diy solar

diy solar

Solar powered Heat and cooling in a Motorhome

Oldbikes

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Feb 8, 2022
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OK Here we go, First post for me.
I have an older ( 1996 Motorhome ) that we use a lot but don't really go camping. We are retired and to get away from hot summer heat we go north in the summer and south in the winter where it is warmer or a couple of months each. We enjoy going to Festivals and car shows and dry camp in parking lots a lot so shore power isn't usually an option.

I recently acquired a used solar package with some missing parts, It is an Eco-Worthy 1200 watt 24 volt package and is now basically it's 800 watts, the previous owner lost one panel on a trip. The panels are still available so I can replace the missing panel if necessary to bring the capacity back up to 1200 watts.
I also received 2 gel batteries with the package, I don't know if that will be enough or it will be necessary to add more.

My plan is set it up as a stand alone package that will power a 9,000 but mini split and perhaps provide a couple of USB ports for phone charging. I intend to leave the existing house battery system alone.

There's not much info. on power consumption for mini splits however as near as I can tell it uses from 300 watts to 800 watts in cooling and I would think the heating would consume about the same. Using the onboard propane tank for Heat isn't really practical, it empty's the propane tank in about 4 days. The appliances on RV's are really very Inefficient !

I'm sure we will need to some guidance on proper grounding and fusing etc.
I'm a retired HVAC contractor so I'm confident that I have the basic skills to deal with the wiring etc.

The Inverter( 2,000 watt) will likely need to be grounded to the frame of the motorhome , I'm not sure if the onboard Generator , Existing converter and Alternator on the motor will allow me to do this or not, the only connection between the two systems would be the chassis ground and solar panel grounds ? Also in the future I might want to add a second inverter to the existing house battery so I can use the 110 volt outlets when we dry camp.

It's ok to to tell me what is wrong with this idea, That's why I joined this board to get some guidance from more experienced users.
Best.
 
In order to get help, it's important to provide as much detail as is reasonable. To that end, we need to know the specific components of your system. Please provide links, so multiple people trying to help don't have to waste time guessing.

PERSPECTIVE:

HVAC, even with a high efficiency mini split, is one of the most demanding applications for an off-grid system.

I don't know what kind of propane tank you have, but let's assume it's the typical 30# bottle. In 4 days, you're consuming 190kWh of energy when burning propane. If that lasts you 4 days, you're using 47.5kWh of energy per day. That is 150% of the total electrical energy consumed by the average U.S. household (30kWh/day). Since an RV furnace is notoriously inefficient, let's say you only need 50% of that or about

So, if you're going to replace your propane use with solar, you're going to need about 5,000W of solar in very good summer sun (you'll only get about 40% of what you need in Winter) and about $4000 worth of Lithium batteries to store the energy.

If you have a electric/propane absorption fridge, don't even think about running it on AC. It will consume 4-5kWh/day.

So, step 1 here is to establish the actual energy consumption of the proposed mini-split.

Step 2, calculate your energy requirements based on anticipated run time.

Step 3, design a system.

It's is highly unlikely the inherited system will allow you to significantly reduce your propane consumption - maybe 10-20% at a guess.
 
Thanks sunshine for the well thought out reply.

When the weather gets a bit warmer I'll install the mini split and then I will have a good idea of how much power it uses.

I guess the biggest question I have is if having the Solar as a Stand alone system going to affect the existing 3 power supplies. As far as I can figure the only thing that connects the 4 systems would be a common ground.

Plan A Install Mini Split and just use the Solar to power the Mini Split.

Plan B would be to attach the Solar to the existing house battery however the mini split is going on the back bumper of the motorhome and the house batteries are in front of the radiator. Also there is a limited amount of space for batteries where they are now. Perhaps this is the best option ?

I don't really want to relocate the batteries however there is a storage bay that would hold 4 batteries and the Solar setup. This would require me to move the existing wires and batteries about 20 feet.

We run the Refrigerator on lp most of the time. Water Heater, Cook Stove and Refrigerator will run all summer on 1 tank of lp the furnace seems to be the gas hog. I replaced the burner ad did a tune up of the Furnace however I guess it is what it is.

The roof air uses about half of our 30 amp power supply so if you want to use the microwave of coffee pot then you need to turn something off Also the roof air isn't very quiet. Running out of propane with the tank bolted to the frame of the motorhome isn't much fun when it's cold outside so having a Mini Split would eliminate that problem. Even better if Solar power would take care of most of the load.
Best
 
Thanks sunshine for the well thought out reply.

When the weather gets a bit warmer I'll install the mini split and then I will have a good idea of how much power it uses.

I guess the biggest question I have is if having the Solar as a Stand alone system going to affect the existing 3 power supplies. As far as I can figure the only thing that connects the 4 systems would be a common ground.

No.

Plan A Install Mini Split and just use the Solar to power the Mini Split.

Based on what would typically be provided by that system, this is probably going to be a severe disappointment unless you're good with only running it a few hours a day.

Plan B would be to attach the Solar to the existing house battery however the mini split is going on the back bumper of the motorhome and the house batteries are in front of the radiator. Also there is a limited amount of space for batteries where they are now. Perhaps this is the best option/
I don't really want to relocate the batteries however there is a storage bay that would hold 4 batteries and the Solar setup. This would require me to move the existing wires and batteries about 20 feet.

The inverter is what needs to be close to the batteries, and you're going to want some cables capable of 200-250A. Running 120VAC to the mini split is a triviality in comparison. If you have a compartment that could house the new system, rather than move or modify the RV in any way, create an "off-grid" system in that compartment. You would plug your umbilical into the inverter output. The existing AC-DC converter would charge from the "off-grid" system. You'd keep your existing batteries as additional 12V "backup" to the off-grid system.

We run the Refrigerator on lp most of the time. Water Heater, Cook Stove and Refrigerator will run all summer on 1 tank of lp the furnace seems to be the gas hog. I replaced the burner ad did a tune up of the Furnace however I guess it is what it is.

I feel our pain. Our 37' 5th wheel furnace burns through a 30# bottle every 2-3 days just keeping the interior at 50° in ~20°F temps, but at least they're removable. Need to skirt the bastid.

The roof air uses about half of our 30 amp power supply so if you want to use the microwave of coffee pot then you need to turn something off Also the roof air isn't very quiet.

Too true!

Running out of propane with the tank bolted to the frame of the motorhome isn't much fun when it's cold outside so having a Mini Split would eliminate that problem.

If you can power it with grid, and your propane furnace isn't in any way required to keep tanks/pipes from freezing, or freezing temps are not a concern, then yes.

Even better if Solar power would take care of most a very small portion of the load.

Revised for perspective. When you need a heat pump is when it's cold. When it's cold, you get crappy solar, especially with panels mounted on a flat roof.

With 800W of solar, you're likely only going to get a few hours "paid for".
 
I installed a 12k BTU LG mini-split in my RV last year. I live in Ohio where it gets hot and humid for about 3 months. Once the RV is cooled down, my mini-split pulls between 300-400 watts, depending on how hot it is outside. I tried running A/C off-grid with 7.5kWh of battery capacity and it wasn't enough for 24x7 use if it was cloudy for a day (I have solar). I have since upgraded to 15kWh of battery and added additional solar (2,000 watts on the roof) and will see how it goes this summer.
 
Thanks K8MEJ for sharing your experience with solar and a Mini split.
I'm putting a 9,000 Btu unit in so I suspect my experience will be similar. Cooling is the main thing for us we don't do a lot of cold weather camping, we tried it this year and the lp use was unbelievable.
Besides the onboard Onan we have a small Honda generator (600 watt) so with solar and the small generator we hope to heat and cool with the mini split, 24 / 7. My plan is to use the onboard Generator and roof air to get the coach cooled off and then use the mini split to maintain.

Also I'm adding an insulated curtain behind the drivers cabin and on the larger windows This is a 25 ft class A and the glass is a large heat loss / gain area.

I was going to start with 400 kWh of battery, sounds like we should plan ahead for more.
 
Thanks K8MEJ for sharing your experience with solar and a Mini split.
I'm putting a 9,000 Btu unit in so I suspect my experience will be similar. Cooling is the main thing for us we don't do a lot of cold weather camping, we tried it this year and the lp use was unbelievable.
Besides the onboard Onan we have a small Honda generator (600 watt) so with solar and the small generator we hope to heat and cool with the mini split, 24 / 7.

Also I'm adding an insulated curtain behind the drivers cabin and on the larger windows This is a 25 ft class A and the glass is a large heat loss / gain area.

I was going to start with 400 kWh of battery, sounds like we should plan ahead for more.

400kWh is enough to power the average U.S. household for about 13 days. Did you mean 400Ah?
 
I haven't tried it, but you might get decent heat from the mini-split if it is a heat pump model. It won't keep your tanks from freezing, unless you have tank heaters installed.
 
Had some nice days this week so I worked on getting the Mini Split installed in the Motor Home.
It was in the mid 70's today so I started the mini split up. It pulls 3.6 amps at 121 volts in cooling mode

This is a C&H unit and has a setting called Dry which cools enough to remove humidity that setting only pulls 1.4 Amps sort of amazing how efficient these units are.

Heating didn't go so well, 6.8 amps at 120 volts I don't know if the amp draw will go down as it approaches the set temp or if it remains fairly constant. So I don't think Heating with solar is going to work as well as I had hoped however the cooling part looks favorable.
This would be fine if we can plug in at a campsite however heating would take a lot of solar and battery reserve as near as I can tell.

I think I will put a Kilowatt meter on it and see how much it uses in a day.
We might turn into fair weather campers.....
 
Here is the weather and energy usage with a 9000 btu heat pump in a 16’ composite box set at 61*
 

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