Is a 40 watt solar panel enough?

[Cam A]

Can Tire has a 40 watt panel/7 amp charge controller and stand, on for $149.99. I was wondering if a 40 watt panel was large enough to bother with. I am not looking for a long term boon-docking setup, but something that will extend my batteries for, say a week, of nightly furnace/lights running.

[Raz]

Originally Posted by Cam A

Can Tire has a 40 watt panel/7 amp charge controller and stand, on for $149.99. I was wondering if a 40 watt panel was large enough to bother with. I am not looking for a long term boon-docking setup, but something that will extend my batteries for, say a week, of nightly furnace/lights running.

I have a 42 watt panel that meets my needs; LED lights, water pump, window fan. The furnace fan might be more than my setup could make up for depending on the duty cycle. If you know how much current each device uses and how long it runs you can calculate the amp-hour use. A 40 watt panel will realistically give about 2 - 2.5 amps in full sun. That times the number of hours of full sun is what is available to replenish what is used. Raz

[Byron Kinnaman]

Originally Posted by Cam A

Can Tire has a 40 watt panel/7 amp charge controller and stand, on for $149.99. I was wondering if a 40 watt panel was large enough to bother with. I am not looking for a long term boon-docking setup, but something that will extend my batteries for, say a week, of nightly furnace/lights running.

Replace all your lights with LEDs. Then the 40 Watt should do the trick provided you use it at least every other day in bright sun light.
I currently use a 65 Watt panel and battery charging interval between 3 and 5 days. Charging depends on how much the furnace runs.

Note: I set my thermostat at 55°F at night, which is the lowest setting I have. Also there's very seldom more than 2 LED fixtures on at one time. I figure there is no limit to the length of time I can keep my batteries charged. The more you run the furnace the more you'll need to recharge.

[cpaharley2008]

Go to here The 12volt Side of Life (Part 1) and read part one and part two. There is a discussion of your daily needs. For example, If you need/use 30 a/h a day and your solar is 3 a/h (40watts/12v=3a/h) over 6 hours or 18 is being put back into your battery. Thus you net drain/loss is 12 a/h per day and if you have a 100 a/h battery 40% is available thus you can go 3 days before needing to recharge.

[Carol H]

A small panel like that works for me. All lights are LED and I use them sparingly and an LED headlight when reading at night. Run the fridge on propane, dont watch tv or own an AC. Just the water pump, fantastic fan and furnace (used only when really needed) and charging up phone and camera battery's and occasional computer usage - with a battery in good shape I only need to plug in ever few days.

[Thomas G.]

That is a decent price buy you can get a 60 watt with controller for about the same on eBay .

[CheekyTracy]

I just bought the Canadian Tire one you are talking about today for my 13' Boler. It will only be needed to run lights, use my laptop propane furnace and stove once in awhile as I do not have a fridge, fan, AC, microwave etc. I know it isn't a high end panel but felt for the price it would do the trick if I need it. It will just be myself relocating from Alberta to BC and using the trailer in the interim until I am settled somewhere. We'll see what happens.

[honda03842]

There are two parts to "What's enough?"

The Usage Side: Certainly 40 watts can be enough if you configure your usage correctly, particularly with the use of LEDs. This was clearly covered by a number of people.

The Collection Side: For most of us, we live in sunlight and it's not much issue to collect enough power to meet our needs. The darker climes, due to lattitude and hours of sunlight during some seasons or some of these desparately cloudy rainy places it may not be enough.

As a reference point we have 80 watts and though parked in Seattle for a rainy month, had no issue keeping an adequate charge.

[Cam A]

My furnace is a Hydroflame D and has a rating of 2.9 amps. That is per hour, I guess. Furnace was on for 12 hours the other day (it froze pretty good at Lake Audy), but at a low setting, so the fan wasn't running for that long at a time. Throw in some lighting draw, and 40 watts, or 3 amps/hour x 8 or 10 hours of charging is starting to look pretty marginal.

[cpaharley2008]

If you need 3 a/h @ 50% cycling that would be 18 a/h for 12 hours heat. That and led lights and pump may increase that to to 5 an hour. With your solar output of 18 a/h per day and use of 18 for heat and maybe another 12 for lights/pump means your net draw from your battery would be about 12 a/h a day. with a 100 a/h battery, only 40 is available thus your days would be limited to 3 before having to plug in again. If you went with a 60 watt panel then your draw on your battery would be nil.