How to Size Solar Panels for EV Charging in Temecula: The Numbers Most Installers Don't Show You

Adrian Marin|Independent Solar Advisor, Temecula CA

Helping Riverside County homeowners navigate SCE rates and solar options since 2020

Most solar proposals in Temecula are built from your last 12 months of SCE electricity bills. That makes sense until you add an electric vehicle. The moment you plug in a Tesla, an F-150 Lightning, or any other EV, your annual electricity demand jumps by 3,000 to 5,000 kWh depending on the vehicle and how much you drive. A system sized for your house before the EV arrives will fall short after it does. This guide walks through the exact math for sizing a system that covers both your home and your EV charging, explains how SCE time-of-use rates change the charging strategy, and shows how battery storage changes the economics under NEM 3.0.

The Calculation Most Installers Skip

Solar installers typically pull your SCE 12-month usage history and size a system to offset a specific percentage of that historical load. The problem is historical usage does not include a vehicle you do not own yet, or one you recently added without telling your installer. If you are planning to buy an EV within the next one to three years, you need to build the EV charging demand into the system size from day one. Retrofitting a larger system later costs more per watt than including those panels in the original installation.

The core formula is simple. Take your vehicle's efficiency rating in miles per kWh, divide your average daily miles by that number to get daily kWh demand, then multiply by 365 to get annual EV charging demand. Add that number to your home's annual kWh usage and size the solar system to the combined total.

Temecula averages 4.5 peak sun hours per day, which is the input used to convert system size in kilowatts to annual production in kilowatt-hours. The conversion factor is 4.5 hours multiplied by 365 days, which equals 1,642. Divide your total annual kWh demand by 1,642 to get your system size in kW. That is the number your installer should be starting from, not ending at.

Vehicle-Specific Numbers for Temecula Drivers

EV efficiency varies significantly by vehicle. The two most common EVs in Inland Southern California right now illustrate the range well.

For context, the average Temecula home uses between 9,000 and 11,000 kWh per year. Adding a Tesla Model 3 increases your annual demand by roughly 3,200 kWh, or about 32 to 36 percent above baseline. Adding an F-150 Lightning adds 5,100 kWh, which is a 46 to 57 percent increase over the same baseline. A system sized on historical usage with no EV will be meaningfully undersized in either case.

Warm Temecula weather also reduces EV efficiency compared to EPA ratings, which are tested in controlled conditions. At 95 to 105 degrees Fahrenheit, most EVs show 5 to 15 percent lower efficiency due to battery thermal management and air conditioning load while driving. Using the EPA efficiency rating as a starting point is appropriate, but building in a 10 percent buffer for summer heat is a conservative and realistic adjustment for Inland Southern California conditions.

Step-by-Step Sizing Calculation for a Temecula EV Owner

Here is the four-step calculation that gives you a starting system size. Use this as a cross-check against whatever your installer proposes.

• 1.
  Pull your last 12 months of SCE usage.Log in to your SCE account at sce.com, navigate to My Energy Use, and pull the monthly kWh totals for the past 12 months. Sum them. This is your baseline home demand. Do not use the dollar amount on your bill because that varies with rates. Use the kWh number only.
• 2.
  Calculate your annual EV charging demand.Divide your average daily miles by your vehicle's efficiency in miles per kWh to get daily kWh. Multiply by 365. If you drive 35 miles per day in a Model 3 at 4 mi/kWh: 35 divided by 4 equals 8.75 kWh per day, times 365 equals 3,194 kWh per year.
• 3.
  Add home demand plus EV demand.Example: 10,000 kWh home plus 3,194 kWh EV equals 13,194 kWh total annual demand. If you have two EVs, add both. If you are planning to add an EV in two years, add a 10 percent buffer on top of the current baseline to leave headroom.
• 4.
  Divide by Temecula's annual solar production factor.Divide total annual kWh by 1,642 to get system size in kW. For the example: 13,194 divided by 1,642 equals approximately 8.0 kW. This is the size that covers 100 percent of combined home and EV demand under ideal conditions. Most installers target 95 to 100 percent offset, so expect a final recommendation in the 7.5 to 9 kW range after accounting for system losses.

The 1,642 production factor assumes 4.5 peak sun hours per day averaged across all months, accounting for seasonal variation and standard system efficiency losses of approximately 80 percent (inverter efficiency, wiring losses, temperature derating, and soiling). Installers using production modeling software like Aurora or PVsyst may arrive at a slightly different number based on exact roof orientation, shading analysis, and specific equipment specs, but 1,642 is a reliable back-of-envelope figure for Temecula.

SCE Time-of-Use Rates and When You Should Actually Plug In

Sizing the system correctly is only half of the economics. The other half is when you charge. Under SCE's TOU-D-4-9PM rate structure, the pricing difference between peak and off-peak hours is significant enough to change your charging behavior materially.

During the 4pm to 9pm peak window, SCE TOU-D-4-9PM charges between $0.55 and $0.65 per kWh. A Level 2 home charger delivering 7.2 kW during that window costs $3.96 to $4.68 per hour to run from the grid. A two-hour charging session from 6pm to 8pm when you first get home costs $7.92 to $9.36 at peak rates. Run that pattern five days a week and you add $40 to $47 per week in peak-rate charging costs, or roughly $2,000 to $2,400 per year.

After 9pm, off-peak rates drop to approximately $0.19 to $0.25 per kWh. The same Level 2 charger running from 9pm to midnight now costs $0.57 to $0.75 per hour from the grid. That same 10 kWh EV charge costs $1.90 to $2.50 at off-peak rates versus $5.50 to $6.50 at peak rates. Setting your EV to charge at 9pm instead of plugging in at 6pm cuts your annual charging cost by 60 to 70 percent if you are drawing from the grid.

All three of the major Level 2 home chargers used in Temecula support scheduled charging. The Tesla Wall Connector has scheduling built into the Tesla app. The ChargePoint Home Flex has a scheduling interface in the ChargePoint app. The Emporia Level 2 Smart Charger has scheduling and real-time rate monitoring built into the Emporia app. Set the scheduled start time to 9pm and the charger handles the rest automatically every night.

The best economic outcome for a Temecula EV owner with solar is the battery storage combination: solar charges your battery during peak production hours from 10am to 3pm, you discharge the battery to charge your EV starting at 9pm, and you avoid both peak-rate grid imports and the low NEM 3.0 export credit for surplus midday production. This strategy consistently outperforms grid-only or solar-only charging under NEM 3.0.

Level 1 vs Level 2 vs DC Fast Charging at Home

The charger you install at home affects how much solar production you can actually capture for EV charging. Here is how the three home charging options compare for Temecula conditions.

• Level 1 - 120V Standard Outlet (1.4 kW)

  Adds 4 to 5 miles of range per hour. A 10-hour overnight session recovers 40 to 50 miles. Adequate for plug-in hybrid vehicles and EV drivers who travel fewer than 25 miles per day and have a guaranteed overnight parking window. Not adequate for most full EV drivers in Temecula, particularly during summer when range derating from heat reduces effective capacity. The low draw rate also means you cannot capture the bulk of afternoon solar production through direct charging. Solar paired with Level 1 means most of the solar value comes from bill credits, not direct EV charging.

• Level 2 - 240V, 40 to 48 Amp Circuit (9.6 to 11.5 kW)

  Adds 25 to 35 miles of range per hour. A standard overnight session from 9pm to 6am adds 225 to 315 miles, which fully refills most EV batteries from near-empty. This is the right charger for the overwhelming majority of Temecula EV owners. Requires a dedicated 240V circuit installed by a licensed electrician, a 50-amp breaker, and either a wall-mounted EVSE or hardwired unit. Cost for permit and installation in Temecula typically runs $800 to $1,500 depending on panel distance and whether your panel needs an upgrade. Tesla Wall Connector, ChargePoint Home Flex, and Emporia Level 2 Smart Charger are the most common options. All three support scheduled charging to hit the 9pm off-peak window automatically.

• DC Fast Charging (Level 3) - For Reference Only

  Home DC fast charging equipment costs $30,000 to $80,000 and requires commercial-grade electrical service. This is not a practical home option for any residential property in Temecula. For occasional fast top-offs, Tesla Superchargers are available at the Temecula Promenade and on Temecula Parkway. Blink and EVgo stations are located at Lowe's and Sam's Club. Public fast charging makes sense for occasional road trips or days when you need a rapid top-off, but daily reliance on public fast charging costs significantly more than home Level 2 charging and defeats the economics of pairing an EV with solar.

Most solar-plus-EV households in Temecula install a Level 2 charger at the same time as the solar system. Some installers bundle the charger installation with the solar contract, which can simplify permitting since both the solar and the new electrical circuit can be pulled on the same permit in many cases. Ask your installer if they offer a bundled EV charger installation option.

Battery Storage: The Missing Piece for EV Owners Under NEM 3.0

Under California's previous net metering policy (NEM 2.0), a Temecula homeowner could export excess midday solar to the grid at a rate close to the retail electricity rate and import grid power to charge an EV at a similarly offset rate. The math was straightforward and batteries were optional.

NEM 3.0, which applies to all new solar customers in California since April 2023, changed the export rate dramatically. Under NEM 3.0, excess solar exported to the SCE grid earns approximately $0.08 per kWh in credit. If your solar system is generating at full capacity from 10am to 2pm and nobody is home to use that power, it exports at $0.08. When you get home and plug in your EV at 6pm during the peak window, you import that same energy back at $0.55 to $0.65 per kWh. The spread between export rate and import rate is $0.47 to $0.57 per kWh, which represents value lost every time this cycle happens.

Battery storage closes this loop. Instead of exporting midday surplus to the grid at $0.08, your battery captures it at zero marginal cost. In the evening when you charge your EV, you draw from the stored solar at an effective rate of $0.08 per kWh (the export credit you forfeited to fill the battery) rather than $0.55 to $0.65 from the grid. The economic improvement is $0.47 to $0.57 per kWh on every kWh cycled through the battery for EV charging. At 10 kWh per night, that is $4.70 to $5.70 per day, or $1,700 to $2,080 per year in avoided peak grid imports.

The sizing question for EV-focused battery storage comes down to your nightly EV charging demand.

For a Temecula household with a Tesla Model 3 driven 35 miles per day and average home loads, one Tesla Powerwall 3 or two Enphase IQ 10T batteries covers EV charging demand and provides several hours of home backup during an outage. For a household with a truck like the F-150 Lightning or two EVs, two Powerwalls or three Enphase batteries becomes the appropriate starting point. Your installer should model the system in software that accounts for daily solar production, household load profile, EV charging schedule, and battery state of charge across all 12 months to confirm the configuration before you purchase.

NEM 3.0 and the Correct EV Solar Strategy

Many Temecula homeowners who installed solar before April 2023 are on NEM 2.0 and will remain on it through 2033 unless they make significant modifications to their system. If you are one of them and you are adding an EV now, the economics of simply oversizing your system and exporting excess power still work reasonably well because your NEM 2.0 export rate is close to the retail rate.

If you are a new solar customer, you are on NEM 3.0 and the export arbitrage strategy is broken. Exporting cheap and importing expensive is the wrong model. Self-consumption is now the right model, and EV charging is the largest controllable load in most Temecula households, which makes it the ideal target for self-consumption optimization.

The NEM 3.0 EV strategy has three components working together. First, size the solar system to generate your combined home and EV demand, not to maximize export. Use the calculation in Section 3 of this article as your benchmark. Second, add battery storage sized to hold at minimum your nightly EV charging demand. Third, set up smart scheduling so the battery charges from solar during midday production and discharges to the EV starting at 9pm when off-peak rates begin on the grid side, for any shortfall the battery cannot cover.

This three-component approach produces the best financial outcome for an EV owner in Temecula under NEM 3.0. The 30 percent federal Investment Tax Credit applies to the full system cost including batteries, which significantly improves the payback on adding storage. A 10 kW solar system with two Enphase batteries and a Level 2 charger installation in Temecula typically totals $35,000 to $48,000 before incentives, and $24,500 to $33,600 after the 30 percent ITC. At $0.55 per kWh avoided SCE peak-rate cost for EV charging alone, the annual savings from the battery-EV-solar combination reaches $2,000 to $3,000 per year before counting household electricity savings.

What to Ask Your Solar Installer Before Signing

Most solar sales conversations in Temecula start with your current SCE bill and end with a system sized to offset it. If you have an EV or plan to buy one, you need to push the conversation further. These are the specific questions to ask before agreeing to any system design.

• -
  Does this system size include my EV charging demand?Ask the installer to show you the total annual kWh the system is designed to offset. If that number is close to your current SCE usage and does not include EV demand, the system is undersized for your actual future needs.
• -
  What is the production estimate based on?Ask if the production model accounts for your specific roof pitch, azimuth (compass direction), and any shading from trees, chimneys, or neighboring structures. A flat-rate kWh-per-kW assumption is less reliable than a site-specific simulation run through Aurora or PVsyst.
• -
  Can the system be expanded if I add a second EV or my usage increases?If you are on a budget and starting with a smaller system, confirm the inverter supports future panel expansion and that there is available roof space and panel interconnect headroom for additional panels without replacing core components.
• -
  What is the payback period including EV charging savings, not just utility bill savings?A complete payback analysis should include avoided EV charging costs at SCE peak rates, the federal ITC, and the California property tax exclusion. Installers who only show you the utility bill offset are presenting an incomplete picture of the return on investment.
• -
  What battery capacity do you recommend for my EV charging pattern, and why?Ask the installer to show the daily production and consumption simulation with the battery included. You should see midday solar charging the battery and evening EV charging drawing it down. If they cannot show this, ask for a production report that includes daily battery state of charge by season.

Real Numbers: What a Complete EV-Plus-Home System Looks Like in Temecula

To make the guidance concrete, here is what a properly designed solar-plus-EV system looks like for a realistic Temecula household.

This example does not include the California property tax exclusion benefit (approximately $440 to $517 per year at 1.1 percent of the $40,000 to $47,000 system cost), which adds another $11,000 to $13,000 in avoided taxes over a 25-year system life. Including that benefit brings the effective payback period down by one to two years.

The Two Mistakes That Derail EV Solar Projects in Temecula

After reviewing common solar-plus-EV project outcomes in Inland Southern California, two mistakes show up repeatedly. Both are avoidable with the information in this guide.

Mistake 1: Installing solar without the EV in the calculation and planning to "add panels later"

Homeowners frequently install a system sized to their current usage with the intention of adding panels when they buy an EV. The problem is that adding panels to an existing system costs more per watt than including them in the original installation. The incremental cost comes from additional design fees, a second permit, mobilization costs for a return site visit, and potential inverter limitations if the original inverter is already near its input capacity. In many cases, adding 2 kW of panels to an existing system costs $3,000 to $5,000 more than if those same panels had been included in the original proposal. If you know you are buying an EV in the next three years, include it in the original sizing.

Mistake 2: Charging during SCE peak hours without changing default behavior

The factory default for most EV charging setups is to start charging immediately when the vehicle is plugged in. Most Temecula EV owners arrive home between 5pm and 7pm, which puts them squarely in the 4pm to 9pm peak window. Without changing the charging schedule, an EV owner on SCE TOU-D-4-9PM rates pays $0.55 to $0.65 per kWh for every mile of EV range added during those hours. The fix takes five minutes in the Tesla app, ChargePoint app, or Emporia app: set the scheduled start time to 9pm. Combined with solar, this single change is worth $800 to $1,500 per year in avoided peak charges.

Frequently Asked Questions