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Solar Washing Machine Calculator

Enter your washer type, weekly loads, and wash temperature — discover the hidden cost of water heating (80% of wash energy) and how solar offsets it.

Washing machine usage
loads/wk
min
$/kWh
Solar sizing for your washing machine
1 × 400W panel to offset annual wash energy
Motor energy per cycle267 Wh
Water heating per cycle405 Wh (60% of total)
Total per cycle672 Wh
Monthly energy17.45 kWh/mo
Annual energy209.6 kWh/yr
Annual electricity cost$29.34/yr
Temperature comparison (same loads/washer)
Cold wash annual cost$13.42/yr
Warm wash annual cost$29.34/yr
Hot wash annual cost$47.03/yr
Cold vs hot savings$33.61/yr
Solar system cost: $1,920 gross, $1,344 after 30% ITC. Payback: 45.8 years. Note: washing machines rarely justify a dedicated solar system — add this to a whole-home solar calculation for best results.
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How to Use This Calculator

Select your washer type and usage frequency

Choose your washing machine type — the motor wattage determines how much electricity the machine itself uses during the cycle. Front-load machines (300W) are the most efficient; standard top-loaders (500W) use the most. Enter your weekly load count honestly: the average US household does 5-8 loads per week. Commercial laundry businesses doing 20+ loads per day have very different economics.

The key insight: water temperature dominates energy use

Here is the most important number in this calculator: approximately 80% of a washing machine's electricity consumption goes to heating water, not running the motor. The motor of a top-loader running a 40-minute cycle uses about 330 Wh. Heating 15 gallons of water to hot wash temperature uses about 900 Wh — nearly 3× as much as the motor. Switching from hot to cold wash costs almost nothing in cleaning effectiveness with modern detergents while cutting per-load electricity by 75-90%.

Hot water source matters as much as temperature

If you have a gas water heater, your washing machine electricity bill is almost entirely just the motor — gas handles the water heating and it never shows up on your electric bill. Households with electric tank water heaters pay the full heat penalty. Heat pump water heaters are 2.5-3× more efficient than electric tanks, dramatically reducing the water heating portion of your wash energy.

The Formula

Motor kWh per Cycle = Washer Watts × Minutes ÷ 60 ÷ 1000 Hot Water kWh per Cycle = 0.90 kWh × Temp Fraction × Heater Factor (Temp Fraction: cold=0.05, warm=0.50, hot=1.0) (Heater Factor: electric tank=0.9, gas=0, heat pump=0.3) Total kWh per Cycle = Motor kWh + Hot Water kWh Weekly kWh = Total kWh × Loads per Week Monthly kWh = Weekly kWh × 4.33 Annual kWh = Weekly kWh × 52 Annual Cost = Annual kWh × Electricity Rate Avg Daily kWh = Annual kWh ÷ 365 System Watts = Daily kWh × 1000 ÷ PSH ÷ 0.80 Panels = System Watts ÷ 400W (round up)

The 0.90 kWh baseline for full hot water heating assumes approximately 15 gallons heated from 60°F to 120°F using an electric tank heater with 90% efficiency. Cold water washing uses only 5% of this (tap temperature variation) while warm wash uses approximately 50%. Gas water heaters add zero to your electricity bill regardless of wash temperature. Heat pump water heaters use ~30% of the energy of a standard electric tank.

Example

The Johnson family — top-load standard, 6 loads/week, warm wash in Chicago

The Johnson family in Chicago does 6 loads per week with their top-load standard washer (500W) on warm setting. They have an electric tank water heater and pay $0.14/kWh.

WasherTop-load standard, 500W
Usage6 loads/week, 40 min/cycle
TemperatureWarm (50% water heating)
Hot waterElectric tank
Rate$0.14/kWh, Chicago (4.4 PSH)

Result

Motor energy per cycle333 Wh
Water heating per cycle405 Wh (55% of total)
Total per cycle738 Wh
Annual energy~230 kWh/yr
Annual cost~$32/yr
Cold wash would cost~$10/yr (savings: $22/yr)
Hot wash would cost~$54/yr (extra $22 vs warm)

Switching to cold wash saves the Johnson family $22/year. For a family doing more loads with electric hot water, the savings are even larger. The solar system needed to offset this is tiny — just 1 panel — because washing machines are actually quite low energy compared to water heaters, dryers, or air conditioners. The real money is in the dryer — combine this with a solar clothes dryer calculator for the full laundry picture.

FAQ

A typical top-load washing machine uses 0.3-1.2 kWh per load depending on water temperature and hot water source. Motor-only (cold wash): 0.25-0.35 kWh. Warm wash with electric tank: 0.6-0.8 kWh. Hot wash with electric tank: 1.0-1.2 kWh. Front-load machines use 20-40% less in all categories due to lower motor wattage and less water used (which means less water to heat). The annual cost for an average household doing 6 warm loads per week: roughly $25-65 depending on electricity rate.
For most everyday laundry, yes — cold water washing works equally well with modern detergents specifically formulated for cold water (Tide Cold Water, Persil, and most major brands). Studies by Consumer Reports and the NRDC confirm cold water cleans effectively for everyday items. Hot water remains preferable for: heavily soiled items, diapers and baby items, heavily contaminated items (when someone is sick), white bedding and towels to kill dust mites, and items that need sanitizing. The energy savings from cold washing are real and significant — 80% lower per-load electricity cost.
Heat pump water heaters (like the Rheem Proterra or A.O. Smith Voltex) use 2.5-3× less electricity than standard electric tank heaters to produce the same hot water. A hot wash cycle that costs $0.08 with a standard electric tank costs only $0.03 with a heat pump water heater — making hot washing more affordable. Heat pump water heaters qualify for the federal 30% tax credit and state incentives in many states. For households with electric water heating, upgrading the water heater is actually more cost-effective than upgrading the washing machine for laundry energy reduction.
A washing machine alone typically uses 100-250 kWh per year — small enough that installing dedicated solar would have a very long payback. The better approach is to include your laundry energy in a whole-home solar calculation. If you're already sizing a solar system, knowing that your washer adds $20-60/year to your bill (and that the dryer typically adds $80-120/year more) gives you more accurate sizing data. The washer and dryer combined are worth accounting for in a residential solar system, but not the primary driver.
The energy savings from switching washer types are real but modest: a front-loader (300W) versus a top-loader standard (500W) saves about $8-15/year on motor electricity for typical usage. The bigger advantage of front-loaders is water efficiency — they use 40-50% less water per load, which matters in drought-prone areas and translates to additional water heating savings. The typical payback purely from energy savings on a front-loader upgrade is 15-25 years, which usually doesn't justify buying a new machine just for energy. However, when your current washer is near end-of-life, choosing a front-load HE model is the right choice.

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