Colorado · Thornton
Solar in Thornton: read your bill before you read any quote
Written by the Solar Learning Lab research deskUpdated August 29, 202611 min read
Two different electric utilities serve addresses inside Thornton city limits. Some homes are Xcel Energy customers. Others belong to United Power, a cooperative. The city itself tells residents to check the name on their utility bill and publishes a service area map, because even the streetlights split between the two companies. Everything about your solar deal, from export credits to program eligibility, depends on which side of that invisible line your roof sits.
This page covers the Xcel side in depth, because that is where we have verified program documents. If your bill says United Power, treat every Xcel-specific paragraph below as inapplicable and get the cooperative's current solar terms in writing before signing anything. An installer who quotes Xcel banking rules to a United Power household has already failed the first competence test.
Know your utility, then size the system
Once the bill question is settled, use our estimator built on Xcel's 2024 average rate and Thornton production data.
Go to the estimatorThe split city problem, and how to resolve it in two minutes
Thornton grew from farmland into Adams County's first fully planned community starting in 1953, and it kept growing right across utility boundaries: 141,867 people at the 2020 census, an estimated 146,689 by 2024, sixth largest city in Colorado, now stretching into Weld County. The practical consequence is documented on the city's electric and gas services page: your provider is Xcel Energy at 800-895-4999 or United Power at 800-468-8809, identified by your bill, with a Utility Service Areas Map for anyone unsure.
For scale on the Xcel side, EIA's 2024 utility table shows Public Service Company of Colorado averaging 15.05 cents per kWh across 1,365,053 residential customers. Colorado grid power is cheap by coastal standards, less than half of what SCE charges in our California coverage, and that single fact reshapes the whole sales conversation. Thornton solar does not pencil on bill shock. It pencils on stable production, tax treatment and the long arc of rates.
Household economics support it. The 2023 ACS shows 73.1 percent of Thornton's 49,579 households own their homes, with median income at $100,985. Plenty of owned roofs, plenty of capacity to buy rather than lease.
Xcel's Solar Bank election is permanent. Choose like it.
When an Xcel system produces more than the house uses in a month, the surplus lands in a Solar Bank, and what happens next depends on an election the customer makes once. Per Xcel's Solar Rewards FAQ, the Continuous Rollover option converts excess into a dollar credit at the prevailing total energy rate, base rate plus per kWh riders, for the period when it was generated. That credit offsets everything on the bill except the Service and Facilities charge and rolls forward month to month, year to year.
Sounds great until you read the conditions. The election is permanent. The bank never pays out in cash. It does not transfer to a new address, and it dies when the home sells. The new customer FAQ describes the alternative: customers who waive the choice default to a year end payout priced at the average hourly incremental cost of electricity over the trailing twelve months. Historical values tell you what that is worth: 2.616 cents in 2014, 1.765 cents in 2015, 1.355 cents in 2016. Pennies. Customers on the payout path get exactly one switch to Continuous Rollover, arranged through solarprogram@xcelenergy.com.
The operator's read: both options are consolation prizes. The winning move is generating kWh your household consumes directly, so the bank barely matters. A big bank balance is not a trophy. It is evidence the system was oversized for the load.
Solar*Rewards pays for your RECs, and caps your size
Separate from banking, Xcel buys the renewable energy credits a Thornton system produces. The program FAQ's worked example uses half a cent per kWh of measured production, paid monthly by check, and only to the system owner, which is one more reason ownership beats third party deals here. Small customer-owned contracts run 20 years with payments across the first 10.
The same program document sets the sizing guardrails an installer must design within. Annual output may not exceed 120 percent of your previous twelve months of usage, with a minimum four months of history or the New Homes Usage Table for new construction. Once an application is in, system size can move only 10 percent in either direction, and 500 kW is the ceiling for a contiguous site. The 120 percent rule is the binding one for homeowners: it means the utility, not your ambition, sets the maximum array, and a contractor promising to oversize for a future hot tub needs usage data to justify it.
| Energy source | Type | Average price | What that means |
|---|---|---|---|
| Xcel Energy (PSCo) | 2024 residential average | 15.05¢ per kWh | EIA Table 6 figure across 1.37 million Colorado customers. The benchmark a self-consumed kWh beats. |
| Solar Bank year end payout | AHIC based surplus check | 1.355¢ to 2.616¢ per kWh, historical | Documented 2014 to 2016 values. Surplus paid at avoided cost, a fraction of retail. |
| Solar*Rewards REC purchase | production payment | 0.5¢ per kWh, worked example | Paid monthly by check to system owners under multi-year contracts. |
| Onsite solar | self-consumed kWh | avoided retail plus REC payment | Consumption behind the meter earns full retail avoidance and still collects the REC check on production. |
EIA Table 6 and the two Xcel Solar Rewards FAQ documents. Program terms come from the FAQs, not from marketing.
Colorado's two exemptions outlived the federal credit
With the federal 25D homeowner credit dead for systems completed after December 31, 2025, per CRS, Colorado's state-level tax treatment carries more of the load. Exemption one: CRS 39-26-724 removes state sales and use tax from renewable energy components, expressly listing solar modules, trackers, racks, inverters, wiring, control systems and switchgear. The fine print matters: labor, energy storage devices and remote monitoring systems are excluded, confirmed by Department of Revenue guidance. A battery attachment is taxed; the panels feeding it are not.
Exemption two: residential renewable energy equipment owned by the homeowner and producing energy for that property is exempt from Colorado property taxation, with the Division of Property Taxation describing the qualifying criteria, including a 100 kW AC limit that no rooftop system approaches. Neither exemption makes headlines. Together they mean a Thornton purchase avoids taxes at the register and on the assessment roll, permanently, without an application queue or a budget that runs dry.
Permit cost: bring the project valuation, get the fee
Thornton prices building permits off project valuation, defined in the 2025 fee schedule as estimated replacement cost including labor, materials, overhead and profit. The published brackets: $30 flat through $500 of valuation, then $30 plus $3.15 per additional $100 up to $2,000, then $75.75 plus $14.40 per additional $1,000 through $25,000, with higher brackets beyond. There is no solar carve-out line, so a typical residential array simply runs through that table. Questions go to the Building Inspection Division, buildings@thorntonco.gov or 303-538-7250.
One thing Thornton has not done, as far as any page we verified shows: adopt SolarAPP+ or another instant permitting platform. The Colorado Energy Office runs an APPS grant program, a $1 million first come, first served fund covering software, staff time, training and up to three years of subscriptions for jurisdictions that adopt automated solar permitting, and Thornton is not named as a participant. So plan for a conventional review timeline, and if permit speed matters to you, that grant program is a reasonable thing to mention to your council member.
At 5,210 feet, the sun is strong and remarkably consistent
Our downtown Thornton PVGIS run models 1,620.8 kWh per installed kW annually. June leads at 158.0 kWh per kW, December trails at 98.9, and the curve between them is unusually flat through spring and summer. Thin, dry Front Range air is doing the work.
June models 158.0 kWh per kW, with March through August all above 148. That long high plateau is a Front Range signature.
PVGIS v5.2 model run by Solar Learning Lab on August 29, 2026, NSRDB radiation database. Fixed south facing mount, 30 degree tilt, 14 percent losses, downtown Thornton coordinates. Your roof will differ. Tool documentation at PVGIS. A companion PVGIS v5.3 run for this location showed a year to year standard deviation of just 23.1 kWh per kWp, the most stable figure among the five cities we modeled this week. In plain terms: Thornton output forecasts deserve more confidence than most, and an installer's production guarantee here is a low-risk promise for them to make. Price it accordingly.
A deep Front Range bench serves Thornton
Five companies with review counts between 305 and 644 came up in our Thornton pull, based in Denver, Broomfield and Westminster. Every one of them has hundreds of rated jobs behind them, which is a luxury smaller markets do not get. Use that depth: three bids minimum, and make each one state your utility territory on page one.
Solar RNR
Denver, CO
5.0(305 Google reviews)
Ratings snapshot: Google Maps, August 2026, via the DataForSEO SERP feed. Zero companies paid us and none are endorsed by us.
Thornton-specific vetting: ask each bidder to walk you through the Solar Bank election tradeoff unprompted, show the 120 percent sizing math against your actual usage history, and separate taxed from untaxed line items on the quote. Anyone fluent in those three topics has done real work in this territory.
Run an estimate on the Xcel numbers
The tool below uses Xcel's 2024 average residential rate and our Thornton production run. It does not model Solar Bank elections, REC checks or United Power territory, so treat it as a sizing and payment comparison, then layer the program details from this page on top.
The 1,621 ceiling is our downtown Thornton PVGIS run at 5,210 feet of elevation. The 1,378 floor assumes a 15 percent haircut. Thornton's year to year output is unusually stable for planning purposes.
Cash quotes in Thornton cluster near $2.66 per watt, against a $3.50 national 2024 median (LBNL). Use your quote.
Assumptions you can change
Use the rate on your actual lease or PPA quote. There is no published statewide average we trust enough to hardcode.
Cash purchase
$13,300 after state credit
- Year 1 benefit
- $102/mo
- Payback
- 10 years
- 20 year net position
- $16,297
The retail input is Xcel's 2024 Colorado residential average. If your Thornton address is in United Power territory instead, this rate does not describe your bill, and none of the Xcel banking rules on this page apply to you.
Solar loan
$173/mo 15 yr payment
- Year 1 net
- -$72/mo
- Upfront
- $0
- 20 year net position
- -$1,628
Colorado exempts solar hardware from state sales tax but not labor or batteries, so a financed quote should show taxed and untaxed line items separately before interest enters the picture.
Lease / PPA
$0 down you buy the power
- Year 1 net
- -$60/mo
- Upfront
- $0
- 20 year net position
- -$15,333
The homeowner 25D credit ended December 31, 2025, and our federal source says nothing about third party arrangements. Judge a Thornton lease on its rate and on who keeps the Solar*Rewards REC payments.
Estimates, not quotes. Inputs use Xcel's 2024 average residential rate from EIA, our Thornton PVGIS run and EnergySage Colorado cost data. Solar Bank elections, REC payments and United Power territory differences are not modeled. We are a solar installer and we also partner with other solar companies. See our disclosures.
We are a solar installer and we also partner with other solar companies.
Thornton answers, sourced
How do I find out if my house is Xcel or United Power?
What happens to solar power I do not use in a month?
How big can my system legally be?
Does Colorado tax solar equipment?
What will the Thornton permit cost?
Evidence list
Every claim above traces to these documents, reviewed August 29, 2026.
- City of Thornton electric and gas utility services and 2025 building permit fee schedule
- Xcel Colorado Solar Rewards FAQ and Solar Rewards new customer FAQ
- CRS 39-26-724, Colorado DOR renewable energy components guidance, and Division of Property Taxation renewable energy page
- Colorado Energy Office APPS grant, CRS IN12611, EIA Table 6, and Thornton history
Get a Thornton estimate matched to your territory
Start with your bill so the quote is built on the right utility from the first line. Then compare it against the numbers on this page.
What does your monthly electric bill look like?
Thornton average is $167 per month (EIA, 2024).