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.

To Bolt or not to Bolt

Over the past 10 days, we've had a dozen or so conversations about Chevrolet's soon-to-be-released, all-electric Bolt. Concurrently, my wife is pondering a new car that's efficient, economical and suitable for a Davis-to-UCDMC commute. To wit, to Bolt or not to Bolt?

After all, what's not to like? Significant -- 238 miles -- all-electric range, a decently sporty design, and a good price tag (less than $40k before $7,500 in federal and $2,500 in state incentives). Pundits have proclaimed General Motors (with the Bolt) has beat Tesla (with its Model 3) to the dance.

General take through our lens: Electric vehicles powered by solar-generated electricity make great economic and environmental sense. Quick 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 $0.25 per kWh, and their median monthly electricity bill is $185. Conversely, their cost to generate solar electricity averages $0.08 per kilowatt hour (kWh), amortized over the warrantied life of their solar panels. 

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 $0.10/mile.

Electric vehicles yield, on average, four 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, $0.06/mile). If your electric car is powered by solar, your annual cost is $240 ($0.02/mile). (And, of course, if you charge at your workplace or one of a half-dozen free sites downtown, your cost is lower.)

Back to the Bolt. A few takes floated over the past week:

- Business Insider: The Chevy Bolt still doesn't compare to Tesla's Model 3

- Electrek: The very good Chevy Bolt reviews are in ... everyone forgot to ask the most important question

The latter from Electrek hits -- aside from design/style/brand cache/Elon-halo-effect virtues -- Tesla's sustainable competitive advantage. General Motors (and other automakers) need to get off their collective rears and solve the charging challenge. Their networks are established: Dealerships are sensible locations for super-charger stations.

Until then, the Bolt will be a bit better than my Leaf: Great for local transport and perhaps a trip to the Bay Area or Tahoe, but nonsensical to take to Oregon or Southern California. Here's hoping General Motors and others will tackle the simple (technology) but complex (logistical) challenge of building a charging network.


Postscript: Great comparison of the Bolt and Model 3 in today's Clean Technica, echoing and amplifying many of our thoughts.

SAS: Solar Acronym Soup

All industries are plagued with too many acronyms; the solar industry could top the charts, cluttering myriad technical, utility and financial acronyms into confusing babble-babble. Here are but a few solar sugar plums, from the basic to the sublime:

- BoS: Balance of System (the soft costs — aside from equipment and installation labor — that complete the cost of your solar system).

- CCA/CCE: Community Choice Aggregation/Community Choice Energy (an alternative form of cleaner energy supply … coming to Yolo County in 2017!).

- CPUC: California Public Utilities Commission (the governing/regulatory body that oversees PG&E and other investor-owned utilities in California; aka, friends of solar and consumer choice).

- eV: Electric Vehicle (aka, peanut butter to solar’s jelly).

- GHG: Greenhouse Gas (a [horrible] gas in the atmosphere that absorbs and emits radiation within the thermal infrared range).

- IRR: Internal Rate of Return (the interest rate at which the net present value of all the cash flows [both positive and negative] from your solar investment equal zero).

- ITC: Investment Tax Credit (the 30%, one-time federal tax credit you receive when you own your solar system).

- kW: Kilowatt (1,000 watts of energy).

- kWh: Kilowatt Hour (a measure of electrical energy equivalent to a power consumption of 1,000 watts for 1 hour).

- NEM: Net-Energy Metering (the program/mechanism by which solar system owners are credited for the electricity they generate).

- PTO: Permission to Operate (notification from your utility that your solar system is connected to the grid, thus commencing monetary credits).

- PPA: Power Purchase Agreement (an agreement to purchase electricity generated by a solar system [on your roof] that is owned by a third-party, tax equity fund … aka, a bad deal for homeowners vis-a-vis solar ownership).

- PV: Photovoltaic (PV cells in your solar panels are specialized semiconductor diodes that convert visible light into direct current electricity).

- TOU: Time of Use (a utility rate schedule whereby you are credited [for solar] and debited [for electricity use] based on the time of generation/use).


And, finally:

- PG&E: Our favorite utility (though they fight solar at every juncture :)

EV+PV: My Leaf Hits 30,000 Miles

The odometer on my 2013 Nissan Leaf rolled past 30,000 miles this morning in-transit to our shop. Over the past 26 months, my affinity for the Leaf has wavered: Fun to drive, great for the environment, and (beyond) cheap to operate; major range and charging anxiety, less-than-cool design, safe as an aluminum can. For $200 a month (thanks to Hanlee's lease) with minimal operating costs, I can't complain.

We've opined about the PB&J beauty of EVs + PV: The ecological and economic benefits can't be beat. At 25 miles/gallon for a gas-fueled car, I have avoided purchasing 1,200 gallons of gasoline.

First, here are the GHG equivalents of 30,000 miles of electric driving (click here for a super-cool EPA GHG calculator):

- 10.7 metric tons of carbon dioxide

- 267 tree seedlings grown for 10 years

- 3.4 tons of waste sent to a landfill

A dent, but certainly meaningful (at least to me). Enter the economic side of the equation and the Leaf truly sparkles:

- Of the 30,000 miles, approximately half were charged for free (primarily at downtown Davis charging stations) and half at home.

- My cost of solar-generated electricity (produced on my roof) is ~ 7 cents per kWh.

- Every kWh of electricity fuels (hah!) four miles of electric vehicle transport.

- 15,000 charge-at-home miles divided by 4 = 3,750 kWh

- 3,750 kWh @ $0.07/kWh = $262.50

Pretty cool and, importantly, not unique to my situation: Two-plus years of heavy driving at a cost (sans the lease payments) of $262.50 with nary a naughty emission. Electric vehicles powered by solar-generated electricity can't be beat.

Tesla Model 3 + Solar PV: Perfect Pair?

A Repower homeowner and Tesla Model S driver asked me this weekend: What impact will Tesla’s just-announced, $35k, 215-mile-per-charge Model 3 have on the solar business? Timely question that prompted navel gazing, given last week’s announcement of the Model 3, the deposit I placed to purchase one, and Repower’s mission to help as many homeowners as possible go solar.

Good question, I replied. Wow, I pondered. Big, I think. Perhaps a game-changer/tipping point for the electric vehicle industry. My thoughts were shallow and streaming, yet to codify.

(BTW, Chuck Jones, one of Repower Director John Walter’s Stanford pals, has a worthy article in Forbes about the Model 3.)

From a car-driving, solar-consuming perspective, a few thoughts:

- Tesla CEO Elon Musk tweeted Saturday that 276,000 $1k deposits have been placed for the Model 3 … in two days. (IMO: The Chevy Bolt is DOA.)

- Today’s reasonably-priced, all-electric vehicles, including my Nissan Leaf, have limited range. Therefore, if you own a contemporary electric vehicle (sans a Tesla S or X), your demand for electricity is moderate.

- Repower homeowners are generating solar electricity for an amortized cost of $0.10 (or less) per kWh.

- For every kWh of electricity, you receive ~4 miles of charge.

You can see where I’m going. For a dollar, you can drive 40 miles (with no emissions). With the Model 3’s extended range, drivers will rack up more electrically-charged miles (versus hybrid electrics like the Volt or my range-constrained Leaf). And, with Tesla’s ever-expanding network of super charging stations, road-tripping to the Bay Area, SoCal, Oregon, et al is now feasible … with a $35k (pre-tax credit) car. At no cost.

What’s the impact on solar for homeowners with extended range electric vehicles? Let’s say you drive 15,000 miles per year and charge your vehicle 50% of the time at home (7,500 miles/year). Divide 7,500 (miles) by 4 (miles/kWh) and you would consume 1,875 kWh of electricity. If your solar system generates ~ 1,400 kWh per kW of capacity, you would need an additional 1.3 kW of solar panels. The math is simple and the trend is, well, trending.

And, the punchline: You purchase a Model 3 for $25,000 (after tax credits); drive 15,000 miles per year (with 50% charging done at home); maintenance with Tesla’s is free; and, your annual automotive expense would be $187.50 for carbon-free, no compromise driving.

That’s cool. Contact us today if you own or are considering acquiring an electric vehicle. 

The future is bright.