Solar Charging CPAP?

[SewTired]

Backcountry depends on where that back country is located. My BIL has a 5 foot solar panel at his lake cabin. It just doesn't provide enough power to charge up the battery to run his son's cpap sans humidifier all night. It can power a light and their phones, but Minnesota just doesn't have strong enough light.

[CapnLoki]

Backcountry depends on where that back country is located. My BIL has a 5 foot solar panel at his lake cabin. It just doesn't provide enough power to charge up the battery to run his son's cpap sans humidifier all night. It can power a light and their phones, but Minnesota just doesn't have strong enough light.

There's got to be a bit more to this story - a large solar panel should generate plenty of power and Minnesota has only slightly less sun than much of the country.

A "5 foot panel" should be at least 100 Watts, more like 150-200 watts. And a cpap should use 5 to 10 Amp-hours, or 60 to 120 watt-hours. This means that the panel should provide enough power if it gets a full shot of sun for only one hour. The "Insolation" of Minnesota is about about 3.7 to 4.7 in the summer, meaning that you can expect s solar panel to act as though it has full power for about 4 hours a day. The number is about a third less in the winter. This is the average, taking into account the cloudiness of a region. In the short run, of course, there can be significant variations, but this is why you need a battery that can cover several days use, or more, depending on your fall back capabilities.

So what might be the problem? My first guess is that the trees shade the panel so that it only gets a small amount of full sun. Panels don't like being partially shaded because all the cells are in series - blocking one cell hurts all of them. The partial shade may feel sunny, but the panel could effectively be turned off. Another possibility is that the battery is too small or is worn out. In either case it will not be able to accept enough current during a brief period of sun to properly charge. Also, I've assumed the panel is a relatively new rooftop style solar panel, but if its very old, or a different style such as a flexible panel, it may provide less juice.

web site provide sun insolation factors:
https://www.nrel.gov/gis/solar.html

[chartle]

One issue not brought up is how much time is going to be available to set up and use any solar panel? I'm assuming the prime sun hours are going to be on the river fighting rapids.

Also in the woods it gets dark a least an hour before real sunset.

[SewTired]

CapnLoki, I don't deny that you may have a point there. In the spot where the panel is located, it probably gets 8-10 hours of sunlight - after that, it is shaded by trees. My BIL has considered replacing it with new tech since the cost of more efficient solar panels comes down over time. But, you know, you can't ignore the topography. Cabins in northern states aren't typically in the prairie or the middle of a field. They are in a hunting area or a lake where there are trees. Duck hunting in S.D. probably has a lot of hunting shacks with no trees. Not a lot of trees there until you get to the western part of the state.

[Meneyl]

Sorry for bumping this old thread, just my $0.02.

I (nearly always) recommend that people determine their power usage (in amp hours or watt hours ) then match the panel to their usage so that it will recharge the battery in a moderate/reasonable amount of time. Trickle charging is OK as long as the trickle makes up or more than makes up for the power usage, in a reasonable amount of time.

Also be aware that most solar panel makers/dealers tend to fudge their panels' out put numbers to give unrealistic watts/specifications. (I have trickle panels that actually put out less than half the maker's specification each (fine for me as it closely tracks with my small, though growing, usage). Right now; if I allow my usage to grow I will out grow the panels and have to add more panels or go to larger panels.
Additionally shaded solar panels will not charge a battery well ... this is a major concern for me since I prefer shady sites... resulting in moving and realigning the panels every hour or two.

Most of the folks that I have met that are happy/satisfied with their camping solar setups are either over paneled or rigorously maintain their energy budget (a bit of a pain until it becomes second nature).

Enjoy!