Grid Performance and Cost Models

This page documents the unified GridPerformanceModel and GridCostModel models, which together represent a flexible, configurable grid interconnection point within an H2I simulation. These components support both power flows and cost accounting for buying and selling electricity through a constrained interconnection. This is a single model that can be configured to either sell electricity to the grid, buy electricity from the grid, or both.

See example/24_solar_battery_grid to see how to set up both buying and selling grid components.

Grid Performance

GridPerformanceModel represents a grid interconnection point that can buy or sell electricity subject to a maximum throughput rating (interconnection_size).

It supports:

• Buying electricity from the grid to meet downstream demand.

• Selling electricity to the grid.

• Enforcing maximum allowed interconnection power.

• Computing unmet demand and unsold electricity due to constraints.

Note

Multiple grid instances may be used within the same plant to represent different interconnection nodes. For buying electricity from the grid, the technology name in the tech_config must start with grid_buy for the logic to work appropriately in financial calculations.

Inputs

Name	Shape	Units	Description
interconnection_size	scalar	kW	Maximum power capacity for grid connection.
electricity_in	array[n_timesteps]	kW	Electricity flowing into the grid (selling to grid).
electricity_set_point	array[n_timesteps]	kW	Electricity set point from downstream technologies.

Outputs

Name	Shape	Units	Description
electricity_out	array[n_timesteps]	kW	Electricity flowing out of the grid (buying).
electricity_sold	array[n_timesteps]	kW	Electricity successfully sold to the grid.
electricity_unmet_demand	array[n_timesteps]	kW	Downstream technology demand not met due to interconnection limits.
electricity_excess	array[n_timesteps]	kW	Electricity that could not be sold due to limits.

Grid Cost

GridCostModel computes all costs and revenues associated with the grid interconnection, including:

• Capital cost based on interconnection rating.

• Fixed annual O&M.

• Variable cost of electricity purchased.

• Revenue from electricity sold.

Inputs

Name	Shape	Units	Description
interconnection_size	scalar	kW	Interconnection capacity for cost calculation.
interconnection_capex_per_kw	scalar	$/kW	Capital cost per kW of interconnection.
interconnection_opex_per_kw	scalar	$/kW/year	Annual O&M cost per kW of interconnection.
fixed_interconnection_cost	scalar	$	One-time fixed cost regardless of size.
electricity_buy_price	scalar or array	$/kWh	Price to buy electricity from grid (optional). Shape is n_timesteps when buy_price_mode is per_timestep, or plant_life when per_year.
buy_price_mode	string	—	"per_timestep" or "per_year". Controls the buy price input shape and cost calculation.
electricity_out	array[n_timesteps]	kW	Electricity flowing out of grid (buying). Present when buy_price_mode is per_timestep (or buy price is not set).
annual_electricity_out	array[plant_life]	kWh/yr	Annual electricity bought from grid. Present when buy_price_mode is per_year.
electricity_sell_price	scalar or array	$/kWh	Price to sell electricity to grid (optional). Shape is n_timesteps when sell_price_mode is per_timestep, or plant_life when per_year.
sell_price_mode	string	—	"per_timestep" or "per_year". Controls the sell price input shape and cost calculation.
electricity_sold	array[n_timesteps]	kW	Electricity flowing into grid (selling). Present when sell_price_mode is per_timestep (or sell price is not set).
annual_electricity_sold	array[plant_life]	kWh/yr	Annual electricity sold to grid. Present when sell_price_mode is per_year.

Outputs

Name	Description
CapEx	Total capital expenditure.
OpEx	Annual O&M cost.
VarOpEx	Variable operating expenses (buying), revenues (selling), or net of expenses and revenues (buying and selling).

The costs of purchasing electricity from the grid are represented as a variable operating expense (VarOpEx) and are represented as a positive value. This allows it to be tracked as an expense in the financial models.

The revenue of selling electricity to the grid is represented as a variable operating expense (VarOpEx) and a represented as a negative value. This is allows it to be tracked as a coproduct in the financial models.

Note

If you're using a price-maker financial model (e.g., calculating the LCOE) and selling all of the electricity to the grid, then the electricity_sell_price should most likely be set to 0. since you want to know the breakeven price of selling that electricity.

Note

The grid components are currently compatible with 5-minute (300-second) to 1-hour (3600-second) time steps.

Price Input Modes

The pricing mode is controlled explicitly via buy_price_mode and sell_price_mode in the grid cost configuration. Each can be set to:

• per_timestep (default): The price is a scalar or an array of length n_timesteps. The cost model uses the timestep-level electricity_out / electricity_sold inputs (in kW) and converts to energy using dt. The resulting VarOpEx is a single value applied uniformly across all years.

• per_year: The price is an array of length plant_life. The cost model uses annual_electricity_out / annual_electricity_sold inputs (in kWh/yr, shape plant_life) directly, producing a per-year VarOpEx array with no dt conversion needed in the cost model.

• constant: The price is a single scalar value applied uniformly to all timesteps. Behaves like per_timestep with a scalar price but makes the intent explicit in the configuration.

Example YAML configuration for per-year pricing:

cost_parameters:
  electricity_buy_price: [0.05, 0.06, 0.07, ...]  # length = plant_life
  buy_price_mode: per_year
  electricity_sell_price: [0.03, 0.04, 0.05, ...]  # length = plant_life
  sell_price_mode: per_year

Example YAML configuration for constant pricing:

cost_parameters:
  electricity_buy_price: 0.10
  buy_price_mode: constant
  electricity_sell_price: 0.05
  sell_price_mode: constant