Solar with a residental fridge

[prepilot_3ck]

All,

I have a question about solar panels for my new (to me) RV. I have a 2016 Thor Outlaw Gas Class-a. I have three main concerns regarding power when not plugged in and not running the generator (which I would like to minimize). Solar seems like the answer but I'm not sure how much to get or what to look for. For the record we live in Vegas and MOST of our camping will be done in the desert where we get 364 1/2 days of unobstructed, direct, blazing hot, relentless, oppressive, and power generating sunlight.

I have a 6V (4 battery) house system. Each 6V battery is marked as 20 Amp Hours. So, 20 AH/6V pair (no current change in series = 12V@20AH), in parallel with a 2nd 6V pair doubling the capacity bringing me up to 40AH @ 12V of battery life. If I can Apollo 13 this thing and keep my current draw down around 5A, I should be able to run for 8 hours ,assuming ideal conditions, before having to plug-in or run the generator. Whew.. ok.


Here's how the three concerns break down.

1.) My main concern is my residential fridge. I have one. Love the size and the look, but don't love the power requirement. I see myself doing a fair amount of dry camping/boondocking (that's what the kids are calling it right?) and I'd like to be able to use the fridge (along with lights, water pump, maybe the radio, charge phones/computers)without concern.

2.) Modern rigs are wonky with low batteries. Even in my old 2000 RV when the batteries were low, the craziest stuff would happen. Things would chirp, the generator wouldn't start, slides acted funny, I'd get weird dash lights, my transmission would go into protection mode and not shift, etc. In a modern coach, with all it's high-tech gizmos and do-dads, I can only expect things to be worse.

3.) Storage. Being in our early 40's we have a LOOOOOOOOOOONG way to go before we can make RVing a long term thing. So, for 4-5 days a week (or longer) our RV will be sitting in a storage lot - with direct sun. We have a battery shut off that seems to work at this point but I'm sure we're still drawing power at some rate. I'd like enough solar to keep everything topped off while in storage so the coach just springs to life when we are ready to go.

SO! We'd like enough juice to keep the fridge running all day/night while we're camping, and keep everything charged in storage. Some simple-ish, math would suggest I just need to be able to provide more juice in, than I'm pulling out. Which means a single 80W panel (80/12 = 6.6A.) probably won't cut it especially when taking into account loss in the charge controller and conversion, and wires, regulators etc.

My plan is to drop a current meter in series with the battery and fire up the things we want to run while dry camping. Make a note of the draw, and then plan on getting enough solar to exceed that by 50% or whatever is economical.

Has anyone done this exercise or is there an easier way to figure this out? Is 200W enough (16A)?

Thanks,
Brian

[69gp]

Glad you are going the solar way.. Just a few points to keep in mind. Fixed solar panels are only going to give you max power for roughly 3 hrs a day if they are facing south. Unless you have a tracker system on your RV or you are going to keep adjusting the modules better triple the amount of solar you think you are going to need. As for buying solar panels check Craigs list for them. When I come across modules I sell good used 250 to 350 watt panels for $100.00. I also get modules where the glass is shattered that I sell for $50 each. Reduction of output on these is only about 10%. You can add clear coat over them to keep the moisture out.

[prepilot_3ck]

Groover wrote:
My inverter shows 20A draw when the fridge is running, most of the time. When in defrost or the ice maker is dumping it can spike quite a bit. But then the fridge doesn't run all of the time either. My Thor coach came with 100amp/hr, batteries, I suspect that yours did too. The batteries can generally get me through a good nights sleep and maybe a little more. I recently upgraded to 120amp/hr and they seem to be doing a little better but I don't think that any lead acid battery is going to give you the rated power without damaging it. If you have incandescent bulbs you need to upgrade them to LED. I have not put in any solar panels but I am thinking about shooting for at least 300 watts if I do. I have been looking at Lithium Iron batteries but just can't convince myself to drop that much money yet.

Good to know! Thanks. I'm headed over to my RV here in a few minutes, I'll double check the ratings on the batteries. My coach is all LEDs so I'm a step ahead there. I'm going to run these batteries until they die then look at something else. By then I'll have a good idea of what type of camping I end up doing more of. If I'm finding myself plugged in 90% of the time, I'll probably stick with cheaper batteries, but if I'm boondocking more (which I hope is the case), it's worth it to spend the cash on the longest lasting/most powerful I can get.

Brian

[Groover]

My inverter shows 20A draw when the fridge is running, most of the time. When in defrost or the ice maker is dumping it can spike quite a bit. But then the fridge doesn't run all of the time either. My Thor coach came with 100amp/hr, batteries, I suspect that yours did too. The batteries can generally get me through a good nights sleep and maybe a little more. I recently upgraded to 120amp/hr and they seem to be doing a little better but I don't think that any lead acid battery is going to give you the rated power without damaging it. If you have incandescent bulbs you need to upgrade them to LED. I have not put in any solar panels but I am thinking about shooting for at least 300 watts if I do. I have been looking at Lithium Iron batteries but just can't convince myself to drop that much money yet.

[Bill_Satellite]

Be it solar or not, the real concern is the battery draw after dark. 4 GC batteries are not going to allow you to run the fridge, watch TV, fix dinner, make coffee, and on and on. If you have propane cook top and oven then you may be able to get by for the night if you don't the convection/microwave and you keep your TV viewing to a minimum along with keeping all unnecessary lights turned off. My 4 - 8D batteries do just fine but that's about 1000 AH capacity.

[prepilot_3ck]

All,

Thanks everyone for the responses. Great info in there. I need to check my batteries and see what the AH rating REALLY is and it sounds like I need to load up on as many panels as I can get my hands on. Solar BLVD has amazing prices, so I'm keeping them on the top of my list.

Again, thanks everyone.

Brian

[full_mosey]

The 20 hour discharge rate of a 220AH GC is 11A, not 20A.

HTH;
John

[prepilot_3ck]

theoldwizard1 wrote:

prepilot_3ck wrote:
Each 6V battery is marked as 20 Amp Hours.

What you are looking at is the Amp Hour discharge rate ! Most GC2 batteries are about 220Ah @ a discharge rate of 20A.

Yeah, I must have read the batteries wrong. I'll check it out and follow up.

Thanks
Brian

[prepilot_3ck]

MrWizard wrote:
My previous RV has a residential fridge
600+ watts of solar, 675 amp hrs of battery bank

For storage ONLY! , 100 watts will work
But to power the fridge and house hold power
200w is not enough, you will run the generator a lot
Remember even though you have many days of sun
Winter is still short on the number of hours of sun per day
The fridge runs day & night, you use lights , tv etc.. At night
To rely on solar, you must have enough to recharge the over night use, while still supplying, daytime power to the fridge etc..
And it has to do this during the five hours of good nearly overhead sun you get per day
I would get at least 600 watts of solar and three pairs of GC batteries aka 6*6v
Or some equivalent of 600 ampHrs of battery bank
AGM batters are a good choice

Solid response. That's what I was looking for... and I must have read the batteries wrong. Thanks! 600W.. I'll start there.

[prepilot_3ck]

2oldman wrote:

prepilot_3ck wrote:
Each 6V battery is marked as 20 Amp Hours.

That's *way* too small of batteries. Are you sure you're reading that correctly?

prepilot_3ck wrote:
Is 200W enough (16A)?

You only get 16a for a short time on a very cold day. The easiest math for solar is get as much as you can possibly afford and fit on the roof.

I must have read it wrong. I should have grabbed a picture when I had the cabinet open...

The more the better though.. I'm with you there.

Brian

[prepilot_3ck]

Acampingwewillgo wrote:
Yep, $400.00 for 100 watts would be expensive! I suggest another location to shop solar. Solar Blvd is your friend at about 100.00 +/- bucks per 150 watt panel. I've been looking for years to address the same issue you are(residential fridge). OH except, my MH is not new...lol

Ohh! I'm checking them out now.

Thanks!
Brian

[2oldman]

Awaiting OP.

[full_mosey]

theoldwizard1 wrote:

prepilot_3ck wrote:
Each 6V battery is marked as 20 Amp Hours.

What you are looking at is the Amp Hour discharge rate ! Most GC2 batteries are about 220Ah @ a discharge rate of 20A.

If you discharge a GC at a 20A rate, it will be dead in 11 hours.



220AH is the typical spec for a GC battery. This is determined by drawing 11A from the battery for 20 hours.

Again; 220AHs is the 20hour spec. That is the only possible use of the number 20.

Restated a third way; A 220AH will be fully discharged by discharging at 11A for 20 hours.

HTH;
John

[valhalla360]

What is the wattage/amperage of the fridge? Let's assume 100w (no idea what it really is for your fridge but 100w makes the math simpler, update the calculation for the real value) For a hot desert use in an RV that isn't air conditioned, I would assume 100% duty cycle (what percentage of the day the compressor is running).

If you have anything else using power, you need to do a similar estimate and add it in.

That means you need 2400w-hr of energy generated to replace what the fridge uses each day.

Solar panels will typically produce around 4 time their rated wattage in w-hr (ie: a 100w panel will generate around 400w-hr per day) So in our example, you would need about 600w of panels assuming no other loads.

You also need to figure out how much the batteries will need to hold. As mentioned, 20amp-hr would be something like a lawn tractor battery. (Find the real amp-hr ratings). Since you have a generator, let's assume if you get an overcast day, you can run the generator for a short period to make up the difference (if you really don't want to run the generator, you need to decide how many overcast days you want before you resort to generator and increase the system size to account for it). Let's assume the longest period you will go without sun is 18hr (late and early day solar isn't generating much of anything)...So the batteries need to hold enough to cover 3/4 of a day or 1800w-hr. 1800w-hr at 12v = 150amp-hr. Of course, you can't use 100% of the ratings on a lead acid battery or they won't last long. Usually, people assume 30-50% is available to use, so you need somewhere around 300-450amp-hr of battery to support the system.

Since the batteries are 6V, you calculate the amp-hr rating by multiplying the rating by the number of batteries and divide by 2 for 12V. (assuming you have 6v golf cart batteries, good chance you have around 400-450amp-hr in your current bank if they are in good condition).

A couple of side issues:
- If you have other electrical draws and they are heavy, you need to account for the Peurkert effect. Under heavy draw, the amp-hrs available are reduced...unlikely to be an issue if it's just the fridge.
- Similarly batteries absorb power more slowly as they near full (why some suggest assuming 30% available as you go from 50-80% charge and back each day). 100% charge can be difficult to achieve. If you do start the generator to give it a boost, do it early in the day so the solar can slowly fill that last part.

[MrWizard]

My previous RV has a residential fridge
600+ watts of solar, 675 amp hrs of battery bank

For storage ONLY! , 100 watts will work
But to power the fridge and house hold power
200w is not enough, you will run the generator a lot
Remember even though you have many days of sun
Winter is still short on the number of hours of sun per day
The fridge runs day & night, you use lights , tv etc.. At night
To rely on solar, you must have enough to recharge the over night use, while still supplying, daytime power to the fridge etc..
And it has to do this during the five hours of good nearly overhead sun you get per day
I would get at least 600 watts of solar and three pairs of GC batteries aka 6*6v
Or some equivalent of 600 ampHrs of battery bank
AGM batters are a good choice