HomeMy WebLinkAboutUTILITY DATA - 19-00075 - 772 Nina Dr - Tesla Powerwall ElectricalSep 14, 2018 CONFIDENTIAL INFORMATION - -- SHARED UNDER NDA ONLY Rev. 1.2
Powerwall 2 AC Utility Interconnection Support
2 Powerwall 2 AC Utility Interconnection Support
CONFIDENTIAL INFORMATION - -- SHARED UNDER NDA ONLY
TABLE OF CONTENTS
1. Introduction .................................................................................................................................................... 3
2. Specifications................................................................................................................................................. 4
Powerwall Electrical Specifications................................................................................................................................................. 4
Powerwall Environmental Specifications ..................................................................................................................................... 4
Powerwall Mechanical Specifications ............................................................................................................................................ 4
Backup Gateway Electrical Specifications .................................................................................................................................. 5
Backup Gateway Environmental Specifications....................................................................................................................... 5
Backup Gateway Mechanical Specifications .............................................................................................................................. 5
3. Certifications and Standards ................................................................................................................... 5
4. Common System Configurations ........................................................................................................... 6
Whole Home Backup – Downstream of Customer Main Breaker ................................................................................... 6
Whole Home Backup – Upstream of Customer Main Breaker.......................................................................................... 6
Partial Home Backup (Backup of Selected Loads) ................................................................................................................ 7
5. Modes of Operation .................................................................................................................................... 8
Backup Mode .............................................................................................................................................................................................. 8
Solar Self-Consumption Mode ........................................................................................................................................................... 9
Load Shifting Mode ............................................................................................................................................................................... 10
6. Frequently Asked Questions ................................................................................................................... 11
Device Specific Questions ................................................................................................................................................................... 11
Mode Specific Questions ..................................................................................................................................................................... 15
7. Interconnection Guide...............................................................................................................................16
Initial Technical Review Process ...................................................................................................................................................... 16
Fast Track Review for Non-Export Storage Systems: Notification Only ................................................................. 20
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1. Introduction
This document provides technical information about Powerwall, Tesla’s home battery solution.
The information provided in this document may be used by Tesla Certified Installers or the
electric utility itself as part of the interconnection process. This document also codifies a general
interconnection process most suitable for grid operators to assess and review interconnection
of the Powerwall and may be useful for other behind-the-meter storage systems.
Tesla Powerwall is a state-of-the-art battery system intended for residential and light
commercial applications. It enables the storage of energy from the grid or renewable sources,
such as solar power, that can then be used at night or during peak periods. Powerwall can also
provide backup power in case of a grid outage.
Powerwall 2 AC is an assembly that consists of lithium-ion battery cells, an isolated DC/DC
converter, an integrated AC inverter and a liquid thermal management system. The battery cells
inside Powerwall are the components closest to being a conventional battery; however, the
installer or user is never exposed to these cells since they are electrically and physically isolated
from contact by maintenance personnel or homeowners.
For backup applications, the Backup Gateway is used to isolate Powerwall from the grid and
facilitate the powering of backed up loads. The Backup Gateway is a separate piece of
equipment from the Powerwall, and is not directly connected to the Powerwall via power cables.
The Gateway is connected to the Powerwall via communication cables and thus functions
together with the Powerwall as a complete system. Within the Backup Gateway enclosure is a
microprocessor controlled power contactor, inclusive of line- and load-side voltage sensing and
current measurement.
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2. Specifications
The specifications below are for reference only. See product datasheets for more detail and
country specific variations.
Powerwall Electrical Specifications
Energy* 13.5 kWh
AC Voltage (Nominal) and
Maximum Continuous Current
120 V, 240 V: 24 A
100 V, 200 V, 220 V, 230 V: 25 A
Frequency (Nominal) 50/60 Hz
Real Power, max continuous 5 kW (charge and discharge)
Real Power, peak (10 s, off-grid/backup) 7 kW (charge and discharge)
Apparent Power, max continuous 5.8 kVA (charge and discharge)
Apparent Power, peak (10 s, off-grid/backup) 7.2 kVA (charge and discharge)
Power Factor Output Range +/- 1.0 adjustable
Power Factor (full-rated power) +/- 0.85
Overvoltage Category Category III
Max Supply Fault Current 10 kA
Max Output Fault Current 32 A
Round Trip Efficiency (Beginning of Life)1 90%
* Values provided for 25°C (77°F), 3.3 kW charge/discharge power.
Powerwall Environmental Specifications
Operating Temperature2 -20°C to 50°C (-4°F to 122°F)
Operating Humidity (RH) Up to 100%, condensing
Storage Conditions (up to 12 months) -20°C to 30°C (-4°F to 86°F)
Up to 95% RH, non-condensing
State of Energy (SoE): 25% initial
Maximum Altitude 3000 m (9843 ft)
Noise Level @ 1 m < 40 dBA at 30°C (86°F)
Enclosure Type NEMA 3R
Ingress Rating IP67 (battery and power electronics)
IP56 (wiring)
Wet Location Rating Yes
Pollution Degree Rating PD3
Seismic Rating AC156, IEEE 693-2005 (high)
2 Performance may be de-rated in extreme ambient temperatures.
Powerwall Mechanical Specifications
Height 1150 mm (45.3 in)
Width 755 mm (29.7 in)
Depth 155 mm (6.1 in)
Weight 125 kg (276 lbs)
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Backup Gateway Electrical Specifications
Disconnect Current 200 A
Overcurrent Protection Breaker*** 100-200 A
Overvoltage Category Category IV
Fault Current Withstand Rating 10 kAIC
AC Meter Revenue grade
Service Rating Suitable for Use as Service Equipment
*** Circuit breaker required for installation at service entrance
Backup Gateway Environmental Specifications
Operating Temperature -20°C to 50°C (-4°F to 122°F)
Operating Humidity (RH) Up to 100%, condensing
Maximum Altitude 3000 m (9843 ft)
Enclosure Type NEMA 3R
Ingress Rating IP44
Pollution Degree Rating PD3
Backup Gateway Mechanical Specifications
Height 740 mm (29.1 in)
Width 378 mm (14.9 in)
Depth 129 mm (5.1 in)
Weight 16.4 kg (36 lbs)
3. Certifications and Standards
The Tesla Powerwall is certified and tested to the standards listed in the following table.
If physical certificates are required, please email powerwall@tesla.com with your request.
Safety UL 1642, UL 1741, UL 1973, UL 9540, UN 38.3, IEEE 1547,
IEC 62109-1, IEC 62109-2, IEC 62619, CSA C22.2.107.1
Grid Standards Worldwide compatibility
Emission FCC Part 15 Class B, ICES 003
Environmental RoHS Directive 2011/65/EU,
WEEE Directive 2012/19/EU,
Battery Directive 2006/66/EC
REACH Regulation
Seismic AC156, IEEE 693-2005 (high)
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4. Common System Configurations
Whole Home Backup - -- Downstream of Customer Main Breaker
Whole Home Backup - -- Upstream of Customer Main Breaker
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Partial Home Backup (Backup of Selected Loads)
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5. Modes of Operation
Three standard modes of operation are available for the Powerwall: Backup, Solar Self-Powered,
and Time-Based Control.
Backup Mode
Backup Mode allows for partial or whole home transition to off-grid during a grid outage.
The Powerwall's interaction with the grid is primarily handled by the Backup Gateway. As shown
in the previous section, the Backup Gateway is installed between the main panel and utility meter
for whole home backup, and between the main panel and an essential loads subpanel for partial
home backup. The Backup Gateway contains a synchronizer within its controller and uses the
synchronizer when transitioning on and off grid. The Backup Gateway manages the
disconnection with the grid through an internal power contactor that is automatically controlled.
The contactor opens and disconnects the backed-up loads from the grid when a grid outage is
detected.
When transitioning the home loads between off-grid and on-grid, the following steps occur:
Disconnect
from Grid
1. Backup Gateway detects grid outage.
2. Backup Gateway sends signal to Powerwall to prepare for off-grid operation.
3. Backup Gateway opens contactor within approximately 30 ms of outage
detection, physically isolating the backed-up loads from the utility grid.
4. Powerwall begins off-grid operation (changing from grid following to grid
forming) within approximately 25 ms of isolation from grid.
Reconnect
to Grid
1. Backup Gateway detects grid within normal operating conditions for the
required amount of time.
2. Backup Gateway sends signal to Powerwall to prepare for on-grid operation.
3. Backup Gateway synchronizes with the grid and closes contactor,
reconnecting to the grid and transitioning on-grid within approximately 25 ms.
If the Powerwall is configured for Backup Mode, it will charge and discharge as follows:
Site
Configuration Charge Discharge
Standalone The Powerwall will charge from the grid. The
default charge power is 3.3 kW per Powerwall.
Only during a grid outage,
when the backed-up loads
are isolated from the utility
grid via the Backup Gateway.
Solar Onsite The Powerwall will charge from any onsite solar
production during normal operation.
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Solar Self-Powered Mode
If the home has solar on site, the customer may choose to operate their Powerwall in Solar Self-
Powered Mode (also known as Self-Consumption Mode). In this mode, the Powerwall will charge
from solar during normal operation and discharge to serve loads behind the customer’s meter.
Solar Self-Powered Mode has a user-configurable Backup Reserve. The Powerwall will reserve
this energy in the event a grid outage occurs and will not use this energy for Solar Self-Power.
If the Powerwall is configured for Solar Self-Powered Mode, during normal operation it will
charge and discharge as follows:
Load Relative to
PV Generation Charge 1 Discharge
Load > PV Will not charge. Will discharge to serve onsite load.
Load < PV Will charge from excess PV. Will not discharge.
Energy from the Powerwall is not exported to the grid. The export of energy is limited to only
PV generation; however, the mode tries to maintain this export of energy as close to zero as
possible. The Backup Gateway monitors the power exchange with the utility through the Tesla-
provided whole home meter. If export is detected, the Backup Gateway quickly commands the
Powerwall to reduce discharge power or increase charge power.
As Solar Self-Powered is a load-following mode of operation, a short duration inadvertent export
from the Powerwall may occur when loads turn off. The magnitude of export is generally limited
to the size of the largest load and the duration is less than 5 seconds.
Solar Non-Export Mode
In some jurisdictions, customers may choose to make the PV inverter non-export in order to go
through a simpler interconnection process or due to a regulatory requirement. Solar Non-Export
Mode limits the export of energy to the grid to zero for both the Powerwall and PV inverter,
even if the Powerwall is fully charged and there is excess PV energy. In this subset of Solar Self-
Powered, short duration inadvertent export may still occur. The interconnection process and
operating criteria of non-export systems are discussed in the section on Fast Track Review for
Non-Export Storage Systems.
1 The Powerwall may charge from the grid during abnormal conditions, such as when the Powerwall’s state
of energy is critically low.
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Time-Based Control Mode
In Time-Based Control Mode (sometimes called time-of-use or TOU mode), the Powerwall
charges during off-peak times when utility rates are low, and discharges to serve onsite loads
during on-peak times when utility rates are high. The on-peak and off-peak times are set by the
customer in the mobile app and based on utility time of use rates. As with Solar Self-Powered
Mode, Time-Based Control Mode has a user configurable Backup Reserve. The Powerwall will
reserve this energy in the event a grid outage occurs and will not use it for load shifting.
If the Powerwall is configured for Time-Based Control Mode, during normal operation it will
charge and discharge as follows:
Site Configuration Charge Discharge
Standalone Will charge from the grid when
utility rates are low.
Will discharge to serve onsite
loads when utility rates are high.
Solar Onsite
(Solar Only Charging)
Will charge from PV when utility
rates are low.
Will discharge to serve onsite
loads when utility rates are high.
Energy from the Powerwall is not exported to the grid. The export of energy is limited to only
PV generation. The Backup Gateway monitors the power exchange with the utility through the
Tesla-provided whole home meter. If export from the Powerwall is detected, the Backup
Gateway quickly commands the Powerwall to reduce discharge power or increase charge
power.
As Time-Based Control is a load-following mode of operation, a short duration inadvertent
export from the Powerwall may occur when loads turn off. The magnitude of export is generally
limited to the size of the largest load and the duration is less than 5 seconds.
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6. Frequently Asked Questions
Provided below are questions commonly asked during the utility interconnection process.
Device Specific Questions
What is the power and energy rating of the Powerwall?
• 5 kW Real Power continuous max.
• 5.8 kVA Apparent Power continuous max.
• 13.5 kWh usable energy.
See the Powerwall datasheet for more specifications.
Is the Powerwall UL 1741 certified?
Yes, the Powerwall is UL 1741 certified.
Can the Powerwall provide advanced inverter features?
The inverter within the Powerwall is able to provide advanced inverter features. For California
and Hawaii, these functions are certified to UL 1741 SA.
Will the Powerwall comply with voltage and frequency ride through requirements, if
applicable?
Yes, if the local jurisdiction has voltage and frequency ride through requirements, the
Powerwall will comply.
Does the Powerwall ever export to the grid?
In all modes, the system is controlled such that energy from the Powerwall is not exported to
the grid. The Backup Gateway monitors the whole-home meter and controls the Powerwall such
that its discharge is only consumed by onsite load. The Powerwall reduces its discharging or
increases its charging to control around the net load at the point of common coupling and
ensure the Powerwall does not export. As Solar Self-Powered and Time-Based Control are load-
following modes of operation, a short duration inadvertent export from the Powerwall may
occur due to a sudden load drop or increase in PV output. The magnitude of export is generally
limited to the size of the largest load.
Does the Powerwall operate in parallel with the grid?
If the Powerwall is operating in Backup Mode, it does not operate in parallel with the grid. The
Powerwall may charge from the grid, but discharges only when disconnected and isolated from
the grid. If the Powerwall is operating in Solar Self-Powered Mode or Time-Based Control Mode,
it does operate in parallel, but only as a current source. A short duration inadvertent export
event may occur when loads are turned off. Details on these modes can be found in the Modes
of Operation section.
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When paired with Solar, does the Powerwall ever charge from the grid?
In the US market, Powerwall is designed to charge from solar power when a solar generator is
present. This is accomplished through software control that matches the Powerwall charging
rate with available solar power.
In exceedingly rare cases, an abnormal condition may cause a Powerwall to charge a small
amount from the grid. If the unit is discharged below its operating range and is at risk of losing
the ability to function, it will charge at low power briefly to maintain its ability to charge when
solar energy returns. The purpose of the brief charge is to keep the Powerwall operational and
does not result in usable energy in the battery. This rare abnormal condition could occur if the
Powerwall is at zero charge and is unable to charge itself for an extended period of time, such
as might happen if the onsite solar generator is not able to operate.
Powerwall also has a feature called Storm Watch, which prepares Powerwall for a likely grid
outage because of an imminent weather event. Tesla monitors weather conditions and remotely
enables Storm Watch in the rare occasion that grid outages are likely. When enabled, Storm
Watch places Powerwall into backup mode and lifts the solar-only charging constraint for as
long as the risk of outages is high. Solar-paired Powerwalls will charge themselves with solar
power when available, but will also charge from the grid for a limited time, up to the Backup
mode default charge rate of 3.3 kW. Powerwall owners can disable and enable Storm Watch
through the Tesla mobile app.
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Does the Powerwall use a traditional 3-pole automatic transfer switch?
The Powerwall does not use a traditional 3-pole automatic transfer switch. This type of switch
would isolate the Powerwall both electrically and mechanically, preventing the Powerwall from
charging. In lieu of a 3-pole automatic transfer switch, the Powerwall uses the Backup Gateway.
The Backup Gateway is designed to detect any abnormal conditions before the Powerwall.
When the Backup Gateway detects an outage, it sends a signal to the Powerwall to prepare for
off-grid operation. The Powerwall cannot go into a grid forming mode until the Backup Gateway
contactors are open. The figures below highlight the difference between a 3-pole transfer switch
and the Backup Gateway.
M
PV Inverter
AC Powerwall
N
Utility
Meter
MCB
HOME PANELBOARD
240/120V
BUS AMPACITY
G
Backup
Gateway
BACKUP GATEWAY – ON GRID
M
PV Inverter
AC Powerwall
N
MCB
HOME PANELBOARD
240/120V
BUS AMPACITY
G
Utility
Meter
Backup
Gateway
BACKUP GATEWAY – OFF GRID
M
PV Inverter
N
Utility
Meter
MCB
HOME PANELBOARD
240/120V
BUS AMPACITY
G
Automatic
Transfer
Switch
Backup
Generator G
TRANSFER SWITCH – ON GRID
M
PV Inverter
N
Utility
Meter
MCB
HOME PANELBOARD
240/120V
BUS AMPACITY
G
Automatic
Transfer
Switch
Backup
Generator G
TRANSFER SWITCH – OFF GRID
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Do the Powerwall and Backup Gateway use an open or closed transition when backing up
loads?
The Powerwall and Backup Gateway do not necessarily use an open or closed transition. When
an outage is detected by the Backup Gateway, it sends a signal to the Powerwall to prepare for
off-grid operation. At the same time, the Backup Gateway also opens its AC contactors, limiting
any parallel operation to the approximately 30 ms response time of the contactors. The
Powerwall’s response resembles a load’s response in the sense that the switching on and off of
a load has the same impact to the grid as switching the Powerwall on and off. The Powerwall is
a current limited source, and does not present the same inertial response as experienced with
traditional generators.
How does the Powerwall synchronize with the grid?
The Backup Gateway contains a synchronizer within its controller and uses the synchronizer
when transitioning on and off grid. The synchronizer is used to check frequency, voltage, and
phase difference before the contactor within the Backup Gateway is opened or closed.
Will the Powerwall be metered separately?
The Powerwall does not have a dedicated meter, but its charge and discharge power and energy
are logged by the Backup Gateway.
What happens if Powerwall loses communication with the Backup Gateway?
If the Powerwall and Backup Gateway lose communication with each other, the Powerwall will
enter a safe mode. The Powerwall will open the AC contactor within 20 seconds and remain
open until communication with the Backup Gateway is resumed. Additionally, the Powerwall’s
compliance to UL 1741 is not dependent on an Internet connection. The Powerwall will detect
when the grid’s voltage and frequency are abnormal or when an island occurs.
The Powerwall and Backup Gateway do not rely on an internet connection to communicate.
While communication with the Backup Gateway is possible through an internet connection, this
path is strictly for monitoring and troubleshooting, and is not related to safety.
Will the Powerwall ever be installed standalone without a behind-the-meter PV system?
Yes, it can be installed without solar and operate in Backup Mode and Time-Based Control Mode.
Does the Powerwall contribute fault current?
Yes, for a short duration and similar to PV inverters. Short circuit testing for the Powerwall
shows a maximum fault current of less than 32 A RMS for a maximum duration of 4 cycles
(67 ms).
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Mode Specific Questions
What is the intended use of the Powerwall?
Three of the intended use cases for Powerwall are:
1. Backup
2. Solar Self-Powered
3. Time-Based Control
Can the customer configure the operation of the battery?
Yes. The customer can configure settings through a user app. Configurable settings include
mode of operation and backup reserve. Operating constraints like solar-only charging and non-
export are not user-configurable.
During a grid outage, what prevents the Powerwall from backfeeding the utility grid?
The Backup Gateway is designed to detect the abnormal condition before the Powerwall,
enabling a smooth transition. The Powerwall cannot go into a grid forming mode until the
Backup Gateway contactors are open. Therefore, it is not physically possible to export when the
grid is down. If for some reason the Backup Gateway did not open its contactors, the Powerwall
would detect the abnormal conditions and trip offline per UL 1741 and IEEE 1547 requirements,
just as a PV inverter would do.
During a grid outage, what happens to excess PV generation when the Powerwall is fully
charged?
When off-grid and when excess PV generation cannot be stored by the Powerwall, the PV
generation will be curtailed or the PV inverter will trip offline.
How are the Powerwall, PV generation, and home load managed?
The Backup Gateway determines how to charge and discharge the Powerwall based on the
mode of operation. Excess PV generation not consumed by onsite load is stored in the
Powerwall, curtailed, or exported. See the Modes of Operation section for more information.
Will adding a Powerwall to a PV system still meet the requirements for NEM eligibility?
NEM eligibility is determined by jurisdiction; however, the Powerwall can be configured such
that it is charged by onsite PV generation during normal operation and, aside from any
inadvertent export events, the Powerwall’s discharge of energy is consumed onsite. In this
configuration, the charging and discharging of energy all occurs behind the meter.
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7. Interconnection Guide
When used for Backup, Solar Self-Powered, or Time-Based Control, the Powerwall can increase
reliability and resiliency, enable customers to consume renewable generation onsite, and reduce
the impact a customer’s load profile has on the electric grid. This reduced impact of distributed
storage systems on the grid allows for a more simplified interconnection process than is
typical of a standalone solar PV system.
Initial Technical Review Process
A proposed and generalized Initial Technical Review Process that reflects the reduced impact
to the grid of storage is described on the following pages. This process is informed by various
mature utility interconnection processes focused on distributed solar PV systems (especially
Net Energy Metered processes), but tailored to reflect the technical differences of distributed
storage systems. The process is applicable to stand-alone energy storage system deployments
as well as storage plus solar PV deployments.
As the Powerwall is a resource that can be configured and dynamically controlled,
interconnection screens should be based on the system’s operating characteristics rather than
the nameplate ratings of the Powerwall and PV inverter. Therefore, these storage system
operating characteristics can be modified to avoid grid upgrades that might otherwise be
triggered if these systems were assessed solely on nameplate capacity. If interconnection
screens are failed such that Supplemental Review is required, the storage system operating
characteristics should also be considered in lieu of nameplate capacities in the Supplemental
Review.
The following diagram provides an overview of the proposed Initial Technical Review Process.
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Inverter Based and UL 1741 Certified
Yes
Single-Phase Generator B
Short Circuit Contribution Ratio G
Network System
Proceed with interconnection
subject to requirements
determined in Initial Review.
Yes
C
Non-Export
No
Distribution Transformer/Secondary Conductor Rating E
Export < 11 kVA
Short Circuit Interrupting Capability H
Transformer Line Configuration I
No
Yes
Pass all screens or does a quick review determine any requirements to address all
applicable failed screens?
Hosting Capacity J
NoYes
Proceed to Supplemental Review.
A
D
F
Initial Technical Review Process
Fast Track Review
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Screen A: Is the equipment inverter based and UL 1741 certified?
This is used as the introductory screen to simplify the process that would otherwise be more
complicated by rotating machine-based generation. Equipment that fails this screen should
follow a different process. UL 1741 certified inverters have had their protective and anti-islanding
functions tested. Inverters are also current limited. Their starting voltage drop and fault current
contribution are significantly less than rotating machine-based generation.
The Powerwall is inverter based and UL 1741 certified. Tesla will also ensure that any PV inverter
used is UL 1741 certified as well.
Screen B: Does the single-phase equipment cause unacceptable imbalance?
This screen ensures that a 120 V connected generator does not cause unacceptable imbalance
across the two 120 V phases.
In most applications, the Powerwall and PV inverter used will be connected at 240 V and will
not contribute to imbalance on the two 120 V phases.
Screen C: Is the equipment interconnecting to a networked secondary system?
This screen addresses whether or not the system is interconnecting to a networked secondary
system, as these systems are designed and operated with network protectors.
If the Powerwall and PV inverter are interconnecting to a networked secondary system,
additional review may be required to ensure reliable operation of the networked secondary
system.
Screen D: Will power be exported across the point of common coupling (PCC)?
Systems passing this screen bypass the remainder of the initial technical review screens. Their
impact on the electric grid is minimal as the grid is still operating within its traditional design
parameters. Systems that only inadvertently export energy should be treated as non-export.
Thermal overload of distribution transformers or secondary conductors from non-export
systems is not expected as any inadvertent export is small in magnitude and short in duration.
Inadvertent export is also load following and generally non-coincident with the inadvertent
export of other systems.
Depending on the application, the Powerwall and PV inverter may be configured to not export
energy across the PCC.
Screen E: Is the distribution transformer or secondary conductor rating exceeded?
This screen addresses whether or not the export of energy will overload the distribution
transformer or secondary conductor.
There may be situations in which the export of energy triggers a transformer or secondary
conductor upgrade. When evaluating possible mitigations, modifying the operating
characteristics of the system should also be considered as it may be more economical to curtail
or charge from this excess energy.
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Screen F: Does the installation export less than 11 kVA across the PCC?
This screen addresses whether or not the system can bypass short circuit, line configuration,
and penetration based screens.
This screen should be based on the operating characteristics of the system. Systems passing
this screen will have a minimal impact on fault current levels, potential overvoltages from loss
of system neutral grounding, and hosting capacity.
Screen G: Is the short circuit contribution ratio within acceptable limits?
This screen addresses whether the installation will impact the transmission and distribution
system’s protection schemes. When measured at the primary side of a distribution transformer
serving the installation, the sum of the short circuit contribution ratios of all installations
connected to the distribution transformer should be less than or equal to 10%. If this screen is
passed, significant impacts are not expected.
Screen H: Is the short circuit interrupting capability exceeded?
This screen addresses whether the installation will cause any equipment overstress on the
transmission and distribution system. In aggregate with other installations, the installation
should not cause any protective devices to exceed 87.5% of their interrupting capability. If this
screen is passed, equipment overstress is not expected.
Screen I: Is the line configuration acceptable?
This screen addresses whether there is a possibility of overvoltages due to a loss of system
neutral grounding.
The Powerwall and PV inverter are typically installed in single phase locations. If connected line-
to-neutral, they will not cause overvoltage from loss of system neutral grounding. If connected
line-to-line, overvoltages would only be possible if other loads were connected line-to-ground,
and would still be unlikely under those conditions. As an additional screen in this scenario, some
utilities use 10% of peak load as a penetration threshold. If a system fails these screens, additional
analysis should be performed before requiring upgrades.
Screen J: Does the export of power exceed hosting capacity thresholds?
This screen addresses whether the export of power from the installation violates any hosting
capacity thresholds. In order to accommodate this screen, a hosting capacity analysis is
recommended to determine how much exported energy can be hosted by the electric grid.
Quick Review: Does a quick review determine any requirements to address all applicable
failed screens?
This screen addresses whether any simple adjustments can be made to the storage and PV
system or grid to pass a previously failed screen. For example, the operating characteristics of
the installation could be easily modified to pass Screen E or J. Operating characteristics may
also be modified to avoid an upgrade that may otherwise be triggered. Distribution system line
equipment settings may also be adjustable to accommodate the system. The intent of this
screen is to avoid the Supplemental Review process and system upgrades if small adjustments
can be made.
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Fast Track Review for Non-Export Storage Systems: Notification Only
In this proposed Initial Technical Review Process, non-export storage systems passing screens
A through D qualify for the simplest review process, where a notification-based approach can
be used in lieu of an interconnection application. This notification-based approach would
appropriately streamline the interconnection process and facilitate deployment of non-export
distributed storage systems.
The impact a non-export system has on the grid is de minimis when compared to traditional
exporting systems. Operating requirements should be defined to ensure this reduced impact,
such as requirements on the amount of energy inadvertently exported. As has been done in
Hawaii 2, California 3,4,5, and Colorado 6, it is appropriate to define within interconnection tariffs
the requirements of a non-export system. Such definition would allow vendors to certify against
such requirements, thus enabling them to utilize a notification-based approach to the
deployment of distributed storage systems.
Sample requirements based on California Rule 213,4,5 include:
• The Generating Facility must utilize only UL 1741 or UL 1741 SA certified inverters.
• The Generating Facility must monitor that total energy export is maintained to be no
more than the Generating Facility’s Gross Nameplate Rating multiplied by 0.1 hours per
day over a rolling 30-day period (e.g., for a 100 kVA gross nameplate Generating Facility,
the maximum energy allowed to be exported for a 30-day period is 300 kWh).
• The Generating Facility must disconnect from the Distribution System, cease to energize
the Distribution System, or halt energy production within two seconds after the period
of continuous export exceeds 30 seconds.
• Failure of the control or inverter system for more than 30 seconds, resulting from loss of
control signal, loss of control power, or a single component failure or related control
sensing of the control circuitry, must result in the Generating Facility entering a safe
operating mode where inadvertent export events will not occur.
2 Rule No. 22. Hawaiian Electric Company (HECO), 2017.
3 Electric Rule No. 21, Pacific Gas & Electric Company (PG&E), 2017.
4 Rule 21, Southern California Edison (SCE), 2017.
5 Rule 21, San Diego Gas & Electric Company (SDG&E), 2017.
6 “Guidance No. 1 for the Interconnection of Electric Storage as Stand-Alone Sources, Parallel
Operation for Customers without Generation, and in Parallel with Self-Generation”, Xcel
Energy, 2017.
Rev 1.2 Sept 14, 2018
Tesla, Inc.
3500 Deer Creek Road
Palo Alto, CA 94304
Tesla Motors Netherlands B.V.
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Tilburg, Netherlands