Solar Basics?

[tx2sturgis]

Another possible thread title: 

"Complex, elaborate, powerful, expensive, solar basics?"

 

[jimindenver]

All I am saying about the 1 to 1 ratio is it is a simple numbers game. Take 300 Ah's out, then you have to produce more that 300 Ah's to put it back. On a short winters day not only is the amount of sun time is less, so is production due to the low sun. I agree that LFP is going to help the situation but it doesn't mean the solar can't get behind.

At 1440 Ah 50% is 720 Ah. 1440 watts is going to produce 90 amps or so at 12v as a peak in the summer, less in the winter and for a shorter time too. 5 or 6 hours of peak production is going to fall short of a recharge and there are some pretty healthy draws listed. So you are now 200 Ah's or so behind with the longest nights requiring power from the bank. Tomorrow you might catch up if you keep your loads down, maybe not.

 

[jimindenver]

Just how big is the cargo trailer going to be? Free, cheap, whatever, that's a lot of panel.

 

[John61CT]

I'm sorry of course inputs must be greater than outgo, thought I made it clear.

Did I miss OP stating their estimated consumption?

Where does 50% come into the picture?

A $5,000 budget does open more possibilities, and few of them are bad.

LFP stores the same usable power at about 80% less weight. . .

 

[John61CT]

It certainly is true that huge usage will require more than solar in a mobile context.

But LFP makes using a bit of dino-juice much shorter, easier and efficient, with no cost in bank longevity.

 

[jonsun]

Could get by on much less solar, much less battery (and therefore lead acid) with just a small generator.

 

[Redbearded]

I guess what I was wanting to know is if there was some critical piece of gear that I was leaving out. There is so much mixed info between all the different chemistries and the requirements I was worried I had missed some critical piece of tech, plus I'm kinda balking at paying $1500 for a hybrid inverter, lol. Now I know I can prolly do what I want without it, and can add it in later if i'm wrong.

I found some battery balancers from Mao's Panda Land on amazon that look promising.

Also my solar guy I know does mainly large PV installs for really fancy houses (retrofit and new const) in silicon valley, he's an EE who used to work at Intel. I'm not sure how up to date he is on basically off grid setups as he does residential, but I'll find out

As far as the trailer, I'm looking at a 8.5 foot wide 16-18 long prolly, in aluminum with some custom frame stuff. I may go with commercial panels as that would give me some extra width, but i'll cross that bridge when I come to it.

 

[jimindenver]

At 18 ft you would be able to get 4-5 grid tied panels up there, even the 435w I use on my truck. 4 would easily leave room for a vent.

 

[becida]

As far as the trailer, I'm looking at a 8.5 foot wide 16-18 long prolly, in aluminum with some custom frame stuff. I may go with commercial panels as that would give me some extra width, but i'll cross that bridge when I come to it.

This will be an interesting write up when you get it up & running!

 

[Redbearded]

I am looking at venting under the raised panels (still need to figure what kind of an air gap would be optimum) using the fantastic Ez-Breeze. It seems low profile and while the Cfm are lower (350 vs 920) than a normal fantastic fan I think if  I do a few of them I can get more solar up and not risk partially shading my panels.

 

[rayrey]

Racking and venting under would allow for 5 300 series. There are 400 series panels out there, maybe your buddy can get his hands on some. 5 of the 435w would get you 2175 watts. That would do the job.

 

[jimindenver]

Rack above the vent will allow for 5 300 or 400 series panels. 5 of my 435w would be 2175 watts if your buddy can get his hands on some.

 

[Redbearded]

Damn! That's a lot of juice! Call me sparky and don't let the angry pixies out...

If I went with that much solar, what kind of a charge controller system would I be looking at? I was looking at the Victron 100/30 MPPT series, but unsure of the best way to wire them up, or how many I would need. They do make a 150 one as well.

 

[John61CT]

Victron does go bigger, just look at the specs sheets for max wattage. This can be exceeded a bit, long as Voc and Imp input max are not.

One SC per panel, if it's not too pricey, gives highest efficiency and best partial shading tolerance.

 

[Redbearded]

Ok, so it seems that one charge controller means I can step down to a bit cheaper lower power option, I can live with that. Will that mean that I will need to run some monster cables up top or something as the cumulative (series) panel voltage will be lower? 

I could also step back to 100AH cells and go for a 48 volt system, or 2x 24V in parallel for not a huge difference in price ($225 for 180AH vs $125 for 100AH). Running the 2x 24V system would give a bit of redundancy, which wouldn't be unwelcome.

 

[jimindenver]

You are going to need a 100 amp controller at 24 volts. After a quick search of the big names you are going to be limited to Victron 100 amp or the Midnight classic 150/96 amps or the Classic lite at 100 amps. A controller for my 435w needs to be at least 15 amp at 24 volts, 20 if tilted.

 

[John61CT]

No idea what you mean about that first paragraph, one SC per huge high-volts panel, there's no series there?

IMO stick to a 12V bank unless very good reasom to go higher.

Fewer strings paralleled, high AH batts is better than more smaller ones. Just 4s2p gives enough redundancy.

Blue Sea Circuit Wizard app for wire sizes.

 

[Weight]

Read through Rod Collins article in the link John posted. I also would stay with 12 volt as it is easier to find stuff. Eliminates DC to DC converters. Using for house banks that stay above the middle, you will be well served with top balancing your LiFePo battery. The EV folks use bottom balancing as they tend to run to lower charge.

 

[Redbearded]

Alright, I think I know where I was getting mixed up...

If I use one MPPT charge controller per large panel I will maximize power to the batteries.

I was getting mixed up when some people were talking about using multiple panels per charge controller (in series) to raise the voltage of the line running back to the controller (to minimize line loss from a low voltage long run). Then there is the issue that if the panels are in series they are more sensitive to partial shading power loss. 

In converse, if in parallel they respond better to partial shading, but because the voltage is lower you need to upsize the cables delivering the power back to the charge controller.

I was trying to figure out whether it was better to live with the power loss from the parallel system due to cabling (low voltage + high amp+ long run = high resistance) in exchange for the benefit of better performance when partial shading. My other option was to go for a series implementation (higher voltage + low amp +long run = no big deal)  to minimize the power loss from the cabling but be more vulnerable to partial shading. But now I see that if I go with giant panels and one charge controller per they will already be maximized for power output with neither of the drawbacks (except $).

 

[John61CT]

> using multiple panels per charge controller

This is the usual approach, because SCs are often less expensive per amp as they get larger, simplifies wiring and takes up less space at the bank.

> (in series) to raise the voltage of the line running back to the controller (to minimize line loss from a low voltage long run)

And also MPPT likes higher voltages for efficiency, but lower 12V nominal voltages (15-22V) used to be all that was commonly available, as higher was wasted with PWM.

> if I go with giant panels and one charge controller per they will already be maximized for power output with neither of the drawbacks

Yes

> (except $)

the cost measure as $ per watt, the larger high volt panels are competitive, can actually be cheaper

But shipping can be expensive, ideally you find a good deal close enough to pick up


The overall efficiency, watts per sq ft, as well as shape/dimensions, maximizing what you can fit on *your* roof is also important

The Victron 75/15 at ~$100, with a 32-65V 200-250W panel (maybe 300W if no costlier) is IMO a great-value pairing to use as a baseline for comparing other options.

That specific SC is unique in actually being cheaper per amp produced than Victron's larger units. But not suitable of course for that giant 400+W panel of Jim's.

Others are happy with "kit" offerings that are less expensive, but IMO the included controllers aren't quite as good.

Creating serial strings and/or paralleling with multiple panels, all going into one big SC is indeed the normal approach, works just fine.

IMO my approach can be just that bit more efficient and cost-effective, but there are lots of variables.

As you see devil's in the details, and you've obviously come a long way in your ability to sort them out.