As long-time Ashland residents, we feel obligated to own a “green” car. Actually we own two, speaking literally, since both are nearly the same shade of gray-green.

One is a Honda CR-V, which has served us faithfully since we bought it new in 2006. It has a combined city/highway EPA mileage rating of 25 mpg, which translates into greenhouse gas (GHG) emissions of 485 grams per mile. Excellent for its era, but now it’s contributing a bit too much to climate change.

So last May we leased a Chevy Volt plug-in hybrid. It travels up to 53 miles on battery before the on-board gas engine kicks in for another 300-plus miles at about 32 mpg combined. That means, while running on gas, we’re down to roughly 320 grams per mile of GHG emissions.

But what about while running on battery? Zero emissions? Well, yes and no. True, there are no tailpipe emissions because the gas engine is not running. But what about emissions created in generating electricity for charging the battery, the so-called “upstream” emissions? We have to include these. And when we do, how many grams per mile am I emitting while running on battery?

The answer is far, far fewer than when running on gas, by a factor of at least four to one and probably better. But pinning it down beyond that is tricky.

With gasoline it’s a simple formula: combusting one gallon produces 8.8 kilograms of GHG. But we also must add about 20 pecent for the upstream emissions created in getting gas into your tank — from exploration, extraction, refining and transportation to the gas station.

With electricity it’s more complicated. If you look at the power we pay for in Ashland, it’s easily computed — and wonderfully green! Our city utility contracts with the Bonneville Power Administration for its electricity, and the power generated by BPA — overwhelmingly hydroelectric — is about 95 percent free of fossil-fuel sources. From that standpoint, when charging in Ashland, any electric vehicle is close to a zero-emissions vehicle.

Alas, it’s not that simple. The power that comes out of my wall outlet is not necessarily the same as what I pay for. BPA’s own power generation is integrated into the same regional power grid as Portland General Electric, Pacific Power and several other providers that burn significant amounts of fossil fuels at their plants. How much of that “dirty” power leaks into my plug?

A precise answer is nearly impossible to compute. The mix of generating sources on the regional grid changes constantly on a seasonal, daily and even hourly basis. When river flows are high and demand is low, cheaper hydro power dominates. When flows are lower and demand spikes, more peak generators — mostly powered by natural gas — are brought online. Wind and solar are increasingly adding to the generation capacity, each with its own variations and cycles.

Nevertheless, if you look at the overall mix of power generation in Oregon and adjacent states, it’s pretty darn (“dam”?) green all around. The average is better than 70 percent GHG-free, and nearly all of the remaining 30 percent is natural gas, which is less polluting than coal. (Oregon has only one coal-fired power plant, slated for closure in 2020.) So even if you figure power in Ashland at the average of the entire West Coast, the Volt comes out at less than 100 grams per mile of GHG on battery, or about five times as green as the CR-V.

No contest. Anywhere you charge up your EV in the Rogue Valley will result in dramatically lower GHG emissions when compared to gasoline-driven. And it will save money, as the electricity required per mile is cheaper than the gasoline needed for a comparably sized car. If you want to compute your savings, you can look up your car and compare it with EVs on a new city of Ashland electric vehicle web page: http://ashland.chooseev.com/.

If those savings look good, you can check out local options with a free Rogue Valley Green Car Guide, available for download on the Southern Oregon Climate Action Now (SOCAN) website: www.socan.eco >Learn >Project Resources>Transportation.

— Bruce Borgerson lives in Ashland.