Solar Under NEM 3.0 and SCE: Is Cleaning Worth It?

Short answer: sometimes, and it depends on your numbers. In a University of California San Diego study of 186 California solar sites, sites would have yielded 0.81 percent more annual energy, on average, if they had been washed halfway through the summer dry spell, and up to 4 percent at the high end. On a 7 kW system that is about 94 to 466 kWh. Whether that pays for a $110 cleaning depends on what a kWh is worth to you, and under NEM 3.0 that is a wide range: about 3 to 6 cents for midday power you export, and 24 to 30 cents or more for power you use yourself.

Use the calculator on this page with your own system size, rate and soiling estimate. We never promise a percentage. Our price is $6 a panel with a $110 minimum, single-story roofs only, from the ground.

Estimate only. This is arithmetic on the numbers you type in. It is not a measurement of your system and not a promise. Your own monitoring app is the better test.

System size (kW)Value of a kWh to you ($)Output lost to dirt (%)Yearly kWh per kW

Power lost to dirt: 0 kWh a month, worth $0 a month.

Our one-time cleaning for about 0 panels: $0. At that loss it pays back in about n/a.

Default sizes: yearly yield 1,450 to 1,700 kWh per kW near Ontario (NREL PVWatts run, south-facing, default losses). Dirt loss: Mejia and Kleissl (2013, 186 California sites) found a mean of 0.051% per day of dry weather, so about 1.5% after 30 dry days and 4.6% after 90; 26% of sites lost more than 0.1% a day (3% after 30 days, 9% after 90). We found no source for a lower figure. Rate: SCE lists 24 to 30 cents per kWh off-peak on TOU-D-PRIME; use 3 to 6 cents instead if the lost power would have been exported, not used at home. All of this is an estimate; see the sources below.

What NEM 3.0 changed, in plain words

NEM 3.0 is the nickname. The California Public Utilities Commission (CPUC) calls it the net billing tariff, and SCE calls it the Solar Billing Plan. Customers applying for interconnection since April 15, 2023 have taken service on the new net billing tariff.

The rule that matters for cleaning is how your power is counted. Under the Net Billing Tariff, onsite generation is first used to serve onsite load, offsetting energy costs. Whatever is left goes to the grid. The credit for exports is based on Avoided Cost Calculator values, usually lower than import rates. Those credits can rise above the retail rate on late summer evenings.

SCE adds that new Solar Billing Plan customers are locked into their export credit values for nine years, and that Solar Billing Plan customers are on its TOU-D-PRIME rate plan. SCE's page also says eligible residential customers who enroll before 2028 receive an additional credit of about $0.04 per kWh, or about $0.09 for income-qualified customers. The calculator does not include that extra credit.

Customers who connected before April 15, 2023 are on older rules (NEM 1.0 or 2.0), which we do not cover here. The math in this guide is for net billing customers.

What a kilowatt-hour is worth on SCE, two ways

SCE's rate advisory lists an average residential rate of 34.4 cents per kWh before its October 1, 2026 rate change and 34.5 cents after it (33.2 and 33.3 cents with the California Climate Credit). That is an average across all customers and plans. Solar Billing Plan customers are on time-of-use pricing, so the number depends on the hour.

The two tables below come from two SCE pages we opened. The first shows what you pay for power you buy from SCE on TOU-D-PRIME, which is what a cleaning-lost kWh is worth if you would have used it yourself. The second shows the average export credit SCE lists for power you send out. SCE says its rates apply to customers who get both delivery and generation from SCE, so a Community Choice customer can see different numbers. Both pages are SCE's, not ours, and rates change.

TOU-D-PRIME (SCE rate page)	Price per kWh
Summer (June to September), weekdays, off-peak (all hours except 4 to 9 p.m.)	26 cents
Summer weekdays, on-peak (4 to 9 p.m.)	61 cents
Summer weekends, mid-peak (4 to 9 p.m.)	39 cents
Winter (October to May), off-peak	30 cents
Winter, super-off-peak (8 a.m. to 4 p.m.)	24 cents
Winter, mid-peak (4 to 9 p.m.)	45 cents

The base charge on that plan is $0.79 a day. There is no baseline credit.

What SCE says it pays for exports

SCE's Solar Billing Plan page lists average Energy Export Credit values by year, with a note that the real value changes with the hour and the month. Credits are higher from 4 to 9 p.m. and in summer, lower from 6 a.m. to 4 p.m. and in winter. For 2026 it shows these averages.

2026 average export credit	Daytime (6 a.m. to 4 p.m.)	Evening (4 to 9 p.m.)	Overnight (9 p.m. to 6 a.m.)
Summer (June to September)	6 cents	21 cents	12 cents
Winter (October to May)	3 cents	10 cents	10 cents

Read the table this way. Your panels make most of their power in the daytime column. A kWh sent out then earns 3 to 6 cents. A kWh you use in your own house at that moment saves the retail price, 24 to 30 cents on the off-peak rows above. That gap is the main fact about NEM 3.0, and it is why self-use and batteries matter more than they used to.

Your numbers will differ. We do not know your plan details, your usage, whether you have a battery, or the year you connected, which sets your locked export values.

Why solar output drops, and what is sourced

A drop in your monitoring app has more than one possible cause. Here is what we could verify, and what we could not.

Dirt (soiling). Mejia and Kleissl (UC San Diego, Solar Energy, 2013) measured 186 residential and commercial California sites during dry periods in 2010. Losses averaged 0.051 percent per day and 26 percent of the sites lost more than 0.1 percent per day. Losses depended mainly on days since the last rain. Over an average 145-day summer drought, that average works out to 7.4 percent by the end. Sites with panels tilted less than 5 degrees lost more, while differences by location were not statistically significant. They also note an earlier study found 0.2 percent per day, which they think may have been biased high.
Age (degradation). The review is by Jordan and Kurtz of NREL. Nearly 2,000 degradation rates from the literature show a median value of 0.5 percent per year. Mejia and Kleissl say a long dry spell of dirt costs more than an order of magnitude more than cell degradation does over the same 145 days. Degradation is a slow loss that cleaning cannot fix.
Heat. The U.S. Department of Energy says solar cells generally work best at low temperatures, and that heat lowers voltage substantially. We did not find a single percent figure on an official page, so check your panel's data sheet for its temperature coefficient.
Season. Winter output is lower because the days are shorter. NREL's PVWatts model for Ontario shows about 104 kWh a month per kW in December and 170 in August (our run, below), so compare the same month a year apart.
Shade. PVWatts has a shading loss setting, and its default of 1 percent represents an array with little or no shading. A new tree or a neighbor's addition can raise that. Partial shade can hurt more than its area suggests, but we did not open a source that quantifies this, so ask your installer.
Inverter or equipment faults. We did not find an official source we could open on inverter problems. If output drops suddenly on a clear day, or the app shows an error, call your installer before booking a cleaning.

Typical yield near Ontario, from NREL

We ran NREL's PVWatts calculator (version 8, weather from the National Solar Radiation Database) for a point near Ontario, California, with the default 14 percent system losses. For a south-facing roof, 1 kW of panels makes about:

Roof setup	Annual energy per kW of panels
South-facing, 10 degree tilt	about 1,593 kWh
South-facing, 18 degree tilt	about 1,654 kWh
South-facing, 20 degree tilt	about 1,665 kWh
South-facing, 30 degree tilt	about 1,693 kWh
West-facing, 20 degree tilt	about 1,465 kWh

Use about 1,450 to 1,700 kWh per kW per year. PVWatts' help text lists a default soiling loss of 2 percent, so a year with always-clean glass would be slightly higher. This is a model, not a measurement of your roof.

Worked example: a 7 kW system

This is an example with invented homeowner details, built from the sources above. It is not a promise.

A 7 kW system near Ontario, facing south at 20 degrees, makes about 11,655 kWh a year in the PVWatts model. That is about 18 panels at 400 watts. A cleaning with us costs $110 (18 panels at $6, with the $110 minimum).

Case	Energy gained from one cleaning	Worth if exported (6 cents)	Worth if used at home (26 cents)
Average of the 186 sites (0.81 percent of a year)	about 94 kWh	$6	$24
High end of those sites (4 percent of a year)	about 466 kWh	$28	$121

Against a $110 visit, the average case does not pay back in energy alone, even at the retail price. The high case roughly breaks even, and only if you use the extra power yourself rather than export it. The study points the same way. On average, the sites would have yielded 0.81% more annual energy if they had been washed halfway through the summer drought period. The high end for individual sites was 4 percent.

So when is it worth it? When your soiling is far above the average: nearly flat panels, a dusty street or lot, long dry spells, or a fire with ash on the glass. Cleaning is also worth a look if the retail price you offset is high and you use much of your solar yourself. It is not worth it if your app shows no change. The honest test is the same one as in our cleaning frequency guide: compare two similar clear days, before and after.

We also do not know if those 2010 sites are typical for your roof. The study says nothing about today's SCE rates or export credits, which is why the calculator on this page lets you enter your own.

How to use the calculator on this page

System size: from your installer's paperwork, in kW.
Electricity rate: use 24 to 30 cents for power you would use at home in the daytime on TOU-D-PRIME, or 3 to 6 cents for power you would export. If you do not know your split, run it twice and read both answers as a range. SCE's page says rates apply to SCE delivery plus generation, so use your own bill if you are on Community Choice.
Soiling percent: the loss at the moment you clean. The Mejia and Kleissl average of 0.051 percent per day gives about 1.5 percent after 30 dry days, 4.6 percent after 90 and 7.4 percent after 145. Because dirt builds up in a straight line, the average loss over that period is about half of the final number. A rate of 0.1 percent a day, which 26 percent of their sites exceeded, gives about 9 percent after 90 days.

Our limits

We clean single-story roofs from the ground with a water-fed pole and pure water. We do not climb. We cannot read your inverter data, tell you your locked export rate or advise on switching rate plans. Ask your installer or SCE for those. We do not sell solar and we do not guarantee any gain.

Common questions

What is NEM 3.0?

It is the nickname for California's net billing tariff, which applies to customers who applied to connect on or after April 15, 2023. The CPUC says exports are credited at avoided cost values that are usually lower than the retail rate, and that onsite generation serves your own load first.

How much does SCE pay for solar exports?

SCE's Solar Billing Plan page lists 2026 averages of 6 cents in summer daytime and 3 cents in winter daytime, and 21 cents in summer evenings. Values change by hour and month and are locked for nine years for new customers.

How much does electricity cost on SCE?

SCE lists an average residential rate of 34.4 cents per kWh, going to 34.5 cents on October 1, 2026. On TOU-D-PRIME, the plan Solar Billing Plan customers use, daytime off-peak is 24 to 30 cents and the 4 to 9 p.m. peak is 45 to 61 cents.

Is it worth cleaning solar panels in California?

Often not on energy alone. A UC San Diego study of 186 sites found sites would have yielded 0.81 percent more annual energy on average if washed mid-summer, up to 4 percent at the high end. It can pay for sites with flat panels, heavy dust or ash.

How much power do dirty panels lose?

That study found an average of 0.051 percent per day of dry weather, with 26 percent of sites losing more than 0.1 percent a day. Rain resets part of it. Your roof may differ.

Should I clean my panels if my output dropped?

First rule out other causes: season, shade, heat, age or an inverter problem. Compare two similar clear days. If the glass is visibly dirty and the app shows a gap, a cleaning is reasonable.

Where this applies

We work in every place within 15 miles of Ontario: Ontario, Upland, Montclair, Chino, Rancho Cucamonga, Claremont, Alta Loma, Eastvale, Pomona, Etiwanda, Chino Hills, Jurupa Valley, La Verne, Norco, Fontana, San Dimas, Diamond Bar, Corona, Walnut, Rialto, Covina, Glendora.

Related services: Solar panel cleaning, Plans, Instant quote.

More guides

Sources

Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “0.81% more annual energy if they had been washed halfway through the summer drought period”
Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “while some sites would have realized solar energy production increases of up to 4%”
Southern California Edison, "Understanding Your Solar Billing Plan" (average Energy Export Credit values for 2026; nine-year lock; bonus credit; checked November 2, 2026). “2026 $0.06 kWh... 2026 $0.03 kWh”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Super-Off-Peak 24¢... Off-Peak 30¢”
California Public Utilities Commission, "Net Energy Metering and Net Billing" (net billing tariff since April 15, 2023; avoided cost export credits; self-use first; nine-year legacy period; TOU-D-PRIME requirement for SCE). Page shows no date; copyright 2026. “customers applying for interconnection have taken service on the new net billing tariff”
California Public Utilities Commission, "Net Energy Metering and Net Billing" (net billing tariff since April 15, 2023; avoided cost export credits; self-use first; nine-year legacy period; TOU-D-PRIME requirement for SCE). Page shows no date; copyright 2026. “onsite generation is first used to serve onsite load under the NBT, offsetting energy costs”
Southern California Edison, "Understanding Your Solar Billing Plan" (average Energy Export Credit values for 2026; nine-year lock; bonus credit; checked November 2, 2026). “rates are locked in for nine years based on the year you began using solar”
Southern California Edison, "Understanding Your Solar Billing Plan" (average Energy Export Credit values for 2026; nine-year lock; bonus credit; checked November 2, 2026). “Solar Billing Plan customers are on the TOU-D-PRIME rate plan”
Southern California Edison, "Understanding Your Solar Billing Plan" (average Energy Export Credit values for 2026; nine-year lock; bonus credit; checked November 2, 2026). “Eligible Solar Billing Plan residential customers who enroll before 2028 also receive an additional credit of about $0.04 per kWh. The credit is about $0.09 per kWh for income-qualified customers”
Southern California Edison, "Rate Advisory: our rates are changing October 1, 2026" (average residential rate before and after the change). “Current Average Residential Rate: 34.4 cents per kWh... New Average Residential Rate: 34.5 cents per kWh”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Weekdays Off-Peak 26¢”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “On-Peak 61¢”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Mid-Peak 39¢”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Weekend Off-Peak 30¢”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Super-Off-Peak 24¢”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Mid-Peak 45¢”
Southern California Edison, "Time-Of-Use Residential Rate Plans" (TOU-D-PRIME prices by season and hour; checked November 2, 2026). “Base Services Charge: $0.79 Per day Baseline Credit: None”
Southern California Edison, "Understanding Your Solar Billing Plan" (average Energy Export Credit values for 2026; nine-year lock; bonus credit; checked November 2, 2026). “2026 $0.06 kWh $0.21 kWh $0.12 kWh”
Southern California Edison, "Understanding Your Solar Billing Plan" (average Energy Export Credit values for 2026; nine-year lock; bonus credit; checked November 2, 2026). “2026 $0.03 kWh $0.10 kWh $0.10 kWh”
Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “186 residential... and commercial PV sites were quantified during dry periods over the course of 2010”
Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “losses averaged 0.051% per day overall and 26% of the sites had losses greater than 0.1% per”
Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “Over an average 145 day summer drought this results in a 7.4% loss in”
Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “had larger soiling losses while differences by location were”
Jordan and Kurtz (NREL, 2012), "Photovoltaic Degradation Rates: An Analytical Review" (median 0.5 percent per year). “Nearly 2000 degradation rates, measured on individual modules or entire systems, have been assembled from the literature, showing a median value of 0.5%/year”
Mejia and Kleissl (2013), "Soiling losses for solar photovoltaic systems in California," Solar Energy (UC San Diego; 186 sites, 2010). “more than an order of magnitude larger than losses”
U.S. Department of Energy, "Solar Performance and Efficiency" (temperature effect on solar cells). “Solar cells generally work best at low temperatures. Higher temperatures cause the semiconductor properties to shift, resulting in a slight increase in current, but a much larger decrease in voltage”
NREL PVWatts Calculator (v8) help text for default soiling and shading losses, and our PVWatts v8 API runs for Ontario, CA on October 13, 2026. “The default value of 1% represents an array with little or no shading”
NREL PVWatts Calculator (v8) help text for default soiling and shading losses, and our PVWatts v8 API runs for Ontario, CA on October 13, 2026. “The default value is 2%”

Written by Foothill Home Services. Local prices on this page are our own draft rates from the price list the quote tool uses. Where we quote an outside page, the quote is linked in the sources above, and we last checked this page on October 13, 2026. Other outside figures are described as the source reports them.

Solar panel cleaning under California NEM 3.0 and SCE: is it worth it near Ontario?