Hybrid Renewable Models
Executive Summary
Key Takeaways
- ✓ A hybrid renewable project combines two or more generation and storage technologies at a shared site, most commonly solar or wind paired with battery storage, typically sharing interconnection infrastructure.
- ✓ The shared interconnection capacity constraint should be modelled explicitly, since combined output from multiple technologies can exceed available grid connection capacity, forcing curtailment decisions the model must represent.
- ✓ Shared costs (interconnection, land, common balance-of-plant infrastructure) should be allocated between the constituent technologies on an explicit, documented basis, not left unallocated or assigned arbitrarily.
- ✓ Storage co-located with generation is frequently charged from otherwise-curtailed generation output, and this internal charging path should be modelled distinctly from grid-charging, since it has no separate marginal energy cost.
- ✓ Whether the project has a single combined offtake agreement or separate agreements for each technology materially affects revenue modelling and should be represented according to the project's actual contractual structure.
Objective¶
This guide covers the modelling mechanics specific to hybrid renewable projects, within Energy Financial Modelling, building on the single-technology treatments in Solar PV Financial Models, Wind Farm Financial Models, and Battery Energy Storage Models.
Shared Interconnection Capacity Constraint¶
A hybrid project's constituent technologies typically share a single grid interconnection point with a defined capacity limit. Combined instantaneous output from generation and storage discharge can exceed this limit, particularly during periods of peak generation, requiring curtailment of one or more technologies. The model should represent this constraint explicitly — testing combined output against the interconnection capacity for each modelled period and applying curtailment where the limit is exceeded — rather than assuming each technology's full theoretical output is always deliverable.
Cost Allocation Between Technologies¶
Shared infrastructure — interconnection capacity, land, and common balance-of-plant equipment — benefits multiple technologies at the site, and its cost should be allocated between them on an explicit, documented basis (such as relative capacity share or relative capital cost contribution). Leaving shared costs unallocated, or assigning them arbitrarily, distorts each technology's standalone project economics if the model is later used to evaluate one technology's contribution separately, for example in a financing structure that treats the generation and storage components differently.
Charging Storage from Co-Located Generation¶
Battery storage co-located with generation is frequently charged using otherwise-curtailed generation output — energy that would have been curtailed due to the interconnection constraint or an oversupply relative to demand — rather than purchased from the grid. This internally sourced charging energy has no separate marginal energy cost, unlike grid-charged energy, which carries the market purchase price at the time of charging. The model should distinguish these two charging sources explicitly, since conflating them overstates the effective cost of charging the storage component.
Combined vs. Separate Offtake Structures¶
Some hybrid projects sell their combined output under a single offtake agreement covering the blended generation-plus-storage profile; others maintain separate offtake agreements for each technology, each with its own pricing and volume terms. The model should represent the project's actual contractual structure — a single blended revenue calculation for a combined offtake, or separate revenue calculations reconciled to a combined total for separate offtakes — rather than assuming one structure applies by default.
Common Construction Pitfalls¶
Interconnection constraint ignored. Modelling each technology's full theoretical output as always deliverable to the grid, without testing against the shared interconnection capacity limit, overstates achievable combined revenue.
Shared costs left unallocated. Failing to allocate shared infrastructure cost between technologies distorts each technology's standalone economics if evaluated separately.
Internal charging costed at market price. Applying the grid market purchase price to storage charging energy that was actually sourced from otherwise-curtailed co-located generation overstates the cost of that charging.
Recommended Practices¶
- Test combined technology output against the site's actual interconnection capacity limit for each modelled period, applying curtailment where exceeded.
- Allocate shared infrastructure cost between constituent technologies on an explicit, documented basis.
- Distinguish internally sourced (curtailed generation) charging energy from grid-purchased charging energy in the storage cost build.
- Model the project's actual offtake structure — combined or separate — rather than assuming a default structure.
Continue Reading¶
Related Pillars¶
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Frequently Asked Questions
What is a hybrid renewable project?
A project combining two or more generation and storage technologies at a shared site — most commonly solar or wind generation paired with battery storage — typically to share interconnection infrastructure, smooth combined output, and improve overall revenue certainty relative to a single-technology project.
Why does the shared interconnection constraint matter for the model?
Because combined instantaneous output from multiple co-located technologies can exceed the site's available grid interconnection capacity, requiring curtailment of one or more technologies at certain times — the model should represent this constraint explicitly rather than assuming each technology's full theoretical output is always deliverable to the grid.
How should shared costs be allocated between technologies?
On an explicit, documented basis reflecting each technology's share of the shared infrastructure (interconnection capacity, land, common balance-of-plant equipment), rather than left unallocated or assigned arbitrarily, since cost allocation directly affects each technology's standalone project economics if evaluated separately.
How should storage charged from co-located generation be modelled?
Distinctly from grid-charging, since energy used to charge storage from otherwise-curtailed co-located generation output has no separate marginal energy cost, whereas grid-charged energy carries the market purchase price — conflating the two overstates the cost of storage charging.
Does a hybrid project always have a single combined offtake agreement?
No — some hybrid projects have a single combined offtake agreement covering the blended output of all technologies, while others maintain separate agreements per technology, and the model should reflect the project's actual contractual structure rather than assuming one approach by default.
References
Related Articles
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