07 April 2011
Economic modeling of a solar system enables users to understand what the cost of a solar system will be in terms of its output. In today’s world of tight finance, it can mean the difference in funding and permitting or sending the project back to the drawing board. Many tools are available to generate performance data or cost analysis, but the Solar Advisor Model (SAM) is well known for doing both.
SAM was developed by the National Renewable Energy Laboratory (NREL) in collaboration with Sandia National Laboratories and in partnership with the US Department of Energy (DOE) Solar Energy Technologies Program (SETP). While the “S” in SAM originally stood for “solar,” it now stands for “system,” as the software is capable of making performance predictions for small wind and geothermal systems as well as and economic estimates for distributed energy and central generation projects.
SAM allows users to investigate the impact of variations in physical, cost, and financial parameters.
The software calculates the cost of generating electricity based on information the user provides about a project's location, installation and operating costs, type of financing, applicable tax credits and incentives, and system specifications. At Abengoa Solar, SAM is the common language for discussions with due-diligence engineers. “Having a SAM model allows all parties, the owner of the plant, the EPC and independent engineers, to talk about same parameters that describe a design and performance results,” according to Diego Arias, Team Leader of R&D Thermal Systems Analysis Group at Abengoa Solar.
SAM allows users to investigate the impact of variations in physical, cost, and financial parameters to better understand their impact on key the following:
- System output
- Peak and annual system efficiency
- Levelised cost of energy (LCOE) measures the cost of generation over the lifetime of the energy asset. It’s arrived at by dividing total system cost by lifetime energy produced.)
- System capital and operating and maintenance (O&M) costs
- Hourly system production
At Abengoa Solar Inc., engineers use SAM extensively for R&D and commercial projects. Arias said, “We use it as a first cut analysis to evaluate designs, technology improvements and their impact on cost of electricity.” He added that the two features upon which they rely are the performance model and the ability to interact with Excel. In performance model, Arias pointed out that the performance of the systems are sequential: solar field, TES and dispatcher, power block and balance of plant. “This allows us to see the energy waterfall, in which we evaluate the effects in a sequential fashion.”
Abengoa engineers have developed in-house models that calculate the required parameters to describe the performance of the plant.
For the empirical model, Abengoa engineers have developed in-house models that calculate the required parameters to describe the performance of the plant (i.e., thermal losses and parasitics consumption). “We link our in-house models with SAM via Excel. This link, combined with SAM's capability of running parametric cases, allows us to evaluate many combinations of design variables,” Arias stated.
The flow of cash
SAM’s hourly simulation engine interacts with performance, cost and finance models to calculate energy output, energy costs and cash flow. The software can take into consideration the effect of all-important incentives on project cash flow. SAM's spreadsheet interface enables the exchange of data with external models developed in Microsoft Excel. The model provides options for parametric studies, sensitivity analysis, optimisation and statistical analyses to investigate impacts of variations and uncertainty in performance, cost, and financial parameters on model results.
SAM models system performance TRNSYS software, which is integrated into SAM. TRNSYS was developed at the University of Wisconsin and is a time-series simulation program. Using hourly data with TRNSYS, SAM can simulate the performance of photovoltaic, concentrating solar power, water heating systems, parabolic trough, Stirling Dish CSP systems, CPV and more.
Variations in cost and place
Some of the assumptions within SAM are based on US data, such as costs and locations, but these can be customised. The values on the Cost pages of the sample files are intended to illustrate the use of the software, not to represent actual project costs, and they were chosen to represent average costs for the US. Actual costs will vary depending on the market, technology and geographic location of a project. More information about costs can be found on System Cost Data page of the SAM website. The California Energy Commission's Emerging Renewables Program web site provides information about systems installed in California, and includes a link to a spreadsheet of total installed system costs for systems installed throughout the state. SolarBuzz provides current and historical price data for the US and around the world based on market studies.
For weather information, users can download EnergyPlus (EPW) files for locations around the world from the EnergyPlus website (found on SAM’s Climate page as well as on other sites).
Solar Advisor Model (SAM) Software Main Screen
The Solar Energy Technologies Program began developing SAM in 2004 originally to support the implementation of the SETP Systems Driven Approach, yet SAM has become a standard simulation tool for renewable energy technologies. Currently in version 2010.11.9, SAM is now used worldwide by those involved in all facets of renewable energy systems from project managers and engineers to incentive program designers, technology developers and researchers. It’s also used for evaluating research and development programs and in academic research itself. SAM provides consistent methodology in developing financing and cost assumptions for the many renewable energy technologies.
See the Solar Novus Today article "Software for Solar Analysis and Design" for more information on solar system design and analysis software.
Written by Anne Fischer, Solar Novus Today Managing Editor
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