Our two gas clunkers, a 1992 Acura Integra & a 1994 Toyota Camry. The peach house in the background has likely used many of the 6,000 extra kWh we've pumped into the local grid with our solar system.

We hit 6,000 banked kWh recently. That’s compared to the total 9,944 kWh our 5.59 kW solar system has produced in its 13 ½ months on our Aurora, Colo. rooftop.

That means we’ve consumed just 40% of the total kWh we’ve made so far, with the other 60%, electrically speaking, going to our neighbors.

The question is: Should we continue to donate the extra solar kWh we're producing to the neighborhood, or trade in our two gas clunkers for an EV and a PHEV and use them ourselves?

Economically speaking, those extra 6,000 kWh are ours, to be used for our future electric car – actually, we’re probably going to need two plug-ins to start to make decent headway into those 6,000 kWh -- thanks to our utility’s lifetime kWh roll-over option, an option that unfortunately apparently very few utilities in the U.S. offer (Xcel Energy = our utility).

It’s interesting to cut our banked 6,000 kWh a few different ways, so here goes.

First, let’s push them through the solar-charged driving dollar savings equation:

6,000 kWh x 3.5 EV miles/kWh = 21,000 Sun Miles®
21,000 miles ÷ 25 mpg = 840 gallons of “solar” gas
840 x $3.80 per gallon = $3,192 worth of “gas”

Second, let’s do the carbon dioxide equation:

9,944 kWh = 16,905 pounds of CO2 saved (according to our SMA 6000 Sunny Boy Inverter)
6,000 banked kWh = 10,000 pounds of CO2 saved

Here, it’s worth noting, I think, that, in my humble view, adding an electric car to the household equation while taking a gasoline car out of that same household equation complicates the CO2 life-cycle analysis. One might even say that it makes the whole equation more interesting, though the whole thing, frankly, is above my head to begin with (I’ll fess up fully to being mathematically challenged, especially when it comes to “word” problems with multiple variables).

Should the solar offset used to power a clothes dryer, refrigerator, air conditioner, count in the same way as solar offset used to replace a gasoline automobile?

And, if the answer is no – I tend to lean this way – what numbers would one use to calculate solar offset for an EV that replaces a gasoline car as opposed to solar offset that replaces coal-fired electricity for an AC unit?

I need to track down an expert life-cycle analyst to tackle questions like this and to crunch the numbers, any takers ;-)

Is it “better” for us not to buy two electric cars in the future and continue to drive our two gas stinkers while continuing to offset the home electric use of our neighbors? Or is it better, environmentally speaking, for us to give up our two gasoline cars for two plug-in vehicles and to use those “extra” solar kWh to fuel our own new EVs?

Third, let’s do the ‘socialist’ equation:

What do I mean by this?

Well, while powering our home 100 percent with solar, so far, we’ve donated 6,000 kWh of clean solar electricity to our neighbors. That’s enough to cover an entire year’s worth of electricity in a reasonably energy conservation minded household – though, according to Xcel, the average household consumes about 7,500 kWh per year on Colorado’s Front Range.

What’s the right thing to do here ethically and environmentally speaking?

Is it “better” for us not to buy two electric cars in the future and continue to drive our two gas stinkers while continuing to offset the home electric use of our neighbors?

Or is it better, environmentally speaking – and, yes, “socially” speaking, for what we’re talking about here is us “donating” our extra kWh for the good of social humanity, hence the “socialism” reference above -- for us to give up our two gasoline cars for two plug-in vehicles and to use those “extra” solar kWh to fuel our own new EVs?

Now that’s an excellent question for a professional environmental life-cycle analyst (I believe they exist, right?).

Not just about carbon
It’s also a question I have never seen posed, much less addressed, anywhere – although I have in fact delved into it a bit here on the pages of SolarChargedDriving.Com in the past.

Before anyone dives into the questions above – and I sure wish some of you would, let’s clarify: I’m not just talking about “carbon” here, but other pollutants – sulfur dioxide, carbon monoxide, particulate matter, nitrogen oxide – all of which profoundly affect our local health and, in my view, matter every bit as much as carbon dioxide.

These have to be taken into account when helping us make the decision about what’s better for the environment: Us continuing to donate our extra solar kWh to our neighbors while we continue to drive our two gas stinkers, or us taking our extra solar kWh for ourselves and using them to power two plug-in replacements for those gas stinkers?

Solar-offset charged driving?
The fact that we’re talking about solar offset electricity here, meaning solar electricity that’s been generated in the past and which won’t technically be flowing directly into the batteries of any EVs that we buy further complicates the whole equation.

If we were to begin to cut into our 6,000 kWh of banked electricity, we would inevitably pull that off the Xcel Energy coal/natural gas-powered grid here on Colorado’s Front Range – although one of neighbors added a 5.2 kW system to their roof in June.

Hmmm…environmentally speaking, my gut is starting to tell me that “donating” our 6,000 kWh, plus each and every “extra” solar kWh we produce for the next 20 years to our neighbors is best for the environment – but, of course, then we’d be driving our gas stinkers for hundreds of thousands of miles more.

What’s your take – should we donate all our solar electricity and keep the gas stinkers, or use it to fuel two gas stinker EV replacement cars?

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