Solar panels are not the point. Not here, anyway.

Ask most people to picture a green building and they will describe a roof covered in solar panels. We did too. Then we asked a plain question: what does a panel on a Seattle roof replace?

It depends where you stand

A solar panel does climate good by pushing dirtier power off the grid. So, its value depends on what the grid burns.

A coal plant emits on the order of 800 to 1,000 grams of carbon dioxide for every kilowatt-hour over its life. A gas plant emits 400 to 500. Hydropower in a cool climate emits a few tens of grams or less.¹ Making a solar panel has a carbon cost of its own, which it has to pay back.

Seattle City Light’s power comes mostly from hydroelectric dams.² Put a panel on a roof in a coal region and it pays back its carbon quickly, then keeps giving. Put the same panel on a roof here and there is very little dirty power for it to push aside. Counted over its whole life, it is probably not a carbon reduction at all. It may be a small carbon cost.

The same goes for water. Seattle’s drinking water flows downhill from protected mountain watersheds, with almost no pumping. A rain tank that would save real energy in a city that pumps water over mountains saves almost none here.

Carbon value is a property of what a system displaces.

Where the carbon is

If not the roof, then where? In Seattle, in rough order:

1. Keeping the existing house. A house that is not rebuilt is the largest single saving on most of our sites. We wrote about that here.
2. Replacing gas with heat pumps. A gas furnace burns fossil fuel in the basement. A heat pump on clean hydropower runs close to carbon-free.
3. The envelope. Insulation, air sealing and good windows shrink every other system.
4. Lower-carbon materials, chosen with their makers’ own published data.

None of these shows from the street. That is the trouble. Visible equipment gets the credit, and the quiet measures that do the work get value-engineered out to pay for it.

What solar is for

We are not against solar panels. On a Seattle building they can still earn their place three ways:

• Resilience. With a battery, they keep the lights and the refrigerator on when the grid is down.
• Certification. Programs like the Living Building Challenge require on-site energy.
• Learning. Running the equipment teaches us what it costs to maintain.

Those are honest reasons. “It cuts carbon” is not one of them, here.

The wider lesson

A design that is right in one place can be wrong in another. A checklist written for the average American city will tell a Seattle builder to spend money where it does the least good.

It also reminds us that carbon is not the only limit. Scientists track nine planetary boundaries, and the latest check found seven of them crossed.³ A battery that looks good on a carbon ledger looks worse once you count the mining. A rain garden that saves no carbon may save salmon.

We may be wrong about the grid. If the power our panels displace turns out to be gas-fired power elsewhere in the West, the math improves, and we will say so here.

Sources and notes

1. Intergovernmental Panel on Climate Change, Fifth Assessment Report, Working Group III, Annex III: Technology-specific cost and performance parameters, 2014. ↩
2. Seattle City Light, Power supply and delivery. ↩
3. Potsdam Institute for Climate Impact Research and Stockholm Resilience Centre, Planetary Health Check 2025. ↩