Solar Show and Tell

[AirMiles]

I just looked up the Specs of the Dometic DC refrigerator. It appears to draw 14.2A on DC https://www.dometic.com/en-us/us/pro...specifications That will put a dent in my EGC2 batteries after dark. Therefore, the only way to run this refrigerator from DC power after dark will be from Lithium batteries. My Duracell EGC2 batteries cannot withstand a 14.2A draw on top of the 7A draw of the furnace. So after dark DC refrigeration is a no go. Now the question remains, will 600W of solar be able to power that energy hog refrigerator during daylight hours or while towing in daylight?

[farafield]

Getting a bit stuck in the weeds here but thank goodness for you solar nerds. Can I ask a couple of dumb questions?

1. "Will I be able to run the TV all day with the inverter, run the refrigerator all day on DC, and still have fully charged batteries at dusk?" Your fridge on DC will also be using the inverter right?

2. A theoretical question:If your batteries are fully charged come morning and you use 45ah watching TV all day (make sure you get out a bit too!) and all of the other things, and 45ah coming in via solar, at any point in time as long as this equation stays the same, your batteries would stay at 100%--is that correct?

[Rocinante]

Is that DC Dometic a danfoss compressor unit, or something else? That’s a heck of a draw.

[lsbrodsky]

I think you can rule out operating a refrig on DC while disconnected from a DC source; it is just too much of a load. If you had a huge battery bank and a huge solar bank, maybe, but not a stock Airstream.
As for your TV and solar question, you are going to have a variety of DC loads during a day. You need to consider the total load, not just the TV. In addition, lead acid batteries are not particularly efficient for receiving a solar charge. Even if you think you are generating a certain amp-hours of charge from the panels, not all of that is going to get into the batteries. It is even more complicated depending on the state of charge of the batteries when you start the charge. I know some people who have kept detail records of how much they charged, how much the batteries changed, amp-hours used, etc. Sort defeats the purpose of getting away from it all. Best advice I can give you is use your trailer the way you want to and monitor your battery state of charge/voltage. If it isn't working for you, add more solar or charge periodically with a small generator.
Larry

[blacklab]

AirMiles,

I'm very much looking forward to your findings on this question as it evolves.

We're looking at a GT 27' and have pondered this very question.

Cheers,

Bryan

[nryn]

Airmiles,

I'm curious as to why you'd go to such lengths to avoid a $15 propane fill every few weeks.

I had to have my fridge replaced in my GT27 while on a long trip this summer; the new fridge worked very well. I ran both the new and old fridges on propane maybe 80% of the time. I was without a fridge for about a month, but throughout the summer I used the propane disconnect for a gas grill and fire ring and ran the furnace a few evenings and mornings. In the end, I filled one of the two propane bottles once over the course of 90 days (I don't use the auto-switch feature on the regulator, so I know all the propane came from one bottle). I was also surprised at how inexpensive a propane bottle fill was, and that was in Alaska.

Totally understand if it's just a personal goal to run off solar–no judgements here, just curiosity.

[uncle_bob]

Hi

I believe the fridge in question is a "three way" ammonia based unit. You are simply creating heat with the 12V to boil the fluid rather than using propane or 120V shore power.

Bob

[pteck]

Congrats AirMiles on your new trailer! Hope you and your family are enjoying it. With all the opportunities to take your experience with your first trailer and improve upon it.

I'd agree with wulfraat that you're going to want more battery. The relationship with generation and storage is tightly intertwined. One can compensate for the other to an extent. At some breakpoint, there is more value to invest into one aspect of the system versus the other, to get more performance all around for different scenarios.

With all the data you posted with your past 400W system, you were already not taking full advantage of its production. Where you regularly produce ~1000 kwh hour in a day, the system is capable of at least 30% more production. Part of this is your usage, but it's also what can be stored - for other opportunities like the fridge.

An upgrade 600W would be further excess capacity that still doesn't result in much more opportunities to leverage without sufficient stores.

Yet I understand to increase the battery bank the classic way with battle borns can be prohibitively expensive. Especially if you're talking about increasing capacity beyond your Duracell EGC2 6V. It would take a minimum of 3x Battle Borns to actually realize a real capacity increase. Plus all the costs of reworking the larger system to accommodate them.

May I suggest you check out a different strategy which could be to implement a second bank of lithium's via something like a Goal Zero Yeti battery? If the goal is to run the fridge, that's the way I would do it (and have done it). As it would never put me in a position that would drain my main bank of batteries dead and leave me power-less. Nights shouldn't be as taxing on the fridge as it would cycle minimally in the cooler temperatures.
http://www.airforums.com/forums/f37/...um-196422.html

[pcskier]

Originally Posted by farafield

Getting a bit stuck in the weeds here

If any thread can get into the weeds, it's this one!

Originally Posted by farafield

Your fridge on DC will also be using the inverter right?

No...remember, inverter converts 12V DC to 120V AC. For example, for the the tv/dvd. The fridge on DC will run on 12V off the batteries, but not use propane. The Globetrotter fridge is 3-way (120V AC from shore power or generator; 12v DC and Propane (12v just to run the control board), and the extra iteration of 12V DC only, which Air Miles is hoping to run on.

Originally Posted by farafield

2. A theoretical question:If your batteries are fully charged come morning and you use 45ah watching TV all day (make sure you get out a bit too!) and all of the other things, and 45ah coming in via solar, at any point in time as long as this equation stays the same, your batteries would stay at 100%--is that correct?

Yes...theoretically. But it should be pretty close actually. I like to look at the Victron Monitor and see if it is reading positive amperage, then I know the batteries aren't discharging. Or if the charge is less than the usage, at least the negative number tells me by how much--for planning/power management purposes.

[CarterKraft]

The show and tell does skew the numbers some.

I showed a 1.5 KWH per day solar harvest but that isn't the amount it took its the amount to charge the battery and sustain the DC loads in my trailer during the day which in my case were very high because that's when I was using the most energy

If you have an extra 15 amps over your old setup I don't see a problem running the DC refrigerator during the day when heat loads are high and so is solar production.

I know for me high altitude severely effected my propane consumption (even adjusted) and 2-30 lb tanks cost a fair bit more than $15, closer to triple that amount.

Last OPINION, Battle Born batteries are great but $ to $ I believe you are only paying extra for the 10 year warranty. These guys buying multiple $950 batteries are in a different use case than myself. IF I needed lithium batteries BB would not be my first choice although they might be the best choice for many of you.
In my case it would take $1900 worth of BB to equal my $220 worth of Duracell's in overnight / low amp usage.

Similarly the solar generator "Yeti" style systems are no better with restrictive solar charging parameters and no component level serviceability requiring complete replacement in the event of failure.

In all cases each person has to decide what is best for them to fit their needs be it lithium, 7500w generator, or portable solar. Different strokes for different folks!

[AirMiles]

Spent the day connecting my 400W of solar removed from my old Airstream. Got started about 8:30 am. Had the old Victron 100/30 connected by 10:00 with a trip to Home Depot for green and yellow 10 Gauge. (the solar wires were about 3' long in my old Airstream and only inches long in the new one). Had the 400W of solar operating by 2:30 and everything completely installed by 5:30. I'm waiting for AmSolar mounting feet, the Victron 100/50 and the 60A circuit breaker to arrive so I can install the additional 200W.

On the questions about running the refrigerator on propane vs DC/Solar. I'm willing to continue running the refrigerator on propane. I use 15# of propane every week to ten days while dry camping. The goal is to use solar to run the refrigerator instead of propane at least some of the time. Even if I can run solar/DC during daylight hours, or while traveling, that will stretch the number of days on propane and possibly increase safety while towing. I will still need propane for heating, cooking, hot water and generator usage.

It appears putting a DC refrigerator in an Airstream is more marketing than function. Even if I installed 400AH of lithium with 600W of solar, I'm not sure that I could run the Globetrotter refrigerator on DC 24 hours per day. 14.5A x 24 = 348AH! The propane savings or convenience cannot justify the cost of that large of battery bank.

I'm just enjoying the challenge to see what I can run on solar with a pair of Golf Cart batteries. I think there is value to having excess solar capacity with a small battery bank. I feel you can never have too much solar, although I'm going to be solar rich and battery poor. We shall see if I've increased the solar too far above the storage capacity to add value. But 600W should still improve performance on marginal solar days such as on dark rainy days with some tree canopy. Sometimes with tree canopy, I can only get a couple of hours of direct sunlight. The ability to produce 45A would definitely be valuable in that instance. I still like the idea of being solar rich.

[pcskier]

Originally Posted by AirMiles

It appears putting a DC refrigerator in an Airstream is more marketing than function.

Reading this update to the thread got me wondering about that. Especially if a trailer comes with group 24s and no solar, what on earth would be the point of DC for the fridge, with the kind of power draw we're talking about here. I guess it's good to have in the quiver for those embarking on BIG solar projects like yours, or those with BIG battery banks...but otherwise, pretty pointless for the average buyer. I can see this forum being inundated with posts in the near future, from unaware GT buyers asking "why were my fully charged batteries dead after a day of dry camping?" because they had the fridge on DC mode.

[Rocinante]

The only DC fridge that would make sense would be one with a danfoss compressor onboard instead of one with a heat-driven ammonia-based system.

[blacklab]

I know the answer to this question probably already resides in another forum thread, but I'm surprised that the TV didn't provide more power to the AS during the tow. Having the batteries being fully discharged by the DC refrig while being towed seems surprising, but not!

Perhaps a DC to DC system from the TV to the AS could solve that problem? I don't recall how many Amps those DC to DC systems provide.

Cheers,

Bryan

[farafield]

Originally Posted by AirMiles

...
But 600W should still improve performance on marginal solar days such as on dark rainy days with some tree canopy. Sometimes with tree canopy, I can only get a couple of hours of direct sunlight. The ability to produce 45A would definitely be valuable in that instance. I still like the idea of being solar rich.

This what I'm interested in the most--how much panel does one need for the cloudy/canopied conditions. Please keep us posted.

p.s. A bit off topic but something I've been wondering: wouldn't it make sense to have fixed panels have a kind of universal joint on one end so that one could tilt them to face the sun?

[Rocinante]

Our panels are hinged and could be tilted, but you’d have to get on a ladder to tilt each one manually, and then put them back down again before moving the rig. In my book, the small gain isn’t worth the effort.

[batman]

Here is a nice little video demonstrating the effect of angle on PV panels.

https://www.youtube.com/watch?v=m_YuPfShbCo

-Dennis

[AirMiles]

I do not tilt my panels. My 400W was capable of avoiding generator charging 97% of the time without tilting. On the occasional need to boost charge with the generator, tilting the panels would not have made the difference. When the generator was needed, it was lack of light (tree canopy) that was the issue and tilt angle would not have made any difference.

I’ve also answered a couple of my DC refrigerator questions. My 400W of solar is capable of running that power hungry DC refrigerator during sunlight hours. Therefore, I should be able to tow on DC during daylight hours (for added safety) and use solar instead of propane on sunny days. Here is how I figured that out.

I went to my Airstream after lunch. The batteries were fully charged and Victron solar controller was in float mode. I turned on only the DC refrigerator. Instantly, controller went into bulk mode and solar production increased from 12W to 255W at 19.3A! After a couple of hours of running the refrigerator on DC (still at 243W and 16.7A), I turned off the refrigerator and instantly the Watts dropped back to the 12W at 0.8A so the batteries were still fully charged. Basically, the solar controller provided all the power the DC refrigerator used. Here’s the pictures for Show & Tell.

[blacklab]

AirMiles,

That's good news.

And that was with your existing 400 watt panels, excluding the additional 200 watts you are adding?

Cheers,

Bryan

[AirMiles]

Originally Posted by blacklab

AirMiles,

That's good news.

And that was with your existing 400 watt panels, excluding the additional 200 watts you are adding?

Cheers,

Bryan

Yes, only 400W installed at this point. With 600W, I will have no problem running the refrigerator on DC during daylight hours, the Fantastic Fans, and recharging the nighttime battery use.

It appears with a big enough Lithium battery bank, I would be able to run the refrigerator on DC continuously. It appears I would need at least 200AH for the nighttime refrigerator use and another 100AH for my nighttime fan or furnace use. Then I'd need 100AH for a reserve. Therefore, 400AH of Lithium would probably suffice with only a single night of Amp Hour storage. I run my golf cart batteries with only a single night of Amp Hour storage and only need to run the generator on 3% of days. Then the question would be could 600W of solar recharge the 300AH of nighttime battery use while providing 20A to 25A of daytime power needs? It may be possible on sunny days, but I think I would need more than 600W of solar to really make it work. I'll just be happy that I can run the refrigerator on DC during daylight hours. Someone else can figure out how to run it continuously with the solar and battery space limitations of an Airstream.