Part 3—Compare Two Locations and Download Data
Step 1-Compare a Southern (Lower Latitude) Location to a Northern One
We look at the power data from Abilene, TX and Petersham, MA (Harvard Forest).
One solar power monitoring program that has data going back almost 10 years is from some schools in Texas, Louisiana, and Arkansas in a project called Watts on Schools. The Abilene, Texas planetarium has been part of this project. All of the information here is available in the "system details" link on each Soltrex system. Below, we see that the Abilene facility has a maximum power capacity of 5 kWac and the Harvard one has a 12 kWac power capacity.
In the table below are the actual solar power data and the modeled potential power monthly and annually at the two sites. The modeled power numbers are not available as a download. Focus on the ratios annually, or monthly.
Each system is performing near its potential indicated by most of the ratios being near 1.0. The only handicaps are weather phenomena which can cover its panels (such as snow or dust) or break components.
Step 2-Download Soltrex Data, Save it in Excel
- On the Soltrex site, you would chose your location, specify a time range and time interval, and choose a parameter (such as Power) to graph. Click on "Refresh Graph" at the bottom of the orange graphing controls box. The download icon and link appears below each graph.
- Click on the download link. A file called "soltrexdata.xls" downloads to your Desktop. You can rename this to be able to download several parameters or sites or time ranges.
- Download from Soltrex the same time range for the Petersham, MA. and name if HF-2008.xls
- Copy the column of power data from the Harvard Forest data to the Abilene data and graph in Excel.
- Duplicate the file "TX-2008_daily.xls" and rename it to "Compare-TX-MA.xls"
- Open Excel and choose the menu File>Open and choose "Compare-TX-MA.xls". Keep columns A and B, but clear the columns with data from C on. Provide a new header in column C labeled "HF Power". Leave the file open.
- Open HF-2008.xls (Harvard Forest), select the column of Power data and copy it. (Edit>Copy)
- Click on the column C header cell in the "Compare-TX-MA.xls" file. Paste (Edit>Paste) the HF Power column into column C .
Note At the Soltrex website, you are limited to 1000 Excel data points in your download file. This is 2.7 years of daily time interval data, 42 days of hourly data or 10 days of 15 minute interval data.
If you had trouble downloading the data or renaming it, here is the Abilene data Excel file (Excel 119kB Apr13 11) and here is the Harvard Forest data Excel file ( 116kB Apr13 11) to continue with the graph. Right-click (PC) or control-click (Mac) the links to download the files.
Step 3-Make a Graph in Excel
- Select both columns of data, including headers, that you wish to graph. The two columns should be highlighted.
- To graph data, choose the Excel menu item Insert>Chart,
- Choose a basic file type Line
- Choose a specific line type with markers
- The first graph appears, small and in need of labeling usually.
- Here is the resulting Excel graph. What can you say about this graph?
You can pull on the corners of the chart to enlarge it. Clicking on the frame away from the corner will let you move it around.
Add the Formatting Palette to the screen by clicking on View>Formatting Palette
Use the Chart Options section of the Formatting Palette to add titles, or make other adjustments to your chart.
Step 4- How to Import File Type csv into Excel
You could also use the Solar School House or Heliotronics Sunviewer websites and download data in comma-separated variable (csv) format. At the Solar Schoolhouse, you can download data for more than one school simultaneously. The data is downloaded as "SSHDownload.csv" to your Desktop. You would rename it with the names of schools. Similarly, if you download data from the Heliotronics Sunviewer website, the default name is "sunlogger.csv", which you could rename with the system location identification. If you have multiple schools data in one file, you would still have to consider the solar panel specifications of the two (or more) installations and realize that the maximum power potential may be different for each school.
- Choose File>Import in the Excel menu, and in the next window, choose "csv" type.
- Next, choose the SSHDownload.csv or your renamed file. Here my file is renamed to barnstableHS-Arpil2011.csv. Select it and click on Get Data,
- Excel will now step though a 3-step wizard as indicated below.
- You can choose to have your chart appear within the same data sheet, or in a new sheet.
- The loaded file will be data in watts every 15 minutes.
- The shapes are similar. When one is high, so are the others.
- The irradiance and PV output are much more variable than the temperature
- More energy is able to be generated in summer than winter.