Looking for guidance on off-grid solar setup for a she-shed trailer

**Mike90250** · 02-07-2021, 11:49 PM

My suggestions

1: Fridge. Use an RV icebox and a $5 block of ice when needed Electric Fridge takes 24hr to self cool from a warm start and consumes >0.9kwh daily
2: Heater. Electric is impossible, unless you only want it on for 10 minutes and flattened batteries. Look into "Mr Buddy" propane heaters.
3: Batteries pass on the Li batteries, and use a pair of 6V 200ah golf cart batteries (wired in series) Flooded would be my first choice, AGM 2nd, Li last.
Li batteries REQUIRE a BMS and integration with all charging sources, so the BMS can shut the chargers down when needed
4: Inverter(s) 1 small one to power lights and chargers, small water pump: 300w Pure Sine Wave.
1 large one (2000W mod-sine) which only powers the electric coffee pot/cooking appliance for 10 min, followed by a sunny day to recharge, and the inverter is only on, while the appliance is on, otherwise the self consumption will drain the batteries. Consider a Induction hot plate, much safer than glow coil, and 70% more efficient.

Or wire up the 120Vac cooking outlets to your generator and avoid the hassle of a transfer switch and ground wire transfer.
Lead acid batteries can charge simultaneously from multiple sources, Li becomes much more complicated because of the BMS interaction required

With reduced load on solar, a single 300w panel, aimed properly, will support the rest. Unless you are in Ecuador, you would rarely have more than 5 prime solar hours a day. You might have 13 hours of daylight, but the noonish hours are the full power hours.

**asloren1** · 02-08-2021, 09:52 PM

Hi Mike,

Thanks for your reply!

After some more thought, we have decided to go with a small wall mount direct vent propane heater (since we were going to have a propane tank anyway), so that now drops my overall power consumption basically in half (now about max 120A/day battery consumption @12v).

Also, to clarify, the coffee maker, toaster and induction hot plate will all run off the generator directly and not off the batteries via the inverter. That leaves really only the lights, water pump and fridge running off the batteries via the 120v inverter. Also, we are only using the trailer for 2, maybe 3 days (2 nights) max and mostly need power for overnight vs. during the daytime.

For the Fridge, this is a small 3.4cu ft 100W under counter dorm-size mini fridge that will only use 1.1A while running (we do plan to bring bags of ice when we first show up to pre-cool the inside to facilitate getting to temp).

I also had some follow up questions to your comments:
1) Regarding batteries, my understanding was that with normal type golf-cart or car batteries (i.e., non-lithium) you only get about 50% of the capacity and much less cycle life than with lithium (which allows for 100% capacity). If the solar kit I am buying has a charge controller anyway, what’s the main advantage of going with lead acid vs. lithium? Also, arent’t there concerns about venting/gas build up with lead acid?

2) Depending on the battery type, I’m still a little confused as to how I connect the generator in to charge the battery. Per your comment, sounds like if I use Flooded or AGM, then I can just connect the generator via 120v to 12V inverter directly to the battery along with the output from the solar charge controller with no need for a transfer switch (which is only needed if using Lithium batteries right)?

3) Regarding the inverter, I think I can now get away with only a 2000W 12v to 120V inverter to power everything given my reduced power needs. I’m a little confused as to your comment on the inverter drain as it shouldn’t be using much if any power just siting there if nothing is actively running?

Thanks again for your help!

-Adam

**Mike90250** · 02-08-2021, 10:17 PM

> For the Fridge, this is a small 3.4cu ft 100W under counter dorm-size mini fridge that will only use 1.1A while running (we do plan to bring bags of ice when we first show up to pre-cool the inside to facilitate getting to temp).

HA. That's about the same as my full size energy star fridge. The mini fridge has less insulation than normal, so it runs more.
50% duty cycle = 100W x 12 hours = 1200wh. At 12 v that's 100ah, half your battery capacity. Or a block of ice, or dry ice, your choice.

I'll let you look up the specs for idle draw and efficiency of your inverter. letting it run all the time, will suck a lot of power. Again - your choice. i still suggest the sure sine,
only 450mA when on. ( 24 hrs = 11 ah consumed. ) compare that to your other inverter choices.

Lithium cannot be used to 100%. Generally, you reserve the top and bottom 20% (40% of your capacity is now gone) for safety because Really Bad things happen when Li gets the least bit overcharged or drained completely. Below 40F, you loose half your capacity. Below frost, you cannot recharge or you destroy the battery,
And with Li battery, you will need to carefully manage charging with solar & generator usage. No easy solution, the BMS must be able to interact with the charger.

Generally, with a trailer, the batteries and propane are outside on the tongue. Batteries don't belong in living space.

**asloren1** · 02-08-2021, 10:54 PM

Thanks - This is helpful info!

For the fridge, I’m likely going to wire a generator outlet next to that outlet in case I need to switch it over to the generator source from battery. I also need to confirm the power draw as we are leaning towards a different fridge than the specs I gave you (smaller fridge).

On the batteries, sounds like flooded or AGM are the way to go...why do you prefer flooded vs AGM?
Also, why go with 2x 6v 200Ah in series which will give me 12v 200AH vs. 2x 12V 100Ah in parallel to get the same?

Thanks!

**Mike90250** · 02-09-2021, 12:46 AM

Flooded Lead acid. Cheap. Forgiving. good to learn on. Then after you get 5 years on them, go for the expensive ones. Just check water every 2 months
AGM costs much more than flooded. overcharge leads to popping the sealed vents and venting H & O2, depleting the fluid in the battery. Shorter lifetime than flooded

Batteries in series share the same current and stay balanced. Batteries in parallel seldom stay balanced, AGM even more sensitive. One battery does more work and ages faster.

**asloren1** · 02-09-2021, 08:20 AM

Thanks!

So, looks like my new setup should be as follows:
- 400W panels mounted to the roof and wired into the charge controller
- Charge controller wired to 2x 6V 200Ah lead acid batteries wired in series (for 12V 200Ah setup) - these would be mounted outside on the trailer tongue
- Batteries to the DC to AC 120v Power inverter (2000w most likely but will confirm specs/drain per your comment above)
- 120V Appliances plugged in to the inverter (2x 15A outlets) - these would be wired out from the inverter to 15A GFCI outlets to serve as breakers on each “circuit”
- Honda EU2200i Generator (with 2x 15A outlets): 1st plug for separate dedicated outlets in the shed wired to the generator for non battery sourced power, 2nd plug wired to a 120V to 12V battery charger then wired to the batteries (connected in the same way as the solar charge controller - no transfer switch needed so they both charge the batts at same time if the generator is running)

some remaining questions:
1) what would you recommend in terms of fuses between the various connections?
2) would you recommend going larger amperage on the batteries at all (ie >200Ah) for more capacity or stick with 200Ah for now?
3) anything else I’m missing from the equation here?

Thanks so much again for your help!

**Mike90250** · 02-09-2021, 11:19 PM

some remaining questions:
1) what would you recommend in terms of fuses between the various connections?

Fuses depend on the wire size, because they protect the wires

2) would you recommend going larger amperage on the batteries at all (ie >200Ah) for more capacity or stick with 200Ah for now?

This is your calculation, From the loads you describe, if you skip the fridge and use propane, or ice, 2 batteries should be fine w/400W of PV

3) anything else I’m missing from the equation here?

What are you expecting to power with that big inverter ? Without the fridge and cooking appliances, 400w ballpark seems right.

Looking for guidance on off-grid solar setup for a she-shed trailer

Looking for guidance on off-grid solar setup for a she-shed trailer

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