(05-29-2018, 07:51 PM)TWIH Wrote: I too am waiting for SW’s full long-term test report on the “new and improved” super bendible (245 degrees) and better warranteed Renogy flexible mono panels (currently $2 a watt on Amazon) in 100w and 160 w sizes which still seem like a really good way to deal with curved roofs and weight issues. I read his earlier post comments and he seems to be less than totally enthused but then he’s not on the water in a sailboat. That crowd seems to use the flex panels a great deal more.
Just like the age old question of “do you get any wetter if you stand still in the rain vs. walk/run”, I wonder if you gather more solar energy while stopped vs. driving? 
The Flex panel I got with the Renogy gift certificate( thanks again) is a SunPower panel that was sold by Renogy, for 50$ more than available elsewhere on line at the time.
The 100 watt flexo 248 degree Renogy 100 watt panel, I only just now became aware of. Renogy had to take a hit with their former flex panel's high failure rate, so i imagine they would not offer another product with similar issues, but perhaps they will take some time in actual use before issues actually crop up. Accellerated aging testing is not perfect, but no company is going to wait for an actual 5 year long test to complete before offering a new potentially profitable product.
I have not installed the SunPower flex panel on my Van's roof, yet. It sometimes gets brought out to feed my workshop battery in parallel with my 100 watt framed renogy panel. Sometimes it was brought out to feed my heating pad showr bag water heater, but the VMP proved too much for the pad, and burnt the heating wire insulation where it was not in contact with the water bag.
When I do install my Suppower Flexpanel the only flexing it will be subjext to the the roof expanding and contracting with temperature, and I will likely be voiding the warranty by trimming the plastic on the side of the panel so it does not overhang the side of my fiberglass roof in the location I plan on installing it.
A lot of these flex panels claim to use the sunpower flexible cells. The flex panel I have is an actual Sunpower brand panel. Not having another brand to compare, I cannot compare them but from what I have read the plastic backing is different thickness on most and the Sunpower is supposedly thicker which likely means less stress on the cells ad their inteconnects in a repeated flexing situation.
Driving, vs parked, the airflow over a flex panel would be greater, which means a cooler panel, which means more output. As long as charge controller is still seeking absorption voltage, and the vehicle's alternator is seeking/holding a voltage less than this, then the solar can reduce the load on the alternator, but it is pretty safe to say a 120 amp alternator is not going to be much relieved by a 100 watt panel at noon on June 21.
Back when solar was new to me, and back before I could control my vehicle's voltage when running, it would seek 14.9v, which was well over my solar controller setpoint. This would trick my charge controller into thinking the batteries were full, with a little improper programming on my part regarding absorption voltage duration, and it would simply choose to hold float voltage the rest of the day rather than hold absorption voltage for much longer as is desirable. Long story short the result was it premature efloatulation which sulfated my batteries prematurely. I was getting ~2 years from a pair of marine flooded 27s that were only shallowly cycled. As a comparison I am now over 4.5 years on a single group 27AGM cycled much deeper, and while the battery is obviously aged, it is not ready for the recyclers anytime soon.
Basically a nightly discharged battery needs to be brought to and held at absorption voltage for a period of time. This time is different for each battery, and changes as it ages, and changes with battery temperature and changes with the state of charge it was discharged to, and changes with the amount of cycles since the last true full recharge, and changes with the initial charge rate, and the presence of other charging sources, like an alternator first thing in the morning.
Those seeking good to very good to excellent battery longevity need to confirm that the battery is indeed full before the Solar controller drops to float voltage. If it drops prematurely to float voltage it will not get full before sundown, and another partial state of charge cycle is accumulated, and this happening day after day, is a battery capacity destroyer.
As an example, I can and do plug in to the grid overnight sometimes, but sometimes I plug in at 10:30PM. My charger is a manual charger, I select the voltage, it gets the battery there with upto 40 amps, and even if I am only 25AH from full, it takes no less than 4 hours to get it full. I am not staying upto 3AM just to turn the voltage down after the battery is full, though this would be ideal, for the battery.
So I will lower voltage to 13.9 volts or thereabouts and goto bed. Next morning, the battery should be full right? Hardly.
The solar soon takes it upto 14.7v, but it still takes 2 to 3.5 hours more for amps to taper to 0.4 or less. So I could have fully charged the battery in 4 hours or so at 14.7v, but chose to lower voltage to 13.9v. It held 13.9v for 7 hours then it still toolk 3+ hours at 14.7 for amps to taper to 0.4 or less, indicating a full battery.
Getting the battery, especially an aged battery to full at float voltage takes FOREVER, and an abused older discharged battery will never get full. Note that 13.6v is the correct float voltage for my specific 77F battery, so 13.9v shoud have had a much better chance of getting the battery to full in a reasonable amount of time, while I slept, but it cannot and does not, although my battery monitor will seem to think so. But amps accepted by the battery at absorption voltage is a true indicator of state of charge, and I ignore the battery monitor's readings often, as they are not perfect, as is no automatic charging source.
Avoid premature float voltage. It is not nice and gentle on the battery, it is abusive to the battery, as it will be forced into another partial state of charge cycle, when the opportunity was likely there to avoid another PSOC cycle had absorption voltage just been held longer.
Those who think that 13.6 only takes a bit longer, should goose voltage abck upto absorption voltage and see the amperage the battery is accepting,( or dip a hydrometer on flooded batts) and they will find the amperage accepted is still well over the threshold indicating the battery is full.
This is the Key to battery longevity in daily deep cycling, get the battery to absorption voltage, hold it there until amperage at absorption voltage, and/or a Hydrometer indicate a true 100% full charge. This can take many many hours, so it is importnat if the day is not quite long enough, to get the battery to absorption voltage earlier in the day. Small strategies can be used like not turning on or simply reducing DC loads until the battery is much closer to absorption voltage later in the morning, but easier is more solar, or running the engine first thing in the morning for no more than 10 minutes idling.
The 10 minutes thing is out of respect for the alternator. It will heat up quickly when maxed out feeding depleted batteries, and heat kills. Driving induces much more underhood airflow keeping it cooler, as does more engine rpms when driving, as they spin the alternator's fan faster too.
Relying on any automatic charging source, or solar controller not programmed correctly, to actually truly fully charge a regularly deeply cycled battery, is unwise.
But for some people fair to middling good battery longevity is good enough, and cheaper than getting the equipment that allows one to actually get the batteries to full, or the stress involved in observing charge algorithms, overriding them to insure that float voltage is not prematurely initiated each and every day.
'Good enough' is subjective.
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