How the combined payback works
Three cash-flow lines drive the result. The solar-only line is the standard payback for the panels assuming your home self-consumes a baseline share and the rest is exported at the net-metering rate. The EV-only line is the standard payback for the vehicle vs. an equivalent gas car. The combined line adds both plus a synergy term: the kWh you reroute from the grid (where they would have earned only the net-metering credit) into the EV (where they offset retail-rate charging instead).
What the synergy is worth, per kWh
For each kWh of EV charging that displaces a grid export, you keep the difference between the retail rate and the net-metering rate. With full one-to-one net metering, that difference is zero - the bundle adds no synergy because exporting and consuming yourself are economically identical. As the net-metering credit drops below retail, the synergy grows.
Inputs that move the answer the most
- Net metering rate. The lower your utility's export credit relative to retail, the bigger the synergy.
- Share of EV charging from solar. Bounded by the surplus your panels would otherwise export. Realistic if you can shift charging to midday.
- Home self-consumption ratio. Without a battery, most homes self-consume 30–50% of solar output. Whatever isn't self-consumed is the pool the EV can draw from for free synergy.
What this calculator deliberately ignores
Time-of-use rate structures, battery storage economics, and the cost of smart-charging hardware are not modeled. See the methodology page for full details.
Frequently asked questions
How is solar self-consumption priced when it charges my EV?
Each kWh you self-consume avoids buying retail electricity. When that kWh is consumed by the EV instead of being exported to the grid, you avoid the retail rate AND give up only the net-metering credit (often less than retail). The bundle synergy per kWh is therefore retail × (1 − net-metering rate). The panel's own LCOE is already paid for in the upfront system cost - it doesn't get charged a second time inside the synergy calculation.
Why is the synergy bigger when net-metering credit is below retail?
If your utility paid you full retail for every exported kWh, there'd be no incentive to consume your own solar - exporting and buying back would be a wash. The lower the export rate, the more you gain by using your panels' output yourself. EV charging is the easiest big load to shift onto your own production, which is why the bundle becomes much more attractive in regions with net-metering haircuts (most of the US in 2026 - California's NEM 3.0, for example).
What changes if I have time-of-use (TOU) electricity rates?
Time-of-use rates make the synergy even larger if your peak rate falls during the hours your EV would otherwise be charging from the grid (typically evenings). Charging from solar during midday avoids the peak retail rate while only giving up the (usually low) midday export credit. This calculator uses a single retail rate for simplicity - if you have TOU, enter your blended evening/peak rate to capture most of the effect.
What changes if my EV is mostly charged at work or at public chargers?
Set 'Share of EV charging from solar' close to zero. The synergy disappears - you're paying for charging at someone else's electricity rate, with no opportunity to displace your own grid exports. Solar still pays back on its own merits and the EV still pays back vs. gas; the bundle just doesn't add anything beyond that.
What's the difference between EV-first and home-first priority?
EV-first means you actively schedule EV charging to coincide with solar production - possible with smart chargers, work-from-home routines, or weekend top-ups. Home-first means your home base load takes solar first and the EV gets only the leftover surplus. The math is similar in both modes if your EV's solar share fits within the energy your panels would have exported. Where they diverge is at high solar-share targets: EV-first lets you pull more, but anything above the export-bound surplus shuffles where home gets its energy without adding new value.
Should I add a battery to my system?
A battery raises home self-consumption, which reduces the surplus that's available for EV charging. If you have an EV that can charge during midday, the EV is effectively a battery you already paid for - it's often a better economic use of solar surplus than a dedicated home battery, unless you also want outage resilience. We don't model batteries in this calculator; if you have one, raise the home self-consumption ratio to reflect what it absorbs.
How is 'payback improvement' calculated?
It's the slower of your two standalone paybacks (solar or EV) minus the bundled payback. The intuition: if you would have eventually done both anyway, this is how many years sooner the bundled cash flow crosses zero compared to waiting for the laggard to pay itself back. Positive numbers mean bundling buys you something; values close to zero mean the synergy is small under your assumptions.
Disclaimer. Estimates are for informational purposes only. Bundling solar with an EV is sensitive to your charging schedule, utility net-metering policy, and local electricity rates. Consult a qualified financial advisor before making purchasing decisions. See our full disclaimer.
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