Strength solar power needed...?

[John Linck]

Originally Posted by Randy J.

Rather than going straight to the solution, first, I would suggest that you evaluate your needs. There are good planning guides online. Here's how I figured mine. I started by listing everything that would run on DC. Then I listed each current draw and multiplied by the number of hours I expected to use each device on an average day to get the daily amp-hour (ah) requirement. Furnace fans are energy hogs. LEDs use very little. Then decide on a battery. The general guide for AGM batteries is to never discharge them by more than 50%, so I figured the battery a.h. rating needed to be at least double my maximum daily usage. For solar panel size figure on having no more than four hours of good sunlight per day. So if you expect to draw 5 a.h. per day, meaning your daily use is 5 amps X 12 volts or 60 watt-hours, you need a solar panel capable of replacing that much power in three or four hours. A 20 watt panel might just do it, but a good rule is to double-up. My system has minimal draw and gets by in this range.

I think Randy's method makes lots of sense. Its the right way to go about it.

But, I was just too lazy. Knowing my roof mounted panel would not be at the ideal angle ever I just doubled the guesstimated need from 50 watts to 100 watts. Most of our camping is off season with the sun low in the sky. Still we achieve full charge by mid afternoon at the latest, often earlier. My panel cost $160 three years ago. Now you can get it for less than $100. I figured I could always add a portable panel to chase the sun if necessary, but it hasn't been. Its simple, no hassle and works, unlike most things in my life.

Cheers, john

PS. Modern sealants make fear of roof penetrations unnecessary. Just check them every 10 years or so.

PS2. We camped under wonderful trees in Yosemite Valley for two weeks with very little solar charging. After 5-6 days we had to tow the Scamp over to a sunny El Capitan Meadow. After a picnic lunch, some reading and a hike our battery was ready for another 5 days. A longer tow would have worked too, sunny or not.

[Raspy]

Originally Posted by Randy J.

Rather than going straight to the solution, first, I would suggest that you evaluate your needs. There are good planning guides online. Here's how I figured mine. I started by listing everything that would run on DC. Then I listed each current draw and multiplied by the number of hours I expected to use each device on an average day to get the daily amp-hour (ah) requirement. Furnace fans are energy hogs. LEDs use very little. Then decide on a battery. The general guide for AGM batteries is to never discharge them by more than 50%, so I figured the battery a.h. rating needed to be at least double my maximum daily usage. For solar panel size figure on having no more than four hours of good sunlight per day. So if you expect to draw 5 a.h. per day, meaning your daily use is 5 amps X 12 volts or 60 watt-hours, you need a solar panel capable of replacing that much power in three or four hours. A 20 watt panel might just do it, but a good rule is to double-up. My system has minimal draw and gets by in this range.

Of course all this is logical and makes sense. The problem is how much to add for various factors like unexpected bad weather, additional use later for other things like charging a laptop or having a movie night with the DVD player or sometimes having to park in a shaded area or, if using a compressor fridge, being in extra hot weather or cooling drinks. You might decide later you want Sirius radio or you might want to run the Ham radio longer than expected each day for entertainment. Then again, you might only want one LED light for an hour a day as your total use.

Once you get the basics covered, add as much as is practical to give you some head room and to be sure your batteries will make it back to full charge. I like having extra battery power to weather heavy use periods or get through a period of no sun. If you plan to only camp in the summer in Arizona or at high altitude in the Eastern Sierras, a much smaller system will give what you'll get on the Oregon coast. Some way to tilt the collectors to the proper angle will also make a big difference.

There is also value in starting small with portable collectors and seeing how it goes. I used two portable 50 watt panels in Death Valley in the summer and got by just fine. It gave me a good baseline and helped me decide on future. upgrades. I didn't even have a charge controller, but I installed an amp meter and calculated how much I was getting and watched the difference as the day wore on or the orientation changed. Fun stuff!