Fire_man, being that the oil is less refined,
I would imagine it would be ok in longer storage. I would not be surprised if there are additive already added, but that’s just a guess. Our tank is 240 gallons, which is approximately what the 4 or use during the year for hot water.
Like TX-L, we are also on automatic delivery and the tank was just topped up with only 56 gallons after 2 months of heating. I estimate that we will only need 2 tanks of oil for the year instead of 5.
Raptor, thanks for the solar heater link. Given that the originator lives in Montana is promising. Son #3 is currently studying renewable energy and I hope to see a return on my investment

Actually, Ontario is currently offering a micro-fit buyback program for solar electricity. It’s reported that people are seeing returns of $1k / month (taxable though). Along with solar heating it is certainly something we are looking into. I’ve also heard of hybrid systems that are tied into existing oil tanks. The idea being to pre-heating the water to cut down the overall energy needed.
Thanks to this post though, I’ve now been inspired to start my own graph to see how things progress from here.