Solar: issues to consider?

I'm wondering what the state of the art is, with respect to adding solar to a TearDrop.

I'm not interested in mounting a panel to the roof, but I am interested in supplementing the electricity by adding a solar panel.

Maybe folks don't think it is "worth it" since the TD battery can be charged from the car.

I'm not sure what the "cut off" is. For example, if you have no plans to be "off the grid" (unplugged from electrical hookup) for more than [X] days, maybe there is no need for solar....

 

The reason I got solar is so that I could charge the battery if I was at a campground without hookups for an extended period of time. I know that I could hook up the car and charge the battery by running the car but that will cost money for the gas. Of course there is the initial layout for the solar panels etc but I would think over the years it would pay for itself depending on how often you camp this way. I have not done a cost benefit analysis. If the solar panel set up costs about $400, that is 100 gallons of gas at $4 a gallon. Not sure how many gallons it takes to charge the battery.

It will also depend on what appliances you are running. I have the refrigerator so my needs are going to be different from someone who has a cooler (although there is the gas for running to the store for more ice.)

If you never plan to camp off grid, you probably don't need the solar.

I haven't gotten the panels yet but will do so probably next year.

 

I have found that by my second night I need a charge. When camping with no hook ups, I set up my solar panels (stored under the bed) as soon as possible. That way it can keep up with the battery drain. I have 3 folding Brunton panels, which are awesome. They daisy chain together for aprox 80watts. I just bungee cord them to a picnick table, roof of tow vehicle, or roof of camper depending on where the sun is.
Btw: i use the fridge too.

 

What size battery do you have? I can go the weekend without needing a charge. I do have the refrigerator but so far have only used the fan and interior lights for any length of time while off grid.

Also what is the full name of your solar panels? I googled and found 26 watt panels. Are these the ones you use?

 

With a 72 ah battery we have camped off grid for a week using lights, water pump, tv for movies and the Fantastic fan as desired. The battery was still in the green. A 12v electric blanket killed the battery in 8 hours on another trip.

Based on the math, a fridge will run about 24 - 30 hours on a warm (75 to 80 degree) day when off grid with the 72 ah battery. Usage of other 12 v things such as a light could decrease that time. An 80W solar panel might buy you 8 more hours before the battery dies.

To run the fridge and maintain the battery at full charge would take a 250W panel. It would have to stay aimed directly at the sun for at least 8 hours on a cloudless day each day. Or, you could charge the battery back up once a day by running the engine at 1,000 rpm for about an hour. ($2 gas)

We use a cooler. ($2 bag of ice)

Hilditch

 

Without the cooler we could do a three day weekend on a single charge with moderate usage. With our 85w solar panel and some sun, we can blast the stereo all weekend without running out. (Don't have the fridge though).

 

Since you didn't provide the math, I am not quite sure how a dc refrigerator will run for 24 to 30 hours in a 24 hour day no matter the temperature. Perhaps you meant for the whole weekend. I am not an electrician or an engineer so I have to rely on anecdotal experience. All that I know is on a 3 day weekend with dc fridge running, my battery gauge went from 12.5 to 12.2. The only other things that we used were the ceiling fan and the interior lights. Now I did get the battery upgrade to AGM so I am not sure how much that plays a role. Cary can probably comment on it's specifics.

As to my choice of the fridge vs the cooler, it is a matter of preference. Not having to deal with ice, wet food and water drainage makes it worth it to me. It was not a matter of economics. If economics were a factor in this, I would have bought a Little Guy.

 

Joan, the panels are made by bruntOn and yes, 26watt each. I have a 72ah battery. Btw. The fridge doesn't run much, it cycles. If yOu keep it closed, it barely runs. I have gone extended stays off grid never having to charge battery from tow vehicle or 120v. The solar keeps up pretty well.

 

I have not seen the chart published showing the run time math for the Dometic fridge in years. Back when they were Waeco brand yet there was a really good chart showing average power consumption based on ambient temperature right in the owner's manual. For some reason when Dometic printed their own version of the manual they omitted this chart. Any one here with a older fridge that could share this chart info?

Anyways, from studying the chart way back (running on memory here) it makes sense what both Joan and Matt are running into. The average summer temp type draw should net you just over two days of run with the 72ah battery. I am guessing because Matt is in a warmer climate he is running about the normal average. Joan is in a cooler climate so her average power consumption would move down the chart and her numbers make sense also. If I remember right the bottom of the chart for temperature with the 72 ah battery netted you something like 3.5 days of fridge run.

Joan, I don't think the AGM will gain you much for run time for the fridge, it is only 6ah more capacity. 4 hours more maybe? I think it is the ambient temp that factors the most in your run time.

So, let's do some actual math. The average run (middle of the chart) for the Dometic fridge is going to be about 1.5 amps averaged. That is 18 watts continuous. When figuring solar you double the load for panel/light averaging. That means we are talking a 36 watt continuous solar need to run the fridge. So, we have something like 10 hours of daylight this time of year? That is 42% of the day. Invert that and you need to take the 36 watts times 2.4 which comes to 86watts of panel needed.

Let's use Matt and Joan for examples again (hope you don't mind?) since they gave us such good data points. Matt lives where there is more sunshine than Joan does. Joan is going to have more cloud cover on average. So, the doubling of the load factoring will skew one way or the other depending on weather/clouds. Matt clearly shows he has more sunshine because he is running a 86watt need on 78watts of panel. He is getting about 10% (or more) more sunshine during the day then the average. Joan has less sunshine but her load requirement is less because of the lower ambient temperature. She probably has a 30 watt or less load requirement due to the lower ambient. Taking that times 2.4 and she only needs 72watts of panel with her average temperature. But, she has less sunshine so if we add Matt's 10% reduction on to her panel need she is now needing a 80 watt panel.

So, in the end Evan had it right all along for panel sizing! Yes, the fridges can also draw an average of over 2amps continuous too as you move up the chart. But, higher ambient temps typically also indicate longer hours of daylight for the panel. If you have hot, short days (Indian summer kind of thing) you could fall short on your panel size then.

Cary

 

Since I have done some research on this, I will provide a few metrics that I have found. The energy consumption of a Dometic CF35 is 45Watts, if I am doing my calculation correctly that means that it draws 3.75 amps if it runs all the time. The running times based on the numbers provided by WAECO for their branded CF35 are:

15% at +20°C ambient temperature,
19% at +32°C ambient temperature,
both at +5°C interior temperature

This means at 32C or 89.6F it will, in theory, be consuming .7125 AH. This implies that in a perfect universe a 72 AH battery will run the CF35 for about 4 days. YMMV.

 

Slumry and Cary,

Thanks for the information. Since, as Cary pointed out, I live in a climate where it is unusual to get to 89 F, my refrigerator is not consuming that much not to mention that the temperature does not remain constant. It might be 89 at 4 PM but it is 52 at 1 AM.

Even for Matt, the temperature may get into the 90s or even 100s but during the course of the day, it is going to cool off. Fortunately for him his has all that sun. (Very jealous.)

At some point, I will be traveling to other parts of the country. This is good information to know regarding my power consumption off grid.

Thanks again.

 

thanks for the great discussion, folks

what other aspects of solar should we discuss?

brands and prices? (likely easily available on the net)
panel storage approaches? (I'd like to hear how and why folks went the way they did)(seems like the only feasible approach is on the bed or in the tow vehicle - doesn't seem worth it to mount on the roof, but maybe a good use of the tow vehicle rook rack? is under the bed feasible)
panel "mounting" (not storage) approaches? (ditto)

ps I also plan to use a cooler full of ice. Ice cold riesling is mandatory for car-camping, IMO. I'm in the market for the best cooler there is.

 

You nerds! Haha! Also I think the fridge cover helps it work more efficiently. On a hot day, it feels cool between fridge and cover, that means the cover is holding in a lot of cold air.

 

I really like the idea of the fold-able solar panels, I just haven't come to terms with the cost. I believe Matt said he stores them under the bed. I also like the idea of just resting them on top of the raindrop or a table out in the sun.

If I don't go that route, I would get the two smaller panels to link together. I haven't done my homework yet as to dimensions or storage container to see if those would fit under the be as well.

Isn't this fun though?

 

Is there empty storage area under the bed?
The foldable ones get pretty small. The non-foldable ones, not so small.

 

On my raindrop, there are 4 storage bins under the bed, one of which has my spare tire in it. Lift up the mattress.

I looked on Camp-Inn's website. A 550 has two storage compartments.

 

I knew about the spare tire, but thought the other also had stuff in it, already. But I have not poked my head in there, yet. (I am sure my wife has.)

 

550 Under Floor Storage-Adds TWO storage compartments, in the cabin floor, under the mattress. Compartment sizes (22 x 22 x 5.5 inches) and (20 x 17.5 x 5.5 inches). Great for storing items like raincoats or tools. One of the storage compartments is sized to fit a 12 inch spare tire.

I don't think I've seen a solar panel that is less than 22 inches long. Maybe the foldable ones are.

 

These panels fold up nice and small. Good for storage in a TD.

and you can string them together, depending on how much juice you want.

http://www.benmeadows.com/search/b...adows.com/search/brunton+solar+solaris+rigid/

 

Oh, those Bruntons are nice. Nice find guys.

Another one I have seen people drooling over is the Global solar military ones. Even pricier though:
http://www.globalsolar.com/products/military/

Cary