SAM Economic Models

GEOPHIRES SAM Economic Models leverage NREL’s SAM Financial Models by transforming GEOPHIRES parameters into SAM parameters and running the corresponding SAM model with PySAM.

SAM Single Owner PPA

Corresponding SAM Financial Model: Power Purchase Agreement (PPA): Single owner

Parameters

The following table describes how GEOPHIRES parameters are transformed into SAM parameters, as implemented in EconomicsSam.py. (Note that the source code implementation determines actual behavior in the case of any discrepancies.)

GEOPHIRES Parameter(s)	SAM Category	SAM Input(s)	SAM Module(s)	SAM Parameter Name(s)	Comment
Maximum Total Electricity Generation	Generation Profile	Nameplate capacity	Singleowner	system_capacity
Utilization Factor	Generation Profile	Nominal capacity factor	Singleowner	user_capacity_factor
Net Electricity Generation	AC Degradation	Annual AC degradation rate schedule	Utilityrate5	degradation	Percentage difference of each year’s Net Electricity Generation from Maximum Total Electricity Generation is input as SAM as the degradation rate schedule in order to match SAM’s generation profile to GEOPHIRES
{Total CAPEX before inflation} × (1 + Accrued financing during construction (%)/100);	Installation Costs	Total Installed Cost	Singleowner	total_installed_cost	Accrued financing during construction (%) = (1+Inflation Rate During Construction) × 100 if Inflation Rate During Construction is provided or ((1+Inflation Rate) ^ Construction Years) × 100 if not.
Total O&M Cost, Inflation Rate	Operating Costs	Fixed operating cost, Escalation rate set to Inflation Rate × -1	Singleowner	om_fixed, om_fixed_escal
Royalty Rate, Royalty Rate Escalation, Royalty Rate Maximum	Operating Costs	Variable operating cost	Singleowner	om_production	The royalty is modeled as a tax-deductible variable operating expense. GEOPHIRES calculates a schedule of $/MWh values based on the PPA price and Royalty Rate for each year, with optional escalation and cap (maximum). This ensures the total annual expense in SAM accurately matches the royalty payment due on gross revenue.
Plant Lifetime	Financial Parameters → Analysis Parameters	Analysis period	CustomGeneration, Singleowner	CustomGeneration.analysis_period, Singleowner.term_tenor
Inflation Rate	Financial Parameters → Analysis Parameters	Inflation rate	Utilityrate5	inflation_rate
Discount Rate	Financial Parameters → Analysis Parameters	Real discount rate	Singleowner	real_discount_rate
Combined Income Tax Rate	Financial Parameters → Project Tax and Insurance Rates	Federal income tax rate: minimum of {21%, CITR}; and State income tax rate: maximum of {0%; CITR - 21%}	Singleowner	federal_tax_rate, state_tax_rate	GEOPHIRES does not have separate parameters for federal and state income tax so the rates are split from the combined rate based on an assumption of a maximum federal tax rate of 21% and the residual amount being the state tax rate.
Property Tax Rate	Financial Parameters	Property tax rate	Singleowner	property_tax_rate
Fraction of Investment in Bonds	Financial Parameters → Project Term Debt	Debt percent	Singleowner	debt_percent
Inflated Bond Interest Rate	Financial Parameters → Project Term Debt	Annual interest rate	Singleowner	term_int_rate
Starting Electricity Sale Price, Ending Electricity Sale Price, Electricity Escalation Rate Per Year, Electricity Escalation Start Year	Revenue	PPA price	Singleowner	ppa_price_input	GEOPHIRES’s pricing model is used to create a PPA price schedule that is passed to SAM.
Total AddOn Profit Gained	Revenue → Capacity Payments	Fixed amount, Capacity payment amount	Singleowner	cp_capacity_payment_type = 1, cp_capacity_payment_amount
Investment Tax Credit Rate	Incentives → Investment Tax Credit (ITC)	Federal → Percentage (%)	Singleowner	itc_fed_percent	Note that unlike the BICYCLE Economic Model’s Total capital costs, SAM Economic Model’s Total CAPEX is the total installed cost and does not subtract ITC value (if present).
Production Tax Credit Electricity	Incentives → Production Tax Credit (PTC)	Federal → Amount ($/kWh)	Singleowner	ptc_fed_amount
Production Tax Credit Duration	Incentives → Production Tax Credit (PTC)	Federal → Term (years)	Singleowner	ptc_fed_term
Production Tax Credit Inflation Adjusted, Inflation Rate	Incentives → Production Tax Credit (PTC)	Federal → Escalation (%/yr)	Singleowner	ptc_fed_escal	If Production Tax Credit Inflation Adjusted = True, GEOPHIRES set’s SAM’s PTC escalation rate to the inflation rate. SAM applies the escalation rate to years 2 and later of the project cash flow. Note that this produces escalation rates that are similar to inflation-adjusted equivalents, but not exactly equal.
Other Incentives + One-time Grants Etc	Incentives → Investment Based Incentive (IBI)	Other → Amount ($)	Singleowner	ibi_oth_amount

Limitations

1. Only Electricity end-use is supported

2. Only 1 construction year is supported. Note that the Inflation Rate During Construction parameter can be used to partially account for longer construction periods.

3. Add-ons with electricity and heat are not currently supported. (Add-ons CAPEX, OPEX, and profit are supported.)

Using SAM Economic Models with Existing GEOPHIRES Inputs

In many cases, all you need to do to use SAM Economic Models for your existing GEOPHIRES inputs is to change the Economic Model parameter value. For example, if your GEOPHIRES .txt file contained the following:

# *** Financial Parameters ***
Economic Model, 2, -- Standard Levelized Cost Model
Discount Rate, .05
Plant Lifetime, 25

You would change it to:

# *** Financial Parameters ***
Economic Model, 5, -- SAM Single Owner PPA Economic Model
Discount Rate, .05
Plant Lifetime, 25

For inputs with the BICYCLE economic model, such as the following:

# *** Financial Parameters ***
Economic Model, 3, -- BICYCLE
Inflated Equity Interest Rate, .08
Plant Lifetime, 30

Change Economic Model and replace Inflated Equity Interest Rate with a suitable Discount Rate and Inflation Rate:

# *** Financial Parameters ***
Economic Model, 5, -- SAM Single Owner PPA Economic Model
Discount Rate, .08
Inflation Rate, .03
Plant Lifetime, 30

Re-creating SAM Economic Model Results in the SAM Desktop Application

First, open src/geophires_sam_economics/Generic_400_MWe.sam in the SAM desktop application.

Next, run GEOPHIRES for your input, e.g.:

python -mgeophires_x my-geophires-input.txt

Then check src/geophires_x/all_messages_conf.log for the SAM Economics Parameter Mapping entry:

23-05-2025 10:09:35 : INFO : EconomicsSam : calculate_sam_economics : 151 : (Process Details : (1378, MainProcess), Thread Details : (8589068352, MainThread)): SAM Economics Parameter Mapping:
-----------------  --------------------  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
SAM Module         Parameter             Value
Custom Generation  analysis_period       20
Custom Generation  user_capacity_factor  90.0
Utility Rate       inflation_rate        2.0
Utility Rate       degradation           [1.2734946600673935, 0.7001040275842613, 0.5267634676194525, 0.4244824247238818, 0.3529717582311231, 0.29852256883429373, 0.2548483024454293, 0.21855974702202877, 0.18762922644042462, 0.1607514026827296, 0.13703877682895466, 0.11586181507372084, 0.09675857340703789, 0.07938054662917803, 0.06345865490418974, 0.0487810281945756, 0.03517801101748528, 0.02251175220012943, 0.010668799824934945, 0.0]
Single Owner       analysis_period       20
Single Owner       total_installed_cost  264606243.76608825
Single Owner       om_fixed              [7193902.821741002]
Single Owner       om_fixed_escal        -2.0
Single Owner       system_capacity       59020.69007804236
Single Owner       federal_tax_rate      [21.0]
Single Owner       state_tax_rate        [7.0]
Single Owner       itc_fed_percent       [30.0]
Single Owner       property_tax_rate     0.0
Single Owner       ppa_price_input       [0.08, 0.08, 0.08322, 0.08644, 0.08966, 0.09288, 0.0961, 0.09932, 0.10254, 0.10576, 0.10898000000000001, 0.1122, 0.11542, 0.11864, 0.12186, 0.12508, 0.1283, 0.13152, 0.13474, 0.13796]
Single Owner       debt_percent          40.0
Single Owner       real_discount_rate    8.0
Single Owner       term_tenor            20
Single Owner       term_int_rate         5.0
Single Owner       ibi_oth_amount        0.0
-----------------  --------------------  -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

You can then manually enter the parameters from the logged mapping into the SAM desktop app.

Add-Ons

SAM Economic Models incorporate add-ons directly, unlike other GEOPHIRES economic models, which calculate separate extended economics. Total Add-on CAPEX is added to Total CAPEX. Total Add-on OPEX is added to Total operating and maintenance costs. Total AddOn Profit Gained per year is treated as fixed amount Capacity payment revenue.

Add-ons CAPEX, OPEX, and profit are supported. Add-ons with electricity and heat are not currently supported, but may be supported in the future.

Add-Ons example web interface link

Royalties

SAM Economic Models can model a royalty agreement where a percentage of the project’s gross revenue is paid to a third party (the “royalty holder”). This feature is enabled by providing the Royalty Rate parameter.

The royalty payment is modeled as a tax-deductible variable operating expense from the perspective of the project developer (Single Owner). This reduces the developer’s taxable income and ensures their final after-tax metrics (NPV, IRR, etc.) are calculated accurately.

This is implemented by having GEOPHIRES create a year-by-year schedule for SAM’s Variable operating cost ( om_production) input. The value for each year is calculated based on that year’s PPA price and the user-provided Royalty Rate, ensuring the expense in SAM matches the royalty due on gross revenue.

Input Parameters:

1. Royalty Rate: The percentage of the project’s gross annual revenue paid to the royalty holder. It can be optionally escalated by providing Royalty Rate Escalation and capped with Royalty Rate Maximum.

2. Royalty Holder Discount Rate (optional): The discount rate used to calculate the Net Present Value (NPV) of the royalty holder’s income stream. This is separate from the project’s main discount rate to reflect the different risk profiles of the two parties.

Output Parameters:

1. Average Annual Royalty Cost: The developer’s average annual royalty expense over the project’s lifetime after construction is complete (Year 1). The same value is also output as Royalty Holder Average Annual Revenue. The individual royalties for each year are included in the cash flow line item O&M production-based expense ($).

2. Royalty Holder Total Revenue: The total gross (pre-tax), undiscounted royalty income over the project’s lifetime.

3. Royalty Holder NPV: The pre-tax Net Present Value of the royalty holder’s income stream, calculated using the Royalty Holder Discount Rate. This is a pre-tax value because the model does not account for the royalty holder’s specific tax liabilities.

Royalties example web interface link

Examples

Case Study: 500 MWe EGS Project Modeled on Fervo Cape Station

Web interface link

See Case Study: 500 MWe EGS Project Modeled on Fervo Cape Station.

SAM Single Owner PPA: 50 MWe

1. SAM Single Owner PPA: 50 MWe

2. SAM Single Owner PPA: 50 MWe with Add-ons

3. SAM Single Owner PPA: 50 MWe with Royalties

SAM Single Owner PPA: 400 MWe BICYCLE Comparison

Web interface link