Solar + EV integration
The seasonal gap between production and demand has a real dollar cost, not just a kWh one. Add your annual need, production, and rates to see exactly what it is.
How it works
Step 1
Start with the seasonal solar output gap tool for the physical kWh picture before looking at the dollar consequence here.
Step 2
This is the single biggest driver of how much the seasonal mismatch actually costs, so get the precise figure from your utility's current tariff.
Step 3
This mismatch cost is usually a small fraction of a solar system's overall annual savings, worth knowing but rarely a reason to reconsider solar entirely.
Knowing how many kWh a given month falls short or runs a surplus, covered in the seasonal solar output gap tool, doesn't directly tell you the dollar consequence, since shortfall and surplus kWh are valued at different rates. This calculator converts that physical mismatch into an actual annual dollar figure by applying your specific grid rate, the kind tracked by EIA electricity data, to shortfall months and your specific export rate to surplus months.
Under full retail net metering, where exports credit at the same rate as grid purchases, a summer surplus almost fully offsets a winter shortfall in dollar terms, leaving only a small residual cost from timing effects. Under net billing or avoided-cost policies with a meaningfully lower export rate, though, that same physical surplus is worth much less, so more of the winter shortfall cost goes uncompensated, producing a larger net annual mismatch cost.
Even under a less favorable net metering policy, this mismatch cost is typically a modest fraction of a solar system's total annual value, since the bulk of savings still comes from self-consumption that isn't affected by seasonal timing at all. It's a real cost worth knowing about and factoring into expectations, but it's rarely large enough on its own to change a decision about whether solar makes sense.
If this mismatch cost looks meaningful under your specific export rate, oversizing the system to reduce winter shortfall is one option, though it comes with the tradeoff of an even larger summer surplus that may not be worth much under the same low export rate. The solar array oversize calculator can help work through that specific tradeoff in more detail.
Factor this figure into your overall annual savings estimate from the solar vs grid cost comparison tool, or revisit your net metering assumptions in the net metering interaction calculator for a fuller picture. Beyond this, the winter vs summer savings comparison is worth a look.
Questions
For a system sized to exactly match annual EV need under a net billing policy with a $0.06 export rate versus a $0.16 grid rate, the net annual cost of the seasonal mismatch runs about $50.61. Under full retail net metering with the same physical production, that cost drops to roughly $18.00.
Under net billing, summer surplus production is credited at a lower export rate than the retail rate you pay to buy grid power during winter shortfall months, so the value gained in summer doesn't fully offset the cost paid in winter. Full retail net metering credits both directions at the same rate, closing that gap almost entirely.
Not necessarily. This mismatch cost is usually a modest fraction of the system's overall annual value, and it mainly reflects a timing effect rather than an inefficiency in the system itself. It's still worth knowing about when setting realistic expectations, especially under a less favorable net metering policy.
Oversizing increases winter production somewhat, which can reduce the shortfall cost, but it also increases summer surplus, which is only valuable if your export rate is reasonably close to retail. Under a low export rate policy, oversizing to fix winter shortfall may not pay for itself as effectively as it would under full retail net metering.
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