Apple is the biggest user of US corporate solar with 400MW of capacity in place, according to latest data from the Solar Energy Industries Association's Solar Means Business report.

The iPhone-maker was followed by retailers Amazon, Target and Walmart, as US commercial solar capacity ballooned to more than 7GW at 35,000 projects, said the SEIA’s Solar Means Business 2018 report. That’s an increase from 2.5GW and 7,000 projects in 2017.

SEIA CEO Abigail Ross Hopper said: “Top companies are increasingly investing in clean, reliable solar energy because it makes economic sense.

“When global brands go solar, the rest of the world takes note, and this report puts the power of corporate solar investment on full display.”

SEIA said falling prices and more flexible financing and procurement structures are behind the massive growth seen in corporate solar since 2016. Decreasing costs of solar plus storage creates resiliency options and new revenue streams, and flexibility is increasing in pursuing large off-site projects.

Commercial solar faces challenges, however. Tariffs on modules will raise domestic prices and limit market potential through 2021, while state-level incentives are declining in many markets. The 30% federal investment tax credit will begin stepping down in 2020 before settling at a permanent 10% at start of 2023.

The headline data includes both on-site and remote installations. When only on-site solar was considered, Target was the biggest user.

The report’s data shows the price to install an on-site commercial system has dropped by nearly 63% over the past decade. Similar price declines are seen across all system sizes. Price declines have been driven by reductions in the cost of panels and other hardware, but also by improvements in labor efficiency and company overhead as markets become more competitive.

Average commercial system sizes for on-site projects climbed above 200 kW for the first time in 2018. Growth in system size is primarily due to falling prices, allowing companies to install more capacity for the same amount of money

Electricity generation from the solar installations tracked in this report offsets more than 7.6 million metric tons of CO2 emissions annually,

Since 2014, at least 31 off-site corporate solar projects have been completed, with a total capacity of 1.5 GW, representing a third of total commercial capacity over that time period. Over the last 18 months, nearly 4 GW of new corporate offsite projects have been procured, with 2 GW/yr expected over the next several year, according to the report.

Off-site projects have been enabled by physical PPAs (in which the corporate buys and takes legal title for the electricity from a system) and virtual PPAs (in which a corporate doesn’t directly take title to the electricity from the system, but the revenue stream from the sale of that electricity on the open market).