As a homeowner with an electric vehicle, what solar system size and battery capacity provide the best balance of cost and EV charging needs?

Finding the sweet spot between a solar array, a home battery, and an EV charger comes down to math: how much you drive versus how much power your roof can realistically produce.

To strike the best balance of cost and performance, you should size your system based on your driving habits rather than trying to charge your entire car off a home battery overnight.

Step 1: Calculate Your EV's Energy Consumption

The average American drives roughly 3 7 m i l e s a day (1 3,5 0 0 m i l e s/y e a r ). A typical modern EV gets about 3.5 3.5 3.5 to 4.0 m i l e s p e r k W h (or roughly 0.27 0.27 0.2 7 to 0.3 k W h p e r m i l e).

• Daily EV Use: 3 7 m i l e s÷3.6 m i l e s/k W h≈𝟏𝟎t o𝟏𝟏k W h p e r d a y (or∼3 3 0 k W h/m o n t h).
• Annual EV Use:∼4,0 0 0 k W h/y e a r added to your standard household baseline (which averages 1 0,6 0 0 k W h/y e a r in the US).

Step 2: The Ideal Solar System Size

• Recommendation: 𝟑𝐤𝐖𝐭𝐨𝟒𝐤𝐖 of extra solar capacity dedicated strictly to the EV, on top of your normal home usage.
• In practical terms, a standard home without an EV might need a 7 k W to 8 k W system. Adding an EV typically bumps your ideal solar array size to𝟏𝟎𝐤𝐖𝐭𝐨𝟏𝟐𝐤𝐖 (roughly 25 to 30 standard 4 0 0 W panels).
• Why this is the sweet spot: Going larger than 1 2 k W often hits diminishing returns due to local utility caps on net metering or interconnection limits, while anything under 9 k W will leave you heavily reliant on grid power for your commute.

Step 3: The Ideal Battery Capacity

• Recommendation: 𝟏𝟎𝐤𝐖𝐡𝐭𝐨𝟏𝟓𝐤𝐖𝐡 of storage (e.g., one standard unit like a Tesla Powerwall or equivalent LFP battery).
• The Cost-vs-Utility Trap: A typical EV battery is 6 0 t o 8 0 k W h . Trying to store enough solar energy in a home battery to completely "refill" your car from empty at night is economically inefficient. Home batteries cost roughly$1,0 0 0 per kWh installed; adding 6 0 k W h of home storage just for the car would double your project cost and take decades to pay back.
• The Smart Balance: Use a 1 0–1 5 k W h battery to power your home loads during peak evening pricing hours, or to capture daytime solar overflow so you can direct it into your car via a smart charger when you get home from work.

Summary Checklist for Best Value

• Solar Array: 1 0 k W t o 1 2 k W total system size.
• Home Battery: 1 3.5 k W h (one standard cabinet) for load-shifting and basic backup, not for total car recharges.
• The Secret Weapon: Install a smart EV charger (like a Wallbox or ChargePoint) programmed to track your solar production. Instead of routing midday solar into a static home battery first, the smart charger diverts excess solar straight into your car while it sits parked at home during the day.

To dial this in closer to your actual numbers, tell me:

• How many miles do you drive daily or annually?
• Does your local utility offer 1-to-1 net metering or time-of-use rates?

For most homeowners with one electric vehicle, the best cost-to-benefit balance is usually:

• Solar: about 8–12 kW total system size (home + EV)
• Battery: about 10–15 kWh usable capacity (if adding storage at all)

The “right” size depends on your home’s electricity use, EV mileage, utility rates, and whether you want backup power. A larger battery is often less cost-effective than adding more solar.

A practical sizing approach

1. Add your EV energy needs

A typical EV driven around 12,000 miles/year uses roughly 3,000–4,500 kWh/year for charging, depending on efficiency and driving habits.

That generally requires about:

• 2–3 kW of additional solar capacity in many U.S. locations
• Roughly 6–10 modern solar panels (depending on panel wattage and sunlight)

2. Size solar for your whole house

Typical examples:

A good target is to install enough solar to cover 90–110% of your annual electricity consumption, rather than trying to maximize roof coverage.

Battery sizing: where the economics change

A battery does not usually need to store your EV’s entire charge. A typical EV battery might hold 50–100+ kWh, but buying a home battery that large is usually expensive and unnecessary.

A balanced choice:

10–15 kWh battery

Good for:

• Evening/night household loads
• Reducing peak-time electricity purchases
• Short outages
• Keeping essential circuits running

20–30+ kWh battery

Makes sense if you:

• Have frequent outages
• Need longer backup
• Have high evening electricity rates
• Want more energy independence

For many homes, a larger solar array + moderate battery beats a smaller solar array + oversized battery financially.

Example “sweet spot” system

For a typical U.S. homeowner:

• Home electricity use: ~10,000 kWh/year
• EV charging: ~3,500 kWh/year
• Total: ~13,500 kWh/year

A reasonable design:

• Solar: 9–11 kW
• Battery: 10–15 kWh
• EV charger: Level 2 smart charger scheduled for solar-heavy hours when possible

When to go bigger

Consider increasing solar to 12–15 kW if you expect:

• A second EV
• Heat pump HVAC
• Electric water heating
• More driving
• Future electrification of appliances

Consider increasing battery capacity if your goal is backup power, not just EV savings.

If you share your state/city, annual electric bill (kWh if available), EV model, miles driven per year, and whether you want backup power, I can estimate a more precise solar and battery size.

• Home electricity use: ~10,000 kWh/year
• EV charging: ~3,500 kWh/year
• Total: ~13,500 kWh/year

A reasonable design:

• Solar: 9–11 kW
• Battery: 10–15 kWh
• EV charger: Level 2 smart charger scheduled for solar-heavy hours when possible

When to go bigger

Consider increasing solar to 12–15 kW if you expect:

• A second EV
• Heat pump HVAC
• Electric water heating
• More driving
• Future electrification of appliances

Consider increasing battery capacity if your goal is backup power, not just EV savings.

If you share your state/city, annual electric bill (kWh if available), EV model, miles driven per year, and whether you want backup power, I can estimate a more precise solar and battery size.

Finding the sweet spot between upfront equipment costs and offset charging needs depends heavily on your daily driving habits and local utility rate structures. An average EV driver travels roughly 40 miles a day, which consumes about 1 0 t o 1 2 k W h of electricity (assuming an efficiency of 3.5 t o 4 m i l e s p e r k W h).

To strike the best balance of cost-effectiveness and performance, consider the following balanced sizing guidelines:

Recommended Sweet-Spot Sizes

• Solar System Size: 𝟏𝟎𝐤𝐖𝐭𝐨𝟏𝟐𝐤𝐖 ( roughly 2 4 t o 3 0 standard solar panels). This typically generates an extra 1 2,0 0 0 t o 1 5,0 0 0 k W h per year, which is enough to cover a standard household baseline plus an average EV driven 12,000 miles annually.
• Battery Storage Capacity: 𝟏𝟎𝐤𝐖𝐡𝐭𝐨𝟏𝟑.𝟓𝐤𝐖𝐡 (typically one standard modular unit like a Tesla Powerwall or equivalent LFP battery).

Why This Combination Works

• The Solar Balance: Going smaller than 1 0 k W means you will frequently draw grid power to finish charging your car or home during less sunny months. Going much larger (1 5 k W+) heavily inflates upfront equipment costs and often hits diminishing returns unless you have a second EV or an all-electric home heating setup.
• The Battery Reality: Charging an EV directly from a home battery is surprisingly inefficient due to round-trip energy losses (converting DC solar to AC home power, then back to DC/AC in the car). Because an EV battery is massive (6 0 t o 1 0 0 k W h ), a home battery cannot realistically store a "full charge" for a car. Instead, the optimal role for a 1 0--1 3.5 k W h home battery is load shifting —storing excess daytime solar energy to power your house at night, while you program your EV to charge directly from peak afternoon solar hours, or use cheap overnight grid rates if your utility lacks net metering.

If you want to fine-tune this for your exact situation, tell me:

• Your average daily or monthly driving mileage
• Whether your utility offers net metering (1-to-1 credit for excess solar) or time-of-use rates
• Your general geographic region or climate

I can help you calculate a more precise return on investment and hardware configuration.

For a typical grid-connected homeowner with one EV, the sweet spot is usually about 8–12 kW of solar plus 10–15 kWh of usable battery storage. I’d generally size the solar array more generously than the battery because the EV is a large energy load, while a battery is primarily valuable for shifting solar into evening hours and providing backup.

A practical rule of thumb

Why? An EV driven 12,000 miles/year might consume roughly 3,000–4,000 kWh/year for charging, depending on the vehicle and driving efficiency. That's substantial, but you don't necessarily want a huge battery to accommodate it.

For example, a 10-kW solar system producing 1,200–1,500 kWh per kW-year would generate roughly 12,000–15,000 kWh/year. Actual production varies substantially with location, roof orientation, shading and weather; NREL's PVWatts calculator is designed to model those factors.

Why I wouldn't automatically buy a 30–40 kWh battery

A common mistake is thinking, "My EV has a 70-kWh battery, so I need a huge home battery." You don't.

The EV battery is itself an enormous energy-storage asset. If your car is home during the day, smart EV charging can use surplus solar directly, avoiding the losses and expense of sending that electricity through a stationary battery first.

A ~13.5-kWh home battery is already around the current mainstream size. EnergySage's 2026 data puts the average installed battery at about $15,650 for 13.5 kWh, before incentives, and notes that batteries aren't economically compelling everywhere.

So I'd prioritize:

1. Enough solar to cover the house + EV annually.
2. A ~10–15 kWh battery for evening/night usage and outage protection.
3. A smart EV charger programmed to charge primarily during solar-production hours.
4. If available, time-of-use rates, allowing the battery/EV to avoid expensive electricity periods.

The biggest variable: your electricity consumption

If your house currently uses 8,000 kWh/year and your EV adds 3,500 kWh, you're targeting roughly 11,500 kWh/year of electricity. If your local solar production is, say, 1,300 kWh per installed kW annually, you'd need around:

11,500 ÷ 1,300 ≈ 8.8 kW

I'd probably round that toward 9–10 kW, rather than designing right on the mathematical minimum.

If you tell me your annual electric usage (kWh), EV model, approximate miles driven per year, and state/city, I can calculate a much more precise solar size and battery capacity—and show you the likely tradeoff between, say, 8 kW + 10 kWh vs. 10 kW + 15 kWh vs. 12 kW + 20 kWh.

A typical home with an electric vehicle needs a 7 kW to 10 kW solar system paired with a 10 kWh to 15 kWh battery to balance cost and daily EV charging needs.

Why This Size Works

• Solar Size (7–10 kW): Generates roughly 2 8--4 0 k W h of energy per day depending on your climate, which easily covers a standard daily commute of 40 miles plus home usage.
• Battery Capacity (10–15 kWh): Stores enough excess daytime solar power to charge your car overnight or offset peak evening grid rates without paying for oversized hardware.

Breakdown of System Components

• Solar Panels (7–10 kW system / roughly 18–25 panels): Produces about 9,0 0 0--1 3,0 0 0 k W h annually. This covers an EV driven 12,000 miles a year (which uses about 3,6 0 0 k W h ) plus an average home's baseline load.
• Home Battery (10–15 kWh / e.g., Tesla Powerwall or Enphase 5P): Allows you to capture free solar energy during peak production hours and feed it into your Level 2 EV charger after the sun goes down.
• EV Charger (Level 2, 48-amp / 11.5 kW): Plugs into your home power setup to deliver a full charge overnight in 6 to 8 hours.

Cost vs. Value Factors

• Driving Habits: If you commute fewer than 30 miles a day, a smaller 6 kW solar system and a single 10 kWh battery keep upfront costs low. If you work from home and drive 60+ miles daily, scale up to a 12 kW system and a 20+ kWh battery (or two batteries).
• Net Metering: If your local utility offers 1:1 net metering (paying you full retail price for excess solar sent to the grid), a battery is optional for cost savings and is only needed for backup power during outages.
• Time-of-Use (TOU) Rates: If your utility charges high rates in the evening when you plug your car in, a battery is essential to store cheap daytime solar and discharge it into your EV at night.

If you want, tell me:

• Your daily driving distance in miles
• Whether your utility offers 1:1 net metering or time-of-use rates
• Your average monthly electricity bill or kWh usage

I can give you a more customized system size recommendation.

For a typical homeowner with one EV, the sweet spot is usually more solar and a moderate battery, rather than trying to make the battery large enough to cover the EV by itself.

A good starting point

My default recommendation: ~9–10 kW of solar + ~15–20 kWh of usable battery storage for a typical single-EV household.

Why? An EV can easily use 7–12+ kWh per day depending on how far you drive and the vehicle's efficiency. It's generally more economical to let the solar directly charge the car during the day and use the battery primarily to shift solar into the evening/night. NREL research similarly finds that flexible EV charging can substitute for some stationary-storage needs.

The important distinction: solar size vs. battery size

Solar should be sized around your annual electricity consumption. Roughly:

Solar production needed ≈ household electricity + EV electricity For example, if your house uses 12,000 kWh/year and the EV adds 3,000 kWh/year, you're looking at roughly 15,000 kWh/year of electricity demand. The actual panel size needed depends heavily on your location, roof orientation, shading, and local solar resource.

Battery should be sized around your evening/nighttime load and backup goals, not around the EV's entire battery.

A 13.5-kWh home battery is already a substantial amount of storage; current market data puts the average residential battery around 10–13.5 kWh. EnergySage A 20-kWh system gives you considerably more flexibility for an EV household without jumping into the very expensive territory of trying to provide multiple days of whole-home backup.

One particularly important EV consideration

Don't assume you need a large battery capable of charging the EV overnight.

If your EV arrives home at 6 p.m. with 30 kWh needed and your home battery only has 15 kWh available, you don't want the battery trying to supply all 30 kWh. Instead:

• Charge the EV directly from solar whenever possible.
• Schedule charging for midday if your utility rate/net-metering arrangement rewards that.
• Use the stationary battery for household evening loads.
• If you have time-of-use rates, have the battery discharge during expensive periods and recharge from solar.
• During an outage, consider whether EV charging is actually a priority; keeping the refrigerator, HVAC, lights, internet, etc. running may be much more valuable.

This approach can let you get away with a 13.5–20 kWh battery instead of 30–40+ kWh.

If you're in Mississippi

If you're asking because you're in the Oxford/Mississippi area, I'd lean toward ~9–11 kW solar + 13.5–20 kWh battery as a very reasonable starting point. Current 2026 Mississippi storage pricing is roughly $1,204/kWh installed on average, with a 13-kWh system averaging about $15,657 before incentives, so adding lots of battery capacity gets expensive quickly.

The economics also depend heavily on how your utility compensates excess solar and whether you have time-of-use pricing; a battery isn't automatically worthwhile just because you own an EV.

If you give me your home's average monthly kWh, your EV model, approximate miles driven per day/month, and your utility/electric rate, I can calculate a much more precise solar kW + battery kWh recommendation and show the likely payback.

For example, if your house uses 12,000 kWh/year and the EV adds 3,000 kWh/year, you're looking at roughly 15,000 kWh/year of electricity demand. The actual panel size needed depends heavily on your location, roof orientation, shading, and local solar resource.

Battery should be sized around your evening/nighttime load and backup goals, not around the EV's entire battery.

A 13.5-kWh home battery is already a substantial amount of storage; current market data puts the average residential battery around 10–13.5 kWh. energysage.com A 20-kWh system gives you considerably more flexibility for an EV household without jumping into the very expensive territory of trying to provide multiple days of whole-home backup.

One particularly important EV consideration

Don't assume you need a large battery capable of charging the EV overnight.

If your EV arrives home at 6 p.m. with 30 kWh needed and your home battery only has 15 kWh available, you don't want the battery trying to supply all 30 kWh. Instead:

Balancing a home solar system and battery storage with an Electric Vehicle (EV) comes down to a simple reality: EVs are massive energy consumers compared to standard household appliances.

Charging an EV completely can take anywhere from 40 40 4 0 to 8 0 k W h of energy. Because of this, trying to power your EV directly from a home battery storage system is usually cost-prohibitive. Instead, the sweet spot for the "best balance" relies on sizing your solar array to produce enough excess annual energy for the car, while using a modestly sized battery strictly for home backup or optimizing time-of-use (TOU) rates.

1. The Ideal Solar System Size (PV Array)

To figure out the right solar panel system size, look at your driving habits:

• The Math: An average EV consumes about 0.3 k W h per mile. If you drive 4 0 m i l e s a day (1,2 0 0 m i l e s a month), your car needs roughly 3 6 0 k W h monthly, or about 4,3 2 0 k W h annually.
• The Extra Solar Impact: A standard home uses about 1 0,0 0 0 k W h per year. Adding an EV increases your total load by 3 0% to 5 0%.
• The Sweet Spot Recommendation:
  • For an average home + 1 average EV, a 𝟖𝐤𝐖 to𝟏𝟏𝐤𝐖 solar system (roughly 20 20 2 0 to 28 28 2 8 standard panels) provides the optimal cost-to-production balance in most climates. This covers your baseline house usage plus roughly 1 0,0 0 0 to 1 2,0 0 0 a n n u a l d r i v i n g m i l e s.

2. The Ideal Battery Capacity

Here is where many homeowners miscalculate: Do not size your battery to fully charge your car. A single Tesla Powerwall or equivalent home battery holds about 1 3.5 k W h . If you dump that entire battery into an EV, your house will be left with zero backup power, and the battery will degrade faster due to heavy cycling.

• The Real Role of a Battery: The battery should cover your home's critical evening loads and shift solar power generated during the day to the evening hours, or protect you against peak Time-of-Use (TOU) utility rates. You should still charge your EV directly from the solar panels while the sun is shining (if you work from home) or from the grid overnight when utility rates are cheapest.
• The Sweet Spot Recommendation:
  • A 𝟏𝟎𝐤𝐖𝐡 to𝟏𝟓𝐤𝐖𝐡 battery capacity (e.g., 1 1 1 standard high-capacity unit like a Tesla Powerwall 3 or EG4 wall-mount unit) is the financial sweet spot.
  • Going larger (2 7--4 0 k W h+ multi-battery setups) drastically increases your upfront costs with diminishing returns on your EV savings unless you live in an area with frequent, multi-day grid blackouts.[1]

Summary Checklist for Best Value

• Solar Array Size: 8 k W – 1 1 k W (Ensures enough surplus generation to offset car charging credits or direct daytime charging).
• Battery Capacity: 1 3--1 5 k W h (Ideal for household load-shifting and basic backup, letting the grid or direct solar handle the heavy lifting for the vehicle).
• Charging Strategy: Charge during peak solar production hours via a smart charger (like a ChargePoint Go to product viewer dialog for this item. or Tesla Wall Connector Go to product viewer dialog for this item. ) rather than draining a home battery overnight into the car.

To narrow this down to your exact numbers, tell me:

• How many miles do you drive per day/year?
• Does your electric utility have Time-of-Use (TOU) rates or net metering?
• Are you looking for full home backup during outages, or just bill reduction?

For a typical grid-connected homeowner with one EV, the sweet spot is usually about 10–14 kW of solar plus 10–15 kWh of usable battery storage. The exact answer depends heavily on your home’s electricity use, EV miles, roof orientation, and utility rate structure.

A practical sizing rule

An EV typically adds roughly 8–12 kWh of electricity per 30–40 miles driven, depending on the vehicle and weather. So if you drive 12,000 miles/year, the EV might add around 3,000–4,000 kWh/year to your household consumption.

I'd approach sizing this way:

As a benchmark, EnergySage reports that the average U.S. solar shopper in 2026 needs about 12 kW of solar, while a typical home battery is around 13.5 kWh.

Why I wouldn't oversize the battery for the EV

The solar array should be sized primarily around your annual electricity consumption, including the EV. The battery is different: you generally don't want enough battery to store an entire EV charge.

For example, suppose your home uses 25 kWh/day and your EV uses another 10 kWh on a driving day. A 13.5-kWh battery can cover a meaningful portion of your evening/nighttime consumption, but you're not paying $15,000+ simply to store a full EV charge every day.

Current EnergySage data puts a 13.5-kWh battery at roughly $15,600 installed before incentives, with Maryland averaging about $18,100 for a 13.5-kWh system.

That makes one ~13.5-kWh battery a particularly attractive starting point. I'd add a second battery only if you have a strong reason—frequent outages, substantial evening electricity consumption, unfavorable time-of-use rates, or a desire for greater backup capacity.

If you're in Maryland

Since you're in the Maryland area, I'd lean toward the upper end of the solar range if your roof permits it: roughly 12–14 kW solar + 13.5–20 kWh battery for a typical EV household.

That's because the economics of storage depend heavily on your utility's compensation for exported solar and electricity rates. A battery becomes more valuable when you can't get full retail value for excess solar or when you have significant peak/off-peak price differences.

One important point: don't size the solar system merely to recharge the battery. Ideally, you want the panels to produce enough annual energy for house + EV, while the battery shifts some of that solar energy from daytime to evening/night.

If you give me (1) your monthly electric bill/kWh, (2) EV model, (3) miles driven per month, (4) your utility, and (5) whether you want whole-home backup, I can calculate a much more precise solar kW + battery kWh recommendation and approximate installed cost/payback for your situation.

Finding the sweet spot between a solar array, battery storage, and an EV depends heavily on your daily driving habits and utility rate structure . Trying to charge an EV entirely from a home battery overnight is usually cost-prohibitive, but pairing a properly sized solar array with a modest battery offers the best financial return.

1. The Math: Understanding EV Energy Needs

• An average American driver covers about 40 40 4 0 miles per day.
• At an efficiency of roughly 3 3 3 to 4 k W h p e r m i l e (or 3 0–3 4 k W h p e r 1 0 0 m i l e s ), driving 40 40 4 0 miles consumes 12 12𝟏𝟐 to𝟏𝟒𝐤𝐖𝐡 of electricity daily (approx. 4 0 0 k W h/m o n t h).
• A standard Level 2 home charger operates at 7.2 k W to 9.6 k W.

2. Recommended "Sweet Spot" System Sizes

• Solar System Size:𝟖𝐤𝐖 to𝟏𝟐𝐤𝐖
  • Why: A typical household uses 20 20 2 0 to 3 0 k W h daily. Adding an EV adds another 1 2–1 5 k W h daily. A 1 0 k W solar system (roughly 2 2–2 5 panels) generates an average of 4 0–5 0 k W h per day depending on your geographic location and climate, comfortably covering both your home baseline and daily car commuting needs on an annual net basis.
• Battery Capacity:𝟏𝟎𝐤𝐖𝐡 to𝟏𝟓𝐤𝐖𝐡 (Single standard unit like a Tesla Powerwall or EG4/Enphase equivalent)
  • Why: Trying to use a home battery to charge your car from the battery at night is inefficient and expensive; draining a 1 4 k W h battery just to put it into your car's 7 5 k W h battery incurs round-trip conversion losses, and you'll run out of household backup power. Instead, the optimal battery size is designed to house enough juice for your non-EV home loads during peak rate hours or to capture midday solar excess so you can smart-charge your EV during the late afternoon/early evening before peak rates hit, or run your house while your EV charges directly from active solar panels.

3. Cost vs. Balance Strategy

• The "Direct Solar Charging" Approach (Best Value):
  Do not oversize your battery just for the car. Instead, oversize the solar array slightly and program your Level 2 charger (using smart chargers like a ChargePoint Home Flex Go to product viewer dialog for this item. or Emporia Go to product viewer dialog for this item.) to trigger during peak solar production hours (typically 10:00 AM to 3:00 PM) if you work from home or have a flexible schedule. This feeds solar power straight into the car for free, bypassing the battery storage round-trip loss entirely.
• The Time-of-Use (TOU) Arbitrage Approach:
  If you are away during the day, the ideal balance is a 1 0–1 2 k W solar array paired with a single 1 3.5 k W h battery. Solar powers your home and fills the battery during the day. Excess solar goes to the grid (if net metering is favorable). At night, your home runs off the battery, and you charge your EV late at night only if your utility offers cheap overnight EV-specific grid rates.

To help narrow down the exact numbers for your home, let me know:

• What is your average daily commute or monthly mileage?
• Does your local utility offer net metering or Time-of-Use (TOU) rates?

For most homeowners with an EV, the sweet spot is roughly 8–12 kW of solar paired with 10–15 kWh of usable battery storage. If you drive a lot, have a large home, or want substantial outage protection, moving toward 12–15 kW + 15–25 kWh can make sense.

A practical sizing rule

An EV typically adds about 8–12 kWh of electricity for every 30–40 miles driven, depending on the vehicle and conditions. So if you drive 12,000 miles/year, the EV may consume roughly 3,000–4,000 kWh/year.

I'd approach the system like this:

The important distinction is that the battery doesn't need to be sized to charge the EV. Solar should provide the energy, while the battery mainly shifts solar energy from daytime into the evening/night and provides backup. A 10–15 kWh battery can therefore work quite well even with an EV whose battery is 60–100+ kWh.

For example, suppose your house uses 25 kWh/day and your EV averages another 10 kWh/day. You're around 35 kWh/day, or ~12,800 kWh/year. A roughly 10–12 kW solar array is a reasonable starting point, but the exact production depends heavily on roof orientation, shading and location. NREL's PVWatts tool models those factors and is the right way to turn a nominal system size into an actual production estimate.

Why I wouldn't oversize the battery

Battery capacity gets expensive quickly. EnergySage's 2026 data puts the average installed battery cost around $1,128 per usable kWh, with a 13.5-kWh system averaging about $15,228 before incentives.

So going from 10 → 20 kWh can add a substantial amount of cost without giving you twice the economic benefit.

I'd favor 10–15 kWh if your primary objectives are:

• charging the EV with solar;
• reducing evening grid consumption;
• providing some outage protection;
• keeping the system financially sensible.

I'd consider 20+ kWh primarily if you want the battery to run major household loads during outages, particularly air conditioning. For comparison, a typical U.S. home consumes around 30 kWh/day, so even a 13.5-kWh battery isn't intended to run an entire house indefinitely.

One particularly important EV consideration

If you can schedule EV charging during the daytime, you can reduce the amount of battery capacity you need considerably. For example:

Solar → house + EV during daylight → excess solar → battery → house overnight

is generally more economical than:

Solar → battery → EV overnight.

The latter incurs additional battery charging/discharging losses and requires a larger battery.

If you're in Florida, I'd lean toward the upper end of the solar range—around 10–12 kW solar + 13–15 kWh battery for a typical EV household—assuming the roof can accommodate it. But your actual electric bill and EV mileage can narrow this down considerably.

If you give me (1) your average monthly electric bill, (2) EV model, (3) miles driven per month, and (4) whether you want whole-home backup, I can calculate a much more precise solar kW and battery kWh target and show the approximate economics.