Planning Solar for a Future EV or Heat Pump

A solar system sized for today’s electricity usage can be meaningfully undersized the moment you add a major new electric load — an EV you plug in at home, or a heat pump replacing a gas furnace. If either is realistically on your horizon, size your system for what you’re planning to add, not just what your last few bills show.

Why Current Usage Alone Isn’t the Right Number

The Solar Panel System Size Calculator sizes a system from your average monthly electricity usage — but that usage is only a snapshot of what you’re using today. It has no way to know that you’re planning to buy an EV next year or replace a gas furnace with a heat pump next winter, because you never told it. If you size a system purely from today’s usage and then add either load afterward, the system covers less of your total electricity bill than you originally planned for.

Practical takeaway: treat “my planned future usage” as a real, separate input to solar sizing — not something to revisit only after the new load already exists and the bill already went up.

Estimating the Load an EV Adds

An EV charged at home doesn’t draw a fixed, universal amount of electricity — it depends on the battery size, how much charge you actually add on a typical day, and your charger’s efficiency. The EV Charging Cost Calculator turns those inputs into an estimated charging cost and a cost per mile, and the same inputs (kWh drawn per charge, times how often you’d realistically charge) give you the added monthly kWh a solar sizing estimate needs to account for.

Practical takeaway: a rough daily commute is usually a more reliable way to estimate this than guessing a monthly total directly — figure out the kWh a typical day’s driving actually draws from the wall, then multiply by how many days a month you’d realistically charge at home, rather than picking a number that feels right.

Estimating the Load a Heat Pump Adds

Replacing a gas furnace with a heat pump shifts heating load from gas onto your electric bill entirely, and a heat pump’s electricity draw scales with the capacity your home actually needs. The Heat Pump Sizing Calculator estimates that capacity, in tons, from your home’s square footage, climate zone, and insulation quality — a bigger, less-insulated home in a harsher climate needs more capacity, and more capacity means more electricity draw once it’s running.

Practical takeaway: a heat pump’s added electric load isn’t a small rounding error the way a single-EV commute sometimes can be — for a home converting off gas heat entirely, this is often the single largest new electric load a solar sizing estimate needs to account for.

Putting It Together

A practical sequence for anyone realistically planning either change: start with your current average monthly usage, add the estimated monthly kWh an EV would draw from home charging (via

EV Charging Cost Calculator) if one is genuinely on your near-term horizon, add the estimated electric heating load a heat pump would add (via Heat Pump Sizing Calculator, converted to expected monthly kWh) if a fuel-switch is realistically planned, then run that combined total — not just today’s bill — through the Solar Panel System Size Calculator. A system sized this way costs more upfront than one sized for today’s usage alone, but it avoids the more expensive alternative: installing a system, then finding out a year later that it only covers a fraction of your new, higher bill once the EV or heat pump is actually in place.