Transmission and Grid Models
Executive Summary
Key Takeaways
- ✓ Interconnection capital cost — connecting the project to the nearest suitable point on the grid — should be modelled explicitly and attributed to the specific project, not blended into general balance-of-plant capital cost.
- ✓ Transmission losses, the reduction in energy between the point of generation and the point of sale or metering, should be modelled as an explicit percentage reduction applied to gross output, sourced from the specific interconnection distance and voltage level.
- ✓ Grid connection queue risk — delay or reordering in an interconnection process managing many competing connection requests — should be assessed and, where material, reflected in the project's development timeline and cost assumptions.
- ✓ Network upgrade cost responsibility, where a project is required to fund upgrades to shared network infrastructure beyond its own direct connection, should be modelled explicitly where applicable, since this can be a material and sometimes uncertain cost component.
- ✓ Interconnection agreements frequently include their own curtailment, availability, or capacity provisions distinct from the project's PPA or capacity contract, and these should be reconciled rather than assumed to be the same instrument.
Objective¶
This guide covers the transmission and grid interconnection mechanics specific to power project financial models, within Energy Financial Modelling, building on Power Project Financial Model Structure.
Interconnection Capital Cost¶
Connecting a power project to the nearest suitable point on the electricity grid is a distinct, often substantial capital cost that should be modelled explicitly and attributed to the specific project, rather than folded into general balance-of-plant capital cost. Keeping this cost visible as its own line lets a reviewer assess it against the project's specific location and grid proximity, rather than obscuring it within an aggregate capital cost figure.
Transmission Losses¶
Energy is reduced between the point of generation and the point of sale or metering due to resistance in the transmission and distribution network. This should be modelled as an explicit percentage reduction applied to gross generated output, sourced from the specific interconnection distance and voltage level for the project — a longer interconnection at a lower voltage typically carries higher losses than a shorter, higher-voltage connection — rather than ignored or assumed to be zero, which would overstate net saleable output.
Grid Connection Queue Risk¶
In markets experiencing high renewable development activity, interconnection processes frequently manage a queue of many competing connection requests for limited available grid capacity, creating risk of delay or reordering in when a specific project's connection is actually completed. Where this risk is material for the project's specific market and location, it should be reflected explicitly in the development timeline and any associated holding or delay cost assumptions, rather than assumed away with a fixed, certain connection date.
Network Upgrade Cost Responsibility¶
Some interconnection frameworks require a connecting project to fund upgrades to shared network infrastructure beyond its own direct connection point, where the existing network lacks capacity to accommodate the new connection. Where this responsibility applies, it can represent a material — and sometimes initially uncertain, pending a formal network study — cost component, and should be modelled explicitly with appropriate contingency, rather than assumed to be limited to the project's own direct connection cost alone.
Reconciling Interconnection Agreement Terms with PPA/Capacity Terms¶
Interconnection agreements frequently include their own curtailment, availability, or capacity-related provisions — for example, a curtailment right the grid operator holds directly under the interconnection agreement, distinct from any curtailment provisions in the project's separate PPA. These should be reconciled explicitly in the model, since assuming the interconnection agreement and the offtake or capacity contract are a single unified instrument with identical terms can miss a genuine, separate source of curtailment or availability risk.
Common Construction Pitfalls¶
Interconnection cost blended into general capital cost. Folding interconnection capital cost into an aggregate balance-of-plant figure obscures its magnitude and specific cost driver.
Transmission losses ignored. Assuming zero transmission loss between generation and the point of sale overstates net saleable output.
Network upgrade cost omitted. Failing to model a network upgrade cost responsibility, where it applies, understates total project capital cost, sometimes materially.
Recommended Practices¶
- Model interconnection capital cost as its own explicit, project-specific line.
- Apply a transmission loss percentage sourced from the project's actual interconnection distance and voltage level.
- Reflect grid connection queue risk explicitly in the development timeline where material to the project's market.
- Model network upgrade cost responsibility explicitly where the applicable interconnection framework imposes it.
- Reconcile interconnection agreement provisions with the project's separate PPA or capacity contract terms.
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Frequently Asked Questions
What is interconnection capital cost, and how should it be modelled?
The capital cost of physically connecting the project to the nearest suitable point on the electricity grid, which should be modelled explicitly and attributed to the specific project as its own capital cost line, rather than blended into general balance-of-plant capital cost where its magnitude and cost driver would no longer be separately visible.
What are transmission losses, and why do they matter?
The reduction in energy between the point of generation and the point of sale or metering, arising from resistance in the transmission and distribution network — this should be modelled as an explicit percentage reduction applied to gross generated output, sourced from the specific interconnection distance and voltage level, rather than ignored or assumed to be zero.
What is grid connection queue risk?
The risk of delay or reordering in an interconnection process that manages many competing connection requests for limited available grid capacity, common in markets experiencing high renewable development activity — where material, this risk should be reflected explicitly in the project's development timeline and any associated holding or delay cost assumptions.
What does network upgrade cost responsibility mean?
Some interconnection frameworks require a connecting project to fund upgrades to shared network infrastructure beyond its own direct connection point, where the existing network lacks capacity to accommodate the new connection — where this responsibility applies, it can represent a material and sometimes uncertain cost component that should be modelled explicitly rather than assumed to be limited to the project's own direct connection cost.
Are interconnection agreement provisions the same as PPA or capacity contract provisions?
Not necessarily — interconnection agreements frequently include their own curtailment, availability, or capacity-related provisions (for example, a curtailment right the grid operator holds under the interconnection agreement itself) that are distinct from, and should be reconciled with, the project's separate PPA or capacity contract terms, rather than assumed to be a single unified instrument.
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