HomeMy WebLinkAboutStaff Report 14589
City of Palo Alto (ID # 14589)
Utilities Advisory Commission Staff Report
Meeting Date: 12/7/2022 Report Type: VII. NEW BUSINESS
City of Palo Alto Page 1
Title: Discussion of Costs and Reliability of Different Back-up Electricity
Technologies
From: Director of Utilities
Lead Department: Utilities
RECOMMENDATION
This report is for the Utilities Advisory Commission’s (UAC) review and discussion of back-up
electricity options at homes. No action is required.
EXECUTIVE SUMMARY
The UAC expressed interest in having City of Palo Alto Utilities (CPAU) staff provide further cost
and reliability information for different back-up electricity options for both everyday power
outages and after major emergencies such as earthquakes. This report presents the analysis
and findings evaluated by CPAU’s Stanford Summer Shultz Fellow and Stanford Graduate
Student Keola Iskander comparing cost and reliability across several different technologies for
back-up power for both single-family homes and multi-family homes.
Any system capable of powering a home during an outage through the home’s electrical system
(i.e. not via extension cords to an external battery or generator) requires involved electrical
wiring and safety switches, which are critical to the safety of utilities workers when restoring
power. The wiring and safety devices require special planning, labor, and materials to install,
additional permitting, extensive interconnection inspections, and associated costs on all
dimensions. Given the extensive time and costs required, there may be limited interest in these
systems, especially with the high electricity reliability of Palo Alto compared to other utilities.
Despite Palo Alto’s generally high reliability, recent outages have been a concern for some
customers.
Some notable takeaways from the study include that for an average Palo Alto single-family
home, a 7 kW solar PV and 13.5kWh battery have a similar annualized price range to a natural
gas whole house generator, and that the solar with battery system is enough to cover energy
needs through a 48-hour outage in a peak summer day. The same system could have potentially
higher reliability in case of fuel disruptions and cover about a third of the peak winter energy,
which could be enough to cover critical winter loads in a major emergency. For context, the
longest electrical outage since 2015 in Palo Alto has been 26 hours. The solar and battery
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system is also silent while the natural gas whole house generator may cause an undesirable
level of noise for some customers.
For a lower annualized cost, a 7 kW solar PV system with single back-up inverter for plug loads
has a similar net cost to portable gasoline generator, and provides about half the back-up
power most days in the summer. Solar PV with a single back-up inverter systems are silent,
convenient, and enough to power refrigerators & WIFI, do not run out of fuel, and does not
have to be run frequently to maintain, and does not carry the risk of carbon monoxide
poisoning. More investigation is needed, but these could be a viable low-cost option for those
who have solar or interested in getting solar. Uninterruptible power supply (UPS) batteries
could be another option for short duration outages for those with critical medical needs.
For multi-family homes, electrifying water heating as well as the heating of the community
room in a specific multifamily residence was found to be cost effective when combined with a
small solar PV and battery installation. The small solar and battery system would be enough to
provide heating or cooling to the community room, as well as refrigeration. This shows some
potential for bundling electrification of heating with solar and storage and allow community
rooms of multifamily residences to function their own emergency shelter in case of a major
emergency, or during a heat-wave or smoke event.
BACKGROUND
A previous study conducted by another Stanford Shultz Fellow in summer 2021 found that
electrification of single-family residential units did not significantly impact the resiliency of
single-family homes.1 The previous study primarily investigated the resiliency value of back-up
power solutions in different widespread or catastrophic disasters. This study compares
additional systems and delves into costs as well as resiliency provided in different types of
outages, not just widespread catastrophic outages.
The UAC and Council have expressed interest in the viability of renewable generation for
providing similar back-up at similar costs to fossil generators, for both everyday outages as well
as in major emergency events. While a great deal of planning is required for wiring of these
systems, proper safety switches and permitting, and thought and pre-prioritization of loads is
needed, this study explores some of the roles for different renewable back-up systems and
their costs, reliability, and in some case other advantages over fossil generators. The reliability
is examined for everyday outages as well as potential major emergencies.
1 Impact of Decarbonization on the Resiliency of Single-Family Homes in Palo Alto
https://www.cityofpaloalto.org/files/assets/public/agendas-minutes-reports/agendas-minutes/utilities-advisory-
commission/archived-agenda-and-minutes/agendas-and-minutes-2021/11-03-2021-regular/id-13608.pdf
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Figure 4. Cumulative distribution of the time to restore service (CAIDI) from an electric outage
in Palo Alto from 2015-July 2022. 90% of these power outages in Palo Alto are less than 8 hours,
and 75% of outages are less than 4.5 hours.
An additional tool which might be worth exploring for interested customers is ReOPT, a publicly
available tool available from the National Renewable Energy Laboratory (NREL). ReOPT is an
optimization tool that that applies an estimated monetary value from avoided outages and
allows users to size energy systems for resiliency.2 Furthermore, building electrification can
enhance resiliency of residential homes because swapping out gas furnaces for electric heat
pumps can provide heating and cooling in the summer. Heat pumps provide heating and
cooling needs, along with protection from wildfire smoke and other air pollutants due to closed
windows and doors during operation. Staff has assessed this tool to be underestimating costs
but it could be used to investigate relative different costs of technologies or provide rough
estimates.
DISCUSSION
Staff evaluated seven different back-up electricity options for single family homes. Staff also
modeled a multifamily residence which has minimal remaining gas appliances, estimated the
net costs of electrifying those appliances, and adding limited back-up power in the form of a
small solar and storage system. This back-up electricity system was sized to provide heating or
cooling, lighting, and refrigeration to the community room in case of an outage.
Single-Family Analysis
Staff examined commercially available back-up energy systems for residential homes such as
solar PV systems with partial back-up solar inverters, grid-forming solar microinverters, battery
storage, whole-house natural gas generators and portable gasoline generators. Generally, solar
2 https://reopt.nrel.gov/tool/
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PV systems will not operate during an outage due to the system being grid-tied. Thus, off-grid
capable solar inverters such as the SMA Sunny Boy inverters and Enphase IQ8 grid-forming
microinverters are required to provide power to homes when there is no available power from
the grid. However, residences must follow proper engineering permitting guidelines and local
regulations to install back-up energy generating systems. Specifically, islanding solar and/or
storage systems from the grid requires an AC disconnect on the property to disconnect the
back-up system from the grid during an outage, thus preventing electricity flow to the grid and
protecting utility workers servicing the power system.
Annualized net costs presented include the costs and financial benefits. Capital costs of solar
and battery systems will vary depending on the financing term and proportion of energy
consumption offset by solar PV and storage systems. Capital cost of fossil-fuel generators
assumes the cost of a Generac 9 kW Natural Gas Whole House Back-up Generator and a
Generac 3.6 kW Portable Gasoline Generator with installation costs included. Paired solar and
battery storage system assumes battery storage is replaced after 10 years.
Solar PV systems currently do not operate when there is a grid outage, which means these
systems are grid-tied. However, there are commercially available specialized inverters that
allow off-grid energy generation of Solar PV systems by disconnecting (islanding) the system
from the grid when an outage is detected. Two off-grid capable inverters are considered for this
study, which are SMA Sunny Boy inverters and Enphase IQ8 microinverters. SMA Sunny Boy
inverters are string inverters with a unique secure power supply (SPS)3 function that provides 2
kW of power to a dedicated single outlet during a power outage. Enphase IQ8 microinverters
are grid-forming inverters that allow solar PV systems to continue operating on the same grid
frequency in an outage event. These microinverters are capable of supplying power to a sub-
panel or main-panel equal to the capacity of the solar PV system. However, it is not
recommended to connect the microinverters to a main electric panel, unless paired with a
battery storage system to provide whole house back-up power.
Two battery storage systems were also considered for resiliency measures. These are the Tesla
Powerwall 2 batteries and Enphase IQ Battery 10 batteries. Enphase IQ Battery 10 have lower
storage capacities than Tesla Powerwall 2 batteries, but Enphase batteries are composed of a
series of micro-inverters that allow the battery system to continue operating when a
microinverter malfunctions. Enphase batteries were only considered in this study when paired
with a solar system and Enphase IQ8 grid-forming microinverters.
Table 1. Home energy systems considered in the study along with their rated power capacity
and available capacity during an outage.
Energy System Rated Capacity (kW) Storage Capacity
(kWh)
Power Supplied in an
Outage (kW)
3 https://www.sma-america.com/products/solarinverters/sunny-boy-30-us-41-77-us-41.html and
https://www.sma-sunny.com/us/how-to-explain-secure-power-supply-to-homeowners/
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Solar + Partial Back-
up Inverter
7 kW None 1.5 kW
(plug loads only)
Solar + Grid-forming
Microinverters
7 kW None 2 kW
(Back-up for 4
circuits)
Stand-alone Battery
Storage
5 kW 13.5 kWh 5 kW
Solar + Battery
Storage
7 kW / 5 kW BESS 13.5 kWh 5 kW
Solar + Grid-forming
Microinverters +
Battery
7 kW / 3.8 kW BESS 10 kWh 2 kW
3.8 kW BESS
Natural Gas Whole
House Generator
9 kW None 9 kW
Portable Gasoline
Generator4
3.6 kW ~50kWh (delivered
electric from 5-gallon
gasoline tank onsite)
3.6 kW
(plug loads only5)
4 Sale of portable gasoline generators to be banned in 2028 https://ww2.arb.ca.gov/news/carb-approves-
updated-regulations-requiring-most-new-small-road-engines-be-zero-emission-2024
5 For modeled costs, generator is assumed to be used with extension cords plugged into a generator sufficiently far
from windows and doors to not present a risk from exhaust. Portable generators can be connected to a whole
house transfer switch, which requires additional wiring, costs, etc.
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Figure 1. Annualized net cost ranges of the energy systems considered in the study. Solar and
battery storage have lower O&M costs, while portable gasoline generators and natural gas
generators have increasing O&M costs with frequent and longer power outages. Higher
electricity bill savings can be achieved with a solar and battery system. The Solar PV + Partial
Plug Load Back-Up is only compatible with some solar inverters.
The solar inverter and storage systems considered have different power capacities which
affects the electric reliability of a home. However, most of the systems considered in the study6
can supply sufficient energy to meet an average all-electric household energy demand in Palo
Alto. These systems are resilient for outages less than seven hours, but the level of electric
reliability provided by these systems decreases with longer-duration outages. This study also
explores the resiliency of these different energy systems by varying duration of outages and
household energy consumption.
On an average day, an average Palo Alto home modeled as all-electric consumes 12,400
kWh/year, or 34 kWh/day, representing a 65% increase in electricity consumption compared to
a mixed-fuel home. By simulating an outage occurring at every hour of the day for various all-
electric residential energy consumption throughout the year, the study found that most of the
energy systems considered in the study can supply sufficient power for an average all-electric
consumption in short to medium term outages (< 12 hours), however resiliency levels can vary
by household consumption, time of year, and hourly performance of solar PV systems.
6 Neither the stand-alone solar PV with partial back-up inverter for 2 kW of plug loads or the grid-forming
microinverters installed without a battery are enough to cover all-electric homes even in the daylight hours of the
summer.
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Figure 2. Average proportion (%) of household load met in an outage for a peak summer
energy consumption scenario of an all-electric single-family home. Modeled peak summer
energy consumption of an all-electric home is 27 kWh/day.
Figure 3. Average proportion (%) of household load met in an outage for a peak winter energy
consumption scenario of an all-electric single-family home. Modeled peak winter energy
consumption of an all-electric home is 92 kWh/day.
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Table 2. Resiliency summary of different energy systems with their respective net system cost
and annualized cost. Energy systems are compared by their level of reliability in different
outage scenarios. High resiliency denotes the system’s capability in providing sufficient
energy for normal consumption in an outage. Moderate resiliency means the system can
provide some energy during an outage but requires consumer behavior modification such as
appliance time-of-use or reduced energy consumption. Low resiliency signifies the system’s
inability to provide adequate energy in longer duration outages and requires users to
conserve energy consumption. Noise level and emissions quantified on separate scale.
Planned Outage
(< 6 hours)
Load Shedding
Event
(< 6 hours)
Storm Event
(6 - 12 hours)
After Major
Earthquake
( >24 hours)
Portable Gasoline
Generator
(Plug Load Back-up)
$120
Solar PV
+ Partial Back-up
Inverter
(Plug-Load Back-up)
$290
Natural Gas
Whole-House
Generator
$630
Solar PV
+ Grid-forming
Microinverters
(Back-up 4 Circuits)
$760
Solar PV + BESS $790
Stand-alone Battery
Storage $1,130
Solar PV
+ Grid-forming
Microinverters
+ Battery
$1,240
Reliability Level Provided For:
Technology Noise Level
Dangerous CO
& CO2
Emissions?
Annualized Cost
($)
Multi-family Analysis
Palo Alto Libraries and community centers can become cooling centers during extreme heat
events, however, in certain conditions, these facilities could be overpopulated and strained to
provide adequate emergency service response. By transforming multi-family common areas to
localized community centers with back-up power, the City can improve community emergency
preparedness and resiliency during a power outage event. During an outage, multi-family
residents can gather in the common area for heating/cooling needs, refrigeration of food or
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medical supplies, cooking, and charging electronics. Adding heat pumps to common areas
provides cooling capabilities and can offer protection from wildfire smoke because it allows
residences to close windows and doors in the common area.
The study found that a stand-alone 7 kW-DC solar PV system has a lifetime cost of $5,700 to
$15,000 depending on the inverter used, and pairing solar PV systems with a 5 kW/13.5 kWh or
a 3.84 kW/10.08 kWh battery storage can increase the system cost range to $16,000 - $25,000.
The estimated cost to add a 10 kW-DC solar PV and 5 kW / 13.5 kWh battery storage on a multi-
family property is $11,000. Stand-alone solar PV systems were found to be a net benefit to
consumers depending on the proportion of daily energy consumption from solar and
equipment financing terms, however the addition of battery storage is still a net cost to
consumer.
Community area and shared gas appliances in multi-family residentials generally include gas
ranges, water heaters, furnaces, and dryers. This study finds that electrification of two central
gas water heaters, one central gas furnace, and two gas dryers removes 21 tons of CO2 annually
and has an estimated cost of $40,000. The estimated 20-year net present value of natural gas
savings is $46,000 with a payback period of 17 years. Savings potential will vary depending on
the multi-family property’s gas consumption. Higher gas consumption for space and water
heating will generate higher savings when switching to the more efficient heat pumps and heat
pump water heaters. Table 3 shows the estimated natural gas savings based on different
discount rates.
The majority of the savings from electrification is the switch to heat pump water heaters from
gas water heaters. Switching from a gas dryer to an electric dryer was found to be a net cost
because electric dryers are usually less energy efficient than gas dryers. In addition, multi-family
property owners must navigate contractual agreements with laundry machine providers to
switch to an electric dryer if the current gas dryers on the property are leased. Multi-family
property owners can also switch to heat pump dryers commercially available that could be
more efficient than current electric and gas dryers
Table 3. Net present value from 20 years of natural gas savings with different discount rates.
Base analysis assumes a discount rate of 5%.
Discount Rate (%) NPV of Natural Gas Savings ($)
3% $55,813
5% $46,047
8% $35,348
This study estimated that a 10 kW-DC solar PV system can provide 95% of the electricity
consumption from average usage of two heat pump water heaters, one 18,000 BTU/hr heat
pump, one refrigerator, one electric stove, and two gas dryers in a small multi-family property.
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The lifetime system cost of a 10 kW-DC solar PV system with a 5 kW/13.5 kWh battery storage
is estimated to be $11,000, including the electricity bill savings following the NEM 2.0 rate and
the 30% investment tax credit (ITC) for the solar and storage system. Paired solar and battery
system assumes battery replacement after 10 years.
With electrification savings, the multi-family property studied can reduce the cost of solar and
storage systems to about $5,000 and increase energy resiliency for multi-family tenants. In
addition, the solar and battery storage system will reduce the cost of electricity for property
owners to a levelized cost of $0.06/kWh, which is lower than the $0.20/kWh Tier 2 electricity
rate in Palo Alto and the $0.14/kWh Tier 1 electricity rate. Solar and storage costs can be
greatly reduced with a different size solar system, having more favorable loan terms, or aligning
the majority of the energy consumption during solar production hours.
Figure 4. Estimated cost of community room and solar with battery storage installation. Total
cost of electrification and adding solar and battery storage system is $4,809 after savings.
The study finds that a 10 kW-DC solar and 5 kW/13.5 kWh battery storage system can maintain
adequate reliability in the common area for long-duration outages. Multi-family property
owners can consider partial back-up inverters or microinverters to provide additional reliability
during an outage, but the decision should be weighed with the incremental cost of the system.
Moreover, full back-up power to individual tenant units needs to be accurately assessed for the
solar and battery system to deliver electricity to support the potential maximum load on the
property.
The solar and battery storage system is limited to the power output of the battery because
solar PV systems will not operate in an outage without off-grid capable inverters. Thus,
behavior modification may be necessary to avoid overloading the energy system.
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Limitations
• Emissions and Toxic Pollutants: Natural gas generators and portable gasoline generators
emit toxic pollutants such as Carbon Monoxide (CO) and Carbon Dioxide (CO2) during
operation. Proper ventilation is required when operating fossil-fuel generators, and indoor
use of portable gasoline generators is highly discouraged. Gasoline generators are known to
produce the highest levels of CO and CO2 emissions among fossil-fuel based generators.7
Portable gasoline generators frequently cause deaths and injuries during outages from
carbon monoxide poisoning. The state of California will ban the sale of portable gasoline
generators on January 1, 2028.
• Fuel supply: Portable gasoline generators and natural gas generators require constant fuel
supply for operation. During an outage, gasoline pumps in Palo Alto do not currently have
back-up power and will be inoperable, thus limiting access to gasoline supply during power
outages. Storing gasoline onsite has issues with fuel stability. Natural gas pipes can be
affected by earthquakes and other physical damage that disrupts fuel supply to specific
areas.
• Maintenance: Both whole-home natural gas generators and portable gasoline generators
are meant to be run for about two hours a month to insure proper engine readiness.
• Grid-powered Battery: Stand-alone battery storage systems such as the Tesla Powerwall
batteries are restricted in their ability to charge from the grid if it is not allowed by the local
utility, or if the battery is owned by a third party.8 The ability to charge from the grid is set
by the local utility, or installer, and the Tesla Powerwall must be in Back-up-only or Time-
Based-Control mode. Tesla Powerwall batteries will not charge from the grid if paired with a
solar system,9 therefore adequate sizing of solar system is required to sufficiently charge
the battery storage and home consumption. Moreover, when Tesla Powerwall batteries are
set to charge from the grid in Back-up Mode, the grid power charge is limited to 3.3 kW.10
• Local regulations: Natural gas generators can produce 55 – 90 dB measured 23ft (7m) away
from the equipment. According to Palo Alto Municipal Code (PAMC) Chapter 9.10, exterior
noise produced by machinery may not exceed six dB above the 40 dB “local ambient”
sound. PAMC 9.10.060 has an exception for residential power equipment that meets a
certain decibel level, at certain hours.11 Additionally, noise-producing equipment are
required to be “located out of setback abutting or within 50 ft of residential properties and
shall be screened from view from the residential property”. Therefore, natural gas
generators may not be allowed to be installed in residential units depending on its location
within the property. There are exemptions for back-up power that may allow both natural
7 https://www.natureworldnews.com/articles/47383/20210908/how-bad-are-generators-for-the-
environment.htm
8 https://www.tesla.com/support/energy/powerwall/mobile-app/powerwall-modes
9 https://www.tesla.com/support/energy/powerwall/learn/combining-systems
10
https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall%202_AC_Datasheet_en_northamerica.pdf
11 https://www.cityofpaloalto.org/files/assets/public/public-works/engineering-services/webpages/forms-and-
permits/other-guidelines/cpa-noise-ordinance-030507.pdf
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gas and gas generators. The sale of portable gasoline generators will be prohibited in
California beginning in 202812.
• Plug-load only supply: Portable gasoline generators and partial back-up inverters such as
the Secure Power Supply on a SMA Sunny Boy inverter13 can only support plug-load
appliances. Hence, appliances requiring 240V cannot be supplied, such as heat pumps,
electric ranges, electric/heat pump water heaters, and electric dryers. Moreover, outlets
are located near the solar inverter or on portable gasoline generators. Thus, plug-load
appliances could only be used outside the home or with an appropriate extension cord. In
contrast, natural gas generators, solar microinverters, and battery storage systems can
provide power for 240V rated appliances and supply electricity to a home’s back-up electric
panel or main electric panel. Portable gas generators could be connected via a whole-home
transfer switch if desired.
• Product compatibility: Enphase IQ8 microinverters are compatible with Tesla Powerwall 2
batteries, but installation and communication between technologies can be challenging. It is
recommended to pair Enphase IQ8 microinverters with an Enphase battery system for
whole-house back-up. Using grid-forming microinverters for back-up power during daylight
hours only supports four critical load circuits. Using the grid-forming microinverters for
whole home back-up power without a battery is currently not a recommend use case.
• Sunlight: Solar PV systems can only operate when there is sunlight and may not output
electricity at maximum power capacity due to sky conditions. Thus, solar PV systems will not
deliver electricity to homes in the evening and in periods of little-to-no sunlight such as
cloudy days or the winter season. Outages occurring at night can only be supported by
battery storage systems and fossil-fuel generators.
Alternative Resiliency Options
Through the partnership with Office of Emergency Services, the team also identified other
resiliency options to enhance residential energy resiliency during an outage. These include:
• Uninterruptable Power Supply (UPS): UPS systems are lower cost short-term back-up
systems that provide electricity to plug load equipment during outages. UPS systems
generally have small power capacity- a 900 W system costs $250- and can last from 30
to 60 minutes depending on the load. These systems could be used to support medically
fragile individuals during an outage as they can power medical equipment such as
ventilators, nebulizers, or oxygen concentrators.
• Solar trailers: Solar trailers are mobile solar PV arrays that are attached to trailers and
can be paired with a battery back-up system. These solar trailers can be attached to a
vehicle with a trailer hitch and provide electricity in open areas with sufficient sunlight.
Depending on the manufacturer and solar capacity, the cost of solar trailers can range
from $40,000 for a 2kW PV + 25 kWh BESS to $86,000 for a 5.6 kW PV + 80 kWh BESS.
12 https://ww2.arb.ca.gov/news/carb-approves-updated-regulations-requiring-most-new-small-road-engines-be-
zero-emission-2024
13 https://www.sma-sunny.com/us/how-to-explain-secure-power-supply-to-homeowners/
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• Vehicle-to-home EV chargers: Bi-directional EV chargers allow bi-directional capable
EVs to supply power to a home back-up electrical panel, which can support households
and neighbors in emergency services during an outage. Additionally, the City could
create a similar pilot program in El Cajon, which utilizes electric school buses as a form
of grid management.14
RESOURCE IMPACT
This is a discussion item, no next steps are specifically recommended by staff at this time.
POLICY IMPLICATIONS
This discussion of back-up power options is consistent with the Utilities Strategic Plan, the
Utilities Electric Integrated Resources Plan, Sustainability Implementation Plans, and the City’s
Sustainability and Climate Action Plan (S/CAP).
ENVIRONMENTAL REVIEW
Staff’s discussion of different back-up power options does not require California Environmental
Quality Act review, because it does not meet the definition of a project under Public Resources
Code Section 21065 and CEQA Guidelines Section 15378(b)(5), as an administrative
governmental activity which will not cause a direct or indirect physical change in the
environment.
NEXT STEPS
Reliability and resiliency planning has been delegated to the Council’s Ad Hoc Sustainability and
Climate Action Plan Committee, which is considering it in the context of a work plan to be
delivered to Council. Next steps will be determined as part of that work plan.
Attachments:
• Attachment A: Presentation
14 https://www.latimes.com/business/story/2022-07-27/electric-school-buses-in-el-cajon-will-send-power-to-the-
grid
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Discussion of costs and reliability of
back-up power options
Keola Iskander, 2022 Stanford Shultz Fellow
Lena Perkins, PhD, Senior Resource Planner CPAU
December 7, 2022
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Figure 1. Annualized net cost ranges of the energy systems considered in the study. Solar and battery storage have lower
O&M costs,while portable gasoline generators and natural gas generators have increasing O&M costs with frequent and
longer power outages. Higher electricity bill savings can be achieved with a solar and battery system.The Solar PV +
Partial Plug Load Back-Up is only compatible with some solar inverters.
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Whole-House
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Microinverters
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Figure 2.Average proportion (%) of household load met in an outage for a peak summer energy
consumption scenario of an all-electric single-family home. Modeled peak summer energy consumption
of an all-electric home is 27 kWh/day.
% Total Loads Covered in Summer Peak
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4-
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OJ u !....
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0%
6 24 48
Duration of Outage (hours)
liiiil Portable Gasoline Generator Iii Solar PV ■ Natural Gas Solar PV ■ Solar PV ■ Battery Only ■ Solar PV
+ Partial Back-up Inverter Whole-House
(Plug Load Back-up) (Plug-Load Back-up) Generator
+ Grid-forming Microinverters + Battery
(Back-up 4 Circuits)
+ Grid-forming Microinverters
+ Battery
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Figure 3. Average proportion (%) of household load met in an outage for a peak winter energy consumption scenario
of an all-electric single-family home. Modeled peak winter energy consumption of an all-electric home is 92
kWh/day.
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75%
50%
25%
0%
% Total Loads Covered in Winter Peak
-
6 24 48
Duration of Outage {hours)
i;;i Portable Gasoline Generator Ii Solar PV ■ Natural Gas i;;i Solar PV ■ Solar PV ■ Battery Only ■ Solar PV
+ Partial Back-up Inverter Whole-House
(Plug Load Back-up) (Plug-Load Back-up) Generator
+ Grid-forming M icroinverters + Battery
(Back-up 4 Circuits)
+ Grid-forming Microinverters
+ Battery
2.a
Packet Pg. 53
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Planned Outage
(< 6 hours)
Load Shedding
Event
(< 6 hours)
Storm Event
(6 - 12 hours)
After Major
Earthquake
( >24 hours)
Portable Gasoline
Generator
(Plug Load Back-up)
$120
Solar PV
+ Partial Back-up
Inverter
(Plug-Load Back-up)
$290
Natural Gas
Whole-House
Generator
$630
Solar PV
+ Grid-forming
Microinverters
(Back-up 4 Circuits)
$760
Solar PV + BESS $790
Stand-alone Battery
Storage $1,130
Solar PV
+ Grid-forming
Microinverters
+ Battery
$1,240
Reliability Level Provided For:
Technology Noise Level
Dangerous CO
& CO2
Emissions?
Annualized Cost
($)
Table 2. Resiliency summary of
different energy systems with their
respective net system cost and
annualized cost. Energy systems are
compared by their level of reliability
in different outage scenarios.
High resiliency denotes the system’s
capability in providing sufficient
energy for normal consumption in an
outage. Moderate resiliency means
the system can provide some energy
during an outage but requires
consumer behavior modification
such as appliance time-of-use or
reduced energy consumption. Low
resiliency signifies the system’s
inability to provide adequate energy
in longer duration outages and
requires users to conserve energy
consumption.
Noise level and emissions quantified
on separate scale.
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Multifamily Analysis
40,250
57,528
4,809
(46,047)(46,922)
-60,000
-40,000
-20,000
0
20,000
40,000
60,000
80,000
Community Room Electrification 10-kW Solar PV + 5 kW/13.5 kWh BESS Total Project Cost
Net
P
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V
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(
$
)
Total Cost Natural Gas Savings NEM 2.0 Savings 30% ITC
Figure 4. Estimated cost of community room and solar with battery storage installation. Total cost of electrification and
adding solar and battery storage system is $4,809 after savings.
■ ■ ■ ■
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