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The System Advisor Model (SAM) was created for users of all levels, but as with all technical and comprehensive software applications, common questions need to be addressed. The following list of commonly asked questions were addressed in the most general way so users of all levels can understand and find value in the answers.
You can send questions and comments to the user support team at solar.advisor.support@nrel.gov.
General Questions
Will SAM run on Unix/Linux?
SAM currently requires Windows 2000 (or later) and/or Intel-based Macintoshes. We do not have versions of SAM for other operating systems.
I do not have TRNSYS installed on my computer. Can I still run SAM?
Yes, SAM uses the TRNSYS simulation engine for performance predictions, but does not require that TRNSYS be installed on your computer.
Can SAM work with @RISK?
Yes. Versions 2009.10.2 and later include a basic capability to interact directly with Excel/VBA and @RISK. You can also use the built-in Statistical Analysis tool to analyze uncertainties in SAM inputs.
Does SAM model dish-Stirling engine CSP systems?
Yes. Versions 2.5 and later include a dish-Stirling model.
Does SAM model concentrating photovoltaic (CPV) systems?
Yes. SAM uses a simple multiple-point efficiency model to represent CPV modules.
Where can I find more information about SAM's calculations and algorithms?
First, check the help system or user guide (you can find both in SAM under the Help menu, or the user guide on the download page of the SAM website). Those documents explain some of the calculations, particularly for economic metrics and for the "calculated" variables which are indicated with blue backgrounds in the user interface. If you're mainly interested in the economic calculations, you can download financial spreadsheets with formulas from the SAM website. If you don't find the information you need there, send a message to user support by clicking User support on the Help menu. If you are modeling CSP trough systems, we've posted a draft version of a reference manual on the SAM website.
How accurate is the cost data in the sample files?
The values on the Cost pages of the sample files are intended to illustrate SAM's use, not to represent actual project costs. We tried to choose values that reasonably represent average costs for the United States. Because costs vary widely by region and by type of project, you should check each cost assumption in your analysis. We've posted some more information about costs on System Cost Data page of the SAM website.
Is there a limit to the size of system that SAM can model?
No. Whether you model PV, parabolic trough, or dish-Stirling systems, you can model as large a system as you like.
Can SAM model systems for locations outside the United States?
Yes. SAM uses weather files in TMY3, TMY2 or EPW format. You can download EPW files for locations around the world from the Energy Plus website — just follow the link on SAM's Climate page. There is more information about weather file formats and sources of data in SAM's help system, just go to the Climate page and click the little round button with a question mark in it at the top right of the page.
Photovoltaic System
I see that you don't have a storage element in the photovoltaic section at this point. Do you have a target for when that will be added?
SAM currently models only grid-connected systems. The photovoltaic model does not include a storage component. Adding storage is on our wish list, but we have no definite plans to do so for now.
Does SAM model loads for PV systems?
Yes. SAM models loads for systems with any technology that you model with the residential or commercial financing option. SAM uses the load data and utility rate data to calculate hour-by-hour electricity buy and sell rates and demand charges. On SAM's Utility Rate page, you can either specify custom rate data or download rate data from the OpenEI utility rate database.
I would like to model a roof-mounted PV system that uses thin-film modules mounted directly on the roof. Can SAM do this?
Yes. Two of SAM's module models (Sandia and CEC) allow you to choose mounting options for an array mounted on the roof. The options determine how SAM calculates the module cell temperature. See the Help topic for SAM's Module page for details.
The PV module I would like to use in my system is not in SAM's list of modules. Can I add my module to the list?
Not very easily. The two module libraries in SAM use a set of parameters for each module developed by either Sandia National Laboratories or the California Energy Commission. The parameters are generated using empirical methods and data that you probably do not have access to. We do update the libraries as soon as we receive new data, and if we receive new module data between software releases, we post the new library on the SAM website's download page. The best option for modeling a module that is not in the library is to use the single-point efficiency model, which is one of the three options on the Module page.
Is there documentation of the underlying algorithm for the PV models?
Yes. You can download documentation of the Sandia PV module and Sandia inverter models from the SAM website. For the CEC PV module model, you can find documentation as part of the CEC-PV program (you will need to install the program to get the documentation), and also in an article published in the Solar Energy Journal, Issue 40 entitled "Improvement and validation of a model for photovoltaic array performance" by De Soto, Klein and Beckman.
Concentrating Solar Power Parabolic Trough Systems
I'm modeling a CSP trough system and would like to vary the solar resource to see how the change would affect system output. I tried changing the value of the Direct Normal Radiation variable on the Solar Field page, but that results in decreasing output as the radiation increases. Why is that?
SAM uses solar radiation, temperature and other data from the weather file that you select on the Climate page to calculate the system output, not the reference values displayed on the Solar Field page. The only way to change the resource data is to choose a different location on the Climate page. The direct normal radiation variable on the Solar Field page is a reference variable that SAM uses to calculate the solar field area when you choose to size the solar field with the solar multiple variable instead of explicitly defining the area. SAM calculates the solar area required under reference conditions to supply sufficient thermal energy to the power block for it to operate at its rated capacity. Increasing the reference solar radiation value decreases the area required to meet that energy requirement. So, comparing two identical systems with the same weather data but different reference direct normal radiation values will result in the system with a higher reference value and therefore smaller solar field to generate less electricity in a year. Section 6.8.2 in the user guide (on page 68) shows the equations involved: The reference direct normal radiation value is in the denominator of the exact area equation, so a larger value results in a smaller solar field area.
How does SAM model thermal energy storage?
SAM models thermal energy storage (TES) as a system that can store up to the Maximum Energy Storage shown on the Storage page with maximum charge and discharge rates shown as Maximum Power To Storage and Maximum Power From Storage on the Storage page. These rates are calculated using the Turbine TES Adj. - Efficiency and Turbine TES Adjustment - Gross Output, and Heat Exchanger Duty variables. To account for TES-related losses, SAM applies a "TES correction factor" to the total system output that is calculated using the Turbine TES Adj. - Efficiency variable and the hourly energy quantities delivered by the TES system and to the power block. For systems with TES, SAM also subtracts the Tank Heat Losses amount from the system output for every hour of the year.
For the parabolic trough systems, what effect does using a different heat transfer fluid (HTF) for the solar field and thermal energy storage system?
The choice of HTF for the solar field and storage determines whether the storage system is a direct storage system or an indirect system. Direct systems use the solar HTF as the storage fluid. Indirect systems require a heat exchanger and use two fluids, one for the solar field HTF, and another for the storage fluid.
How does SAM model thermocline and two-tank storage systems?
SAM only models two-tank storage systems.
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