extra panels to the system easily to increase capacity.

Trackers. Solar Panels will be much more efficient at producing electricity if they are always facing the sun. There are trackers available that serve as the panel mounting system and will automatically point them towards the sun. There are two types of trackers to choose from; passive and active.

Passive Trackers use a system in which a liquid moves as it is heated by the afternoon sun and causes the panel to move, automatically returning to the correct position for the morning. This type is likely to be the least expensive, has been reported to provide satisfactory results, and there is very little that can go wrong with it.

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Active Trackers use electric motors to angle the panels. These are controlled by a light sensor sensing the position of the sun, or by a timer moving the panels to predetermined positions.

Solar Cell Efficiency. Cells used in photovoltaic panels for electricity production are usually single junction type with an efficiency of somewhere around 15%. An increase in efficiency of around 40%, has been achieved using multi-junction cells (multiple layers of silicon), each layer tuned to trap different frequencies (colors) of light. This type of cell is expensive to produce and used in spaces where efficiency may be more important.

Increasing the amount of light entering the cell also increases efficiency. Silicon is a naturally shiny substance and cells coated with non-reflective layers ensure that as much light as possible enters the cell. The following factors also contribute to solar panel efficiency.

Solar Panel Construction. Solar panels will normally have a layer of glass protecting the cells through which the light must pass before entering cells. There is opportunity to reduce light reflected from the glass and to trap light that is not striking the panel at 90°.

Panel Mounting and Positioning. The two most important factors are the angle at which the panels are mounted and the amount of sunshine falling on the particular location/avoidance of shade. Small areas of shade on a panel can have a significant effect on the power produced.

Effects of Temperature. Temperature affects the output of a solar cell, and therefore a solar panel. The power output is reduced between 0.25% (amorphous cells), and 0.5% (most crystalline cells), for each degree C of temperature rise. Panel temperatures in the summer in warm climates can easily reach 50 °C, resulting in a 12% reduction in output compared to the rated output at 25 °C.

Partial Shading. Solar panels produce less power when they are shaded and should ideally be situated where there will never be any shadows on them. A shadow falling on a small part of a panel can have a surprisingly large effect on output. Not only will the cells that are shaded produce less power but because the cells within a panel are wired in series, the shaded cells affect the current flow of the whole panel.

If the affected panel is wired in series (in a string) with other panels, then the output of all those panels will be affected by the partial shading of one panel as well.

Working with electrical equipment can be dangerous and may result in injury or death. Follow all recommended safety procedures. Only qualified electrical technicians should wire or ground a PV system.

Grounding. Grounding means connecting part of the system structure and/or wiring electrically to the earth. An equipment ground is installed to prevent unwanted currents from flowing and causing equipment damage, personal injury, or even death, given the right conditions, when a person is exposed to the equipment’s metal case.

Low voltage power is more dangerous than high voltage power, because low voltage causes the muscles to contract so that it may not be possible to let go of the power source.

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Grounding and Lightning Protection. Lightning and related static discharge is the number one cause of sudden, unexpected failures in PV systems. Lightning does not have to strike directly to cause damage to sensitive electronic equipment such as inverters, and controls. It can be miles away, not visible, and still induce high voltage surges in wiring, especially in long lines. Proper system grounding may prevent most cases of lightning damages.

During lightning storms, the clouds build up a static electric charge. This causes accumulation of the opposite charge in objects on the ground. Objects insulated from the earth tend to accumulate the charge more strongly than the surrounding earth. If the potential difference (voltage) between sky and the object is great enough, lightning will jump the gap.

Grounding the system does the following.

• Drains off accumulated charges so that lightning is NOT HIGHLY ATTRACTED to the system

• Provides a safe path for discharge directly to the earth rather than through the wiring if lightning does strike, or if a high charge builds up

• Reduces shock hazard from the higher voltage (AC) parts of the system

• Reduces electrical hum and radio caused by inverters, motors, fluorescent lights and other devices etc.

Grounding is Required by the National Electrical Code® (NEC). Article 690 of the NEC includes photovoltaic systems and does not exempt low voltage systems from other requirements of the NEC. Use the following guidelines to achieve effective grounding.

Install a Proper Grounding System. Provide minimal grounding by a copper-plated ground rod, usually 10 ft. long, driven into the earth. This is the minimal procedure required in an area where the ground is moist (electrically conductive). More rods are installed - at least 10 feet apart - in areas where the ground may be dry, especially sandy, or where lightning may be particularly severe.

Connect or Bond All Ground Rods Together. Use #6 copper wire or larger (see NEC) and bury the wire. Refer to latest revision of FAA-STD-019.

PV Array Wiring. Wiring for the PV array should be done by tucking minimal lengths of wire into the metal framework, and then running the remaining lengths of wire through metal conduit. Run positive and negative wires together wherever possible, rather than some distance apart. This will minimize induction from lightning surges.

Bury Long Wire Runs. Bury long outdoor wire runs instead of running them overhead. For maximum protection, place them in grounded metal conduit.

Surge Protection. Surge protection devices (surge protectors) are recommended to bypass high voltages induced by lightning, particularly in lightning-prone areas. They are also recommended for additional protection where good grounding is not feasible, such as on a dry rocky mountain top, especially if long lines are being run to an array, pump, antenna, or between buildings.

Make sure the surge protectors installed are designed specifically for low voltage systems.

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Effects of System Design on Panel Efficiency. Apart from positioning and angling the panels in order to capture as much light energy as possible, other factors affect the efficiency of a PV system.

The inherent characteristics of solar cells result in current produced by a particular light level being virtually constant up to a voltage of 0.4 volts. For example, a solar panel with a nominal voltage of 24 volts would normally have 72 cells, resulting in a constant current up to 28.8 volts [0.4V x 72].

Above 24V, current drops off rapidly, resulting in power produced at around 28.8 volts. Below 24V the power output will be proportionally lower, due to the current remaining constant [power = voltage x current].

When the panel is connected to the battery with a simple charge controller, it pulls down the voltage of the battery. This results in the panel only being able to produce its maximum power when the battery is fully charged.

A Maximum Power Point Tracking (MPPT) Charge Controller can assist in maintaining the panels at their optimum voltage while producing the voltage required by the battery.

Blocking and By-Pass Diodes in Solar Panels. The two types of diodes (blocking and by-pass) produce different possibilities as follows.

Blocking Diodes. Figure 2-4 shows a simple setup with two panels charging a battery and no controller, and a blocking diode in series with the panels. The panels are also wired in series. When the sun shines, as long as the voltage produced by the two panels is greater than that of the battery, charging will take place.

In the dark, however, when panels do not produce voltage, the voltage of the battery causes a current to flow in the opposite direction through the panels, discharging the battery. The blocking diode prevents this reversal of current.

Blocking diodes are an advantage in any system using solar panels to charge a battery.

Because blocking diodes are usually included in the construction of solar panels, additional diodes are not necessary.

By-Pass Diodes. Shading of part of a panel may be caused by a tree branch, debris, or snow. If one of the panels in figure 2-4 is shaded, that panel will not produce any significant power and will have high resistance, blocking the flow of power produced by the unshaded panel. By-pass diodes allow the current produced by the unshaded panel to flow through the diode and avoid the high resistance produced by the unshaded panel.

By-pass diodes only help series connected panels produce higher voltage. They produce the most benefit when an MPPT Controller or String Inverter is used with panels in series to produce voltages well above the minimum input voltage.

Some solar panels are constructed with the cells divided into groups, with each group having a built-in by-pass diode.

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Figure 2-4. Battery Charged by Two Solar Panels

Basic Requirements for a Solar System. In its simplest form a solar power system only requires a panel to collect the sun's energy and a battery to store that energy (figure 2-5). When the sun is shining, the panel will produce a voltage higher than that of the battery, causing the battery to be charged.

Most panels will include a blocking diode (an electrical component that will only allow electricity to pass in one direction), ensuring that the battery does not discharge through the panel when the sun is not shining.

A simple system like the one shown in figure 2-5 can be used to power a small piece of equipment in a location where there is no power.

With this system, if more power is produced than used, the battery may be charged to a voltage that is high enough to damage the battery. In addition, if more power is used than is generated, the battery voltage will drop to a low level, which can also damage the battery and reduce its life.

Figure 2-5. A Simple Solar System

2-9

The addition of a charge controller as shown in figure 2-6, will improve the system and help protect the life of the battery.

Figure 2-6. Solar System with Controller

The charge controller simply connects between the panel and the battery where it monitors and controls the current flow. In its simplest form, the charge controller will stop the current flow from the panel if the battery voltage exceeds a pre-set level.

Most controllers also have a connection from which current may be drawn for lighting or powering equipment. This current flow is stopped by the controller if the battery voltage drops below a pre-set level. In many cases however, the power requirement is for a supply that is similar to "mains" electricity i.e., 120 or 230 volts AC (alternating current).

To meet this requirement, an inverter (figure 2-7) is added.

Figure 2-7. Solar System with Controller and Inverter

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A complete PV system with battery storage connected to a power grid is shown in figure 2-8.

Figure 2-8.Typical Grid Connected PV System with Battery Storage

Solar Charge Controllers. Solar charge controllers are used to optimize the battery bank charging and to prevent electricity flowing from the batteries to the solar panels when there is no sun.

Always connect battery terminals to the charge controller before connecting the solar panel(s) to the charge controller. Never connect solar panels to charge controller until battery is connected.

Types of Charge Controllers. There are two types of widely used charge controllers;

a Maximum Power Point Tracking (MPPT) controller, and a Pulse Width Modulated (PWM) controller.

MPPT Solar Charge Controllers. The MPPT solar controller actually detects the optimum operating voltage and amperage of the solar panel array and matches it with the battery bank. This results in an additional 15-30% more power out of a solar array compared to a PWM solar controller. Although the MPPT solar charge controller is more expensive than its PWM counterpart, it is worth the investment for solar electric system over 200 watts.

WARNING

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PWM Solar Charge Controllers. A PWM solar charge controller is the traditional style. They are robust, inexpensive and widely used in solar panel applications. In applications where electrical interference is an issue, the PWM shunt controller is used.

Additionally, some solar controllers offer adjustable control voltage set points, low voltage disconnect, overload protection, and metering. The solar charge controller connects directly to a DC load. If the solar controller is equipped with a low voltage disconnect (LVD), it can detect when the battery voltage is low and shut off the DC load until the battery is charged.

Some charge controllers and inverters come with built-in temperature sensors. A temperature sensor starts or stops battery charging based on battery voltage and significant temperature changes (e.g. differences of 20 degrees F over the year).

Sizing a Charge Controller. A solar charge controller must support the voltage of the solar panel array, and then output to the battery bank's voltage (usually 12, 24, or 48V dc).

The solar charge controller must have enough capacity to handle the current (in amps) from the solar panel array. The solar panels’ wattage divided by the battery bank's voltage will give a rough estimate of how many amps the controller needs.

The basic formula for sizing a solar charge controller is to take the short circuit current (Isc) of the array and multiply it by 1.56. Make sure that the selected solar controller can handle at least that many amps.

Some available charge controller brands are MidNite, Morningstar, OutBack Power Inc., and Xantrex.

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3-1

Standards and Tolerances

General. This chapter prescribes the standards and tolerances for Solar Photovoltaic Systems, as defined and described in Order 6000.15, General Maintenance Handbook for National Airspace System (NAS) Facilities. The standards and tolerances in this chapter are generic in nature. Refer to the manufacturer’s operator manual for specific standards and tolerances for each PV model array and its system components. All key performance parameters and/or key inspection elements are clearly identified by an arrow (→) placed to the left of the applicable item.

Photovoltaic System (Generic)

Parameter Maintenance Reference Paragraph

Standard (Nominal)

Tolerance/Limit(Min/Max)

Initial Operating

Photovoltaic Array Components.

a. Visual Inspection. 5-5.

(1) Panel/Module .................. 5-3., 5-6, 5-14 Free of dirt and debris N/A N/A

(2) Mounting Structure ......... 5-4 Mechanically sound N/A N/A

(3) Electrical Wiring and Connections .................... 5-4 Intact and secure;

No exposed wires N/A N/A

(4) Junction or Combination Boxes (if used) ................ 5-7 Connections secure N/A N/A

(5) Mini Inverters (if used) .... Connections secure N/A N/A

(6) Charge Controller ........... Connections secure N/A N/A

(7) Disconnect Switch and Circuit Breakers .............. 5-8 Connections secure N/A N/A

b. PV Output. 5-11

(1) Panel/Module Open Circuit Voltage ................ Rated Mfg. Voc -5% ,10% De-rated with age

(2) Panel/Module Short Circuit Current ............... 5-11 Rated Mfg. Isc Irradiation dependent.

De-rated with age

(3) String Open Circuit Voltage .......................... 5-11 Per design Voc -5%, 10% De-rated with age

(4) Array Open Circuit Voltage .......................... Per design -5%, 10% De-rated with age

Inverter DC to AC volts. 5-9

a. Input DC Volt ........................ Per Design -5%, 10% Same as Initial

b. Input Current ........................ Per Design Site specific Manufacturer’s

Instruction Book

(MIB)

3-2

Photovoltaic System (Generic) (Continued)

Parameter Maintenance Reference Paragraph

Standard

c. Output AC Volt ..................... 120V ac ± 10% Same as initial

d. Output Frequency ............... 60 Hz ±3 Hz Same as initial

e. Total Harmonic Distortion .. <5% <5% Same as initial

f. Output Current ..................... Per Design Site Specific MIB

Tracker (if used to generate 5% more electricity) ................. MIB MIB MIB MIB

PV System Power Output........ 5-9 Site specific May reduce

1% from base design per year

Same as initial;

reduces to 80% in 20 years

a. Power Output ....................... Commissioned Value

≤1% per year drop (Isolate and correct if

>1% drop per year)

Same as initial

b. Reserved.

Charge Controller (if used) Charge

Controller Instructions

Charge controller manual (CCM) per

System Design Base line value

a. Operational if Charge Controller used .................... Battery volts

>10.5 Volt Same as standard

Same as Standard

b. Open…