Must a new California home be net zero?

No. The Energy Code requires solar on most new homes and compares the design with a standard design. It sets no requirement that a year of use be offset by on-site generation.

Do new homes need a battery?

Not prescriptively. Single-family homes with more than 125 amps of service must be battery-ready, and adding a qualifying battery of at least 7.5 kWh reduces the required PV size by 25 per cent.

What does zero net energy mean in California?

The Department of General Services defined it in 2016 as an energy-efficient building whose actual annual consumed energy, on a source energy basis, is no more than its on-site renewable generation.

Is the 2030 commercial goal a code requirement?

No. It is listed as a goal on the CPUC's zero net energy page. Like the 2020 residential goal, it is a policy target rather than a requirement of Part 6.

Are New California Homes Zero Net Energy?

Not by code: zero net energy was a state policy goal for new homes by 2020, and the 2025 Energy Code does not use the term. What the code requires of most new houses is a solar PV system sized by formula, heat pumps in the prescriptive baseline and, where the electrical service exceeds 125 amps, battery-ready wiring.

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Where the 2020 target came from

The California Public Utilities Commission sets out the state's zero net energy goals as written in the California Energy Efficiency Strategic Plan:

all new residential construction zero net energy by 2020;
all new commercial construction zero net energy by 2030;
half of commercial buildings retrofitted to zero net energy by 2030;
half of new major renovations of state buildings zero net energy by 2025.

In 2016 the Department of General Services defined a zero net energy building as an energy-efficient building where, on a source energy basis, the actual annual consumed energy is less than or equal to the on-site renewable generated energy. Note the word actual. That is a result measured over a year of use, while a building code governs a design before anyone moves in.

What the code did instead

The 2019 Energy Code, which took effect on 1 January 2020, added a prescriptive solar photovoltaic requirement for new low-rise residential buildings. The Energy Commission's overview of that code put new low-rise homes at 7 per cent more efficient than under the 2016 standards, and at an average 53 per cent lower energy consumption with the solar counted.

The same overview was candid about the goal. Under "lessons learned" it said new developments had significant impacts on zero net energy goals, listing alongside that the large utility-scale solar built for the renewables standard and the net energy metering and time-of-use rules for customer generation. Its direction for future codes was a greenhouse-gas-based metric that promotes electrification, and a move away from equal hourly netting to support grid flexibility. The 2025 code measures performance in source energy and long-term system cost, not in annual net energy.

What a new house needs under the 2025 code

Solar. Section 150.1(c)14 sets the annual output of the PV system at no less than the smaller of a formula based on floor area, dwelling units and climate zone, or the solar access roof area times 18 for steep roofs or 14 for low-slope roofs. Below 1.8 kWdc none is needed, and a qualifying battery of at least 7.5 kWh cuts the size by 25 per cent. The details are in solar on new homes.
Battery-ready. Section 150.0(s) applies to single-family homes whose dwelling unit service is over 125 amps: backed-up interconnection equipment or a raceway to a subpanel, at least four identified circuits including the refrigerator, a 225-amp main busbar, and space for a future transfer switch. A home with a battery installed is exempt.
Heat pumps. The prescriptive baseline assumes heat pumps for space and water heating. Gas is still possible through the performance path, with electric-ready wiring; see all-electric new homes.

Under the performance path, the proposed home must match or beat the standard design on source energy and long-term system cost, with PV, batteries and demand flexibility counted in the total. That is a comparison with a reference house, not a balance of a year's use against a year's generation.

If you want a zero net energy home anyway

It is a design goal you can pursue above code. Size the solar to the home's expected use rather than to the formula, cut the load first, and judge success the way the state definition does, against a year of metered consumption. Some cities set requirements above the state code through reach codes.