Expanding your solar system to charge an electric vehicle

Increasingly — at least once each week — we are contacted by solar homeowners who recently purchased, or are contemplating buying, an electric vehicle (eV). To wit, they are interested in adding panels to their current solar system to cover fueling (charging!) their new eV.

The good news: Solar-charged electric vehicles are the least expensive form of four-wheel transportation, let alone the virtue of aborting fossil fuels. For RepowerYolo homeowners, the average cost to generate solar electricity on their rooftop is 8 cents per kilowatt hour (kWh). For every kWh of charge, eV owners garner ~4 miles of range. Hence, if you have an electric car that’s powered by sunshine, your cost to drive is ~2 cents per mile.

The challenge: While it’s technically (almost lego-esque) easy to add solar panels to a system, the process is, unfortunately, somewhat pricey. There are two scenarios:

1. Your current inverter has sufficient capacity to accommodate additional panels. If this is the case, then the challenge is locating and purchasing comparable (wattage) solar panels. Depending on the vintage of your current system, this could be simple, or it may be that you need to purchase used/refurbished panels.

2. Your current inverter cannot accommodate additional solar panels. Thereby — this is what I did when I added nine panels on my roof to charge my Leaf — you need to either add a second inverter or proceed with micro-inverters. Again, securing compatible panels is the next step.

In both scenarios, we are required to perform full design-engineering-permitting for your additional solar capacity. Though this is not complicated, it adds to the cost; it’s not simply lego-esque, snap-a-few-panels-in-and-go.

An additional caveat: Homeowners can only claim the 30% Federal tax credit once every five years. So, if you went solar in the past five years, you may want to wait until you re-qualify for the credit. 

Net-net, we’re happy to help. There’s no cost to receive an assessment of your current system, analysis of your historical net-energy use, modeling of your future electricity demand (for your eV), and an analysis + recommendations for your additional solar capacity. Feel free to contact us or swing my our workspace.

Electric cars + solar panels: Does 1+1=3?

A quick note of thanks to The Enterprise for publishing the below article online today and in tomorrow's print edition. You can access the story here, and below is the prose.

A few times each week, we tender conversations with homeowners who own (or are considering purchasing) an electric vehicle and are thereby contemplating installing solar panels.

The psychology is similar: Electric cars (and solar) are good for the environment, and electric cars (and solar) are pragmatic/less expensive than the alternatives. Seems like a no-brainer – power your electric vehicle with cheap, clean energy generated by your solar panels.

But, is it?

Since 2010, nearly half of all plug-in electric vehicles sold in the United States are registered in California; the top-three models — Chevrolet’s Volt, Nissan’s Leaf and Tesla’s Model S — dominate the electric highway.

(And, many see the advent of Chevy’s all-electric Bolt in late 2016 and Tesla’s Model 3 — my deposit is in; please, Elon, late 2017? — as a tipping point for electric vehicles.)

Similarly, nearly half of all solar electric systems in the U.S. sit atop California households. (As we’ve shared, nearly one in four single-family residences in Davis now has a solar electric system, far out-pacing an estimated 5-percent penetration in PG&E territory.)

As transportation is increasingly electrified and energy generation is decentralized (from carbon-based, utility delivery to solar-generated, homeowner systems), does going solar to power your home and transport make sense? Let’s do the math.

Electricity costs
We have had the fortune of helping several hundred Yolo County homeowners evaluate solar. What we’ve learned: Their average cost of PG&E electricity is 25 cents per kWh, and their median monthly electricity bill is $185. Conversely, their cost to generate solar electricity averages 8 cents per kilowatt hour (kWh), amortized over the warrantied life of their solar panels. Solar saves money.

Transportation costs
For comparison, let’s assume an average car is driven 12,000 miles each year. If the car averages 25 miles per gallon, powered by petroleum, it will guzzle 480 gallons of gas annually. At $2.50 per gallon, annual fuel costs are $1,200, or 10 cents per mile.

Electric vehicles yield, on average, 4 miles of range per kWh. Hence, you will consume 3,000 kWh to drive 12,000 miles. If you are purchasing electricity from PG&E, your annual “fuel” cost is $750 (or, 6 cents per mile). If your electric car is powered by solar, your annual cost is $240 (2 cents per mile).

And, of course, if you charge at your workplace or one of a half-dozen free sites downtown, your cost is lower.

Environmental benefits
I can’t conceive an environmental virtue of driving a gas-powered car, though admittedly my family owns three (along with an all-electric vehicle). The environmental outcomes of electrifying your transportation with solar, though, are striking.

According to the EPA, over three years (36,000 miles) the greenhouse gas equivalents of clean transportation are:

* Retirement of 12.84 metric tons of carbon dioxide;
* Planting 320 tree seedlings, grown for 10 years; or,
* Averting 4.08 tons of waste sent to a landfill.

Many suns will set before electric vehicles become mainstream. Though cool and cheap and clean, their drawbacks are obvious: Range anxiety (Can I get from here to there?), charging anxiety (Do I need to charge it?), technology phobia (Is it too early/will it work?).

Danny Kennedy, managing director of California Clean Energy Fund, recently opined, “We’re now in a tech world, rather than a resource world. Resources are bound by scarcity — the more you use them, the more expensive they become. With tech, the more you use it, the cheaper it becomes.”

As the cost of solar and electric cars continue to descend, as the efficacy of both improve, and as PG&E rates further escalate, it will become increasingly difficult to dispute solar-fueled transportation.

The future is bright.