Propane-powered appliances vs propane generator

Hello all!

My first post! I have been reading these forums for a bit now and would just like to thank everyone for all this amazing knowledge. I don't believe this question has been asked before.
 
I am building my second cart. It will be on a 5x10 trailer hitch. It will have two steamtables, a reefer, freezer, 42" flattop, a backup 5000w LPG generator, and two 50-lb propane tanks. The steamtables and reefer will be electric. The flattop will be propane. But I am at a crossroads with the freezer. The cart will mainly be used to attend multi-day festivals up to 1,000 miles from home base. So the freezer (which will hold all the prepared food) will need to be off-grid for at least a day or two at a time - this is why I went with propane. But I have two options. (1) A propane-powered freezer, or (2) an electric freezer that would utilize the propane-powered generator.
 
As far as a propane-powered freezer, I can get a 12 cu. ft. freezer that runs on 2 lbs of propane per day. Seems super efficient to me. With the flattop using 5 lbs max per day, that would allow me to go 15 days before refilling my tanks (WAY more than I need). The CONS are that the propane freezers are more expensive than electric.
 
The other option is to go with an electric freezer and power the freezer by running the generator while on the road. The first cart didn't have a generator (it sits right in town where there is electric provided - no need to be nomadic), so I have no experience with generator efficiency. But from the numbers they give on the generator specs (1.5 lbs per hour @ 1500w), it seems not very efficient. The PROS are that the freezer can be plugged in once we get to the destination. Also, is it legal to be running a generator on the cart while driving. I would think it's okay.
 
Or is there an even better way to do this that I didn't even think of. Thanks for all of your help in advance.
 
Best,
Matt

either way remember not to leave the propane or genny on while getting gasoline for the hauler....

Frozen food in a freezer that size should stay frozen for 24 hrs or more if it isn't opened.   Another option is to use dry ice (or regular ice) in the freezer when moving or to reduce power consumption.    ... Just picture a freezer as being an over-size ice chest.

go the route of the blue water boaters and go with a cold plate set up..... it will use the juice from the genny to freeze down the plates, but will only need an hour or two per day depending on climate and use(open/close)  cheaper then a propane freezer, can stay off the grid a lot longer, cheaper to operate.....
build the freezer enclosure yourself and save big bucks, then all your doing is buying the unit itself and adding it in

edwmax
Frozen food in a freezer that size should stay frozen for 24 hrs or more if it isn't opened.   Another option is to use dry ice (or regular ice) in the freezer when moving or to reduce power consumption.    ... Just picture a freezer as being an over-size ice chest.

 
regular ice can actually start the thawing process.... i know it sounds crazy, but think about it..... 

i have 2 questions ??
first, where you find 50lb tanks ?
and second, a 42" flatop only using 5lbs a day ??

Since your already have a generator for other equipment, your real question is how to power the freezer at off hours (during transit or at night). The 5000w genny will be inefficient for just the fridge, but if you run it intermittantly it will get you by. Anoth option is a small gas generator just large enough for the fridge (1500W?) just for using at off hours.

the real secret to a freezer staying frozen is to fill it as much as possible(as little air space as possible) and let it pull down to as cold as it will get before you unplug it...... then only open when absolutely necessary, keep a food log so you only have to open it to grab what you need..... not to see what you have left (old boater trick) 

a pound of propane has roughly 22,000 btu's......
 
your garden variety 42" flat top will consume 90,000 btu's an hour
that works out to a little over 4 lbs per hour when you are wide open
that gives you a little less then 12 hours of propane wide open use on 100 pounds......
 
now....... adding in a little "creative figuring".......
maxed out 2 hours a day(1 hour breakfast/1 hour lunch)....180,000 btu's
half max 2 hours a day    (same as above)...........................90,000 btu's
just your griddle usage will be approx..................................270,000 btu's
 
this gives you just over 8 days of propane just from the griddle
 
figure in the 2 lbs a day for the freezer (best idea) and you are down to 7 days
 
a rough guess on adding in a propane genny..... now your down to around 3 days, maybe 4 at best.....
 
and these are good hot summer days..... when it cools off, and at higher altitude (i noticed your based in colorado) you can shave a few more hours off your time due to propane being less efficient when cold
 
 
i just checked, a 5k propane genny uses around 2lbs an hour at half load......
you would be MUCH better off going gas on the steam tables and reefer as well.....
and maybe add another one of those 50lb tanks (i still want to know about them :) )
that mixed with as much 12 volt as you can do (led lights/water pump/etc) and a big battery bank w/solar charging, and you can possibly do 5 days no problem......

but remember (within reason)
a bigger genny running at half load is better all the way around (efficiency/longevity/operating costs/etc...) then a smaller one running wide open

yea, just looked, you can run both a propane freezer and fridge(15cf freezer 12cf fridge) for less then 3 lbs a day(24 hrs).....
that 5k genny is going to suck that much down in around an hour and a half
what you spend extra for the equipment now will very soon pay for itself in propane savings
 
so yes..... if you can swing it.....i would go all propane and 12 volt w/solar charging
bill yourself as the go green guy....people like that out your way

BackAlleyBurger


yea, just looked, you can run both a propane freezer and fridge(15cf freezer 12cf fridge) for less then 3 lbs a day(24 hrs).....
that 5k genny is going to suck that much down in around an hour and a half
what you spend extra for the equipment now will very soon pay for itself in propane savings

so yes..... if you can swing it.....i would go all propane and 12 volt w/solar charging
bill yourself as the go green guy....people like that out your way

 
hmmm interesting option. I'll have to find out if they make propane powered prep tables...

Everyone, thank you for your posts! Hopefully this can be a learning experience for everyone!
 
BackAlley, a special thanks! I love hearing your feedback.
 
To answer some of your questions,
 
(1) As far as the flattop propane usage, it only runs on one (out of three) burners. It stays way hot and produces more than enough cooking heat without cooling down - we are only warming tortillas on one side. We will only be on the road 5 days max at a time, so the propane will more than last - I have no doubt about that.
 
(2) Currently, we have two 25-lb tanks for a home-town location. I calculated 50-lb tanks for the needed increased propane supply on the road. But I had no idea whether they made 50-lb tanks! I guess they don't. And now with the new calculations, it seems two 100-lb tanks would be needed for worry-free transit.
 
(3) We decided to go with a 240w solar installation on the roof. More for the environmental standards to help us get approved for festivals. But it will still help our energy efficiency and off-grid longevity.
 
We've also concluded that we will only be off-grid for 24 hours twice a week, since almost every festival provides electrical hookups. At home base, we have freezer and fridge (F&F) storage. So doing some quick math, it seems that running a propane genny for 1 day to power the F&F while on the road will use 48 lbs of propane (...the steamtable, lights, music, etc will only be on when hooked up to an electrical supply) while a propane-powered F&F will use 3 lbs per day.
 
It seems more efficient to go propane in the long run.  Averaging 5 days a week on the road, a propane-powered F&F uses 15 lbs per week. If we go with an electric F&F, the genny will be on for 2 days max, using 100 lbs a week. At $1 per pound of propane, it will be additional $85 per week for propane. Buying a propane-powered F&F will cost an additional $1100 over electric appliances. So it will only take about 13 weeks to make up the added initial cost by going with a propane F&F.
 
However, add in the solar setup and the electric F&F setup uses even less electric while off-grid. Plus add 3 or 4 deep cycle batteries that we can charge while on the grid and it reduces our off-grid electricity consumption even further. So figure that now we're down to only about 12 hours off-grid twice a week. So it takes 26 weeks to make up the additional cost for the propane F&F.
 
I think that if I was looking for maximum off-grid capability, propane-powered appliances with a supplementary solar setup would be the way to go. But for 2 days a week off grid (1 day every 3 days), it seems more efficient (at least in the 2 year term) to go with electric appliances. Hopefully we can build our next truck with maximum off-grid capabilities!!!
 
Unless I'm missing something here, it seems sensible to go with an electric F&F. And for shorter travel times, it would take even longer to make up the initial cost of propane appliances. Feel free to correct me if I'm wrong. Again, thanks for your help! Very much appreciated!
 
Cheers!
BelizeNut

I have run an under counter 110vAC refrigerator and a  undercounter 110vAC freezer up to 10 hours (overnight) with no power at all. We did that all the way out to NM from NC in the heat of the summer (July) thru TX. Temps were hitting 100F and up. These are the units in our RV. Normally we run on no power since we only travel roughly 8 hours per day. But coming out we had cart food packed into the freezer (frozen solid) and it held just fine over night (for safety, we did not run the generator while we slept). Freezer temps were well under -0F during the day. We did not open the freezer when it was not powered. Ditto for refrigerator. I will suggest one thing. Do NOT use an RV refrigerator. They are dangerous (catch fire) and do not cool well once temps get high. They only cool a certain number of degrees below ambient temps. Also it does get too cold for the propane refrigerator to operate. I would suggest you get your fridge and freezer from the solar folks.
 
The biggest thing is.... will your HD approve a propane freezer/refrigerator?

lornaschinske,
 
thanks for the response. Great point that the fridge and freezer stay cold for hours without being on. We are definitely going with electric appliances, a solar system, and a LPG generator for backup.
 
Happy cooking!
BelizeNut

Does anyone have any proof a solar system will really work? Is there anyone that vends know of anyone that uses a a solar system?

BackAlleyBurger
 

but remember (within reason) 
a bigger genny running at half load is better all the way around (efficiency/longevity/operating costs/etc...) then a smaller one running wide open 

 
 
Not busting your chops here but I'm interested in your opinion:
 
I've been told, by a friend who designed and manufactured generators, that a non-inverter generator runs at a set RPM, produces full capacity current, and dumps any unused current to ground.  By that logic, a half-utilized generator is not particularly efficient. 
 
I'm with you on the greater longevity won by running below capacity....

Dr BBQ,
We are going with a supplementary 240w solar setup to get started. The trailer build will be finished in January. I'll let you know how it works out.