PV-Plus-Storage Solicitation Language for Availability…

Key Takeaways

• Specify the requirement when bids include PV-plus-storage dispatch results, not just PV nameplate capacity.
• Ask bidders to state the software, battery model, dispatch method, and availability-loss treatment.
• SAM documents that PV Battery dispatch is affected by system availability losses, while PVWatts Battery and some other battery models ignore them.
• Require bidders to distinguish constant, time-series, and custom-period availability losses when they are used.
• Do not turn this into a country-specific purchasing rule unless local law or tender documents separately require it.
• For non-SAM tools, the treatment is unknown from the supplied sources, so require disclosure instead of assuming equivalence.

Summary

PV-plus-storage solicitations should specify whether system-availability losses affect battery dispatch whenever bidders are asked to submit a performance model with battery dispatch results. In SAM, system availability represents output reductions from maintenance downtime, grid outages, or other operating factors that prevent the system from operating as designed; SAM notes that PV Battery dispatch is affected by system availability losses, while PVWatts Battery, Custom Generation Profile - Battery, and Standalone Battery dispatch ignore them SAM PVWatts System Design. That difference can make submitted models less comparable unless the solicitation tells bidders how to document or normalize the assumption.

Which Solicitations Should Include the Requirement

The requirement is most useful for solicitations that ask for PV-plus-storage energy simulations, dispatch schedules, bill-savings analysis, peak-shaving analysis, outage modeling, or battery-size optimization. The reason is narrow but important: the same source describes availability losses as reductions in system output caused by operating requirements such as maintenance downtime or other situations that prevent normal operation, and it separately states that battery dispatch is affected in the PV Battery model but ignored in several other battery model types SAM PVWatts System Design.

It should also be included when the buyer allows either detailed PV Battery modeling or PVWatts Battery modeling. SAM says the PVWatts Battery model is a simplified version of the detailed model, and for PV Battery the battery dispatch is affected by system availability losses, while for PVWatts Battery it is ignored SAM PVWatts System Design. A procurement team should therefore ask bidders to name the model used and state whether availability losses were applied before or after dispatch, or whether dispatch ignored those losses.

The clause is especially relevant when submitted results include hourly or time-step outputs. SAM’s Edit Losses guidance states that constant losses apply to all simulation time steps and time-series losses apply to specific time steps SAM Edit Losses. If one bidder models downtime as time-series availability loss and another uses a model where dispatch ignores that loss, the buyer may not be comparing the same dispatch logic.

What the Solicitation Should Ask Bidders to Declare

A practical solicitation should ask each bidder to disclose the performance model, battery model, dispatch option, availability-loss method, and whether the dispatch calculation itself was affected by the availability-loss input. This is a recommendation, not a claim that every software tool behaves like SAM. The supported point is that SAM documents different behavior by model type: PV Battery dispatch is affected by system availability losses, while PVWatts Battery, Custom Generation Profile - Battery, and Standalone Battery dispatch ignore them SAM PVWatts System Design.

The solicitation can also ask bidders to identify whether availability losses are constant, time-series, or custom-period losses. SAM’s Edit Losses window allows constant losses, time-series losses, and custom-period losses; it also states that all losses applying to a given time step are applied SAM Edit Losses. That matters because a modeled outage, maintenance period, or grid-related operating limit can be represented differently across bids.

If the solicitation uses REopt-linked sizing or dispatch inside SAM, the buyer should require bidders to disclose that workflow. SAM says Optimal Sizing and Dispatch from REopt can automatically size the battery bank and calculate hour-by-hour dispatch for PV behind-the-meter systems with battery storage, and that it is available for PV - Battery or PVWatts - Battery under stated requirements including hourly simulation time step SAM PVWatts System Design. The source does not establish how every external optimization tool treats availability losses, so that treatment should be declared rather than assumed.

Model Comparability Risk

The core risk is not that one model is always right and another is always wrong. The risk is that two compliant-looking submissions may use different loss-dispatch relationships. SAM defines system availability losses as reductions in output caused by maintenance downtime, grid outages, and other operating factors SAM PVWatts System Design. SAM also documents that some battery dispatch workflows are affected by those losses and others ignore them SAM PVWatts System Design. A solicitation that does not ask for this disclosure may leave reviewers unable to identify whether differences in modeled battery behavior come from equipment, dispatch strategy, or modeling convention.

This requirement should not be written as a United States-only purchasing rule. The cited SAM documentation describes model inputs and behavior; it does not say that only U.S. buyers should use them, and it does not establish legal purchasing obligations for any country. For international B2B procurement, the safer framing is technical: require transparent modeling assumptions wherever the submitted model includes PV-plus-storage dispatch.

Suggested Bid Language

Recommended language: “For each PV-plus-storage simulation, bidder shall identify the software and battery model used, the battery dispatch method, the system-availability loss input, whether availability losses affect battery dispatch in that model, and whether losses are constant, time-series, or custom-period. If the selected model ignores availability losses for dispatch, bidder shall state that condition in the modeling notes.”

This clause is supported by SAM’s documented distinction between PV Battery and PVWatts Battery dispatch behavior, and by SAM’s loss-input options for constant and time-specific losses SAM PVWatts System Design, SAM Edit Losses. It does not require bidders to use a specific product, country rule, price, certification, or savings estimate; it only requires them to make the dispatch-loss assumption reviewable.

FAQ

Which solicitations should include this requirement?

Any PV-plus-storage solicitation that asks bidders to submit battery dispatch, hourly simulation outputs, bill-savings analysis, peak-shaving analysis, outage modeling, or battery optimization results.

Why does this matter in SAM?

SAM states that PV Battery dispatch is affected by system availability losses, while PVWatts Battery, Custom Generation Profile - Battery, and Standalone Battery dispatch ignore those losses.

What are system-availability losses?

SAM describes them as output reductions caused by maintenance downtime, grid outages, and other operational factors that prevent the system from operating as designed.

Should the buyer require a specific model?

The supplied sources do not support requiring one model. A safer recommendation is to require clear disclosure of the model and loss-dispatch treatment.

Do constant and time-series losses need to be separated?

Yes. SAM supports constant losses, time-series losses, and custom-period losses, and applies all losses that apply to a given time step.

Does this apply only to U.S. projects?

No country-specific purchasing rule is supported by the supplied sources. The requirement should be framed as a technical modeling-disclosure requirement.

What if the bidder uses software other than SAM?

The supplied sources do not prove how other tools treat availability losses. The solicitation should require the bidder to disclose the treatment used by that tool.

Should REopt-linked submissions disclose this too?

Yes. SAM describes REopt-linked battery sizing and hour-by-hour dispatch for eligible PV Battery or PVWatts Battery workflows, so the workflow and assumptions should be declared.