Hi Cal,
The panel you refer to there would likely be called a 12v panel and ones referred to as 24V might be around 45 Voc rather than around the 37Voc you indicate. It all depends on the number of cells in the panel. Some might have 36 cells in series in the module and some 72. The terminology usually meaning suitable for a 12 V or 24V battery system on their own or indicating whether for a 48V system how many and which modules you need to wire in series to obtain a suitable voltage for your system to match to a conttroller.
Really the only way is to do the calculations and also base them on the temperature coefficients you get in the data sheets, to make sure in your expected conditions you don't exceed the controller rating in cold conditions and also to ensure that min voltages at max temperature do exceed battery voltage. Bear in mind in that case that usually the MPPT voltage output will need to be around plus 5V over actual battery voltage to start an MPPT up to charge. You can also get buck boost controllers like Genasun.
As others have said choose your panels first and then match your controller which includes calculating cabling losses. I know you said you don't have a Windows PC and sadly the spreadsheet I referred you to, which does all this, doesn't work with Open Office. The sheet really does work well though and you can see how the calculations are done and can input non Victron panels and then choose a non Victron MPPT if you wish. Attached the data used in the calcs.
Screenshot example attached of 2 x 24V panels in series with accepted correct controller. You should get the idea. All these calcs can be done manually but it's much easier with a spreadsheet to match controller to panels.
Thanks re blog and yes I'm very sad re deteriorating health (and age!) that I need to sell my boat. It's simply getting too much. Last year I couldn't sail at all due to an operation. I'm hoping to get a motorhome and electric bicycle instead that will be easier for me and so I can still play with the tech.
John R
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