San Diego Infrastructure Underwriting: How Rate Design Decides What a Rooftop Kilowatt-Hour Is Worth
For commercial and multifamily assets in San Diego, two comparable properties can carry identical solar arrays, produce the same annual kilowatt-hours and still land in very different places on the operating statement. The difference is rarely the equipment. It is the rate design attached to each account: how demand is measured, when on-peak windows fall, how exports are valued and where credits are recorded. Rate structure is an underwriting variable, and it deserves the same discipline given to roof condition or service capacity.
That is the premise behind Rooftops Into Revenue™: treat the rooftop as infrastructure and the tariff as the revenue model. Before modeling income from production, underwrite what the account actually pays, what it avoids and who receives the credit.
Demand charges: the component solar does not automatically solve
SDG&E's Understanding Demand guide describes three distinct demand components on commercial bills. Non-coincident peak demand is based on the higher of the maximum monthly demand or 50 percent of the maximum annual demand. On-peak demand and generation demand each reflect the highest 15-minute interval during defined windows, with on-peak hours running 4:00 PM to 9:00 PM daily. The summer season runs June 1 through October 31, with winter covering the remainder of the year.
The underwriting tension is structural: solar production declines through the late-afternoon hours precisely when on-peak demand charges are set. An array can substantially offset midday energy charges while leaving peak demand components largely intact. This is where battery storage re-enters the model as a demand-management tool rather than an energy add-on: shifting or shaving load across the 4:00 PM to 9:00 PM window addresses the interval that sets the charge.
The screening question is therefore not "does the property have demand charges?" but "which demand component does the proposed system actually affect, and can that effect be demonstrated in interval data?" Underwrite the Utility Margin Capture™ the account structure supports, not a generic savings percentage.
AL-TOU and the mandatory time-of-use environment
Schedule AL-TOU is mandatory for SDG&E non-residential customers with demand of 20 kW or more, as described in the AL-TOU tariff schedule. Energy charges vary by season and by peak period, and the commercial time-of-use periods applicable to all non-residential customers except PAT1 define those windows. For most commercial and larger multifamily accounts, time-of-use pricing is not an option to elect; it is the environment the asset already operates in.
That changes the production question. Two systems with equal annual output can produce different value depending on how much generation coincides with priced periods versus how much lands outside them. A San Diego underwriting model should test production against the account's actual interval data and the applicable TOU windows, rather than valuing annual kilowatt-hours at a single blended rate. Site-specific factors, including a franchise fee differential within the City of San Diego, can also affect the effective cost on an account, so the applicable tariff and location should be confirmed rather than assumed.
The Solar Billing Plan decouples exports from retail rates
Under SDG&E's successor framework, the SDG&E Solar Billing Plan keeps commercial customers on their existing pricing plan and distinguishes imports from exports. Export compensation is determined by the export rates associated with the customer's applicable tariff, which are tied to avoided-cost-based hourly values rather than full retail netting. In practical terms, commercial savings come primarily from consumption offset and demand-charge management, not from selling power back to the utility.
For underwriting, the consequence is direct: a model that assigns retail value to all exported production overstates the achievable margin. The defensible approach values owner-consumed production against the applicable tariff and treats exports at the applicable export rate, then discloses both assumptions.
Multi-meter properties: credits, allocations and who receives the value
Meter topology interacts with rate design. Where a property has multiple separately metered accounts, virtual net billing arrangements apply: as described by the CPUC's virtual net energy metering framework and reflected in successor-tariff implementations, non-residential benefiting accounts receive a proportional share of export compensation as a dollar bill credit, with no interval netting between accounts.
That structure makes credit allocation an underwriting item. The account receiving the credit, the proportion assigned and the lease reimbursement language determine whether the benefit reaches the owner's operating statement, reduces tenant bills or is passed through and offset elsewhere. A projected saving that lands on a tenant meter, under a gross lease with a pro-rata passthrough, may improve tenant economics without moving NOI at all.
Rate-structure screening table
Underwriting category | Screening question | Potential pro forma consequence |
Applicable tariff schedule | Which schedule is the account on today, and what is the transition or eligibility status under the Solar Billing Plan? | The tariff defines both the cost base and the export value; the wrong schedule assumption skews the entire model. |
Demand components | Does the bill include non-coincident, on-peak or generation demand components, and how is each set? | Each component responds differently to solar and storage; unaddressed demand persists in the pro forma. |
On-peak interval exposure | What do interval data show during the 4:00 PM to 9:00 PM window across seasons? | This is the interval that sets peak demand charges; it defines the battery dispatch case. |
TOU alignment | How much production coincides with priced periods, and how much falls outside them? | Equal annual output can carry unequal value; alignment, not volume, sets the energy offset. |
Export value gap | What is the spread between the import rate and the applicable export rate for the account? | Assigning retail value to exports overstates Utility Margin Capture™; the gap must be modeled explicitly. |
Meter topology and credit eligibility | Is the property single-meter or multi-meter, and which accounts qualify as benefiting accounts under virtual net billing? | Allocation determines whether credits accrue to the owner, tenants or shared accounts. |
Battery dispatch case | Is storage modeled against demand windows and interval data, or added as generic output? | Demand management is the storage business case; generic dispatch undermines the return. |
Seasonality | Do summer and winter rate periods, June 1 through October 31 versus the remainder of the year, change the value of production? | Seasonal rate differences can reshape monthly savings patterns and reserve assumptions. |
Lease and reimbursement treatment | Who bears the utility cost and who receives the credit under each lease? | The same physical system can improve NOI, tenant economics or neither, depending on contract language. |
NOI translation | After tariff treatment, allocations and contract language, what net change reaches the operating statement? | Only the net figure supports expense-ratio, debt-service coverage and cap-rate analysis. |
Model the margin, not the kilowatt-hours
The financial chain runs directly from rate design to valuation: tariff components and export treatment shape the monthly cost profile; consumption offset, demand management and credit allocation determine what actually changes on the bill; the verified net change flows to operating expenses and expense ratio; that change supports NOI, debt-service coverage and, with supportable assumptions, a cap-rate effect. Skipping the tariff step and modeling gross production as if it were income breaks the chain at its first link.
Rate design, like service capacity and metering topology, is part of the property-side underwriting package. Rooftops Into Revenue™ treats it that way: read the tariff, verify the intervals, confirm the allocations, and only then underwrite the margin the account structure can actually deliver.
Save On Solar Now is a national energy infrastructure firm helping multifamily and commercial property owners convert utility expense into structured revenue. Through Rooftops Into Revenue™ and Utility Expense Repositioning strategies, we design and deploy solar generation and battery storage systems to strengthen asset performance and long-term operating stability.
Phone: (858) 400-3524
Web: saveonsolarnow.com
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