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To meet climate targets, the Northwest needs to build unprecedented amounts of wind and solar power and the electric transmission lines to carry it.  

Easier said than done.  

Utility-scale renewable projects—like acres-large solar installations or miles-long corridors of wind turbines—and the electric wires that connect them to cities and towns increasingly inspire opposition. They can require vast tracts of land, and, if not planned responsibly, can threaten sensitive habitats, prime farmland, and tribal rights.  

In light of these challenges, some advocates argue that the region could avoid building transmission lines and large renewable projects if it instead dramatically scaled up what is known as “distributed solar.” Unlike their utility-scale counterparts, distributed solar projects generate electricity close to where it is consumed—say, on home and business rooftops, over parking lots, on small, unused fields—and bypass the transmission grid altogether. Distributed solar typically ranges in size from small, 0.001 megawatt (1 kilowatt) projects to medium, roughly 5-megawatt (MW) projects. For comparison, utility-scale solar farms in the United States tend to have installed capacities of 100 to 200 MW. The biggest farms in the country top 500 MW. 

Graph showing how distributed solar is only 1% of utility solar

Unlike other parts of the United States, though, distributed solar has limited potential to offset the need for new transmission capacity in Cascadia. That’s in large part because most places in the region that are on the receiving end of transmission constraints need most of their power in the winter, when the sun is weakest. The biggest exception is southern Idaho, which, with its strong sun and high demand for summer power to irrigate farms, could be a prime candidate for scaling up distributed solar.    

Even so, distributed solar, especially when combined with storage, can help decarbonize Cascadia. Local generation helps the region hedge against the risk that we simply won’t build new transmission lines and utility-scale renewable projects fast enough. But the Northwest is lagging in installing the most promising type of distributed solar infrastructure: midsize projects in the range of 1–5 MW. Idaho and Washington are especially behind. Policymakers in these states would be smart to lift project size limits to net metering and look closely at community solar, which has catalyzed midsize solar growth in other states, including Oregon.1Net metering refers to systems in which owners of distributed solar resources, like rooftop solar arrays, get reimbursed from their electric utilities for any electricity they produce that they don’t use (less any electricity they buy from the utility). The rate at which owners are reimbursed depends on the state.

Distributed solar holds the most potential for offsetting transmission buildout in the few “summer peaking” parts of Cascadia  

In the Pacific Northwest, as elsewhere, more transmission capacity is needed to 1) meet rising electricity demand associated with electrifying everything from cars to stoves and 2) replace the supply of power that today comes from burning gas or coal. We’re especially short of transmission lines to bring clean power to cities and towns in western Oregon and Washington and southern Idaho 

The argument that distributed solar can prevent transmission buildout is that by producing more power close to the people who use it, you won’t need to generate as much far away and thus won’t need to build transmission lines. Plus, you’ll lose less electricity in transit. Indeed, in 2018, California’s independent grid operator recommended canceling 18 transmission expansion projects to save $2.6 billion. It cited reductions in projected electricity demand thanks to increasing levels of rooftop solar and energy efficiency. (And note that distributed solar isn’t the only way some places could prevent or defer building transmission lines. Others include upgrading existing lines, increasing energy efficiency, rolling out demand response programs, and installing distributed storage—all with different potential in different locales.2Demand response programs encourage electricity customers to reduce or shift the timing of their electricity consumption to better match available supply. They can reduce peak electricity demand.
These are not the focus of this article but are topics Sightline will analyze at a later date.) 

Graphic showing the path of electricity, from generation, transmission, to distribution.

However, the vast majority of the Northwest’s transmission-constrained areas use most of their power in the winter, when sun in those areas is weakest. This unusual “winter peaking” pattern happens because of the region’s famously temperate summers, which have historically rendered air conditioning unnecessary, and high reliance on electric resistance heaters. Of the 11 load service areas west of the Cascades in Oregon and Washington, none sees its electricity demand peak in the summer, according to the Bonneville Power Administration’s (BPA) 2021 Transmission Report.3Load service areas are cities or groupings of cities or towns that are either geographically or electrically near to one another. Together their demand forms the electric “load” of the area.
(Portland is “dual-peaking,” meaning its highest demand for electricity occurs in both summer and winter.) Distributed solar in winter-peaking areas of Cascadia can do little to offset the grid buildout necessary for meeting peak power demand, since it does not produce enough energy at that time of year.4 Grids are built to handle the highest electricity demand a given area has, even if that peak happens only a few hours a year.

Distributed solar in most of western Oregon and Washington also can’t sufficiently replace retiring fossil fuel resources. To help illustrate why, the chart below shows the energy generation and consumption patterns of some friends’ Seattle home with rooftop solar. The home is indicative of what we can expect in future: it is fully electric and relies on a high-efficiency heat pump to both warm in the winter and cool in the summer. From May to October, the output of the solar panels (shown by the green line) entirely offsets the family’s electricity use (shown by the orange bars). But from November through April, the home requires at least some power from its electric utility. (The home also likely relies on the grid for nighttime power in the summer since it is not equipped with battery storage.  

Chart showing the two peaks of energy use, and how distributed solar can provide support

My friends’ electric utility is Seattle City Light, which is powered overwhelmingly by hydropower. But if they lived in that same house in say Olympia or Bellevue, Washington, which have similar climate patterns to Seattle, they would be served by Puget Sound Energy (PSE). PSE relies on gas and coal for about half of its generating capacity. That means it needs to build or buy new renewable power to meet a large chunk of winter power demand as it drops its carbon-spewing gas and coal power. The story is the same for the other investor-owned electric utilities in the region, which depend heavily on fossil fuels.5Investor-owned utilities (IOU) are for-profit monopoly utilities regulated by a state’s public utilities commission (PUC). In Washington and Oregon, they are subject to clean electricity laws. Investor-owned utilities serve about 80 percent of Idaho’s electric customers, 75 percent of Oregon’s, and 43 percent of Washington’s, according to the US Energy Information Administration. Other types of utilities are Public Utility Districts, rural electric cooperatives, and municipal utilities (like Seattle City Light), which, in the Northwest, primarily rely on hydropower from the Bonneville Power Administration. Electricity mix data for investor-owned utilities: Oregon IOUs; Puget Sound Energy; Avista; Idaho Power; PacifiCorp.
Distributed solar doesn’t produce enough power in the winter in western Washington (or western Oregon) to completely fill that gap. Instead, most of the new power will have to be found in places with year-round strong sun or wind. And we will need big power lines to carry that juice. 

That said, distributed solar could help mitigate some transmission constraints in the few summer-peaking areas in Cascadia. Southern Idaho already uses most of its electricity in the summer because of air conditioning and irrigation pumps. Plus, it’s a solar hotspot: the conditions are superb for solar power generation. Even here, though, in order for distributed solar to offset building more transmission, the area would need to meet further conditions, including ensuring the distribution system has adequate capacity to hook up the projects.  

Notably, too, several other areas are likely to transition from winter to summer peaking as the climate changes and more northwesterners install air conditioning and as high-efficiency heat pumps replace electric resistance systems. BPA expects Portland and Salem in Oregon to become summer-peaking by the end of the decade. And the Seattle-Tacoma-Olympia area may flip from winter to summer peaking in 20 years, according to Sightline’s analysis of BPA’s data. (BPA likely bases these forecasts on historical energy use patterns, not a modeled future of widespread electrification and fossil fuel retirement, so they may underestimate future energy demand. Nonetheless, these trends paint an indicative picture of a changing seasonality of energy use.) Distributed solar could help render unnecessary some new transmission capacity associated with meeting this growing summer demand. But it can barely contribute to the larger challenges of meeting colossal increases in year-round power demand that will come with widespread electrification and backfilling the gap left by retiring fossil fuels.  

Distributed solar is still a good idea 

So, is distributed solar a waste of time and money? Not at all. It’s true that large, utility-scale arrays of solar collectors are the cheapest and most efficient way to harness the sun. It’s also true that transmission lines can reduce over-build of new energy projects by allowing regions with different energy profiles to share resources. (That’s part of Idaho Power’s stated rationale for the controversial Boardman-to-Hemingway transmission line connecting eastern Oregon and western Idaho: it should help southern Idaho meet its early summer peak with excess hydropower from the Pacific Northwest rather than with new generating resources.)  

But utility-scale renewable projects and transmission lines are increasingly difficult to site and build. Take, for example, the opposition in Benton County, Washington, to the proposed 1,150-MW Horse Heaven Hills wind, solar, and storage facility or the controversies with the Boardman-to-Hemingway transmission line, which has been in development for 20 years. Several counties in south central Washington have imposed moratoriums on solar development, though the state can override them.  

“Siting is probably the biggest challenge for utility-scale solar,” Jack Watson, Policy and Regulatory Affairs Director of the Oregon Solar and Storage Industries Association (OSSIA) told Sightline. Both Oregon and Washington are going through multi-stakeholder processes to identify land suitable for solar development that will cause the least harm to farmland and natural habitat and will respect tribal rights.  

The 150-MW Lund Hill Solar Farm in Klickitat County, Washington, the largest in the state as of this writing. The county recently imposed a solar moratorium.  

The 150-MW Lund Hill Solar Farm in Klickitat County, Washington, the largest in the state as of this writing. The county recently imposed a solar moratorium.

In the meantime, distributed solar, which largely avoids siting and land-use challenges, can keep us marching toward clean energy goals.  

“Distributed solar can act as a hedge,” Sashwat Roy, Technology and Policy Manager at the advocacy group Renewable Northwest told Sightline. “Unless and until we figure out the siting and interconnection backlog, distributed solar and storage seem like low-hanging fruit,” he said. Distributed solar can offer other benefits too, especially when combined with storage, he emphasized, like resiliency in the case of a power outage caused by a wildfire. Indeed, some Northwest utilities are planning more distributed solar than ever, some naming grid constraints as a primary motivator.  

The big opportunity is midsize solar 

Prioritizing midsize commercial scale solar projects in the range of 1–5 MW can help alleviate the high costs of distributed systems. These projects, like the one IKEA installed on its rooftop in Renton, Washington (see below), cost roughly twice the amount of utility-scale ones, while small, residential-scale solar systems cost roughly triple. In fact, 1–5 MW projects can actually be more cost-effective than utility-scale systems when installed in certain locations. Residential rooftop solar, by contrast, is unlikely to ever beat utility-scale solar on cost-effectiveness. And, of course, by virtue of their larger size, thousands fewer 1–5 MW systems are required to help clean the grid than if we relied on residential rooftop solar alone.  

IKEA’s 1.13 MW rooftop solar installation in Renton, Washington. Photo Credit A&R Solar

IKEA’s 1.13 MW rooftop solar installation in Renton, Washington. Photo Credit A&R Solar

“If you really can’t build transmission [lines], you can talk about doing more generation locally. The best way to do that is not residential rooftops usually,” Dr. Severin Borenstein, director of the Energy Institute at University of California, Berkeley’s Haas School of Business, told Sightline. A friendly critic of distributed solar and net metering in California, he emphasized that flat, roof-mounted or ground-mounted systems are most cost-effective. That’s because developers of these projects can buy panels in bulk, reducing costs, and also install trackers to follow the sun, upping energy output. This technology is not possible on tilted home roofs.  

But Idaho and Washington are skimping on these midsize systems, trailing Oregon. Idaho’s capacity from moderately sized systems is just 1 percent—and Washington’s just 11 percent—of Oregon’s, as shown by the chart below.6Sightline used size as a proxy for distributed solar. These figures include all systems under 5 MW in each state, according to data from the US Energy Information Administration.
Midsized projects, from 1–5 MW, are in yellow, and small projects, less than 1 MW, are in blue. 

Chart showing solar energy distribution

And none of the Northwest states meets its full potential, according to a 2016 study by the National Renewable Energy Laboratory.7Not all, but most distributed solar today is on rooftops. The technical potential for all distributed solar would be even higher than this if it included ground-mounted systems.
Even a cursory glance at the area near the Washington IKEA reveals dozens more similarly large commercial roofs, none with solar panels, as shown below.  

gif of Google Maps showing solar panels on top of the IKEA in Renton, WA -- and none on the surrounding buildings

Idaho and Washington restrict midsize solar growth in two big ways  

It is impossible to trace solar growth in Oregon to a single policy. Plus, barriers to distributed solar in Oregon persist, including building codes and upgrades required to the distribution system, Jack Watson of OSSIA told Sightline.  

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  • But two key policies in Oregon that encourage moderately sized systems are notably absent in Idaho and Washington. And the Washington legislature missed an opportunity to pass bills in the 2023 legislative session that could have helped the state catch up.  

    1. Idaho and Washington exclude midsize systems from net metering 

    Net metering refers to systems in which owners of distributed solar resources, like rooftop solar arrays, get reimbursed from their electric utilities for any electricity they produce that they don’t use, less any electricity they buy from the utility. The rate at which owners are reimbursed depends on the state. It’s a tool that has enabled distributed solar growth in much of the United States. But in Washington and Idaho, only residential or commercial systems with a capacity up to 0.1 MW (100 kW) can participate. In Oregon, by contrast, the limit is 20 times higher for commercial systems, or 2 MW. Other states sharing Oregon’s higher limits include New York, Illinois, and Florida 

    By not allowing projects greater than 0.1 MW to net meter, Idaho and Washington disincentivize owners of buildings with larger roofs, like supermarkets or warehouses, or farmers with fallow fields, to install solar panels.  

    “Having worked for a solar installer for 13 years, we weren’t developing any projects [in Washington] above 100 kilowatts [0.1 MW],” Markus Virta, the president of Washington Solar Energy Industries Association (WASEIA) told Sightline. He believes the lack of a Washington market for midsize systems helps explain why Puget Sound Energy, the largest electric utility in Washington, is now on its third attempt to source the 80 MW of non-residential distributed solar it needs by 2025 to stay on track with meeting Washington’s Clean Energy Transformation Act. 

    “If you really can’t build transmission [lines], you can talk about doing more generation locally. The best way to do that is not residential rooftops usually.” –Dr. Severin Borenstein, director of the Energy Institute at University of California, Berkeley’s Haas School of Business

    In Idaho, many farmers are interested in installing solar panels to help meet their summer power needs, but the financing doesn’t pencil out with the current 0.1 MW net metering limit, according to Brad Heusinkveld of the Idaho Conservation League.  

    The Washington legislature had a chance to raise the state’s net metering limit to 2 MW in the 2023 legislative session with House Bill 1427, which Representative Sharlett Mena sponsored.8The 2-MW limit would have applied to projects in investor-owned utility service areas. The limit would be 200 kW in consumer-owned utility territories.
    But many utilities in Washington and elsewhere oppose net metering because the arrangement typically requires them to purchase electricity at a higher rate than they would on the wholesale market.  

    Utilities also generally make their case against net metering by arguing that it is unfair to low-income customers, who utilities say are subsidizing the cost of rooftop solar for wealthier homeowners. The evidence for this cost-shifting is mixed at best (see here, here, and here for skeptical takes on utilities’ claims about cost-shifting and here for arguments that it is indeed a concern). There is no data showing cost-shifting has occurred from net metering in Washington. Nonetheless, HB 1427 took these worries seriously and would have convened a multi-stakeholder working group to develop a fair “value of solar” estimate to support low-income customers, much like other states have done, that would replace the current net metering policy.  

    In any case, the electric companies fought the bill, and it never made it to a vote on the House floor.   

    2. Idaho and Washington hold back community solar 

    A second policy that has facilitated growth of midsize systems in Oregon and elsewhere is “community solar.” Community solar programs allow multiple individuals or businesses to subscribe to a solar project that is located near but not on their property. They then earn money on the energy from the sun that the system sends back to the grid. 

    Community solar policies have helped several states drive midsize solar installations. In the United States, community solar projects have a median size of 1 MW. Minnesota passed a community solar law in 2013 and now boasts 834 MW of community solar, 60 percent more capacity than all the solar in Washington today. Oregon established its community solar program in 2016, and projects began launching in 2021. The program will add at least 161 MW of community solar to the state, and each project can be up to 3 MW in size. (See examples of some Oregon Community Solar project sites here.) 

    Idaho, meanwhile, has no community solar program, and Washington has one in name only. Washington’s program, which the legislature passed in 2022, is missing key ingredients that have allowed other states’ programs to take off. Most importantly, utility participation is optional. This means that if any entity other than a utility—say, the Washington nonprofit Olympia Community Solar—wants to set up a community solar project, it can’t offer potential subscribers credits on their electricity bill, limiting the ability to scale projects. 

    Unlike Washington’s program, Oregon’s requires the state’s three investor-owned utilities, Portland General Electric, PacifiCorp, and Idaho Power, to purchase power from community solar projects. Nonprofits and private sector developers, including the Oregon Clean Power Cooperative, Sulus Solar, and Conifer Energy Partners, are building the projects. Utility customers who subscribe to the projects receive credit directly on their electricity bills for the energy flowing from the solar arrays.  

    Without a similar requirement, midsize community solar projects are unlikely to expand much in Idaho or Washington. Among investor-owned utilities in these states, only Puget Sound Energy (PSE) in Washington has an active community solar program. (Avista has one tiny community solar project in Spokane that was fully subscribed in 2015.) PSE plans to up its community solar capacity to about 25 MW by 2025. But that’s still just 15 percent as much expansion as Oregon’s utilities plan over the same time period. Plus, PSE pays customers who subscribe to its program less than half the rate that the Oregon Public Utilities Commission requires Oregon utilities to pay 

    In the 2023 legislative session, Washington state Representative David Hackney introduced House Bill 1509 to develop a community solar program in Washington more akin to Oregon’s and other states. It would have allocated 50 percent of the program to low-income customers, who today are largely shut out from rooftop solar and who suffer disproportionately high energy cost burdens. Like HB 1427, HB 1509 took fire from Washington’s three investor-owned electric utilities, who again would lose money from the arrangement. The bill never made it out of committee. 

    Distributed solar for Cascadia: A worthwhile solution, but it can’t succeed alone 

    As transmission constraints mount in Cascadia and opposition grows to utility-scale renewable projects, many are understandably hoping distributed solar can provide an alternative—a way to meet climate commitments without long transmission lines or big wind and solar farms. But for much of the Northwest affected by transmission constraints, distributed solar by and large won’t get us out of the bind. The combination of our unusually high winter electricity demand, huge new demand for electricity, and retirement of fossil fuel-based generation sources serving winter load precludes that. Possible exceptions to this rule include southern Idaho, which enjoys strong sun and needs a lot of summer power, and some cities in Oregon. 

    Nonetheless, distributed solar can help Pacific Northwest states continue cleaning up the grid, as a complement to utility-scale projects and transmission expansion. Today, Cascadia is nowhere close to tapping its potential for distributed solar, and Idaho and Washington lag woefully in midsize systems. State leaders looking for ways to meet climate goals in light of limited transmission capacity would be smart to look again at lifting barriers to net metering and community solar. If they do, the region’s energy future could be a great deal brighter.