Micro-Solar Setup : My First Experience w/Off-Grid Electricity

[bruss01]

Efforts yesterday and today have the platform re-populated with components and it's taking shape fast now. Bluetooth working on the BMS and the MPPT charge controller. Tomorrow I need to re-braise/solder the aluminum bar, install my 12 volt outlets and mount the lid... that should wrap this project up for the present. At that point we can determine what kind of testing to do so we know if the basic system goals will work or not.

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Here's a plug-in for the input from the solar panels, allowing the power box to be unplugged and wheeled away, no tools necessary.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Getting down to the finishing line... the end is in sight!
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[flock6]

Do you have it fixed so that you can charge the batteries with ac current as well?

[bruss01]

Do you have it fixed so that you can charge the batteries with ac current as well?

Page 21 of this thread, post 206 has pics if you want to see the 120v AC charger (blue). It was spec'd at 75 amps but on first run it was charging at 80 amps.

https://www.whenshtf.com/threads/469...067#post784067

Link to product on Amazon:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Nice little unit mounted on the end next to the BMS, it's tucked out of the way but still wired in. Has LiFePO4 setting, making things easy for the BMS and batteries. This capacity is really worth insisting on to charge in a couple of hours from wall outlet or generator to cover high use or a few days of overcast.

The purchaser comments on Amazon mention that there is a small parasitic drain from leaving this unit connected... at 12v, it's 3.5 with the switch on, and around a tenth of a watt with switch off... inconsequential for my purposes since I have the solar panels connected.

Of greater concern is something I just noticed in the manual for the solar charge controller yesterday. Apparently it will not start sending a charge to the batteries until the voltage coming in from the panels is at least 5v higher than the battery bank. This isn't what I expected from an MPPT charger. If I had known this previously I'd have chosen smaller wattage cells and gotten several more of them to boost the voltage more without exceeding the wattage limits on the controller.

I'll have to just wait and see what kind of impact this makes, if any. Partial shade, overcast, and early/late day sun are some of the situations I had wanted to address by going from PWM to MPPT. Time will tell if I'm painted into a corner on that score. Worst case scenario... the new 210w panels can go onto the trailer as replacement upgrades for the 140w panels on there now (for an additional 210w total, a 50% increase), and replace the three 210w panels with seven 100w panels on the roof here at home. That would still keep me within the 700w capacity of the charger and get me 7x12= 84 volts at the charger input, still inside the 100v limit... with the consequence of higher voltage with less light in the sky, meaning more collectable hours in the day. Ah well... we shall see... the question is how many hours of daylight are putting at least SOME juice into the batteries... if we're talking losing 30 minutes in the AM and another 30 in the PM that's not so bad. If we're talking a couple of hours on both ends on an overcast day... no bueno. Four hours of lost collection on an already short winter day... sub-optimal would be putting it lightly. We'll see once it actually goes into production.

[bacpacker1513]

This is a great thread. I'm learning a lot as you build. Thanks for documenting this in such detail and reporting for all of us to follow

[bruss01]

This is a great thread. I'm learning a lot as you build. Thanks for documenting this in such detail and reporting for all of us to follow

Thanks BP - that's the kind of feedback that makes doing it worthwhile... my successes are sweeter and mistakes more bearable when I know others might profit from them.

Doing some battery and inverter testing today. Here's a small space heater consuming 600 watts on the inverter. It's been running about 90 minutes and has brought the battery bank down about 5% according to the BMS software, drawing right at 60 amps DC. No hot spots in the wiring and the BMS is cool as a cucumber so far. Inverter fan is off at this comparitively low load so we're running silent so far. Have to ramp up the load at some point to make sure tge fan does actually work... some may recall my original inverter for the trailer had a defective fan right from the factory that never worked... which wasn't discovered until out on a camping excursion. Bad time and place to discover shortcomings in your gear.

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Got the aluminum bar re-soldered, painted and re-mounted. Hoping to get my 12v outlets done today and the lid back in place so I can wheel it into position, plug in the solar panels and start seeing what the collection looks like tomorrow.

Cell balancing appears to be taking place... initially there was .4v difference between highest and lowest cell voltage... today I'm seeing it at .04, a 90% reduction. This is what I was hoping for... a few drain/charge cycles should even it out a bit more.

[Winni]

Nice job Bruss, great documentation. I was "on vacation" for a while, and might have missed your reasoning for not going with higher voltage on your battery bank, with smaller wires and perhaps less expensive parts? Enquiring minds want to know

[bruss01]

Fair question Winnie. DC accessories are quite common such as those intended for portable use with automotive 12v sockets. Due to the automotive, marine and RV industries 12v components and accessories are always going to be readily available... 24/48v, much less so. I don't want 100% of my ability to use such things to be reliant on an inverter or converter. You always have some conversion losses, which are important to minimize with off-grid implementation. This system is reasonably compact and self-contained, and thus transmission losses over distance for 12v aren't really the dis-incentive here as they would be if I were running 12v all over the house. I may change my tune at some point but for now, that's my school of thought.

Here's the nearly-completed unit ready to get wheeled into position and plugged into the panels:

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In order to keep the polarity straight and the color coding correct (red = +) it is necessary to use a polarity reverse adapter. So as to avoid error, I have installed one to the incoming line and affixed it with heat-shrink.

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Dawn comes at 7:24 am here today and rain is expected. Should be a decent test for the minimal collection capability that is an area of concern for the new panels. I have drawn down the battery bank to 75% to see what kind of charging performance we get. Readings will be collected every 15 minutes starting half an hour before sunup, until we have a full charge on the battery (if possible) with zero load.

Part used:
Sunway Solar SAE Polarity Reverse Adapter
https://www.amazon.com/Sunway-Solar-...omotive&sr=1-1

[bruss01]

Dawn came at 7:24 but there was voltage on the panels in the pre-dawn light. Sky was overcast and sprinkling.

By 7:45 there was a tiny trickle of current flowing into the system, about a tenth of an amp, and by 8:15 there was current flowing at about .5 amps with the panels reading 8 watts. By this time the rain was coming down pretty steadily.

I'm having to guess/average these numbers because they jump around pretty fast, but I'm in the ballpark. Will track through the day, I have a spreadsheet to collect the data as it comes in.

Looks like concerns over lengthy no-production periods of the day were unjustified. If it's producing current to the battery within 30 minutes of sunrise on an overcast day, I can't complain too loudly about that. Remaining to be seen though is how much useful power we can harvest on a short, overcast winter day.

ETA: The depth of cloud cover, though consistently overcast, has varied between light and heavy all morning, so momentary numbers are up, down and sideways. In a case like this, the cumulative numbers are typically more useful. Coming in just around noon, we have accumulated 90 watt-hours so far this morning. That will serve as our benchmark for this afternoon's collection. If I'm not mistaken, 1800 watt hours is what our fridge consumes per day... have to get out my Kill-A-Watt and re-verify that.

ETA2: One hour later, and (while still overcast) it's brightened considerably outside. The cumulative total is up to 150 watt hours now. That's a nice little bump. Panels are cranking out over 100 watts now and putting juice into the battery at nearly 8 amps. Battery bank now up to 77% ... started at 75% pre-dawn this morning.

ETA3: Found previous post stating the fridge used 1.22 kWh in just short of a day, so 1500 watt-hours is probably in the ball park. That being the case today would likely go on the books as a deficit day (if we were running the fridge off the Power Box) unless we have a really stellar afternoon (unlikely according to the forecast).

ETA4: 3:30 pm here now... The skies are clearing, with patches of blue and some high-level cirrus clouds but not overcast, I am seeing patches of sunlight on the ground. However, it looks like we are getting some interference from some (bare) trees because the panels are only pulling in 20 watts at this point, charging amps are reduced to 1.5 - that's disappointing. Well, 20 watts is still 20 watts. I wonder if re-wiring for parallel instead of series would benefit the collection? That's how I was set up previously with the PWM charge controller. Question there is would there be enough voltage to even turn on the MPPT? Possibly not. If so, then maybe the MPPT was an expensive mistake. But we'll see how the rest of the week goes before changing anything. Anyhoo - we're up to 260 watt hours for today and it's doubtful at this point we'll see 300.

ETA5: Done for the day now. I shouldn't grouse much, after all we did add 3% to the battery charge with the 270 watt hours that were collected despite inclement weather. Looks like this time of year, our main collection hours will be between 9:30 AM and 2:30 PM. We'd have done substantially better today if most of the late morning hadn't been heavily clouded (the sky was so dark at one point it was generating zero amps) as illustrated by how well we did in the early afternoon (nearly 120 watts at one point) despite lighter but still overcast skies.

[bacpacker1513]

Lots of good data. Thats best way I can think of to get a true test of the system.

[Winni]

Fair question Winnie. DC accessories are quite common such as those intended for portable use with automotive 12v sockets. Due to the automotive, marine and RV industries 12v components and accessories are always going to be readily available... 24/48v, much less so. I don't want 100% of my ability to use such things to be reliant on an inverter or converter. .....

Very true, my solar powered mountain top radio site was 12V also, mainly because I owed all 12V radios that I was planning on installing. This was back in the 80's, 36W panels, I know, WOW... I ended up replacing them with modern tech, but I was stuck with the 12V footprint. Too old to hike up the 3,000 foot mountain these days, but fond memories remain.