That’s why we’ve asked a fundamental question as we plan for the future: Is the grid up for the challenge of growing EV adoption?

The answer is yes, according to a recent grid impact analysis for ������Ƶ.

Given steady adoption, EVs aren’t driving an immediate, overnight increase in demand. That provides time for proactive planning to manage complexity and maintain stability, even as electric vehicles become more commonplace.

The study, finalized in January, identified where and how fast EV adoption is happening today across our community and extrapolated future growth based on market forecasts. The study analyzed residential growth, as well as broader fleet conversions and growing demand for public charging infrastructure.

“The study was valuable in identifying areas where the potential for EV adoption is high, to create greater visibility into the growth needs in those areas,” said Camila Martins-Bekat, Principal of Beneficial Electrification. “That is incredibly useful information that allows us to take steps to accommodate the increased usage we’ll expect over time.”

The analysis identified some long-term, local grid constraints in areas of high EV adoption or with public fast charging infrastructure. These areas will likely require future investment as well as a potential reconfiguration of existing infrastructure. For example, public fast chargers are expected to be concentrated at points of interest for highway travel where there might not be sufficient electric infrastructure.

Customer education and peak demand management are key to mitigating grid impacts and costs, Martins-Bekat noted. Customer behavior can help manage peak demand in a number of ways:

• Managed overnight charging. While some EV drivers plug in their vehicles when they come home from work, that can be a busy time on our local energy grid. Incentives to charge overnight or at other times of lower demand could help us manage load with less need for new resources.
• More workplace charging stations. This could help make the most of plentiful solar production at midday, offsetting the need to plug in during peak times.

“Electric vehicles are just one of the growth drivers we’ll expect in the coming years,” said Donovan Sandoval, Manager of Distribution Planning and Engineering. “We’re very focused on planning for that growth, so we can effectively meet our customers needs while maintaining affordability and ensuring grid resiliency.”

������Ƶ expects to expand our energy storage capacity from about 50 megawatts (MW) today to more than 1,300 MW by 2038. These resources will play a key role as ������Ƶ works toward net zero greenhouse gas emissions by 2050.

One of the biggest benefits provided by battery energy storage systems is their ability to store solar energy generated at midday when it’s abundant and typically costs less than power during peak usage periods, said Neil Saunders, Principal Renewable Development Manager.

“Essentially, you’re moving power you created during the day to the evening peak by using a battery.  The abundance of solar in the midday when customers’ energy needs are relatively low can lead to curtailments of solar production,” Saunders said. “Battery systems can maximize solar production by storing clean energy for our afternoon and evening peaks.”

Construction is now underway on ������Ƶ’s 200 MW Roadrunner Reserve, our newest and largest battery energy storage system. The project is designed to store 800 megawatt-hours (MWh) of energy, enough to serve approximately 42,000 homes for four hours when deploying at full capacity. The system will be among the largest in Arizona when it’s up and running the summer of 2025.

“For ������Ƶ, the Roadrunner Reserve system is really a game changer in terms of solar shifting,” said Lauren Briggs, Director of Resource Procurement & Planning. “When it comes online, we’ll be storing a lot more energy produced in the morning, then delivering that energy during times of peak demand when customers’ energy needs are greatest.”

Battery systems provide other important benefits, Briggs said.

������Ƶ has more than 447,000 customers with energy needs that change from moment to moment throughout the day. We must respond instantly, delivering enough energy to meet those needs. This makes wind and solar resources more challenging because their production varies throughout the day, sometimes in unpredictable ways.

“Batteries can release energy extremely quickly, much more quickly than traditional generation. If a cloud passes over and the sun goes away, the energy produced by solar panels will drop. Batteries can react very quickly to fill in the gaps,” Briggs said.

Battery energy storage systems are considered “inverter-based resources,” a class of energy resources including solar panels and wind turbines that rely on devices called inverters to convert electricity from direct current to alternating current before being delivered to the grid.

Battery systems will also play a key role as ������Ƶ works toward net zero direct greenhouse gas emissions by 2050. The goal is aspirational, reflecting confidence that advancements in long-duration storage and other types of non-carbon emitting technologies will emerge as cost-effective options. While solar plus storage is currently more expensive than natural gas resources, cost projections indicate these costs are expected to decrease over the next 10-12 years.

������Ƶ worked closely with district officials for more than a year, providing technical assistance and other support for its successful application for an Environmental Protection Agency grant. ������Ƶ also committed to providing funding for charging infrastructure and supplementing the grant to ensure that TUSD pays no more than the cost of conventional buses for its new electric models.

The zero-emission vehicles will contribute to cleaner air for everyone while providing other potential benefits to our community and our local energy grid.

“We are working with the district to determine how to feed energy from the bus batteries back onto the grid during summer peak periods when schools are out of service, and customer usage is high,” said Gabriella Abou-Zeid, ������Ƶ Program Manager for Beneficial Electrification.

“We’re proud of our role in supporting a key educational institution in transitioning their bus fleet to help improve air quality, reduce lifetime maintenance costs and support the grid for broader system-wide benefits,” said Camila Martins-Bekat, �շ���’s Principal for Beneficial Electrification.

The district cannot confirm when or how soon the school buses will be running and have not finalized agreements or formalized contracts as they continue working with stakeholders to understand the scope of work.

They’re just the latest highlight from our longstanding partnership with TUSD, which won a ������Ƶ in 2023 for its work toward energy conservation and a brighter future.

������Ƶ also has been working for years to promote cleaner transit by supporting the electrification of Sun Tran’s bus fleet, powering Tucson’s electric streetcar and donating  for use in the Sabino Canyon Recreation Area.

TUSD representatives said they were excited to receive the award. “We are working in partnership with ������Ƶ (������Ƶ) to finalize the logistics and move forward with the program,” said Karla Escamilla, Director of Communications & Media Relations for TUSD.  “This is an amazing opportunity that will benefit our district, students, families, and the Tucson community.”

������Ƶ is working to simplify and accelerate EV adoption under a transportation electrification plan approved by the Arizona Corporation Commission.

It depends. Unlike conventional power plants, wind and solar power systems only produce energy when its windy or sunny. Their output also varies with the weather and the time of day, as solar arrays produce less power when it’s cloudy or when the sun isn’t directly overhead.

You can check current clean energy levels anytime using the ������Ƶ Clean Energy Tracker on tep.com. The tracker shows how real-time output from our 17 community-scale solar arrays and four wind farms compares to current energy use across our community.

Our clean energy systems can produce a combined 740 megawatts (MW) and provide more than 20 percent of the power our customers use over the course of a year. But that percentage varies widely throughout the year, from as low as zero on dark, still nights to as high as 100 percent during periods of high production and low energy use.

Renewable energy reduces our community’s impact on the environment, helping us respond to a changing climate and contributing to our plans for a cleaner energy portfolio that will produce 80 percent less carbon dioxide by 2035.

The following answers to common questions help explain how the Clean Energy Tracker works.

How does the tracker display the output of �շ���’s renewable resources?

In addition to providing total MW production, the Clean Energy Tracker estimates the number of homes that could be served by that energy. This is calculated by dividing total production by the average residential electric usage for that same hour. The number of customers served by the same level of energy production varies by season and even time of day.

When are clean energy levels typically the highest, as a percentage of total usage?

Our tracker typically shows larger percentages and higher levels of homes served in the winter. Although we see comparable clean energy production in other seasons, energy usage rises in the spring, summer and fall due to increased reliance on air conditioning.

Sometimes, when temperatures are moderate and usage is very low, our wind and solar power systems can actually produce more energy than our customers are using!  During these brief periods, any excess energy from our renewable and conventional generating systems flows to other users on the regional energy grid.

Conversely, that same level of production might represent less than 30 percent of peak energy demands in the summer. And our systems are generally producing at lower levels during those late afternoon hours because the sun is sinking toward the western horizon.

How do I find the hours of highest renewable energy production for ������Ƶ?

�շ���’s Clean Energy Tracker includes a chart that shows both renewable energy production and total energy usage throughout the day. Below that chart, you’ll find “Renewable daily max,” which indicates the total amount of renewable energy ������Ƶ produced so far for the day. Tip for reading the chart: When the blue and green areas of the chart are closest together, the highest percentage of customers are being powered by clean energy!

How can I be assured I’m using the greatest amount of renewable energy to power my home?

The best way to do this is to shift your energy usage to times when renewable resources are most productive and avoiding energy usage during times of high demand in late afternoon and early evening.  Typically, the highest production of solar energy occurs late morning through midafternoon when the sun is highest in the sky and energy usage by customers is at its lowest. Customers should try to shift energy usage to midday, early afternoon and at night, when wind power is generated. These are the best times to use appliances and electronics and run pool pumps and air conditioning.

Can ������Ƶ store solar energy for use later in the day?

We are expanding our use of energy storage systems to help us make better use of solar energy. For now, our largest such resource is a 30-MW battery system charged by a 100-MW solar array at the Wilmot Energy Center in southeast Tucson. On most days, the 314,000 solar panels charge the batteries in the morning and early afternoon when solar resources are most productive. The system then delivers stored energy during peak usage periods later in the afternoon and early evening.

Our long-range plans call for the addition of more than 1,000 MW of new energy storage systems by 2035. Such systems are critical to our plans for a cleaner energy future because they can “shift” solar energy generated at midday for use during peak usage periods. They also help compensate for the intermittent output of solar and wind power systems and can support reliability during cloudy weather.

Does the Clean Energy Tracker include energy produced by rooftop solar arrays?

No. Our tool can only track energy produced by the large-scale systems owned and operated by ������Ƶ or built by others to sell us energy. For this reason, the percentage of clean energy on our grid could be higher than shown on our tracker due to excess energy from rooftop solar arrays – particularly at midday on sunny days. As of September 2023, more than 46,800 ������Ƶ customers have installed private solar arrays that can produce a total of 574 MW.

The reductions reflect our replacement of retiring coal resources with cleaner energy as part of our plan to reduce carbon emissions 80 percent by 2035. Emissions decreased by 3.5 million metric tons over that period.

“We have taken our commitment seriously to respond to the challenge of delivering cleaner energy in the face of a changing climate, and importantly, we’re doing it while continuing to prioritize reliability and affordability,” said Chief Sustainability Officer Erik Bakken. “We’re excited to see the significant difference we’ve been able to make in a short period of time, and we’re prepared to do much more in the coming years.”

anticipates providing more than 70 percent of our community’s power from renewable resources by 2035. It also calls for the retirement of Units 1 and 2 at �շ���’s coal-fired Springerville Generating Station in 2027 and 2032, contributing to an anticipated reduction of more than 50 million tons of CO₂ by 2035.

The significant reduction reflects �շ���’s steady expansion of wind and solar resources. Over the past few years, ������Ƶ has more than doubled its renewable energy portfolio with three new, large systems that include:

• The Oso Grande Wind Project, located in southeastern New Mexico. Owned and operated by ������Ƶ, the 250-megawatt (MW) wind farm generates enough energy each year to serve the annual electric needs of about 100,000 homes.
• The Wilmot Energy Center, which includes a 100-MW solar array and a 30-MW battery energy storage system on 1,130 acres south of Tucson International Airport. The array generates enough power every year to serve more than 25,000 homes.
• The Borderlands Wind Project, located in northwest New Mexico, includes 34 turbines that produce a combined 99 MW. Over the course of a year, the wind farm generates enough power to serve the annual electric needs of more than 26,000 homes.

These new systems helped replace �շ���’s share of the coal-fired Navajo and San Juan Generating Stations, which retired in 2019 and 2022, respectively.  ������Ƶ also installed fast-ramping natural-gas generators at our largest local power plant in 2019 and 2020, helping us compensate for intermittent renewable resources while producing significantly less CO₂ than coal-fired generation.

This year, we anticipate that nearly 30 percent of our community’s power will be produced from renewable resources. Customers can see how much energy �շ���’s renewable resources are producing in real-time by visiting �շ���’s Clean Energy Tracker.

The Oso Grand Wind farm is �շ���’s single largest renewable resource. It can generate up to  250 megawatts of power and produces enough power each year to serve the annual electric needs of 100,000 homes.

The wind farm itself spans 24,000 acres; that’s roughly 20,000 football fields, or the size of Florida’s Walt Disney World Resort. The closest city is Roswell, about 65 miles away. Reaching the system takes a full day’s drive from Tucson.

That means the team on site must have backup plans at the ready when replacement parts, equipment or specialized services aren’t available for our turbines, substation or lines.

When the team learned last year that an underground cable required maintenance, the Oso Grande staff needed to get creative. Under state law, they needed to have the line’s location marked before digging.

The problem was that Oso Grande staff didn’t have the capability to perform line location. Moreover, since ������Ƶ shares the leased land with others, the Oso Grande team would be responsible for responding to line marking requests from other land users in addition to serving their own on-site needs.

“We quickly recognized that line locating services would be needed to support our needs as well those of the local landowners and gas and oil companies whose lines may be located inside our facility boundaries,” said �շ���’s Michael Bryan, Asset Manager for Oso Grande.

Several options were considered, included calling in help from the ������Ƶ line locating staff in Tucson and possibly using a contractor, but neither was feasible.

“Our line locators in Tucson are a nine-hour drive away and already have a heavy workload. By law, we also need to mark the lines within 48 hours of the request,” Bryan said. “We researched using local vendors, but the cost was too high and too variable and that runs counter to our focus on keeping rates as low as possible. We had no idea how many tickets we might get since this was our first year, and we needed a cost-effective solution to keep overall costs down.”

After brainstorming ideas with Transmission & Distribution leadership, the team decided to train Oso Grande wind technicians on how to locate lines. After procuring the proper equipment, the team brought in a vendor to provide training. The technicians also received hands-on training with �շ���’s Tucson line locators with additional training scheduled for this year in Tucson.

“This was the best option for us and our customers. Training the Oso Grande staff just made good business sense and it gave them new skills. We were able to reduce costs while meeting the needs of our remote site,” Bryan said. “I’m sure other unexpected items will come up at Oso Grande in the future, but I’m confident we’ll bring innovative approaches to those challenges as well.”

So using clean, renewable energy was just an extension of her conservation ethic.

“I’ve always been intrigued by solar because like most people, I recognized that climate change was on the horizon. I also wanted to be more in control of my billing and finances,” said the retired health care practice administrator.

After researching her options, she determined a private rooftop system wasn’t for her. She wasn’t a fan of the aesthetics and didn’t want the hassle of maintenance on the rooftop of the central area townhome she’s owned for nearly four decades.

When she learned about �շ���’s GoSolar Home program, which allows customers to power their homes with energy from our large-scale solar arrays, she signed up.

She made the choice in part because of finances.

“I really appreciate that our rates are locked for 10 years, especially since you look around and the cost of everything is going up,” she said. “Plus, our summers just seem to getting a lot hotter so I wanted to have that confidence that I had more control over my financial destiny.

“It was so easy. I literally did nothing other than filling out an application,” she said. “They called, made an appointment to change my meter, gave me a way to clearly track usage and put me on a rate that is very easy on my budget.”

Lynda said she also made the choice because of her own values.

“I appreciate the fact that I’m consuming electricity without burning coal. We have a lot of open land, so I’m glad we’re able to use it for solar that can serve the whole community. It just seems more cost-effective than all of us having to put individual systems on our homes,” she said.

She’s since told her neighbors and has been glad to see that the program has worked for several of them.

“It’s just ideal for homeowners who don’t want the maintenance but still want to take advantage of the natural sunlight that’s so plentiful here.”

featuring Lynda and her neighbors.

Solar energy is most abundant during midday hours when the sun shines most directly on photovoltaic systems, including those built to track the sun. So by shifting your usage to midday, you can reduce your carbon footprint – and possibly your electric bills – while supporting our community’s transition to cleaner, greener resources.

“Because our grid operates in real-time, we can really only leverage renewable resources if customers are using energy when they’re producing power,” said Sam Rugel, �շ���’s Director of System Control & Reliability. “The good news is that for most of us, it just takes a few adjustments in our usage to make the most of those clean resources.”

Solar energy production typically ramps up in the late morning and then begins to wane as the sun starts to set. Unfortunately, that’s about the time that most customers start using the most power during the summer, forcing ������Ƶ to fire up additional fossil-fueled resources to keep energy flowing.

We’re working to expand our energy storage systems to help us save more solar energy for later in the day. But you can help support a cleaner energy mix right away by shifting energy use to off peak periods. Midday usage makes better use of our solar resources, while overnight consumption is supported by higher production from our wind resources.

Here are some simple strategies to try:

• Use the “delay start” feature on your dishwasher so that it runs late at night or mid-day.
• During the summer, pre-cool your home. Set the thermostat temperature three degrees lower than your preferred setting at noon, then adjust your thermostat several degrees higher than your normal setting at 3 p.m.
• If you own an electric vehicle and a home charger, charge it mid-day on the weekends or during your remote work schedule or overnight while you’re sleeping.
• Program your pool pump to operate at midday instead of late afternoons and early evenings.
• Plan your meals ahead of time by preparing them in the early morning or night before and then just reheating them in the microwave.

Customers can check out just how much clean energy ������Ƶ is generating at any time by checking our online Clean Energy Tracker. This dashboard shows real-time output in megawatts and indicates how many homes could be served by the energy flowing from each resource. It also displays the daily and monthly energy production for each resource as well as days of historically high production.

“Customers can see real-time and historical data, dating back to 2018,” said Bryan Rosenbaum, ������Ƶ Web Communications Specialist, who developed the dashboard on �շ���’s website. “It also shows them our overall energy usage and renewable energy production changes over the course of a year and how weather affects energy usage and production.”

For example, May 20,^, 2022 was a particularly windy day as our wind farms produced nearly 400 MW of energy to meet about 93 percent of our customers’ energy needs.

By shifting as much energy usage to mid-day and evenings, customers also may be able to reduce their electric bills by avoiding on-peak times. This is especially important for customers with Time-of-Use and Demand pricing plans.

These plans offer lower energy rates during off-peak periods but higher costs during on-peak hours. From May 1 through Sept. 30, on-peak hours are weekdays from 3-7 p.m. In the winter from Oct. 1 through April 30, on-peak periods are weekdays from 6-9 a.m. and 6-9 p.m. Weekends and major holidays are always off-peak.

“Being mindful of when you’re using energy and making slight adjustments ensures you’re getting your share of sun and wind power, supports our renewable resources and can help reduce your energy costs,” said Dylan Bearce, �շ���’s Senior Director of Energy Resources. “It also reduces the strain on our grid during peak times of energy demand.”

That’s exactly why we’re asking a diverse group of stakeholders and local leaders to help us design a plan to satisfy our community’s future energy needs.

With more than a dozen members, �շ���’s Resource Planning Advisory Council will meet over the next several months to evaluate potential energy options and provide input that will help guide �շ���’s resource decisions over the next 15 years. Members include residential and business customers, environmentalists, low-income advocates, local government officials, educators, and representatives of the solar and electric vehicle (EV) industries.

“We’re excited to begin working with this diverse, knowledgeable group, sharing information about the resource opportunities and challenges we face,” said Lee Alter, a ������Ƶ energy resource planner who hosted the group’s first meeting last month.  “The community’s feedback is a critical part of this process. We appreciate the time and energy the members are contributing to help achieve our sustainability goals as we work to maintain reliable, affordable electric service for customers.”

Our community’s energy needs are growing, with new peak energy demand records set in both 2020 and 2021. ������Ƶ is working to meet those needs with a cleaner energy mix. �շ���’s 2020 Integrated Resource Plan (IRP) outlined our ambitious, achievable plan to provide more than 70 percent of our power from wind and solar resources while reducing carbon emissions 80 percent by 2035.

During last month’s meeting, �շ���’s planning team offered an overview of current market conditions, including rising energy costs, coal supply issues, drought-related risks to hydropower and other challenges. The team also described �շ���’s need to secure additional energy resources in coming years to maintain reliability, especially during the hottest months of summer.

Input from the advisory council will be incorporated into �շ���’s next IRP, which assesses current and future energy needs while identifying potential ways to meet them. Our plan will include at least 10 potential resource portfolios that consider several factors such as cost, emissions reduction, and savings from energy efficiency programs. The plan will be filed with the Arizona Corporation Commission by August 2023.

By then, ������Ƶ will be well on its way to adding even more clean energy and capacity to its portfolio. We issued an all-source request for proposals (ASRFP)  in April 2022, seeking new wind and solar generation, energy storage systems and other resources that can commence service by May 1, 2025. The company received more than 100 proposals, the majority of which combine solar and battery energy storage. We plan to announce the outcome of the ASRFP as part of our 2023 filings.

Coupling a photovoltaic (PV) system with energy storage – known as solar-plus-storage – can help solve that dilemma.

That’s true at the utility level, where our largest battery storage system at the Wilmot Energy Center banks energy generated when the 314,000 solar panels on the site are most productive. It’s also true in customers’ own homes.

“Customers are adding systems to store energy when the sun shines during the day and their usage is lower,” explained Neil Saunders, Energy Program Engineer for ������Ƶ, noting the concept is called “solar shifting.”

“When the sun goes down, they discharge the energy from the battery to power the home. That’s a good thing for solar homeowners and for the grid.”

Energy storage systems allow homeowners to take advantage of the midday sun to generate and store electricity. During times of peak demand, when rates are higher on our time of use pricing plans, the stored energy can be released to power some or all of the home.

Adding a battery system to your home can also add energy security. While grid-connected solar systems without storage will shut down automatically during power outages for safety reasons, solar-plus-storage systems can continue to generate electricity and use stored energy.

“With solar-plus-storage systems, it is possible for a customer to remain in power when the ������Ƶ grid power goes down,” explained Don McAdams, Principal Energy Services Engineer. “This is done by installing a ‘smart switch’ at or near the main service panel that is wired to sense the loss of electricity from ������Ƶ and automatically opens a contact that isolates the solar-plus- storage system from the grid. When the system senses power is restored, it will reconnect to the grid.”

While energy storage systems provide convenience, resiliency and peace of mind, there are a few things to keep in mind before you invest in one.

Storage size

The first consideration is determining the size of your storage system. The right capacity depends on your PV system, your total household energy use and the length of time you would like to power critical appliances and electronics.

“Installers tend to stack batteries if homeowners want more stored energy capacity. Batteries can range from 3.5 to 13.5 kilowatt hours each,” noted Saunders, “and you may need several to provide the stored power you want.”

Battery storage systems are flexible in that they can provide a lot of power in a short time or less power for a longer time, unless your system is producing energy while you are using it. If you want to run your whole household on power from your storage system, you may only have electricity for a few hours. By reducing your load, you will have electricity for a longer period.

“Some customers install enough batteries to provide whole home backup for several hours,” McAdams noted. “Most homeowners, however, determine what their critical loads are such as the refrigerator, microwave oven and various home electronics, and move those loads off the main service panel to their critical loads panel that can be served by their energy storage system.”

Cost

Storage systems are expensive, and the more batteries you need, the greater the cost. They range in price from , depending on the brand, number and size of batteries and other factors. Available can help offset the upfront cost, but there is likely to be a long payback period.

Limited lifetime

Another factor to consider is the useful life of the batteries, which is 7-10 years. Be prepared to replace them at least once during the life of your solar energy system.

Battery systems also are not 100 percent efficient, as some energy is always lost through energy conversation and retrieval. “Tesla, for example, has a 10-year warranty on its lithium-ion battery, but there is some degradation of performance over time, so you’ll need to eventually replace them,” Saunders said.

Because extreme heat or cold can further reduce battery performance and life, Saunders recommends placing your storage system in a garage or room with conditioned air.

Battery disposal

Since batteries contain , they should never be discarded in the trash to avoid the risk of fire or contamination of the soil or groundwater.

Fortunately, an increasing number of can safely recycle the batteries. Several are located in the Phoenix area.

Adding energy storage to a new or existing solar system can help homeowners meet their green energy goals, provide greater resiliency and reduce energy usage during on-peak times when rates are higher on time-of-use pricing plans. As technology advances, battery performance, cost and recycling options will improve.

“Energy storage systems have been around for a while, and they’re getting better and better all the time,” Saunders said. “Solar customers thinking about adding battery storage should rely on their installer to recommend a system that’s right for their system size and meet their expectations and budget so that it can provide the power they need, when they need it.”