Roy
I've learned some in the two years since I bought my panels and the biggest thing is that all of the formulas, charts, graphs etc. only give you a educated guess as to what you need. Until each user puts what they have chosen into use, it's a******shoot.
I thought my 230w set up was overkill until we had a 99% cloudy day and I watched the battery gain ground painfully slow.
Running the 8-D test to more understand the power you use and have to replace daily was a real eye opener. In the end it's a numbers game, amps out have to be replaced and the 220w panel didn't put out enough to do the job in the time frame, it would have taken both panels if not a third to do it. Not only wasn't there enough time, the 12a the 220w panel put out just wasn't enough to really get the beast going. Then again 12a x 6 hr = 72ah and I needed 120ah at least.
Both my panel run at 30a and a third closer to 45a. That would di it but that's a big system.