What a California Solar System Doesn't Cover

How your system got its size in the first place

Nobody at the sizing stage asked what your life would look like in three years. They asked what your meter showed for the past twelve months. That's not a sales shortcut — it's the law.

The CSLB/CPUC "Solar Energy System Supporting Information" form — developed by the two agencies under Business & Professions Code § 7169(c) — requires every residential solar contract to state "My Annual Electricity Usage (past 12 months)" in kWh as its first input, set directly against the estimated annual solar generation. If a full 12 months of billing data wasn't available, the contractor has to write in an explanation of how usage was estimated instead — there's no version of the form that skips the historical-usage step.

CPUC Decision 20-08-001, issued in August 2020 under the authority of Public Utilities Code § 2854.6, adopted the standardized inputs behind that field: providers must build the required bill-savings estimate off the customer's trailing 12 months of electric consumption data, disclosed before the contract is signed. The form's own required output is an estimate of savings in the first year only, not a multi-year forecast, and its instructions call for that calculation to assume no rate escalation — current average escalation rates are published separately at the CPUC's own solar guide, cpuc.ca.gov/solarguide.

Nothing in the disclosure rules stops a contractor from also walking you through a forward-looking scenario, but the standard form doesn't require one, and in practice almost no contract includes it — it adds complexity and liability nobody's making them take on. The result: your system is priced against the year behind you, full stop.

The 50% cushion, and why most people never get it

If you're served by PG&E, San Diego Gas & Electric, or Southern California Edison, your system falls under the Net Billing Tariff, effective April 15, 2023 under CPUC Decision 22-12-056. The tariff caps system size at your customer's annual electric load, "plus up to 50% if customer attests to need."

Read that condition closely. The extra capacity isn't automatic — it requires the customer to sign a written attestation, at the time of sizing, naming a specific anticipated future need: a known EV purchase, a planned heat pump conversion, whatever it is. Absent that attestation, installers size to 100% of trailing usage, not 150%.

Most homeowners who bought solar before deciding to also buy an EV, or before a room addition was on the table, never signed that attestation, because the future need wasn't known yet. That's not an oversight anyone made — it's just sequencing. But it means the system sitting on your roof was very likely sized to exactly what you were using the year before, with no built-in room for what came next. Publicly owned utilities — LADWP, SMUD, MID, Anaheim, Roseville, Lodi, and others — are not subject to this CPUC tariff and set their own sizing rules, so the specifics differ if you're on one of those systems; check with your utility directly.

Gas heat and gas appliances: never part of the equation

This is the one that surprises people the most, and it's also the simplest to explain: solar panels generate electricity. They have no mechanism for offsetting a gas bill, because a gas furnace, gas water heater, or gas range was never counted in the "annual electricity usage" figure the system was sized against in the first place.

If your home heats water and space with natural gas, that gas bill sits completely outside the solar contract's math — not because of some limitation in the panels, but because gas consumption was never part of the input. A contractor's claim that solar "eliminates your energy bills" is only accurate for a household that's already 100% electric. For anyone with a gas connection, it's an overstatement the CPUC's Solar Consumer Protection Guide and the disclosure form's mandatory "estimate, not a guarantee" language exist specifically to head off.

The practical version: if you're planning to convert a gas furnace or water heater to an electric heat pump down the line, that's new electric load your existing system doesn't know about. It's worth running the numbers on the added consumption before you assume your current panels will absorb it — they were never asked to.

An EV bought after the panels go up

A Level 2 home charger used for average driving typically adds somewhere in the range of 3,000 to 5,000 kWh a year to a household's electric consumption, according to U.S. Department of Energy and Energy Information Administration data — the figure runs higher for a larger or less efficient EV and lower for a light-driving household. If you bought your EV after your solar system was already sized and interconnected, that charging load simply wasn't in the trailing-12-months figure the installer used.

Unless you signed the Net Billing Tariff's 50%-cushion attestation specifically naming a future EV before your system went in, the extra draw from a home charger comes straight from the grid, billed at your full retail rate (or the AB 205 flat-rate-adjusted structure once that's live for your utility), with no additional solar production offsetting it. Your existing panels keep generating exactly what they always generated; they just don't generate more because your car now needs power too.

The fix, if there is one, isn't a warranty claim — it's a second, smaller project: additional panels sized specifically to the new EV load, run through its own interconnection request with your utility. Ask an installer to run the math on incremental capacity against your actual charging pattern before assuming your existing system already has you covered.

Pool pumps, spas, and other loads added later

The same mechanism applies to a pool or spa added after your solar contract was signed. An older single-speed pool pump can run 2,500 to 3,000 kWh a year on its own, per ENERGY STAR's own pool pump data — a load that, if the pool didn't exist yet at the time of your 12-month billing lookback, was never part of what your system was sized to offset.

There's no CSLB or CPUC rule that names pool pumps or spas specifically; this follows from the same historical-sizing logic that governs every other load discussed here. The mechanism doesn't care what the new appliance is — a pump, a spa heater, a home server rack, a second refrigerator — anything added to the house's electric draw after the installer pulled your billing history sits outside the original calculation, unless it was captured in an attestation at signing.

If a pool is already in your plans, this is worth raising with your installer before signing, not after: naming it explicitly, even in general terms, gives you a shot at capturing some of that 50% cushion under the Net Billing Tariff rather than discovering the gap in your first post-pool electric bill.

Additions, ADUs, and general load growth

California's ADU laws have made it substantially easier to add a second unit to a property, but I found no CSLB or CPUC rule that addresses solar sizing specifically for ADUs or room additions. What's documented is the general principle, and it applies here with more force than almost anywhere else: an ADU can add a full second household's worth of consumption — its own lighting, HVAC, appliances, possibly its own EV charging — into a system that was sized against the original single household's trailing usage.

Whether an ADU requires its own separate utility interconnection or is simply treated as added load behind the existing meter is a utility-tariff-level question that varies; that specific procedural detail should be confirmed directly with your utility's interconnection rules before you build, not assumed from general principle.

The honest framing: if an ADU or major addition is anywhere in your plans, even a few years out, say so before your solar contract is signed. It costs you nothing to mention it, and it's the only way to get that need captured in an attestation rather than discovered later as a bill that's higher than the number you were shown at signing.

The one thing solar was never going to touch: the flat grid charge

This is worth its own callout because it applies to every solar customer, regardless of how well the system was sized or how disciplined the household has been about usage. Under AB 205 (2022) and CPUC Decision 24-05-028 in Rulemaking R.22-07-005, PG&E, SCE, and SDG&E residential bills are restructuring into a per-kWh usage rate — cut by roughly 5 to 7 cents under the decision — plus a new flat monthly charge of $24.15 for non-CARE/FERA customers, covering grid infrastructure costs.

The CPUC's own language on this is direct: "All residential customers, including those with rooftop solar, will transition to flat rates." The stated reasoning is that solar households still rely on grid infrastructure day and night — drawing power when panels aren't producing, exporting power back during the day — and the flat charge is simply that existing cost moved to its own line item rather than eliminated. Discounted versions exist: $6/month for CARE-enrolled low-income customers, $12/month for FERA enrollees and qualifying affordable housing residents. The rollout the CPUC's fact sheet projected for "late 2025 and early 2026" is now underway — public reporting has SDG&E and SCE showing the charge on bills starting in late 2025, with PG&E following in early 2026 — so confirm the current line-item status on your own bill, since utility-by-utility timing can still vary.

There's no version of solar sizing, past or future, that offsets this charge — it isn't consumption-based, so panels don't touch it. Budget for it as a fixed cost of grid connection, solar or not.