3.10.1 Photovoltaic Systems

Candidate buildings may have photovoltaic (PV) systems and the energy generated by these systems may offset the power used by HVAC, lighting, and other building systems. Since most PV systems work under a net metering arrangement whereby the utility grid is used as a storage battery, accepting excess energy when it is available and providing power back to the building at night and other times when the PV system is not generating, the simulation of PV systems need to be on an hourly time step so that it can be aligned with the building loads and the utility rate structure.

This section describes one set of building descriptors for specifying a PV system. This set of building descriptors is based on the five-parameter model.1 Other models may be used for PV systems. The inputs apply only to the proposed design, as the baseline building is modeled without a PV system.

Configuration

This set of building descriptors addresses the overall layout and design of the PV system, including the orientation and slope of the collectors, how they are wired together, and how they are linked to an inverter that converts DC power to AC and synchronizes it with the grid.

PV System Name

Applicability

All PV systems

Definition

A unique identifier that can be used to reference the PV system and associate it with the construction documents

Units

Text, unique

Input Restrictions

The name should provide a link to the construction documents.

Baseline Rules

None (PV not modeled for the baseline building)

 

Number of Modules in a String

Applicability

All PV systems

Definition

This is the number of modules in a series string. Modules in series increase voltage which is often needed in order to match output voltage with the inverter requirements; modules in parallel increase current.

Units

Numeric: integer

Input Restrictions

As designed

Baseline Rules

None (PV not modeled for the baseline building)

 

Number of Strings

Applicability

All PV systems

Definition

This is the number of strings of modules in parallel. Modules in series increase voltage; modules in parallel increase current.

Units

Numeric: integer

Input Restrictions

As designed

Baseline Rules

None (PV not modeled for the baseline building)

 

Collector Area

Applicability

All PV systems

Definition

The area of the collector module.

Units

Square feet (ft²)

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

 

Slope

Applicability

All PV systems

Definition

The slope of the collector modules relative to the horizontal.

Units

Degrees (°)

Input Restrictions

As designed

Baseline Rules

None (PV not modeled for the baseline building)

 

Azimuth

Applicability

All PV systems

Definition

The orientation of the collector modules relative to due North. An azimuth of 180° faces due south; 90° faces east, etc.

Units

Degrees (°)

Input Restrictions

As designed

Baseline Rules

None (PV not modeled for the baseline building)

 

PV Mounting Height

Applicability

All PV systems

Definition

The height of the collectors above the ground.

Units

Feet (ft)

Input Restrictions

As designed.

Baseline Rules

None (PV not modeled for the baseline building)

Shading

Shading of PV systems results in significant reduction of production and must be accounted for in an acceptable manner. A method is implied in the following building descriptors that is consistent with the NSHP Calculator2. With this method, the area around the solar system is divided into 22.5° cones and the height and distance to shading objects is entered for each quadrant. Other methods may be used, including use of the building shade inputs (see building site characteristics under project data)

Shading Azimuth

Applicability

All PV systems

Definition

A quadrant where the height and distance of shading objects is specified.

Units

List: ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW

Input Restrictions

As estimated from existing surrounding buildings and shading structures

Baseline Rules

None (PV not modeled for the baseline building)

 

Shading Object Height

Applicability

All PV systems

Definition

The height of the building or shading object in the 22.5° cone

Units

Feet (ft)

Input Restrictions

As estimated from existing surrounding buildings and shading structures

Baseline Rules

None (PV not modeled for the baseline building)

 

Shading Object Distance

Applicability

All PV systems

Definition

The horizontal distance from the shading object to the collectors

Units

Feet (ft)

Input Restrictions

As estimated from existing surrounding buildings and shading structures

Baseline Rules

None (PV not modeled for the baseline building)

Collector Performance

The collector performance can be characterized by the following five variables that are available from PV array manufacturers: the open-circuit voltage, the short-circuit current, the voltage and current at the maximum power-point, and the temperature coefficient of the open-circuit voltage. These are described below.

Short-circuit Current

Applicability

All PV systems

Definition

Isc - current measured with zero voltage

Units

Amps

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

 

Open-circuit Voltage

Applicability

All PV systems

Definition

Voc - voltage measured with an open circuit

Units

Volts

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

 

Maximum Power-Point Voltage and Current

Applicability

All PV systems

Definition

Imp, Vmp - current and voltage at the maximum power-point condition. These parameters are typically reported at Standard Test Conditions of 1000 W/m2 and a cell temperature of 25°C.

Units

Amps and Volts

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

 

Open-circuit Temperature Coefficient

Applicability

All PV systems

Definition

Voc - temperature coefficient at open-circuit voltage

Units

I/C

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

 

Short-circuit Temperature Coefficient

Applicability

All PV systems

Definition

Voc - temperature coefficient at short-circuit current. This is supplied the manufacturer.

Units

V/C

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

 

Normal Operating Cell Temperature (NOCT)

Applicability

All PV systems

Definition

The normal operating cell temperature, typically between 45°C and 55°C

Units

Degrees Celsius (°C)

Input Restrictions

From manufacturer's specification

Baseline Rules

None (PV not modeled for the baseline building)

  • 1. De Soto, W., S.A. Klein, and W.A. Beckman, “Improvement and validation of a model for photovoltaic array performance”, Solar Energy, Volume 80, Issue 1, January 2006, Pages 78-88
  • 2. More information is available at http://www.gosolarcalifornia.ca.gov/nshp/ [23].
Building EQ

Candidate buildings may have photovoltaic (PV) systems and the energy generated by these systems may offset the power used by HVAC, lighting, and other building systems. Since most PV systems work under a net metering arrangement whereby the utility grid is used as a storage battery, accepting excess energy when it is available and providing power back to the building at night and other times when the PV system is not generating, the simulation of PV systems need to be on an hourly time step so that it can be aligned with the building loads and the utility rate structure.

This section describes one set of building descriptors for specifying a PV system. This set of building descriptors is based on the five-parameter model1. Other models may be used for PV systems. The inputs apply only to the proposed design, as the baseline building is modeled without a PV system.

Configuration

This set of building descriptors addresses the overall layout and design of the PV system, including the orientation and slope of the collectors, how they are wired together, and how they are linked to an inverter that converts DC power to AC and synchronizes it with the grid.

PV System Name
Applicability All PV systems
Definition A unique identifier that can be used to reference the PV system and associate it with the construction documents
Units Text, unique
Input Restrictions The name should provide a link to the construction documents.
Number of Modules in a String
Applicability All PV systems
Definition This is the number of modules in a series string. Modules in series increase voltage which is often needed in order to match output voltage with the inverter requirements; modules in parallel increase current.
Units Numeric: integer
Input Restrictions As designed
Number of Strings
Applicability All PV systems
Definition This is the number of strings of modules in parallel. Modules in series increase voltage; modules in parallel increase current.
Units Numeric: integer
Input Restrictions As designed
Collector Area
Applicability All PV systems
Definition The area of the collector module.
Units Square feet (ft²)
Input Restrictions From manufacturer's specification
Slope
Applicability All PV systems
Definition The slope of the collector modules relative to the horizontal.
Units Degrees (°)
Input Restrictions As designed
Azimuth
Applicability All PV systems
Definition The orientation of the collector modules relative to due North. An azimuth of 180° faces due south; 90° faces east, etc.
Units Degrees (°)
Input Restrictions As designed
PV Mounting Height
Applicability All PV systems
Definition The height of the collectors above the ground.
Units Feet (ft)
Input Restrictions As designed.

Shading

Shading of PV systems results in significant reduction of production and must be accounted for in an acceptable manner. A method is implied in the following building descriptors that is consistent with the NSHP Calculator2. With this method, the area around the solar system is divided into 22.5° cones and the height and distance to shading objects is entered for each quadrant. Other methods may be used, including use of the building shade inputs (see building site characteristics under project data)

Shading Azimuth
Applicability All PV systems
Definition A quadrant where the height and distance of shading objects is specified.
Units List: ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW
Input Restrictions As estimated from existing surrounding buildings and shading structures
Shading Object Height
Applicability All PV systems
Definition The height of the building or shading object in the 22.5° cone
Units Feet (ft)
Input Restrictions As estimated from existing surrounding buildings and shading structures
Shading Object Distance
Applicability All PV systems
Definition The horizontal distance from the shading object to the collectors
Units Feet (ft)
Input Restrictions As estimated from existing surrounding buildings and shading structures

Collector Performance

The collector performance can be characterized by the following five variables that are available from PV array manufacturers: the open-circuit voltage, the short-circuit current, the voltage and current at the maximum power-point, and the temperature coefficient of the open-circuit voltage. These are described below.

Short-circuit Current
Applicability All PV systems
Definition Isc - current measured with zero voltage
Units Amps
Input Restrictions From manufacturer's specification
Open-circuit Voltage
Applicability All PV systems
Definition Voc - voltage measured with an open circuit
Units Volts
Input Restrictions From manufacturer's specification
Maximum Power-Point Voltage and Current
Applicability All PV systems
Definition Imp, Vmp - current and voltage at the maximum power-point condition. These parameters are typically reported at Standard Test Conditions of 1000 W/m2 and a cell temperature of 25°C.
Units Amps and Volts
Input Restrictions From manufacturer's specification
Open-circuit Temperature Coefficient
Applicability All PV systems
Definition Voc - temperature coefficient at open-circuit voltage
Units I/C
Input Restrictions From manufacturer's specification
Short-circuit Temperature Coefficient
Applicability All PV systems
Definition Voc - temperature coefficient at short-circuit current. This is supplied the manufacturer.
Units V/C
Input Restrictions From manufacturer's specification
Normal Operating Cell Temperature (NOCT)
Applicability All PV systems
Definition The normal operating cell temperature, typically between 45°C and 55°C
Units Degrees Celsius (°C)
Input Restrictions From manufacturer's specification
  • 1. De Soto, W., S.A. Klein, and W.A. Beckman, “Improvement and validation of a model for photovoltaic array performance”, Solar Energy, Volume 80, Issue 1, January 2006, Pages 78-88
  • 2. More information is available at http://www.gosolarcalifornia.ca.gov/nshp/.
Energy Star

Candidate buildings may have photovoltaic (PV) systems and the energy generated by these systems may offset the power used by HVAC, lighting, and other building systems. Since most PV systems work under a net metering arrangement whereby the utility grid is used as a storage battery, accepting excess energy when it is available and providing power back to the building at night and other times when the PV system is not generating, the simulation of PV systems need to be on an hourly time step so that it can be aligned with the building loads and the utility rate structure.

This section describes one set of building descriptors for specifying a PV system. This set of building descriptors is based on the five-parameter model1. Other models may be used for PV systems. The inputs apply only to the proposed design, as the baseline building is modeled without a PV system.

Configuration

This set of building descriptors addresses the overall layout and design of the PV system, including the orientation and slope of the collectors, how they are wired together, and how they are linked to an inverter that converts DC power to AC and synchronizes it with the grid.

PV System Name
Applicability All PV systems
Definition A unique identifier that can be used to reference the PV system and associate it with the construction documents
Units Text, unique
Input Restrictions The name should provide a link to the construction documents.
Number of Modules in a String
Applicability All PV systems
Definition This is the number of modules in a series string. Modules in series increase voltage which is often needed in order to match output voltage with the inverter requirements; modules in parallel increase current.
Units Numeric: integer
Input Restrictions As designed
Number of Strings
Applicability All PV systems
Definition This is the number of strings of modules in parallel. Modules in series increase voltage; modules in parallel increase current.
Units Numeric: integer
Input Restrictions As designed
Collector Area
Applicability All PV systems
Definition The area of the collector module.
Units Square feet (ft²)
Input Restrictions From manufacturer's specification
Slope
Applicability All PV systems
Definition The slope of the collector modules relative to the horizontal.
Units Degrees (°)
Input Restrictions As designed
Azimuth
Applicability All PV systems
Definition The orientation of the collector modules relative to due North. An azimuth of 180° faces due south; 90° faces east, etc.
Units Degrees (°)
Input Restrictions As designed
PV Mounting Height
Applicability All PV systems
Definition The height of the collectors above the ground.
Units Feet (ft)
Input Restrictions As designed.

Shading

Shading of PV systems results in significant reduction of production and must be accounted for in an acceptable manner. A method is implied in the following building descriptors that is consistent with the NSHP Calculator2. With this method, the area around the solar system is divided into 22.5° cones and the height and distance to shading objects is entered for each quadrant. Other methods may be used, including use of the building shade inputs (see building site characteristics under project data)

Shading Azimuth
Applicability All PV systems
Definition A quadrant where the height and distance of shading objects is specified.
Units List: ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW
Input Restrictions As estimated from existing surrounding buildings and shading structures
Shading Object Height
Applicability All PV systems
Definition The height of the building or shading object in the 22.5° cone
Units Feet (ft)
Input Restrictions As estimated from existing surrounding buildings and shading structures
Shading Object Distance
Applicability All PV systems
Definition The horizontal distance from the shading object to the collectors
Units Feet (ft)
Input Restrictions As estimated from existing surrounding buildings and shading structures

Collector Performance

The collector performance can be characterized by the following five variables that are available from PV array manufacturers: the open-circuit voltage, the short-circuit current, the voltage and current at the maximum power-point, and the temperature coefficient of the open-circuit voltage. These are described below.

Short-circuit Current
Applicability All PV systems
Definition Isc - current measured with zero voltage
Units Amps
Input Restrictions From manufacturer's specification
Open-circuit Voltage
Applicability All PV systems
Definition Voc - voltage measured with an open circuit
Units Volts
Input Restrictions From manufacturer's specification
Maximum Power-Point Voltage and Current
Applicability All PV systems
Definition Imp, Vmp - current and voltage at the maximum power-point condition. These parameters are typically reported at Standard Test Conditions of 1000 W/m2 and a cell temperature of 25°C.
Units Amps and Volts
Input Restrictions From manufacturer's specification
Open-circuit Temperature Coefficient
Applicability All PV systems
Definition Voc - temperature coefficient at open-circuit voltage
Units I/C
Input Restrictions From manufacturer's specification
Short-circuit Temperature Coefficient
Applicability All PV systems
Definition Voc - temperature coefficient at short-circuit current. This is supplied the manufacturer.
Units V/C
Input Restrictions From manufacturer's specification
Normal Operating Cell Temperature (NOCT)
Applicability All PV systems
Definition The normal operating cell temperature, typically between 45°C and 55°C
Units Degrees Celsius (°C)
Input Restrictions From manufacturer's specification
  • 1. De Soto, W., S.A. Klein, and W.A. Beckman, “Improvement and validation of a model for photovoltaic array performance”, Solar Energy, Volume 80, Issue 1, January 2006, Pages 78-88
  • 2. More information is available at http://www.gosolarcalifornia.ca.gov/nshp/.