The following article was written by Michael Ross, Expert Instructor of HeatSpring’s Mastering RETScreen 4 for Clean Energy Project Analysis course– approved for 16 AIA CEUs!
RETScreen is the name given to two widely used software tools available for free download from the Government of Canada.
Looking at the website, the tools are described in the following way:
- RETScreen 4 “helps decision makers quickly and inexpensively determine the technical and financial viability of potential clean energy projects”.
- RETScreen Plus “allows project owners to easily verify the ongoing energy performance of their facilities”.
I think that those descriptions are accurate, but incomplete.
Reading the above descriptions, you’d think that if you don’t have a potential clean energy project that you are investigating, or an existing project whose performance you are tracking, you don’t need RETScreen. You may also conclude that because you already have tools for these tasks, there’s no point to opening RETScreen.
However, looking at how I actually use RETScreen, it is comparatively rare that I use the tools for their intended purposes. Rather, I tend to frequently draw upon RETScreen as a handy toolbox, database, and source of information organized around the skeleton of two software tools… and sometimes it is not even the tools themselves that I find useful, but rather the manuals, case studies, and web resources that are associated with the tool.
Let me illustrate this by looking back over just the past two weeks, and the times that I drew upon RETScreen.
- The closest I came to the intended purpose of RETScreen 4 was its use to quickly get some ballpark estimates of monthly electrical output from fixed tilt photovoltaic arrays installed in a particular Middle Eastern country for which I am preparing a planning document. Initially I used the global horizontal irradiance (GHI) estimates that are built into RETScreen’s database. But then I found some monthly GHI estimates from a high resolution satellite-derived database and I simply copied the 12 numbers over to RETScreen.
- I supplemented RETScreen 4’s output for those photovoltaic systems with some spreadsheet models of my own. I needed monthly average temperature data for my spreadsheets. No need to search for the web for climate data: I just picked up the data out of RETScreen’s database.
- Eventually my spreadsheet models got more complex. I needed to do some calculations breaking daily average radiation into typical hourly profiles. I could have found most of these relations for this in my well-thumbed copy of Duffie and Beckman’s Solar Engineering of Thermal Processes, but it seemed just as easy to look it up in the RETScreen 4 Engineering Manual, a pdf that I downloaded from the RETScreen website. As a bonus, I found a gem of an empirical equation relating the cell temperature to the monthly average temperature—and this one is not in Duffie and Beckman, so I would have had to search the archives of Solar Energy Journal all the way back to 1981 to find this. As a further bonus, I could check my implementation of the method by comparing my output with the RETScreen output for the same inputs.
- My models also needed typical values for the decrease in monocrystalline silicon photovoltaic modules with a rise in cell temperature. I opened RETScreen and picked out the default parameter for this. I could have checked specifications for a half-dozen common modules and taken an average, or looked for a more rigorous scientific study, but I know that I’ll be in the ballpark with the RETScreen estimate.
- In the scientific literature, I found some monthly solar radiation averages measured at ground stations in nearby countries over short (one to four year) time periods. I wanted to compare these with daily satellite-derived estimates from NASA. I used RETScreen Plus as a portal into the NASA data, and downloaded the data for the corresponding years. Then I grouped the NASA daily data by month and calculated the resulting monthly averages (all one step using RETScreen Plus). I exported this to an Excel file so I could compare it to the ground station data.
- Natural gas generation is currently the norm in this country, and I needed a GHG emissions factor for this. Easy: I found the factor in RETScreen 4’s emissions analysis page.
So, even though I didn’t need to assess the technical and financial viability of a clean energy project, or track the performance of a project, RETScreen and all the data and information that is wrapped around it was highly useful in my work. I could have used other tools and sources of information, but it is conveniently organized and easy-to-understand in the RETScreen package, making it handy toolbox for general analysis of clean energy projects.
About Michael Ross
Michael M. D. Ross has taught RETScreen courses to thousands of people across Canada, in the United States, and in France, and has assisted RETScreen International in the preparation of much of its e-learning course material. Over the past 15 years, he has held research and consulting positions related to renewable energy and energy efficiency in both Canada and Europe. He obtained a Bachelor of Applied Science degree (Systems Design Engineering) from the University of Waterloo.
Michael is currently teaching: