Too much or too little Solar?

[jimindenver]

Here is another thing to consider.

I'd look with Google earth and see if the campgrounds you are thinking of are treed. Solar and trees, not such good friends.

When I talk of the balance I should also mention budget, room and practicality. We use solar because we exclusively dry camp. Even then there are things that we could do but they are not practical at this time. Most of the time our solar sits with the batteries in float, so there is plenty of power that could run the hot water heater or use a hot plate to cook on. The thing is by the time I buy the induction burner and new cookware or the heating element, wires, switches, fuses, etc. for the water heater. it will take years to recoup the cost vs the pennies it cost to do those things with propane. It might be worth it if we boondocked 24/7/365 but not for a handful of trips a year. ( not to mention we like to start the day with a shower, not sit around grungy until the afternoon when the batteries are charged and the solar has a chance to heat the water)

So are there hook up sites that you might be able to use where you thought of dry camping? If you are not going to be dry camping a lot in the future it may be cheaper just to pay for the hook ups now. I would run the numbers to see.

You mentioned a PSW inverter "in case" you wanted to run your strobe. PSW is the recommended type of inverter but the cost difference between a industrial MSW inverter of that size and a quality PSW inverter is huge. Last year we used a Power Jack 3000w PSW inverter that cost $200, it lasted one season. A quality PSW inverter cost many times that so this year we are using a Tripp Lite 1250w industrial MSW inverter. If I were to get another PSW inverter it would be a small Morningstar 300w fanless unit for electronics and leave the heavy lifting for the Trip lite.

 

[SternWake]

What batteries are you getting that are rated at 125 amp hours?

While 12V deep cycle batteries can hold slightly higher voltages under very high loads compared to golf cart batteries, the golf cart batteries are more durable when cycled, and need less persuasion to return to full charge.

While a pair of GC batteries is 232 AH, vs 250 AH for the batteries you are looking at, I'd have to say the GC's are the better choice for the reasons above and a couple more as well.

A 2000 watt load on 2 batteries will not allow the inverter to run very long before the low voltage alarm starts sounding.

Lots of people tend to buy huge inverters and power them with small batteries. This is like having a drag racing vehicle that only has a pint sized gas tank.

An 400 watt inverter powering a 200 watt load will be much more efficient than a 2000 watt inverter powering a 200 watt load.

 

[Matt71]

So, I found three 210W solar panels on Craigslist for $500. If I went to using four Trojan T-105 6V 225Ah batteries that'll give me 450Ah with 630W of solar and the cost will be about the same as the 400W with two 12V 125Ah batteries. And it would probably leave me room to add two more Trojans to the mix if I find I need them.

Does that sound doable?
Would I need to get a higher amp power controller with the bigger panels? 40Amp? 50Amp?

 

[akrvbob]

You can boondock fairly close by at most of those places and save so much in park fees you can pay for the inverter. In Grand Tetons, the cheapest place is $50 a night for a tent but the nicest boondocking spot I've ever been in was free and literally looked right at the Tetons.
Bob

 

[jimindenver]

$50 a night for a tent spot...OMG!

 

[jimindenver]

To add

Nice find on the panels. Check them out on a sunny day if you can and take a multimeter to test them out. DC volts to check the Voc and the amp meter to test the Isc. There should be a piece of paper on the back with the ratings that you should get close to. The morning star TS-MPPT-45 is the first controller that comes to mind for that array mounted flat.

 

[Matt71]

Colter Bay Village Campground is only $23 a night, but no hookups

 

[Matt71]

I looked up the Panels I found and they are guaranteed to produce the Watts on the tag plus up to 5 watts.

I managed to get my estimated amp usage down to 270 amps
Assuming those panels actually produce 210 Watts, and assuming 5 hours of sunlight a day, I should be able to keep the 4 GC batteries above 40%

I will have to limit my usage of thing alike my projector and the AC for when we have shore power.

One thing I’m wondering about the 12V cooler. Do those things actually draw power the whole time they are plugged in or are they like a regular refrigerator and only power on then the internal temp hits a certain point? It’s by far my biggest power dray, but I have it calculated at 24hours a day. If it’s actually drawing power less than that it would be nice.

 

[Seraphim]

Kind of hard to say what your panel's will likely produce withing seein the specs.

I figure the most the three panels will produce will actually be about 535 watts (15% efficiency loss). So on on optimum day, optimum positioning at 14.5v (using an MPPT controller) the max you'll get is 36 amps. That's when the battery is down. When the battery is closer to a full charge, it won't draw as much and the charging rate will slow down, IIRC. On a heavily overcast day, you may only get 12 amps. But if everything is perfect, 36 amps for five great hours of sunlight is 180 amps. That should cover 165 amps of usage. (Some law about needing more amps than used to recharge the battery. Ask Sternwake lol).

But most days aren't going to be perfect for you. So I wouldn't gamble on getting close to those numbers.

Specs on the panel's would help, if you know the manufacturer and model number.

 

[jimindenver]

Matt

My 245w panels at 10.000 ft on a cold clear day can produce 220w and 17a. You might get more going even higher but that's about as close to perfect as you will get. You will see lest at lower altitudes and higher temperatures. My full 720 watts on the ground and tracking can produce 50 Ah x how ever many hours you have full sunlight. That's 5-600 Ah's in the long summer days but closer to 300 Ah's in the winter.

 

[Matt71]

 

[jimindenver]

yeah, those are not going to get 210w Matt.

 

[Seraphim]

Spec sheet:


http://www.ibc-solar.de/en/fileadmi...POLYSOL_210_VG_DATASHEET_SOLAR_MODULES_EN.pdf

 

[Seraphim]

Each panel is an 18.3v panel offering 11.48 amps at maximum output. Multiply those two numbers and they come to a tad over 210 watts - before any efficiency reduction. That wattage is a theoretical rating. Using a PWM controller the best amperage you'll ever get is 11.48 amps x 3 = 34.47 per hour. Times 5 hours is 172.35 amps under ideal conditions. That's before any efficiency loss from the panel's, and any loss running it through the inverter. More like 146.5 amps, at an estimate. I'm using a 15% loss based on what a solar panel manufacturer once told me. So a 40 amp PWM controller should be sufficient. Using an MPPT controller, you might get 37 amps max. A higher amp MPPT controller might be a good idea, just in case. None of this includes resistance loss, either.

I'm not expert, so bear that in mind, but I learned a great deal here sizing my own system. And those numbers are all under ideal conditions - perfect sun, panel's tilted directly to sun, etc.

 

[Seraphim]

If you want and idea of how many amps an AC device will pull, find the wattage it will actually use and divide by 10. That will give you an idea of how many amps are being pulled out of the battery, and factor in inverter loss as well.

 

[jimindenver]

You don't see many 12v 200w+ panels.

 

[highdesertranger]

depends on what type of "cooler" you are talking about. the peltier coolers run all the time and only lower the temp inside them by 40 degrees. I have tried them and they are not worth it. an absorption refer also runs continually and is a power hog if run on 12v, I have also tried these. a 12v compressor refer is the way to go, sips power. these cycle on and off like your house refer these are buy far the best choice for a refer run off 12v. speaking of house refers the dorm refers are also power hogs, they are meant to be used in a house which usually has a more stable temp, plus with these you must run through an invertor which also has losses. I have also tried these. now if I would have just taken the money I wasted on all these other types of refers and just got a 12v I would be dollars ahead. highdesertranger

 

[Matt71]

What's a good 12v compressor frog that's not gonna cost me an arm and a leg? The only ones I can find are $500 or more

 

[Matt71]

I'm a bit confused. I get all the math, but I don't get how I'm seeing all of these builds on youtube and elsewhere where people have fridges and microwaves and TVs and one or 2 100W solar panels to run them

 

[Almost There]

What's a good 12v compressor frog that's not gonna cost me an arm and a leg? The only ones I can find are $500 or more

The other choice is just to stick with coolers that require blocks of ice. Cubes melt within the day during hot summer weather but a block will get you at least a couple of day. I've gotten at least 3 days from most blocks. The downside of the cooler/ice is that you have to deal with draining it and protecting the food from floating in it. They also take up valuable room inside the cooler but then you just buy a larger cooler to compensate for this.

To figure your cost on this, take the length of the trip and multiply it by, say an average of $1.50 per day for ice.

If you're going to be travelling continuously on a road trip even if it's for months then this may be the way to go if you don't want to bite the bullet and get a 12v compressor fridge.

The less expensive 12V coolers aren't worth the money except for transporting food to and from a summer home IMO. They're only meant to reduce the inside temp of the cooler to about 40 degrees cooler than the ambient air which won't keep fresh meat safe on a hot day in a vehicle. They're built to also keep things warm by the same variance to outside air temp if that gives you any indication of their intended market.

It's either pay as you go (ice), pay before you go (good compressor fridge) or pay for a huge solar system to power a regular RV fridge, which btw aren't cheap either.

The dorm fridge is the absolute last choice because a) it's not designed for the bumps and jars that travelling with it is a certainty, even the potholes on the interstates would be too much for it after a while and b) they require an inverter to work which eats up more power (more expense).