contemplating new solar setup

[tx2sturgis]

I just wired my panels for 24 volt to charge a 12 volt set of batteries and my charge controller , (which is supposed to be MPPT), did not charge the batteries well. I re wired panels for 12 volt and the controller works just fine. It is quite hot here, so maybe the heat generated from changing the 40 volts solar to 14 volts created too much heat for the controller.

Interesting, in fact the MPPT controllers do generate some heat when there is a large gap in voltage. 

What prompted you to re-arrange the wiring?

 

[tx2sturgis]

So in theory anyway the generator will run for about 60 hours on 20 lb, ( 3 hours per lb). Propane is sold by the gallon. Propane weighs 4.2 lbs per gallon. 5 gallons of propane weighs 21 lbs.  

Even less in reality....20 lb tanks are limited now to about 16 pounds, and the exchange tanks are usually at around 13-14 pounds of propane. Sad, but true.

 

[unicutie]

Wow long and informative post thanks. Yea in the end if I did this I would have just under 1kw panels. And yea I'm looking into doing a power wall style diy bank of 18650s iat hopefully 5kwh. I do also have a Honda 2200 generator in the mix which I run while I work to keep my dog cozy. It can run my ac at 100% compressor duty cycle for about 5.5hrs on one gallon of gas.

In the end the way it is gonna work best is by having a lithium bank and having enough insulation so that the duty cycle stays low. I actually have a bunch of 3" polyiso insulation boards that I'm gonna use, which I rescued from a roof remodel. The idea being if it only has to run for ten minutes every hour you save a lot of battery.

 

[John61CT]

Do not do a DIY 18650 style bank in your enclosed living space.

The only non-lead solution safe enough for that is LFP prismatics.

"Risk of thermal runaway" means explosive fires.

 

[Weight]

What john said. Plus add salvaged EV batteries as really a bad idea. LiFePo, and related Fe, is the only lithium chemistry to trust.

 

[DannyB1954]

What prompted you to re-arrange the wiring?

It can get quite warm here in Southern Nevada before the sun is high enough to produce full power at the panels to run a 5,000 BTU AC.
I thought if panels were wired for 24 volt, (two 12 v in series), It might produce power sooner. It seemed to work OK at first but then the controller said zero amps charging in the noon sun. The voltage was over 40 volts.  It was over 100 degrees that day, so I thought maybe the controller was getting hot and shutting down. I ran all the wires from the pv panels back to near the controller so it was easy enough to rewire the panels for 12 volt. The controller then said charge rate was over 40 amps, (I have 960 watts of panels).

 

[DannyB1954]

Even less in reality....20 lb tanks are limited now to about 16 pounds, and the exchange tanks are usually at around 13-14 pounds of propane. Sad, but true.

Maybe less, but maybe more. There are times when the compressor is shut down and the AC has a energy saving mode that turns off the fan at set point. So some of the time the inverter type generator is just idling. Also my solar panels never shut off so they add electricity during the day even when cloudy.  This reduces the load on the generator, (if I run the AC off of an inverter). On a sunny day from about 10 am to about 5 pm I can run the AC just off of solar and turn the generator off. I am also not in my van 24 / 7, so a bottle should last me quite a while. I will know more as time goes on as this is a new system that I put in just recently. I will be leaving my home base probably in August and see how things go.

The generator powers a 40 amp charger and the solar panels charge the battery as well. If the solar panels are putting out say 10 amps on an over cast day, and the AC is using 35 amps, that means the generator and charger will only need to come up with about 25 amps.  At 120 volts the charger would be using about 2.5 amps, (not a very big load).  Yes there are losses so everything is approximate. But all theory aside the system works for me. In materials I have about $2k invested, and it does cost money to run the generator, but it hasn't cost me $10k to keep the dog and I comfortable. Looking at the National weather map, it gets hot over probably 80% of the country. Not everyone can live in the 20% that is cooler. I for one can not take very high altitudes. I can forget about 8,000 feet let alone 10,000.



I carry a spare 20 lb bottle so I don't do exchanges. I think that they may be convenient, but a rip off.
When I get the tanks refilled at a propane dealer they always fill them until liquid comes out, so I know that they are full. I am only paying for the propane that is actually used. Say one bottle was not filled completely. That bottle would run out sooner then it should, but it would not cost me anything more.