To me this question is rather like asking, should I leave an unused alkaline battery in open or short circuit? The durability of a solar panel is not just a measure of the intrinsic loss of output over time but also the build standard of the panel. No point having high quality mono crystalline silicon when the panel edges and seal fails after five years. Cheap Chinese panels have a cheap Chinese lifespan. Buy German - it lasts.
Unless you are building a solar farm where ever joule counts towards the bottom line, arguing over a few amp-hours is a waste of time. Especially if you are designing for capacity redundancy. Let us not forget the inverters too which can burn the spreadsheet numbers when they fail. What is the MTBF of the inverters?
Tip: Google "solar farm used solar panels" - the solar farms often off load aging and under performing panels. Also, thanks to green energy grants, panels are financially depreciated to zero over 4 to 5 years. So to make the most of capital allowances, farms upgade to new panels just for the tax-free money. A five year old panel can be a real bargain - ball park, a panel still outputting 200W+ is us$100 re-fitted. So it may pay to use and replace 'preloved' panels for a short period, rather than try squeeze the claimed 25 year lifespan out of full price new ones.