How Long Does It Take to Go Solar? NREL Data Puts the Typical Wait at About 4.5 Months

For a typical home solar system, expect about 4.5 months, and often longer, from signing a contract to the day your utility lets you turn it on. The National Renewable Energy Laboratory (NREL) found a median of 97 business days in 2023 for solar-only systems, about 4.5 months. With a battery, the median was 159 business days, a little over 7 months. Crews usually install the panels in a few days; the rest of the wait is design, permits, inspection and utility approval.

This guide breaks the wait into steps, shows where delays come from, and lists what to ask before you sign. It uses NREL’s November 2025 retrospective review of about 875,000 residential and small commercial projects installed from 2017 through 2023, the most recent years covered by that NREL series. All NREL figures are in business days: five make a week and about 21 make a month on average.

The Short Answer, by Step

These are NREL’s median figures for 2023 solar-only projects, from the date the contract is signed.

Source: NREL, Table A-1. NREL notes that the step medians do not add up to the total median, because the slow steps are not always on the same projects. Use each step’s figure as a rough guide to where time goes, not as a schedule.

How the Wait Has Changed

The median wait fell from 96 business days in 2017 to 75 in 2019, then rose to 97 by 2022 and 2023. NREL says recent projects took about 20 business days longer than in 2019 and 2020, a 20% to 30% increase.

Most of the growth came before installation. The median time from contract to installation rose from 41 business days in 2020 to 58 in 2023. Design alone grew from about 2.5 weeks to about 4 weeks. NREL points to permit volume surges, staffing shortages and California’s rush to file before its net metering change in April 2023 as possible causes, though it says the causes remain unclear.

The spread is wide. In 2023, a quarter of solar-only projects took 3 months or less, 10% took more than 9 months, and 5% took a year or more.

Adding a Battery

Solar-plus-storage projects took a median of 159 business days in 2023 (mean 181), about 13 weeks longer than solar alone. In 2019 the gap was about 4 weeks. The median time before installation doubled from 55 business days in 2020 to 110 in 2023.

In NREL’s 2023 storage data, design took a median of 41 business days (20 for solar alone), permit and utility review 12 (10 for solar alone), installation scheduling 30 (15), and the steps after installation 38. Outside California, NREL found utility review took about 1 to 2 weeks for solar alone and 2 to 4 weeks with storage.

If backup power is the reason you are buying, plan for the longer timeline. Our battery sizing guide covers how to avoid paying for more storage than you need.

Where You Live Matters

NREL’s state figures for 2023 solar-only projects show how much location matters:

NREL links Colorado’s longer times to interconnection delays at Xcel Energy. Permit review alone ranged from same-day approval in some places to 15 business days or more for a quarter of projects, and 30 or more for the slowest 10%.

System size made little difference. Medians for systems up to 10 kW and those from 10 to 20 kW have been within about 1% of each other since 2021.

Keep in mind that NREL’s data comes from participating installers, is weighted toward larger companies, and is about 45% California projects. It covers retrofits on existing homes, not new construction.

Instant Online Permitting

Some cities and counties approve standard home solar permits online, almost instantly, through SolarAPP+, a free tool NREL developed. NREL reports that permit review in early adopters fell from as many as 20 business days to under one. An earlier study cited in NREL’s review found online-instant permitting saved an average of 14.5 days, or 31%, across permitting, installation and inspection.

The Department of Energy said in December 2023 that 160 communities in 10 states were using SolarAPP+. Ask your installer or your local building department whether your jurisdiction is one of them. Battery systems became eligible in early 2023.

Why the Wait Can Cost You

A long timeline is more than an inconvenience. Check these points before you sign:

• Loan payments may start before the system runs. Ask when your first payment is due and whether it is tied to installation or to PTO.
• Rate and net metering deadlines. When a utility or state changes how it credits solar, current customers are often protected based on their application or interconnection date. If a change is coming, ask your installer which date counts and how confident they are in meeting it. Our net metering guide covers the rules by state.
• Contract milestones. A good contract states when the installer will file permits, when installation is expected, and what happens if deadlines slip. Our guide on how to compare solar quotes lists the other numbers to check.
• Don’t switch it on early. Solar United Neighbors, a nonprofit that helps homeowners go solar, advises that an installed system “is not yet on” until the utility grants PTO. The utility may also need to install or reprogram your meter so exports are credited.

What to Ask Your Installer

1. How long did your last 10 projects in my town take from contract to PTO?
2. What do you need from me, and when, to keep my project moving?
3. Does my city or county offer instant online permitting?
4. Does my utility require approval before installation, and how long is it taking now?
5. When does my first payment start: at signing, at installation or at PTO?
6. If a rate or net metering change is coming, what date does it depend on, and what happens if we miss it?

Limitations

NREL’s most recent published data covers 2017 through 2023. Timelines in 2026 may differ, especially where permit volumes or utility staffing have changed. NREL’s figures are medians across many projects; your installer’s recent local track record is a better predictor for your home.

Sources and verification