Efficiency LSC vs Total LSC: Why Solar Cannot Fix a Failing Efficiency Result
Because the performance budget has two scoreboards and panels only count on one. Efficiency LSC covers space conditioning, water heating, mechanical ventilation and the self-utilization credit. PV feeds only total LSC, so extra panels cannot make up an efficiency shortfall. The trade runs one way: a more efficient house can use a smaller array.
- Choose your report
- Upload your plans
- Pay securely
- Permit-ready report by email
What each scoreboard holds
Section 150.1(b)1 splits the long-term system cost budget in two. The efficiency component adds up space conditioning, water heating, mechanical ventilation and the self-utilization credit. The total component starts from that and adds the PV system, battery storage, lighting, demand flexibility and other plug loads. Solar sits entirely in the second list, and the compliance manual says plainly that substituting PV for efficiency measures is not possible because PV has no impact on the efficiency compliance metric.
The trade that does work
A better envelope or heat pump lets the building comply with a smaller solar system, so efficiency can buy down panels but panels cannot buy back efficiency. The standard design array is sized from the modelled annual electrical use of the building as a mixed-fuel design, whatever fuel you install.
The battery exception
When PV is paired with a battery of at least 5 kWh compliance cycling capacity, part of the available credit may be spent on efficiency trade-offs; the manual calls it a modest credit for buildings with marginal difficulty complying. A stand-alone battery earns none.
Solar water heating is the odd one out
A solar water heating system cannot replace the required PV, but it is modelled in the efficiency LSC, so it can be traded for efficiency measures or for a smaller PV array.
Prescriptive is a different question
On the prescriptive route the array is sized by an equation of floor area and dwelling units, and may be reduced by 25 percent if installed with a battery of at least 7.5 kWh cycling capacity. It is separate from the performance trade; see solar system size for a new home.
What to change instead
Look at the envelope, the heat pump, the water heater and duct location. Anything that credits equipment above the minimum needs a rater test; see which credits need a test. A diagnosis path is in reading a failing result, and the units are explained on the energy budget page. Orders start on the residential report page.
Common Title 24 Questions
- What is Title 24?
- Do I need a Title 24 report?
- How much does a Title 24 report cost?
- How long does a Title 24 report take?
- What is included in a Title 24 report?
- What plans do I need to upload?
Frequently Asked Questions
Partly. Solar paired with a battery of at least 5 kWh cycling capacity unlocks a modest credit for efficiency trade-offs. A battery alone gives none.
Yes. It is modelled with the water-heating system in efficiency LSC, though it cannot replace the required PV.
Explore Performance Calculations
- Existing + Addition + Alteration: How the Performance Method Works
- Prescriptive vs Performance Compliance for Home Additions
- Prescriptive vs Performance Compliance
- How Much Compliance Margin Should I Keep Before Construction?
- Title 24 Trade-Offs: A Worked Example of What Can and Cannot Move
View all Performance Calculations guides → · Reports and Calculations · Title 24 guide