Frequently asked questions

Generator Step Up Transformer (or sometime referred to as the Main Transformer) is the large

locate in a substation or switchyard that steps up the voltage of the system from distribution to transmission levels.

Hazard Mitigation Analysis is an evaluation of the potential failure modes of a system and the safety-related consequences attributed to those failures.

Heating, Ventilation, and Air Conditioning is the system that provide the necesaary heating and colling for critical system components and typically requires HVAC certifications to perfom maintenance on the system.

Current-voltage characteristic curve, the "I" stands for current, and the "V" standards for voltage. An I-V curve is a graphical representation of the relationship between the voltage applied across an electrical device and the current flowing through it. It is one of the most common methods of determining how an electrical device functions in a circuit and is used in O&M of PV systems.

Interconnection Agreement

IBR stands for Inverter-Based Resource.

An IBR is a power generation or storage system that connects to the grid using power electronics (inverters) instead of traditional spinning generators.

IBRs do not use rotating mass to produce electricity [they convert DC or variable power to AC through inverters].

• Solar PV plants

• Battery Energy Storage Systems (BESS)

• Many modern wind turbines
  

IBRs require advanced controls (like a Power Plant Controller) to support grid voltage, frequency, and stability. IBRs are modern, inverter-controlled power sources connected to the grid.

Inverters play a crucial role in converting the direct current (DC) electricity generated by solar panels into usable alternating current (AC) electricity that can be used by homes, businesses, and fed into the electrical grid.

Independent Power Providers build, operate, and maintenain power generation systems to sell the power and energy to the utility market.

Infrared is a spectrum of light that is not visible to the human eye and typically used to produce thermal images. IR imaging is commonly used in testing and O&M to find "hot spots" on PV modules or electricla connections which is an indication that there is an electrical issue at that spot.

Short circuit current for solar PV is the maximum amount of current a solar panel can produce when there is no load on the output. This is the highest level of current that can be produced and is measured in Amps (A).

Independent System Operator facilitates open-access to transmission lines across the U.S and parts of Canada. They operate the transmission system independently of, and foster competition for electricity generation among, wholesale market participants (i.e utilities). Also see regional transmission organizations (RTOs). Both ISOs and RTOs are regulated by FERC.

Internet Service Provider is the company that provides the internet service for transmission of data and information.

InvestmentTax Credit is a tax credit percentage for the construction and captial costs for renewable electricity systems.

Key Performance Indicator is a measurable value that demonstrates how effectively a company is achieving key business objectives. Organizations use KPIs at multiple levels to track performance measures.

Lower Explosive Limit is the lowest concentration (percentage) of a gas or vapor in air capable of producing a flash of fire in presence of an ignition source (arc, flame, heat). Concentrations lower than LEL are 'too lean' to burn. Also called lower flammable limit (LFL).

Job Hazard Analysis is a hazard analysis technique that focuses on job tasks as a way to identify hazards before they occur. It focuses on the relationship between the worker, the task, the tools, and the work environment.

Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specific purpose.

Lithium Iron Phosphate is a type of lithium-ion battery that uses lithium (Li), iron (Fe), and phosphate (PO_4) in its chemistry to store energy.

Limited Notice to Proceed is a stage in the Sales process before Notice to Proceed (NTP)

Lockout/Tagout (or Hazardous Energy Control) is the procedure (required by OSHA) to protect workers from hazardous energy (ie. energy that can seriously injury or kill a person) by physically locking and tagging equipment with "Do Not Operate" or "Danger Tag" during commissioning or maintenance activities. Typically the person who does the work on the equipment is in charge of the key(s) to the lock(s) in order prevent someone else from accidently unlocking live equipment while they are still working.

Lightning Protection System is designed to protect a structure from damage by intercepting such strikes and safely passing their extremely high voltage currents to "ground." This system includes a network of air terminals, bonding conductors, and ground electrodes designed to provide a low impedance path to ground against potential strikes.

Mechanical Completion (MC) is the project milestone where all physical construction and installation work has been completed in accordance with the design, specifications, and contract requirements [and the system is ready for commissioning].

Mechanical Completion means the equipment is installed correctly and ready to be tested.

At Mechanical Completion:

• Major equipment is installed (inverters, transformers, turbines, BESS containers, trackers, switchgear)

• Mechanical and electrical installation is complete

• Cabling is pulled and terminated

• Bolting, torqueing, and alignments are complete

• Grounding is installed

• Civil work related to equipment placement is complete

• Construction inspections are closed

• Punch list items are minor and non-safety related

The system is physically built — but not yet fully tested or energized for commercial operation.

Mechanical Completion does not mean:

• The plant is energized

• Performance testing is complete

• The system is fully commissioned

• The project has reached COD (Commercial Operation Date)

It means construction is finished and commissioning can begin.

Utility-Scale Solar

• Modules installed

• Trackers assembled and aligned

• Inverters set and wired

• MV collection system terminated

• Substation equipment installed

Wind

• Turbines erected

• Blades installed

• Nacelle connected

• Internal cabling complete

BESS

• Containers set

• Racks installed

• HVAC and fire systems installed

• Power conversion system connected

Main Circuit Breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit.

A micro inverter is an inverter that is connected to an individual solar module (panel) to convert the DC (direct current) electrical from the panel to AC (Alternating current) for grid applications.

Module-level Power Electronic is an electrical device that modifies the energy output of a PV array at a module level. MLPE usually refers to PV optimizers and microinverters. There are usually paired one-to-one with PV modules, but other versions exist that can connect two, three, or four PV modules to one MLPE.

Data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). The Modbus protocol uses character serial communication lines, Ethernet, or the Internet protocol for communication to and from multiple devices connected to the same cable or Ethernet network. For example, there can be a device that measures temperature and another device to measure humidity connected to the same cable, both communicating measurements to the same computer. Modbus is often used to connect a plant/system supervisory computer with a remote terminal unit (RTU) in Supervisory Control and Data Acquisition (SCADA) systems in the electric power industry.

Maximum Power Point is the maximum power produced by a PV module or string of modules, graphically represented as the "knee" of an I-V curve where the current and voltage produce the maximum power.

Maximum Power Point Tracker is a feature of PV inverters to track the power output and adjust the voltage in order to generate the maximum power for that circuit.

MTBF stands for Mean Time Between Failures. It is a reliability metric that estimates the average time a piece of equipment operates before it fails.

MTBF = The average operating time between one failure and the next.

MTBF=Total Operating TimeNumber of FailuresMTBF=Number of FailuresTotal Operating Time​

Example:

If a solar inverter runs for 100,000 hours total and experiences 5 failures:

MTBF = 100,000 ÷ 5 = 20,000 hours

This means, on average, the inverter runs 20,000 hours between failures.

• Higher MTBF = More reliable equipment

• Lower MTBF = More frequent failures

• Used for maintenance planning and spare parts forecasting

https://www.truckroll.tech/post/best-unused-metrics-in-renewables-mtbf-and-mttr-to-enhance-performance-and-control-costs

MTTR stands for Mean Time To Repair. It measures the average time required to repair equipment and return it to normal operation after a failure.

MTTR = The average time it takes to fix a failure and restore equipment to service.

MTTR=Total DowntimeNumber of RepairsMTTR=Number of RepairsTotal Downtime​

Example:

If a solar inverter fails 5 times in a year and the total downtime across those events is 50 hours:

MTTR = 50 ÷ 5 = 10 hours

This means, on average, it takes 10 hours to diagnose, repair, and return the inverter to service.

• Lower MTTR = Faster repairs and less downtime

• Higher MTTR = Longer outages and greater production loss

• Helps evaluate maintenance team effectiveness and spare parts strategy

• MTTR includes troubleshooting, repair, testing, and restart time.

• It does not measure how often failures happen (that’s MTBF).

• Reducing MTTR improves system availability and revenue performance.

https://www.truckroll.tech/post/best-unused-metrics-in-renewables-mtbf-and-mttr-to-enhance-performance-and-control-costs

Master Service Agreement is the contractual obligation of services, material, or goods.

Main Service Panel For grid-connected systems, the electrical panel of an address where the utility service conductors are connected. This panel will be the first thing after a utility meter and will typically have one to six service disconnects.

Minimum Viable Product is a product that meets the bare minimum requirements to launch and be successful. This can be a physical product, a software product, or even a set of documents (like user manuals and spec sheets). This is often used to define the minimum requirements needed to launch a new product or service with the intention of improving and adding more functionality and/or information later.

National Electrical Code is the regulations for electrical and fire safety published by the NFPA every three years and enforced by local jurisdictions. The intent of the NEC is to protect life and property by preventing electrical dangers and fires, it does not cover performance issues like whether a PV system is producing the expected energy.

https://www.nfpa.org/education-and-research/electrical/understanding-nfpa-70-national-electrical-code

NERC stands for the North American Electric Reliability Corporation.

NERC is the organization responsible for developing and enforcing reliability standards for the bulk electric power system in North America.

• Sets reliability and operational standards

• Monitors grid performance

• Investigates major grid disturbances

• Oversees compliance and enforcement

NERC standards apply to:

• Transmission operators

• Balancing authorities

• Generator owners/operators (including large solar, wind, and BESS plants)

• Reliability coordinators

Utility-scale renewable projects connected to the bulk power system may be subject to:

• NERC reliability standards

• Registration requirements

• Compliance audits

This ensures renewable plants operate safely and support overall grid stability.

https://www.nerc.com

NEMA ratings are enclosure classifications developed by the National Electrical Manufacturers Association (NEMA)that define how well electrical equipment enclosures protect against environmental conditions.

A NEMA rating tells you how protected an electrical enclosure is from water, dust, corrosion, and other hazards.

NEMA ratings apply to electrical enclosures, not entire facilities.

In clean energy, this includes:

• Inverter cabinets

• Combiner boxes

• Disconnect switches

• Switchgear enclosures

• SCADA cabinets

• Battery enclosures (external housings)

Purpose:

• Ensure equipment survives outdoor exposure

• Prevent water intrusion and faults

• Reduce corrosion and failure rates

• Maintain safety compliance

• Support long-term reliability

Incorrect enclosure selection can lead to:

• Ground faults

• Arc flash risk

• Premature equipment failure

NEMA 1

• Indoor use only

• Protects against basic contact

• No protection against water

Used for: Indoor panels in electrical rooms.

NEMA 3R

• Outdoor use

• Protects against rain and ice

• Not fully dust-tight

Used for:

• Outdoor disconnects

• Meter cabinets

• Some combiner boxes

Very common in utility-scale solar.

NEMA 4

• Indoor or outdoor

• Protects against windblown dust and splashing water

Used for:

• Control panels

• Certain inverter components

NEMA 4X

• Same as NEMA 4

• Plus corrosion resistance

Used for:

• Coastal solar projects

• BESS enclosures

• Harsh environments

NEMA 12

• Indoor industrial use

• Protects against dust, dirt, and dripping liquids

Used for:

• Control cabinets inside inverter stations

National Electrical Safety Code is the electrical regulations for the utility industry.

https://standards.ieee.org/products-programs/nesc/

National Fire Protection Association is a global self-funded nonprofit organization, established in 1896, devoted to eliminating death, injury, property, and economic loss due to fire, electrical and related hazards. NFPA delivers information and knowledge through more than 300 consensus codes and standards, research, training, education, outreach, and advocacy.

https://www.nfpa.org

National Renewable Energy Laboratory is a national laboratory of the US Department of Energy.

now know as the National Laboratory of the Rockies.

https://www.nlr.gov/index

Notice to Proceed is approval to proceed with project development usually to the next agreed upon check-in point."

Operations and Maintenance includes activities related to properly operating and maintaining each piece of equipment and the system as a whole such that it continues to produce energy safely, optimally, and meets all relevant codes and standards.

The event in which the battery cell case vents gas due to a rise in the internal pressure of the cell. See NFPA 855.

Occupational Safety and Health Administration is a government body belonging to the US Department of Labor created by Congress with the Occupational Safety and Health Act of 1970. OSHA ensures safe and healthful working conditions for working persons by setting and enforcing standards and by providing training, outreach, education, and assistance.

https://www.osha.gov/

Power Conversion System (or sometimes referred to as a Power Conversaion Station) is a metal or concret skid that houses the inverter, pad mount transofmer, communications equipment, and tracker controls equipment). Also see inverter.

Permissible Exposure Limit is a legal limit for exposure of an employee to a chemical substance or physical agent such as high level noise.

Power Factor (PF) measures how efficiently electrical power is being used in an AC system. It shows the relationship between the power that actually performs useful work and the total power supplied.

Power Factor = How effectively electrical power is converted into useful work.

Power Factor=Real Power (kW)Apparent Power (kVA)Power Factor=Apparent Power (kVA)Real Power (kW)​

• Real Power (kW) = Power that does useful work

• Apparent Power (kVA) = Total power supplied

PF is expressed as a number between 0 and 1 (or as a percentage).

If a facility draws:

• 900 kW of real power

• 1,000 kVA of apparent power

PF=900÷1000=0.90PF=900÷1000=0.90

Power Factor = 0.90 (90%)

That means 90% of the supplied power is doing useful work.

Why it matters:

• Higher PF (closer to 1.0) = More efficient system

• Lower PF = More reactive power, higher losses

• Utilities may charge penalties for low PF

• Impacts equipment sizing (transformers, cables, breakers)

Maintaining proper power factor:

• Reduces losses

• Improves grid stability

• Ensures compliance with interconnection agreements

A PV system with rigid PV modules that are NOT building-integrated (i.e. not PV shingles nor PV tiles).

Programmable Logic Control is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.

Pad Mount Trandformer (or MV Transformer) is the step up transformer from the output of the inverter to the distribution or transmission level voltages.

Point of Interconnect is the pont at which the system is connected to the larger electrical power grid. This is also a point of demarcation between where the scope of work for the utility is and the service provider for the system is.

Power Purchase Agreement is the formal agreement on the pricing structure and commitment of power to be generaated.

Personal Protective Equipment is designed to protect the wearer's body from injury or infection.

PR stands for Performance Ratio. It measures how efficiently a solar plant converts available sunlight into usable AC energy, after accounting for system losses.

PR = How well the solar plant performs compared to its theoretical maximum output.

PR=Actual Energy OutputTheoretical Energy Output Based on IrradiancePR=Theoretical Energy Output Based on IrradianceActual Energy Output​

It is expressed as a percentage.

If a solar plant should theoretically produce 1,000 MWh based on measured sunlight, but actually produces 850 MWh:

PR=850÷1000=0.85PR=850÷1000=0.85

PR = 85%

This means the plant converted 85% of the available solar energy into electricity.

PR reflects system losses such as:

• Inverter losses

• DC to AC conversion losses

• Soiling (dust on panels)

• Temperature losses

• Wiring losses

• Mismatch losses

• Transformer losses

It removes weather variability [so it measures system efficiency, not how sunny it was].

• Key KPI for solar asset performance

• Used in EPC acceptance testing

• Monitored by owners and lenders

• Helps identify degradation or equipment issues

• PR is primarily used for solar PV systems.

• High availability does not guarantee high PR.

• A typical healthy utility-scale solar plant PR may range from 80–90%, depending on design and location.

Availability tells you if the plant is running.

PR tells you how well it is running.

Potential Transformer or Voltage Transformer (VT) is an Instrument used for measuring voltage. It is specially designed to maintain an accurate voltage phase angle reference between the source and the Instrument Transformer`s output along with excellent voltage regulation to obtain accurate voltage measurements.

Production Tax Credit is an inflation-adjusted per-kilowatt-hour (kWh) tax credit for electricity generated by qualified energy resources and sold by the taxpayer to an unrelated person during the taxable year.

Photovoltaics is the process to generate power using devices that absorb energy from sunlight and convert it into electrical energy through semiconducting materials.

Quality Assurance/Quality Control - the combination of quality assurance, the process or set of processes used to measure and assure the quality of a product, and quality control, the process of ensuring products and services meet consumer expectations.

Qualified Electrical Worker is one who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Responsible Accountable Consulted Informed, this is a document that summarizes the roles and responsibilities of those involved in a project or program.

Root Cause Analysis is a collective term that describes a wide range of approaches, tools, and techniques used to uncover causes of problems.

Raw Material Index is equipment pricing that adjusts monthly based on the pricing of key raw material commodities (such as lithium, copper, electrolyte) that are used to manufacture that product. Raw material costs generally use a three month average.

Roundtrip Efficiency is the ratio of total output energy divided by total input energy over one charging/discharging cycle using rated input and output power. "Energy In" includes energy losses during charging due to the switchgear, AC lines, auxilary loads, transformer, inverter, and DC conductors. "Energy Out" includes energy losses during discharge due to the battery storage system, DC lines, inverter, transformer, auxilary loads, and switchgear. Site temperature, discharge duration, cycling profile, and auxilary load assumptions will impact RTE.

Regional Transmission Organizations are similar to ISOs and regulated by FERC, a joint group of utilities who operate the transmission systems for a particular region and develop innovative procedures to manage the transmission of electricity equitably. See definition of ISOs

Remote Terminal Unit is a microprocessor-controlled electronic device that interfaces mechanical and/or electrical equipment in the physical world to a SCADA system. RTUs send telemetry data to the supervisory computer(s) of a SCADA system and receive commands to control the equipment on site. Other terms that may be used for RTU are remote telemetry unit and remote telecontrol unit.

see RTU, RTAC is specific manufacturer.

Storage as a Transmission Asset is the use of an energy storage system as part of the electric transmission or distribution infrastructure to assist with the delivery, rather than supply, of electricity.By integrating storage into transmission equipment, SAT can inject or absorb electricity to facilitate power flows on transmission lines over a certain period of time. Used in this way, storage can enhance existing transmission lines or even serve as an alternative to building new transmission projects.

Substantial Completion is the stage when the construction of a project is deemed sufficiently completed and the site is capable of operating though may not yet have permission to operate from the utility and/or some final steps may still need to be completed. This milestone can vary project to project but is usually defined in the contract and may have legal implications if substantial completion is not done by the agreed upon date. It is a major milestone for any project which is why you may see a press release or announcement from an EPC when a project reaches substantial completion.

Supervisory Control and Data Acquisition is used for large-scale data collection and controls commonly used in a variety of industrial applications such as utility-scale power plants. Similar to monitoring but with the added ability to control the system and more often incorporates AI learning.

Safety Data Sheet (formerly known as MSDS) includes information such as the properties of each chemical, the physical, health, and environmental health hazards, protective measures,and safety precautions for handling, storing, and transporting the chemical.

SIF = Serious Injury or Fatality

A Serious Injury or Fatality is any workplace incident that results in:

• Death

• Life-threatening injury

• Permanent disability

• Significant hospitalization (amputation, severe burns, paralysis, etc.)

In clean energy construction and operations, SIF events typically involve:

• Falls from height (trackers, turbines, substation steel)

• Electrical contact (arc flash, medium voltage, backfeed)

• Heavy equipment struck-by incidents

• Trenching collapses

• Rigging/lifting failures

• Battery thermal runaway incidents in BESS facilities

The key point: SIF events are low frequency, but extremely high severity.

pSIF = Potential Serious Injury or Fatality

A pSIF is an incident or near-miss that could have resulted in a serious injury or fatality—even if no one was hurt.