Question about a solar panel

[garyland]

I recently bought a 13 watt solar panel in the hopes of charging my battery for my CPAP. I called the company to find out if this will be able to charge my battery in one full day of sunshine but they did not get back to me. Does anyone have any experience with a 13 W solar panel and do they know whether or not a full day of sun will give me a full nights worth of battery power.

[KSMike]

It will depend on several things, including the number of hours of sun and how directly it hits the panel; the efficiency level of the panel (not all 13W panels are created equal); the length of the wire run from the panel to the charger; and the capacity and condition of the battery. Does your panel have a self-contained charge controller, or are you using a separate charger... all these things feed into the equation.

So you can see that when you get down to specifics, it's not easy to give you a simple yes or no answer. This is why it sometimes is simpler to buy a prepackaged solution that includes all the components, already designed for a specific application.

[archangle]

I recently bought a 13 watt solar panel in the hopes of charging my battery for my CPAP. I called the company to find out if this will be able to charge my battery in one full day of sunshine but they did not get back to me. Does anyone have any experience with a 13 W solar panel and do they know whether or not a full day of sun will give me a full nights worth of battery power.

No, 13 watts will not provide enough power in a day of sunshine to run your CPAP all night long.

What machine do you have, and what pressure do you use?

Solar power is a lot more difficult than most people think it is. A 13 watt charger only provides 13 watts at noon, on a clear day, when the panel is angled to be pointed directly at the sun, when there is no shade on the panel, etc. As the sun moves, the power goes down. There's less sun hours in the winter. You may only get the equivalent of 4 "sun hours" per day at some times of year on a clear day. Then if it's even a little overcast or partly cloudy, you get less sun hours.

For every watt hour your put into the battery, you only get part of it back out. You also need a "charge controller" to properly charge a battery off of a solar panel. You need a battery big enough to get you through the number of cloudy days you need to plan for.

[-tim]

135W maybe. The theoretical best with 100% efficiency is at least 60 W panel at 12V. There are other posts where people talk about how much energy their battery system uses and you might want to look at them. Also running the humidifier may make this worse.

I just looked up a 135W panel (KD135GX ) that is 5 foot x 2 foot and claims its 95W according to normal test specs. That is what you are likely to see on average for 4 hours a day so it may not be able to change it enough in one day to run all night.

My S9 takes 36 VA or 16 Watts according to the cheap tester but peaks to about 60 when I just plugged it in and put it on leak test. If I figure using 20 Watts for 8 hours while sleeping means that I would need 40 watts for 4 hours to recharge the battery but there are losses at every step of that conversion. And that was without the power hungry humidifier an a pressure of 13 or so. Higher pressure and older machines mean lower efficiency.

If you have a 13W solar panel, send it back. It would take the thing nearly a month to fully recharge a dead car battery.

[garyland]

Thank you all for your advice, I really appreciate it. It's clear to me now that 13 W isn't going to cut it. My pressure is 10 and I don't have to use humidity but I live in central New York where the winter sun is pathetic. I will be returning it.