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| Solar Power Calculator Solar panels have come a long way in recent years to the point where they can supply the total energy needs for a small cruising Yacht. The S/V Star incorporated two Kyocera panels rated at 120 watts each on top of the Bimini where they are completely out of sight and out of mind. These panels powered the refrigerator/freezer, computer, single sideband radio and all the lights on board the yacht for the entire two years time that we have been out cruising in the Bahamas and along the East Coast of the U.S. There are no moving parts, no gas to store, no carbon monoxide, no noise, and we don’t disturb the neighbors.
The installation at first did not provide the power that was needed but there were no reliable estimates for exactly how much power they should provide and we thought that that was just the way it was. The power out of a Solar Panel varies significantly with the time of day, the time of year, temperature, the cloud cover, both your latitude and longitude, the heading of the boat and the mounting of the panels themselves. The problem is so complicated that manufactures of the panels do not even try to explain how they work. Here is what one wrote to me when I asked them how to relate the rated power to real life. “The wattage of a solar panel is calculated in a perfect situation, in a vacuum with maximum solar radiance at optimum temperatures which is not a real life scenario” So what is a real life scenario? what is maximum solar radiance? How can a solar panel rig be designed without knowing how much power it will produce? The answer is – a rig can’t be designed in a vacuum so to speak. You don’t want to outfit in Baltimore and wait until you arrive in the Caribbean to discover that you have to run the engine every day to keep the beer cold.
During our spare time we developed the Icarus Solar Designer® to predict the actual real life power out of a solar panel as a function of time of day, time of year, and latitude / longitude, as an aid to us in tuning and designing our rig for traveling to different parts of the world. Knowing exactly what to expect we discovered that our rig was only producing half of the power that could be provided. Shadows and alignment of the panels were all contributing to a huge loss that we were able to fix with the Icarus Solar Designer® truth model. After adjustments we are very pleased with our modest configuration and in fact have turned on the engine only 6 times to charge the batteries during our two full years of living aboard. The big problem here is that if you don’t know how much power can be provided you will never know if your installation is working correctly. Furthermore you will not be able to size your rig and know for sure that x number of panels will work for you while you are in Maine or the Bahamas or the Caribbean, or the Mediterranean.
This Icarus Solar Designer® spread sheet estimates the current that a typical solar panel can produce under real life conditions including both full sun and various cloud covers. The user specifies the Date, Latitude, and Longitude, and the solar panel specifications including power and geometry – all entries have defaults if you don’t know the exact number. The program evaluates the azimuth and elevation position of the sun as a function time, computes the insolation (power from the sun at the surface of the earth), and evaluates the battery charging amps at any time during the day. It also evaluates the total daily amphours over the entire year, the total daily amphours vs. the boat heading, and the total daily AmpHrs vs. Latitude. The outputs are shown in both graphical and tabular form. Sheet two of the spread sheet allows the user to enter his own measurements of charging amps, the exact time of day, lat/long etc and compare them directly with the prediction. The spread sheet will indicate OK, Marginal or fail depending on how the measurements agree with the predictions. A Fail indication indicates a serious problem with your installation. Not to worry, however, as the same thing happened to Star and we made a series of small adjustments using the spread sheet to guide us until the rig passed the test.
Figure 1 shows a typical output of the spread sheet giving the amps vs the time of day for two 120 watt panels: Figure 1 - Showing amps vs time of day for two 120 watt panels Donating Money All software is free, however, we would appreciate small donations to help provide beer and wine for a happy crew obaord our sailboat Star. To donate money see: Donate Money Download the software To download the software from YachtSoftware.org click in the links in the table below. Feedback would be greatly appreciated especially any testimonials that you may be willing to share on our web site.
Notes on running the software The software is Excel based software backed up by a very powerful Visual Basic program. The Visual Basic program is called a Macro by Microsoft and they automatically issue a warning when a spreadsheet containing a Macro is started to help reduce the probability of spreading viruses. Macros are widely used thoroughout the world, however, and particularly by the engineering community where they are safe and secure. The following Microsoft approved procedure allows you to enable Macros on a case by case basis so you can run the Designer and still maintain security for other applications. To do this follow the simple steps outlined below Start Excel Click Tools on Toolbar at top of sheet Click Options Click Security Tab Click Macro Security Click Medium Security which means that you can choose whether or not to run Macros instead of disabling Macros for all applications Click OK
To start the Isoftware click on download link above and save the software in a convenient folder of your choosing. Start Excel, open the file, enable Macros in the dialog box that comes up, and you are off and running. Copy Right and Distribution All the software is copyrighted and you do not have permission to include any parts of the code or Web Page for use in your own products without permission. You do not have permission to distribute the software. When publishing results in a forum please include a reference to http://YachtSoftware.org | |
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