Tower System Costs

To view the Tower System Costs page, click Tower System Costs on the main window's navigation menu. Note that for the power tower input pages to be available, the technology option in the Technology and Market window must be Concentrating Solar Power - Power Tower System.

Solar Advisor uses the variables on the Tower System Costs page to calculate the project investment cost and annual operating costs reported in the project cash flow and used to calculate cost metrics reported in the Metrics table.

Because only the Total Installed Cost value affects the cash flow calculations, you can assign capital costs to the different cost categories in whatever way makes sense for your analysis. For example, you could assign the cost of designing the solar field to the solar field cost category or to the engineer-procure-construct category with equivalent results. The categories are provided to help you keep track of the different costs, but do not affect the economic calculations. After assigning costs to the categories, verify that the total installed costs value is what you expect.

Variable values in boxes with white backgrounds are values that you can edit. Boxes with blue backgrounds contain calculated values or values from other pages that Solar Advisor displays for your information.

Note: The cost values in the sample files are intended to illustrate Solar Advisor's use. The cost data are meant to be realistic, but not to represent actual costs for a specific project. Actual costs will vary depending on the market, technology and geographic location of a project. Because of price volatility in solar markets, the cost data in the sample files is likely to be out of date. For more information see the Solar Advisor Model website, https://www.nrel.gov/analysis/sam/cost_data.html.

Contents

►	Input Variable Reference describes the input variables on the Tower System Costs page.

►	Entering Periodic Operation and Maintenance Costs explains how to use annual schedules to assign operation and maintenance costs to particular years in the project cash flow.

Input Variable Reference

Direct Capital Costs

A direct capital cost represents an expense for a specific piece of equipment or installation service that applies in year zero of the cash flow.

Note: Because Solar Advisor uses only the Total Installed Cost value in cash flow calculations, how you distribute costs among the different direct capital cost categories does not affect the final results.

Variable	Description	Units
Site Improvements	A cost per square meter of total reflective area from the Heliostat Field page to account for expenses related to site preparation and other equipment not included in the heliostat field cost category.	$/m2
Heliostat Field	A cost per square meter of total reflective area from the Heliostat Field page to account for expenses related to installation of the heliostats, including heliostat parts, field wiring, drives, labor, and equipment.	$/m2
Balance of Plant	A cost per electric kilowatt of power cycle nameplate capacity from the Power Cycle page expenses related to installation of the balance-of-plant components and controls, and construction of buildings, including labor and equipment.	$/kWe
Power Block	A cost per electric kilowatt of power cycle nameplate capacity from the Power Cycle page expenses related to installation of the power block components, including labor and equipment. The Power Block and Balance of Plant costs are rolled together into a single number for calculation purposes.	$/kWe
Storage System	Cost per thermal megawatt-hour of storage capacity from the Thermal Storage page to account for the installation of a thermal energy storage system, including equipment and labor.	$/kWht
Fixed Solar Field Cost	An additional fixed cost in dollars to include as a direct cost that is not accounted for by any of the above categories.	$
Fixed Tower Cost	A fixed cost to account for tower construction, materials and labor costs. The fixed tower cost serves as the multiplier in the tower cost scaling equation shown below.	$
Tower Cost Scaling Exponent	Solar Advisor uses the tower cost in the optimization calculations. The tower cost scaling exponent defines the nonlinear relationship between tower cost and tower height. See Total Tower Cost below.	--
Total Tower Cost	Total Tower Cost = Fixed Tower Costs x exp (Tower Height x Tower Cost Scaling Exponent)	$
Receiver Reference Cost	The cost per receiver reference area to account for receiver installation costs, including labor and equipment.	$
Receiver Reference Area	The receiver area on which the receiver reference cost is based.	m2
Receiver Cost Scaling Exponent	Solar Advisor uses the receiver cost in the optimization calculations. The receiver cost scaling exponent defines the nonlinear relationship between receiver cost and receiver area based on the reference cost conditions provided.	--
Total Receiver Cost	Receiver Cost = Receiver Reference Cost x (Receiver Area / Receiver Reference Area ) ^ Receiver Cost Scaling Exponent.	$
Contingency	A percentage of the sum of the site improvements, heliostat field, balance of plant, power block, storage system, fixed solar field, total tower, and total receiver costs to account for expected uncertainties in direct cost estimates.	%
Total Direct Cost	The sum of improvements, site improvements, heliostat field, balance of plant, power block, storage system, fixed solar field, total tower, total receiver, and contingency costs.	$

Indirect Capital Costs

An indirect cost is typically one that cannot be identified with a specific piece of equipment or installation service, and may include all other costs that are built into the price of the system, such as profit, overhead, and shipping costs. Depending on the purpose of your analysis, you may decide to distribute profit among the direct cost categories or include them as a single value in an indirect category.

Note: Because Solar Advisor uses only the total installed cost value in cash flow calculations, how you distribute costs among the different indirect capital cost categories does not affect the final results.

Variable	Description	Units
Engineer, Procure, Construct	Costs associated with design and construction of the project, calculated as the sum of a percentage of Total Direct Cost and a fixed cost.	% and $
Project, Land, Miscellaneous	Costs associated with profit, overhead (including marketing), permitting, or shipping, calculated as the sum of a percentage of Total Direct Cost and a fixed cost.	% and $
Sales Tax	Percentage of direct costs to which sales tax applies, calculated by multiplying Total Direct Cost by the sales tax rate from the Financials page and the percentage that you specify.	%
Total Indirect Cost	The sum of Engineer-Procure-Construct costs, Project-Land-Miscellaneous costs, and sales tax.	$

Total Installed Cost

The total installed cost is the project's investment cost that applies in year zero of the project cash flow. Solar Advisor uses this value to calculate loan amounts and debt interest payments based on inputs on the Financing page, and to calculate tax credit and incentive payment amounts for incentive based tax credits and incentives defined on the Tax Credit Incentives page and Payment Incentives pages.

Variable	Description	Units
Total Installed Cost	The sum of total direct cost and total indirect cost.	$
Total Installed Cost per Capacity	Total installed cost divided by the total system capacity in Watts-DC of array capacity for PV systems and electric kilowatts of power block nameplate capacity for CSP systems. This value is provided for reference only and not used in cash flow calculations.	$/Wdc or $/kW

Operation and Maintenance Costs

Operation and Maintenance (O&M) costs represent annual expenditures on equipment and services that occur after the system is installed. Solar Advisor allows you to enter O&M costs in three ways: Fixed annual, fixed by capacity, and variable by generation. O&M costs are reported on the project cash flow.

For each O&M cost category, you can specify an annual escalation rate to represent an expected annual increase in O&M cost above the annual inflation rate specified on the Financing page. For an escalation rate of zero, the O&M cost in years two and later is the year one cost adjusted for inflation. For a non-zero escalation rate, the O&M cost in years two and later is the year one cost adjusted for inflation plus escalation.

For expenses such as component replacements that occur in particular years, you can use an annual schedule to assign costs to individual years. See below for details.

O&M Cost Category	Description	Units
Fixed Annual Cost	A fixed annual cost applied to each year in the project cash flow.	$/yr
Fixed Cost by Capacity	A fixed annual cost proportional to the array capacity in DC kilowatts.	$/kWdc-yr
Variable Cost by Generation	A variable annual cost proportional to the system's total annual electrical output in AC megawatt-hours. The annual output depends on either the performance model's calculated first year value and the degradation rate specified on the Annual Performance page, or on an annual schedule of costs, depending on the option chosen.	$/MWh-yr
Fossil Fuel Cost	The cost per million British thermal units for fuel. Solar Advisor uses the conversion factor 1 MWh = 3.413 MMBtu. Applies only to the generic fossil, CSP trough, and CSP tower systems. The photovoltaic and CSP dish models ignore the fuel cost input variable. (When the fossil fill fraction variable on the Thermal Storage page for troughs or towers is greater than zero, the systems consume fuel for backup energy.)	$/MMBtu

Note. For information on water consumption and other operation and maintenance costs and requirements for concentrating parabolic trough systems, see the Troughnet website: http://www.nrel.gov/csp/troughnet/power_plant_systems.html. For information on operation and maintenance costs for photovoltaic systems, see the California Energy Commission's online Distributed Energy Resource guide http://www.energy.ca.gov/distgen/economics/operation.html.

Entering Periodic Operation and Maintenance Costs

Solar Advisor allows you to specify any of the four operation and maintenance cost categories as an annual schedule. An annual schedule makes it possible to assign a cost to particular years in the analysis period. Annual schedules can be used to account for inverter replacement costs and other periodic costs that do not recur on a regular annual basis.

After running simulations, you will see the periodic costs in the project cash flow, and they will be accounted for in the other results displayed in the Metrics table.

Note. Solar Advisor does not calculate any residual or salvage value remaining in inverters or other system components at the end of the analysis period.

To assign costs to particular years:

1.	In the Fixed Annual Cost category, note that the "Value" label is blue indicating that the single value mode is active for the variable.

2.	Click the button with the "Sched" label to change the mode to schedule and activate the Edit button.

3.	Click Edit.

4.	In the Edit Schedule window, use the horizontal scroll bar to find the first year in which a cost occurs, and type the cost in current or constant dollars for that year.

To delete a value, select it and press the Delete key on your keyboard.

Note. You must type a value for each year. If you delete a value, Solar Advisor will clear the cell, and you must type a number in the cell or Solar Advisor will consider the schedule to be invalid. Type a zero for years with no inverter replacement cost.

5.	When you have finished editing the schedule, click Accept.

Because you must specify an O&M cost category as either an annual cost or annual schedule, to assign both a recurring annual fixed cost and periodic replacement cost, you must type the recurring cost in each year of the annual schedule, and for years with replacement costs, type the sum of the recurring and replacement costs. Note that dollar values in the annual schedule are in nominal or current dollars. Inflation and escalation rates do not apply to values in annual schedules.