Monday, Apr 15, 2013 at 16:41
Hi Rob,
I was going to explain how one might work out what you need, but I see you've already looked at the solar article by Collyn Rivers on this site.
I agree with
John in his reply below that my use of the total watts of the power bricks was an overestimate, but it did give us a starting point. Perhaps the numbers would be closer to the mark if the power supply was charging a flat laptop battery and running the laptop as
well, but once the battery is charged and the brick is just running the computer then clearly the power draw would be reduced.
You've given figures from your power supplies of about 76 and 60 watts for your computers and I think the same argument would hold. Collyn Rivers suggests 20 to 50 for laptops, but let's go with the worst-case scenario and use your figures.
I have a spreadsheet prepared by an electrical engineer for working out solar needs in the brand of caravan he and I own. Using it is much simpler that explaining the calcs here. I have attached it so you can play with it.
You make your inputs in the yellow cells. DO NOT CHANGE ANY OTHER CELLS, just the yellow ones.
Input your loads, your battery size, how low you are prepared to let your battery go, the size and number of solar panels and it will tell you how long you can
camp, based on solar charging, for each season.
I have set all our caravan inputs to zero, and made a couple of dummy entries (Inverter and Redarc Relay) that make it total the daily load match your 61.3 amp-hours. The fridge is included in that, so the specific fridge entry is set to 0. I have assumed a 120Ah battery and that you're prepared to let it discharge to 50%. I think the peak sun hours are for
Sydney.
Based on 180 watts of panels, camped near
Sydney you would get 2 days in winter, 4 days in autumn, 5 days in spring and unlimited days in summer before that 120Ah battery dropped below 50%.
Play around with it, see how you go. I found it very useful.
(50% is the rule-of-thumb sweet spot between minimising battery wear and tear and practical use for regular discharge of a deep cycle battery)
The author wishes all readers to know that this spreadsheet grew from an original posted on ExplorOz some years ago.
Cheers
![Solar Spreadsheet](https://cdn.exploroz.com/images/Gallery/FileTypes/xls__TN600F.png?gid=75513)
Solar Spreadsheet
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