Solar Cars Save Money

Originally published on Clean Power Research.
By Gavin Novotny

Is it possible to save more money by combining an electric vehicle (EV) with a home solar PV system rather than considering each individually? Often the answer is yes, and the additional savings can be substantial.

To help energy consumers answer that question, residents of New York State now have access to a WattPlan® EV + solar energy planning tool via the New York State Energy Research and Development Authority (NYSERDA). A WattPlan EV + solar planning tool is also available to residential customers of California’s investor-owned utilities via a California Solar Initiative (CSI) Research, Development, Demonstration and Deployment (RD&D) Program grant through September 30, 2016.


Quantifying the benefits of an EV + solar is complex, and requires consideration of multiple moving parts, all of which can substantially impact the viability of an EV + solar combination. Variables include:

  • Electric rate selection
  • Solar system sizing
  • Vehicle charge time
  • Charger capacity
  • Frequency of public charging

WattPlan simplifies the EV + solar analysis by sizing a solar PV system to fit a customer’s energy use including charging an EV, and recommending the best electric rate for their situation. Consumers can tailor results by specifying the EV make and model, when they plan to charge, the type of charger they plan to install, and how much they plan to charge away from home, among other factors.

With WattPlan, energy consumers are provided just the information they need—in an easy-to-understand format—to make a smart energy decision. Surveys indicate incentives, savings and environmental benefits are the most relevant information for consumers considering purchasing an EV.

Free money (a.k.a., incentives)

By bundling an EV with solar, utility customers can take advantage of additional incentives. For example, New York residents can receive a $7,500 Plug-in Electric Drive Vehicle Credit, and up to $11,000 in solar incentives for a typical system1:

Residents in California can receive more than $16,0002 in combined EV and solar incentives, compared to $10,000 for an EV alone.

Bigger solar means bigger savings, bigger environmental benefits

Savings from an EV + solar can be greater than the savings achieved from solar and an EV considered independently. How is this possible? It all has to do with the size of the solar PV system.

When a homeowner purchases an EV, the amount of electricity (the load) they need to power their home (through which their EV is charged) increases. Because the electric load is greater with an EV, customers can install a larger solar system and increase the size of the pie available for savings with solar. The result is greater savings when considering an EV + solar together, both financially and environmentally.

Let’s use WattPlan to compare the savings of Solar Only, EV Only and EV + Solar scenarios for a California homeowner. For the Solar Only scenario, Figure 1 shows that a customer spending $100 per month (or $1,200 per year) on electricity can save approximately $77 per month ($100 – $23 = $77) by installing a solar PV system. That is equivalent to $924 in savings per year (12 x $77 = $924).


As shown in Figure 2, an EV Only scenario using a Nissan Leaf would lead to savings of $764 per year. The annual savings from combining the Solar Only and EV Only scenarios together would be $1,688 ($924 + $764 = $1,688).


In the Solar Only and EV Only examples, the savings also includes the benefits of switching from the standard rate to a solar or EV time-of-use rate. For comparison, if standard electric rates are used, the combined savings for these two scenarios would be $683 less per year, a 40% reduction in savings.

Now let’s look at the savings for a homeowner considering an EV + Solar together. As shown in Figure 3, by sizing the solar PV system based on the home’s higher electric load with an EV, a homeowner could save $2,339 per year. That’s a savings increase of $651, or 38% more per year, over the combined savings of $1,688 of the Solar Only and EV Only scenarios.


The higher savings are due to the additional solar capacity that WattPlan has calculated in the EV + Solar scenario. In the Solar Only scenario (Figure 4a), the optimal solar PV system size is 3.25 kW, and in the EV + Solar scenario (Figure 4b), the optimal size is 5.5 kW. This is the primary advantage of combining solar with electric vehicles: more electricity use allows for a larger solar PV system and greater savings.


Of course, consumers should also take into account capital costs. Comparing the results of combining the EV Only and Solar Only scenarios with the EV + Solar scenario, the simple payback for both cases is approximately 8.5 years (assuming $2.80/W after incentives for solar, and a $5,000 premium for an EV compared to a gas vehicle).

The key is that the EV + Solar scenario will continue to provide $651 per year greater savings for every year thereafter. An equivalent payback period with greater lifetime savings lends further credence to the idea that when considering EV + Solar, the whole is greater than the sum of its parts.

EV + solar is here to stay

The synergy of electric vehicles and solar is obvious: instead of going to the corner station and pumping gas to fuel your vehicle, you can install solar and “fuel” your vehicle with sunshine. There is also an overlap in consumer interest. California’s Center for Sustainable Energy surveyed recipients of the Clean Vehicle Rebate Project and found that 40% of people purchasing or leasing a plug-in electric vehicle either already have, or are considering, solar for their home.

EV + solar is an unmistakably powerful combination that provides independence for consumers’ two primary energy needs. WattPlan makes it easy to calculate just how much homeowners can save by purchasing an EV, going solar or doing both. With WattPlan, homeowners in California and New York now have a way to explore their options, and take advantage of the EV + solar opportunity.

1Assumes a 5 kW system with a total installed cost of $20k, and a $500/kW NY-sun incentive payment for upstate New York residents. Includes negative federal tax impacts resulting from state tax credits and rebates for an individual in the 25% federal tax bracket.
2Residents of California are eligible for a $2,500 rebate from the California Clean Vehicle Rebate Project in addition to the $7,500 Plug-in Electric Drive Vehicle Credit and the 30% federal investment tax credit.

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