solar plus eV

How PG&E’s “EV” rate schedule benefits solar homeowners

Screen Shot 2019-02-12 at 1.59.59 PM.png

We have had the fortune of helping more than 50 electric vehicle owners go solar. As shared in prior posts, fueling your car with solar electricity is the least expensive form of (automotive) transport: Your amortized cost to generate solar electricity is ~8 cents per kWh, and you yield about four miles per kWh of electricity. Trite but true: Driving on sunshine makes sense.

Better yet, when you enjoy an electric vehicle you can employ PG&E’s “EV” rate schedule. This time-of-use rate program incents EV drivers to charge their car (and shift other electricity demand) to “off-peak” hours, namely 11 pm to 7 am, Monday through Friday, and all weekend/holiday hours, sans 3-7 pm.

Here are PG&E’s “EV” rates per kWh:

pge eV rates.png
  • Peak (2-9 pm, M-F): $0.33 (winter); $0.48 (summer)

  • Part Peak (7am-2pm; 9-11pm M-F): $0.20 (winter); $0.26 (summer)

  • Off Peak (11pm-7am M-F; weekends/holidays all hours except 3-7pm): $0.13

When your solar panels make more energy than your home uses, you are credited by PG&E via their net-metering program. Hence, the greater the delta (solar generation less household consumption) during “peak” periods, your monetary credits are amplified.

Generally, Repower homeowners who enroll in PG&E’s EV rate schedule only generate ~80% of the electricity they use to cover 100% of their electricity costs. This is simply due to the time-of-use rate schedule and the advantage of buying electricity at a low rate and getting credited at nearly 4x. Very cool.

With apologies for the bevy of metrics, let’s review an example. Below is the electricity use for a fairly standard Davis homeowner who charges their electric vehicle 12,000 miles per year at home.

Pre-solar electricity use and costs (on PG&E’s “E-1” program):

E1 use.png

We then sized and modeled a solar system to eliminate the homeowner’s electricity bill: A 4.8 kW, 15-panel system installed at 270-degree azimuth (due west), no shading. The solar panels are projected to generate 6,493 kWh in year one, thus covering 70% of the homeowner’s electricity use.

If the homeowner did not own an electric vehicle, they would (upon going solar) enroll in PG&E’s “TOU-A” rate schedule. Like the EV rate, TOU-A values electricity based on demand (“peak” period is 3-8 pm), but there’s little difference between peak and off-peak periods.

Solar economics under the default E-TOU (A) rate schedule:

ETOU use.png

The homeowner’s year-end, true-up cost would be $645 — the solar system is too small. This is not bad, but …

… under the EV rate schedule, the homeowner generates significant time-of-generation credits/leverage. Their year-end bill would be $108.

EV use good.png

Simple but lucrative: The homeowner will save an additional $500 per year through the EV rate schedule. Contact us today with questions and/or if you’d like a free solar assessment.

Shade on my solar panels: What to do?

Solar panels with shade.jpeg

A few times each week we tender discussions with homeowners (who are interested in going solar) that begin with a similar question: How do I know if my home/roof is a good candidate for solar, given shading from surrounding trees? Or, perhaps it's a statement: Solar won't work at my home because I have too much shading.

With kudos and thanks to THE GREAT Mike Kluk -- one of hundreds of terrific Cool Davis volunteers that propel our community's sustainability -- we now have an in-depth look at technologies we employ to help mitigate shading (and, thereby, maximize electricity generation of solar panels that are shaded). Mike just published an article in The Enterprise, Rooftop solar: Partial fixes for partial shade. If you're contemplating solar, it's well worth a read.

We had the pleasure of sitting down with Mike to help inform his research and prose. An excerpt:

Every residential solar installation is unique. Roof size, angle, and orientation to the sun all affect production. But for installations where intermittent shading is an issue, the addition of optimizers or microinverters typically increases production from 15 to as much as 25%. Over the lifetime of a system, 20 to 30 years typically, that is a tremendous amount of power that you will not need to pay for.

Our take: Solar does not work for everyone. However, by employing SolarEdge's power optimizers, the downside of shading is mitigated.

Most important, we are happy to perform an assessment and quantify the impact of shading. The end result may be a no-go, but it's worth contemplating.

 

 

Considering an electric vehicle and/or solar?

More than half of the homeowners we talk to either own or are, in the near term, considering purchasing an electric vehicle. Part of the combinatorial interest -- clean energy + clean vehicle -- is values based. However, most homeowners who go solar and fuel their transport with sunshine do it for pragmatic reasons: Solar electricity is significantly less expensive than PG&E's energy, and fueling an electric vehicle is much cheaper than pumping gas. Here's a prior post quantifying the economics of solar + eVs.

Though the math is simple, the decision -- which car to purchase or lease, at what time, and how to size my solar system to cover my electric vehicle charging -- has more to it. To wit, there's a delightful new tool for California homeowners to determine if a solar-powered vehicle makes sense. In a few minutes, you can compare options and model the economics/scenarios. Take a peek, poke around, and (we're confident) you'll be impressed by the savings.

And, of course, feel free to contact us if you have questions about electric vehicles and the potential to power your eV with solar. We will perform a no-cost assessment for you, modeling various alternatives and quantifying the impacts.