Dear Hakeem,

I think it highly depends on your specific scope. There are different Energy Modelling tools that are open source, for which I suggest you to check the open energy modelling initiative (https://openmod-initiative.org/), where you can find both models and dataset that could include Renewable Energy Systems.

Regards.

I have developed models for three biomass plants and five combined heat and power (CHP) systems integrated with paper mills. I built these plus a hundred other models using GateCycle. GateCycle V5.61 is a wonderful tool; but G.E. quit updating it in 2005, so it only runs on XP. The team I work with has been struggling to find newer software to replace GateCycle. Aspen and EBSILON work well, but are complicated. PEPSE works, but requires much more effort to create and tune a model. PEPSE is used almost exclusively in nuclear plants, where they're accustomed to spending a fortune and taking forever to do anything. Thermoflow is quick for approximate analysis, but doesn't meet our standards for accuracy. Modelica is intended for transient analysis, not steady-state, and also takes a long time to develop a complete system model. T-Cycle out of the U of Delft is supposed to be quite good (and cheap), but doesn't handle the range of designs we need and may not handle the renewable energy systems you're interested in. All this is to say that I don't have an answer for you and hope someone else does. I wrote the first thermodynamic cycle modeling program to ever run on a microcomputer back in 1983 when we only had 640kB of memory. It will still run in a command prompt on XP. I've been working on a Windows version, but it's still a long way from complete. I hope to make it open source. If you find a GateCycle hardlock key on Ebay, buy it!

For geothermal energy (but also nuclear waste disposal, underground water flows and everything related to underground heat flux and fluid flow) take a look at TOUGH family of numerical codes (https://tough.lbl.gov).

It's open source but not free, anyway the licence fee is affordable.

Many free open source tools are available for pre and post processing, as well as proprietary software.

Take a look at http://software.dicam.unibo.it/dicam-software

Hakeem Niyas For purely renewable energy system modeling I'd second Ibrahim's recommendation that you take a look at the System Advisor Model (SAM) from the USA's National Renewable Energy Laboratory (NREL):

https://sam.nrel.gov/

SAM is not open source, but there is no cost to download and use it. Installers for Windows, MacOS and Linux are available to download at the link above.

SAM is pretty well documented and NREL staff host (and post on youtube and the SAM website) periodic webinars on using SAM. SAM also has a good Application Programming Interface (API) / Software Development Kit (SDK) that lets you incorporate its models into your own code or platform if you are handy with software development.

EBSILON Professional is also able to model PV, wind and Concentrating Solar Power (CSP) systems:

https://www.ebsilon.com/en

Contrary to what Dudley J Benton posts, it is, in my opinion, the best available replacement for GateCycle. The better part of the old GateCycle development team now works on and with EBSILON. It does everything GateCycle does and much more, including renewable energy systems. It is costly for commercial users like Mr. Benton's team (10s of thousands of Euros initial cost) due mainly to the fact that the market for such software is small. It is nowhere near as costly as ASPEN and "burdensome" is among the last words I would use to describe EBSILON unless one considers amazing flexibility and breadth in a modeling tool to be "burdensome".

EBSILON is available for academic users at a substantial discount in exchange for citing EBSILON's use in any work, papers or presentation that it was used in. I'd be happy to send you additional details if you are interested in learning more. I have attached a description of the available add-on modules for EBSILON. The PV, wind, time-series and solar / wind data components are all part of the base package. Modeling CSP systems requires the EbsSolar add-on.

I just published a (really cheap) book that describes how to solve thermodynamic cycles and includes code to handle conventional and combined cycle systems (sorry, no user interface yet) https://www.amazon.com/dp/B07SLBZJK3 Two interesting examples provided use random numbers to generate initial estimates of the extraction flows for feed water heaters and steam production for 3-pressure HRSGs to demonstrate that the iterations converge for tens of thousands of initial values using the recommended formulas and proving that advanced algorithms are unnecessary. The steam properties are free for non-commercial use and come in C source code plus an Excel Add-In.

I was too harsh in my comments about EBSILON. My team did find that it was the best currently available alternative to GateCycle V5.61. EBSILON has many excellent features and additional capabilities. I faced the challenge of being given only 80 hours (determined by Sales & Marketing) to develop a system model, validation cases, and a complete set of correction curves. Our director insisted on 0.1%/0.1° agreement with design heat balances and 0.2%/0.5° agreement across the range of corrections, demonstrated by random cases. This was very difficult to achieve with GateCycle, but much more so with EBSILON, given the available controls and adjustments. Forcing a model to fit the EPC's heat balances, which contain multiple unspecified and proprietary margins, is a daunting task indeed. This raises an issue of much debate: how I (the performance testing engineer) think a system will perform vs. how they (the EPC's engineers) are willing to guarantee it will perform (including possible liquidated damages). If I am not liable for the liquidated damages, I don't get to decide how the system "should" perform, which means I don't get to loosely match the information provided. This is implied in ASME PTC-46, depending on who you ask. As a performance testing contractor, it was my responsibility to represent as accurately as possible what the EPC committed to delivering, not how I thought a system was going to perform. When a big discrepancy arose (and they occasionally did), I informed the parties that there might be a problem meeting the guarantees. If the performance test proved otherwise, that's OK. EPC's engineers will tell you stories like... This or that vendor always come up 5% (or 1°) short, so we just add 6% (or 1.5°). We save $20M on the project, come in lowest bidder, and still achieve the guarantees without getting sued. If time were not such a hard constraint for me (as in a nuclear plant, for instance) or if agreement with an EPC's margins were negotiable or if I were designing the system (rather than working with someone else's design), the evaluation criteria would be different, as would my conclusion. The fit between GateCycle V5.61 and the performance testing company I worked for was fortuitous indeed. I think 80 hours is unreasonable for such a complex task, but that's the market reality I had to work with. I should think EBSILON an excellent choice for many other circumstances and applications.