Solar Power

Things are starting to coalesce. I received my solar charger. Looks like it will do the job, but for a few minutes wasn't sure if I had undersized it. I got a 30 amp unit, thinking I wouldn't exceed that with 2 panels. That is, until I found some panels that could very easily overpower the unit.

After a lot of reading and YouTube videos, I've written off the flexible panels. The two major issues are real estate and failure rate. It takes much more square footage to equal the output of a hard panel, and and very very easy to break or develop hot spots making them useless. Warranty is typically less than half the life of a hard panel. Price is also much higher per watt. These fill a need for some and have a place, just not in my system. I found a panel that I think fits my needs. Renogy makes a 270 watt @ 24VDC poly panel for about $1 a watt. I could do better cost-wise, down to 70 cents a watt for 100 watt panels, but I'd have to get more panels to make up the difference and occupy more space. Since space is at a premium, I'm willing to spend a little more to get a lot more. They also make a 300 watt mono panel, but the poly has a higher open circuit voltage with less sun.

So, I'm going to get one 270 watt panel and test it out. (2) 270 watt panels at 24 volts is 22.5 Amps / 540 watts when wired in parallel. This is where wire sizing comes in. If you think of your home wiring, if you have a 20 amp circuit, you wire with 12 gauge wire. I'm exceeding that already. 10 gauge at a minimum, and if you wire any distance, an even heavy wire is needed to prevent loss and overheating. I could wire the panels in series, which doubles the voltage (48VDC) but halves the amps (11.25A). Smaller wire size could be used, but you run into an issue: If one panel goes into the shade or fails, the entire PV array stops working. A parallel system will continue to produce power for whatever panel is still working. In reality, I happen to have a significant length of 4-wire 12-gauge stranded rubber jacketed wire. I can use one pair of wires in the bundle for each panel (11.25A) and then combine them at the solar charger unit with a very short piece of 8 gauge. Well within wire loads using lighter wire.

Battery storage is still an unknown.

As far as the fridge goes...... ok, maybe I was being overly ambitious to get a solar fridge. Still on my radar, but not for the initial prototype. I'm going to go with the nested cooler setup. I have a few of the cheap styrofoam containers from Omaha Steaks. Going to get a larger cooler to fit two of these. When I ordered knishes from NY, it came in an insulated bag which just happens to fit perfectly inside the styrofoam cooler. Filling 1/2 gallon milk containers with water and freezing them. Perfect size for the coolers and no melted ice water everywhere. This should be good to keep stuff cold a long while.
 
would something like that run a Window AC Unit in the summer / during the day?
Yes, with enough battery and a large enough inverter. There are vids of people doing it, but you need massive panel and battery to make it run for more than a few minutes.
 
So, for better or worse, I've ordered the 270 watt poly panel. Ordered it thru Walmart, same price as everywhere else, free shipping plus a discount ($8) for picking it up at the store rather than home ship.

Also ordered a termination tool kit for the MC4 connector. These connectors are the "standard" for solar panel hookups. And discovered something interesting.... The connectors are only good for a 10-12 gauge wire and 30 amps. If you have 4 panels at 270 watts in parallel, that's 45 amps at 24VDC. Like I said before, real easy to underestimate the wiring.
 

GURPS

INGSOC
PREMO Member
Yes, with enough battery and a large enough inverter. ...... to make it run for more than a few minutes.

I only want to offset usage during the day ... 700 ish watts ish when running with a surg of 1800 - 2000


so 4 * 270 = 1080 that should cover it
 
Don't forget those numbers are maximum theoretical. I'd knock 25% off the top, just because. And then your battery bank/inverter has to be able to maintain that load during any cloudy times, so figure what is acceptable.

I'd suggest reviewing some of the videos from people who have tried it.
 
I only want to offset usage during the day ... 700 ish watts ish when running with a surg of 1800 - 2000


so 4 * 270 = 1080 that should cover it
If you're serious about doing a/c on solar, check out this product. It softens the start-up power surge.
 
I've been discovering the down side to being retired. WAY too much time to think about things. Since I have no big debts, there's lots of expendable cash available. And I have a pretty active curiosity. Bad combination. or good. Depends on your outlook!

The solar fridge thing was bugging me. A lot. To the point where I went to Waldork today an bought a 3.5 cubic Ft freezer just to experiment. I figured what the heck. If the solar thing doesn't work out, I can replace my bigger freezer that's mostly empty with this little guy. Found one at Best Buy for $150, had the lowest annual KiloWattHours of any other.

Got it home and unpacked it. First thing I did was attach a watt meter to it, then fired it up. Let it run for a while, then did the calculations.

Mind blown.

Power on current at 120VAC was 905 watts. Immediately settled down between 94 and 97 watts. Less than a 100 watt bulb. Within 30 minutes the freezer was down to 20 degrees. I only need it to go to 34.

So, when running, it uses about 100 WattHours, that's 100 watts per hour. One solar panel rated for 270 WattHours, figure for argument's sake, 200 WattHours available. That's 200 watts available EACH HOUR. The freezer can run indefinitely as long as there is usable sun, but it shouldn't have to run that often. If it got to 20 gegrees in a half hour, it won't run very often at all to keep it at 34 degrees. So now it becomes a matter of how much battery you want to have on hand. The more battery, the longer it will run into the night. But I'm thinking that's not a big issue. Come dark, cover the freezer with a thermal blanket and wait for daylight. It's insulated better than a cooler, so that should work. My solar panel arrives Friday, so by Saturday I should be able to have a test rig set up and see just how much power I can really get from the panel to the battery.

So, next item to procure is a 12VDC to 120VAC inverter. Now that I have an idea of how much 120VAC power I'll need, I can select an appropriate inverter. Not considering the cheaper modified sine wave, going for a full sine wave inverter.
 
Gets even better.... I figured the power usage would have been higher for the initial power on and 1st cycling, so I reset the meter to catch subsequent power usage.

Took no time at all to stabilize at 0 degreesF. From then on, power-on surge is between 140 and 220 watts. I account some of that deviation to the speed and sample rate of the meter. It was $12... Run power usage is around 88 watts.
 

PeoplesElbow

Well-Known Member
How are you planning on changing the freezer's temperature? I am guessing you can fake it out to think it is actually colder than it is, maybe they use a thermistor?
 
An External thermostat, goes on the plug to the freezer. something like this, haven't made a decision on which one yet. This one doesn't require power, but isn't as accurate. Another digital I'm looking at is much nicer, more accurate, but is powered by the line, which is probably not a big deal.
 
I let the freezer run overnight with the thermostat set to max cold. It was stable at -10F. The watt meter really isn't fast enough to catch the power-on surge correctly, so my numbers of under 200 watts is just plain wrong. Still seeing surge between 900 and 1100 watts. Run current is still pretty low, less than 90 watts. The meter does have an actual runtime reading. In 12 hours, it ran about 3.5 hours, so a little over 30% actual runtime. I hope this to be significantly less when reset to 34 degrees.
 
Downloaded and read the install and specs manual for the solar panel. Missed something quite important.... I was expounding on the wiring of the panel, parallel vs series and how wiring in series requires smaller wire sizes but parallel was better for shading and panel failure. As it turns out, these panels have bypass diodes in them which allow the current to bypass the panel if it's not producing. So they can be wired in series to lessen the amps and wire size needed, and the entire array will still produce if a panel stops working for whatever reason.

This just made my panel-to-controller wiring much easier. Just one 2-wire stranded 12 gauge will accommodate up to 3 panels in series (my max input to the controller is 100VDC/1700W, each panel puts out about 32VDC/270W) and I won't exceed 10 amps.

Instead of buying expensive solar wire, it's been recommended to use 12 gauge landscape wire. It's direct burial if needed and UV protected. I think Lowes has a 100' roll for about $60.
 

Chris0nllyn

Well-Known Member
Instead of buying expensive solar wire, it's been recommended to use 12 gauge landscape wire. It's direct burial if needed and UV protected. I think Lowes has a 100' roll for about $60.
Great work so far.

Make sure your wiring is as short as possible. While ampacity of the wire is important, voltage drop in low voltage systems can be a problem.

Have you thought about possibly adding a small wind turbine? Obviously, it'll only help if it's windy (usually around 8mph start up speed and around 15mph charging speed) but may help ride through nights with the freezer on.
 
Thanx, Chris.
I actually oversized the wire. 14 gauge would have handled it (8-9A), but I upsized to 12 gauge to cover voltage drop loss up to about 50 feet. That should be plenty.

Wind may be a future consideration, but since this is a portable system for camping, a turbine may be a bit much. Other campers may not appreciate the turbine whine. I'd also have to swap out the solar charger, it's only designed for PV panels. There are units out there that have separate inputs for PV and wind.

I've been working with a small 17AH battery which won't accept a full charge. I did a quick welding job for a neighbor today and he gave me a 45Ah battery in real good condition. That will make my testing a bit easier.

Freezer was running at about a 30% duty cycle to maintain -10 degrees. Earlier today I set the thermostat to it's warmest setting. It stabilized around +10 degrees. Going to let it run more, but indications are that it's running at an 18% duty cycle to hold +10. Testing is in the garage where its been about 60 degrees, so I fully expect cycle times to rise as it gets hotter.

Got a cheapo inverter from WallyWorld just to continue testing. It has no real over/under voltage protection and is modified sine wave so I won't want to use it in the "production" system, but it will help me get wattage numbers for the freezer.

Really looking forward to getting the PV panel.
 

PeoplesElbow

Well-Known Member
Thanx, Chris.
I actually oversized the wire. 14 gauge would have handled it (8-9A), but I upsized to 12 gauge to cover voltage drop loss up to about 50 feet. That should be plenty.

Wind may be a future consideration, but since this is a portable system for camping, a turbine may be a bit much. Other campers may not appreciate the turbine whine. I'd also have to swap out the solar charger, it's only designed for PV panels. There are units out there that have separate inputs for PV and wind.

I've been working with a small 17AH battery which won't accept a full charge. I did a quick welding job for a neighbor today and he gave me a 45Ah battery in real good condition. That will make my testing a bit easier.

Freezer was running at about a 30% duty cycle to maintain -10 degrees. Earlier today I set the thermostat to it's warmest setting. It stabilized around +10 degrees. Going to let it run more, but indications are that it's running at an 18% duty cycle to hold +10. Testing is in the garage where its been about 60 degrees, so I fully expect cycle times to rise as it gets hotter.

Got a cheapo inverter from WallyWorld just to continue testing. It has no real over/under voltage protection and is modified sine wave so I won't want to use it in the "production" system, but it will help me get wattage numbers for the freezer.

Really looking forward to getting the PV panel.
FWIW the difference in temperature between the inside and outside can be used, so a duty cycle for -10 inside and 60 outside should be really close for one 10 inside and 80 outside.
 
Well, just set up the fridge to run off of the 750Watt inverter powered by a standalone battery, no recharge. Started at 13.0VDC, will let it run until I hit 11.0VDC, low battery warning on the inverter is 10.5VDC.

Just going to see how long it will run with the freezer temp at +10 degrees before the battery runs out. The inverter draws 6 watts with no load.
 
Started monitoring at 5:30pm. It's now 11:30pm, so it's been running for 6 hours, and holding fine at +10 degrees. Actual freezer run time so far is 57 minutes.

Started with a 45Ah battery at 13VDC, which is approx 55% charged. It wasn't fully charged to begin. 6 hours later, it's at 12.3VDC or 41% remaining. My cutoff is 11.0VDC. Not even halfway there yet after 6 hours. I expect as time progresses, the voltage will drop much faster towards the end.

This is so much better than I could have expected. No doubt in my mind that a larger fully charged battery will carry this all night long with power to spare. The only annoying thing is the beep alarm on the inverter when the freezer starts up. A warning for over-current draw. The permanent inverter will have a little more capacity and shouldn't trigger surge alarms.

I wouldn't be surprised if it's still running in the AM.
 
Still running. Battery is at 12.0VDC and 30% remaining at idle, sags to 11.6VDC when the freezer kicks in. Low battery warning lights, but it's still making 115VAC (inverter nominal output). Still +10 degrees. Total run time since yesterday evening is 2 hours 9 minutes. Disconnected everything. The inverter doesn't have a low voltage shutoff and I don't want to damage the freezer.

This was a great experiment. A few more tests after I get the PV panel, but pretty sure this will work just fine in the wild.
 
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