Generator vs. Solar

[containercabin]

I am trying to quantify if a solar system makes more sense for my upcoming 12'x12' cabin.
Electric needs:

RV pump
5 23w cfl lights (will rarely run at the same time)
Small lcd tv (19")
television streamer with external hard drive
random laptop charging
small fridge
random tool usage

That's it.

The cabin will be used for a weekend once every two weeks on average.

I have a Honda 2000i generator.

Quantifying the costs with a lot of assumptions. (after some of you give more input I will recalculate)

Let's say the solar system - PV panels, inverter, batteries, and so on, costs $1,500. Let's also assume that on a weekend I will use an average of 1 gallon of fuel for the generator. If I will spend every other weekend there, that is 26 weekends in a year, then that is 26 gallons in a year. I can buy gas in NJ on my way to the cabin then let's say that the average price per gallon is $3.5 -> That's $91 a year. At this scheme it will take about 16.5 years until the solar pays back. I feel like my estimate for solar system cost might be high though... If I can get a solar system for $750 then it becomes just under 8.2 years and if $1000 then just under 11 years.

After I get some input here - we'll see if my calculations are plausible.

Benefits I see for the generator:

- theft: I don't need to leave it there. Unlike the solar system that will get stolen if someone breaks in
- I want to use it in winter so I believe that snow might cover the PV so I won't have power.

Can't wait to hear people's thoughts here.

[MountainDon]

I do have a bias against generators. Okay I have that out of the way.   

What I don't see in the above question is an honest estimate of the amount of power needed for the typical stay at the cabin. The watt-hours used per day determines the needed storage capacity and that in turn with the worst case expected sun hours determines PV array capacity. Without real numbers it's just a guessing game and that, IMO, will most likely lead to being unhappy with the PV system because the guess will be too low.

http://countryplans.com/smf/index.php?topic=8192.msg105900#msg105900


In particular the small fridge may be a deciding factor. Small fridges tend to be less efficient than their larger brethern. At least there are few, if any, that manufacturers have submitted for testing. Do you have one? Get a Kill-A-Watt meter and measure it's use. IMO, for brief stays a "extreme" cooler with frozen plastic bottles of water works very well, since you are carrying the food up with you more than likely.

We use a propane refrigerator May through September or October. In spring after we can drive in (April?) and again in fall when we can still drive we use a large Coleman Xtreme series cooler. In winter we don't pack in much other than some veggies. We leave a smaller cooler at the cabin for winter use and the weather is usually cold enough to have provided us with several bottles of ice. Or the cooler stays outside in the freezing cold and keeps the food that needs to be cool quite well.

Snow slides off ours readily

[flyingvan]

  Is wind power an option for you?  It's worth considering if you're looking at watts per dollar.  Some pole mounted models are easy to stow when you're gone.  Fridge options include the RV 3-ways, (inefficient) dorm model fridges, and thermopile style 12 volt (you'll get cold milk but your ice cream's gonna melt).  Solar panels do lose efficiency over time, between .5%/1% per year, and these numbers are getting better with new materials....
  In Winter, there is no more efficient appliance in a home than a fridge.  Every watt it uses is translated to heat for the cabin's interior while pulling heat out of food and putting it in the room

[kenhill]

I use an igloo cooler and an ice maker.  Fred Meyers Superstore puts an Emerson on sale for $99 every few months.  Runs at 130 watts.  It runs on non-inverter power just fine.  It makes a set of icecubes about every 7 minutes.  I put them in a ziplock gallon bag and place them in the cooler.  You also have ice for refreshing drinks!  We stay for 3 days, so this is adequate.  We also freeze everything we can before going (Bread, meat, etc). We drive 2 hours, hike 1 hour, and canoe 30 minutes to get there in the summer.

[alex trent]

Sounds like an ideal solution for cooling things for short stays.

I have a small reefer at my cabin but when going up I take 15 lbs of ice once or twice a week and everything I put in is frozen.  Right now, I am up most every day and a night or two as well. This works fine with just an hour of battery power a day.

48 degrees in the AM when I get there and  at 38 when I leave after the battery run.

If I were doing it again i'd go the cooler route..the icemaker sounds like a great bonus.

[containercabin]

I will more than likely start my stays there with this generator.

I am working on that solar spreadsheet don posted. I am figuring things out as I go. I found this really efficient pump which I think should be enough for my use - http://www.shurflo.com/rv-products/rv-pumps/classic-series-water-pumps/115-vac-park-model/default.html
I saw it for $125 online.

Also, is this even the kind of Pump I need? (I will have rain collection barrels located outside the cabin from which the pump will pull water)

I filled the spread sheet but I am not sure how to proceed. How do I find days without sun. The links are down. I am not even sure if my system will be 12 or 24...

My weekly usage came in at 5716. Of that 4300 is 48 hours of a 90w small fridge.

Any help on what next to size the solar system?

[MountainDon]

I found this really efficient pump which I think should be enough for my use - http://www.shurflo.com/rv-products/rv-pumps/classic-series-water-pumps/115-vac-park-model/default.html

That's the same pump I have except I have a DC version. I chose the DC as that lets it be powered right off the batteries w/o the inverter powering up. Slightly more efficient electrically.

[NM_Shooter]

The fridge is a killer.

Unless you power it while you are not there, getting it cold again is a pain.  Fridges take a long time to cool off. 

I don't like generators either..... I don't want to go to my cabin and listen to a generator, no matter how quiet it is.  I have to put up with them when I am camping in campgrounds. 

Stick with an ice box.  Buy a minimalist PV system, and don't use an inverter.  Get a DC LCD TV.  Your hard drive runs off of DC too.  Get some high efficiency DC/DC converters to get the voltage level where you want it.  Use your generator for running tools. 

I have a 190W solar panel that is locked in my cabin when I am not there, and I use a 15W panel mounted on the roof to keep the batteries topped off.  When I show up, I drag the big panel outside, and attach it along with the little panel.

[MountainDon]

I filled the spread sheet but I am not sure how to proceed. How do I find days without sun. The links are down. I am not even sure if my system will be 12 or 24...

My weekly usage came in at 5716. Of that 4300 is 48 hours of a 90w small fridge.

....so the 5716 watt hours a week is actually spread over two days not a 7 day week???  And 75% of that is the fridge.

BUT that 4300 is arrived at by math, figuring 48 hours at 90 watts. It is unlikely it would run all the time, though it will run for a while at first while turned on and cooling down. That's why I suggested using a real world measurement with a Kill-A-Watt.  Plug in and ket cool down, run 48 hours and see the total used.

The nrel links seem to work for me. If they are not available use Google to find the sun hours for your location. Use the worst time of year.   I'll look later at the linked topic and check the links further.

Without the fridge you'd have a very small need, small PV requirement and could do the other stuff with a couple of golf cart batteries (2 x 6 = 12 volts. With the fridge it would be more like 12 to 14 of those batteries.

# of panels depend on the sun hours on the panels.  Maybe only 300 watts worth w/o the fridge....  that's a guess without knowing where you are or the sun hours.


You/we need that to take out the guesswork.  ...  And thunk about whether or not the small fridge is worth it for a weekend.

[containercabin]

NM shooter - That's a good point: I'll run the whole idea of skipping the fridge and getting an ice box instead. I am thinking off maybe even building a very well insulated storage box, where a fridge will go and bring those ice pack with us everytime we go up. The more I think about it - it seems crazy to have a small fridge there.... 75% usage to keep milk cool for two days every other weekend? I will try to look up online how people have approached it.

Moving on to Don:

Lets say without the fridge. I looked at those maps and I think my area (sullivan county NY) is in the greenish/yellowish (more green) area. That's kWh/m^2/Day map. So I am 4.5-4.63?

That's hours of sun a day? Not sure if I am right.

[MountainDon]

For what month?   That's a bit optimistic I think.  I know that Binghamton, just a little north and west has an average of about 3 hours, worst case of about 1.5 and a high of not quite 4.  (have friends there).  So if you are needing power in the worst months I'd use no more than 2 hours. In summer you'd then have lots of power.

If summer is the main time of use half the # of panels would likely do the job.
~ 250 watts of panels in summer and 500 winter. That's 2 days autonomy, 50% discharge max and cold down to 10 F.

The Coleman Xtreme cooler is available in many sizes. We have a 36 and a 70 qt. Work great in the SW summer too.

[containercabin]

My place is exactly 2 hours (south) from Binghamton so that will be a good measure. Then can you now give a break down of what I need for the solar system or do you need more info?

[Squirl]

2 hours south of Binghamton puts it in the Poconos?  Or is it SE in Sullivan County?

The problem with the generator is it produces a bit of power, then when you shut it off, no more power.  Things like lights and lower drawing electronics draw very low amounts of wattage over a long period vs. even the toned down wattage of a honda 2000.  It is a terrible waste of gas, energy, and money.  I think you are underestimating the amount of usage of gas too.  Not to mention you haven't factored in the maintenance and depreciation cost on one of the most expensive generators made.

If the cabin is just for weekends, I would save my money and just get a set of golf cart batteries, a 12v charger, build or buy an ice chest, and freeze a block of ice at home.  The Amish build little boxes with caster wheels to move their batteries around easier. Shooter's idea of straight DC usage is a great idea, but if you are not an electrical engineer (Shooter  ) you can also just buy a very low wattage inverter and it would save a lot of money. It will cost less, last longer, and give you more enjoyment with not having to deal with a generator.    This option has worked for me and my neighbors for years.  You always have the generator as a backup if needed to run tools and high wattage devices.

If you want a solar option, I would opt for a large battery bank and a smaller array.  You can leave the array to top off the batteries over a week, while just using it on weekends. 

23 watt cfls are a lot of lumens for a 12x12 cabin.

If tilted to a maximum winter power angle, snow will slide off of most panels.

[MountainDon]

For a 12 x 12 w/o the refrigerator I would probably buy two 6 volt golf cart batteries and connect in series.

Then I'd consider using DC for the lights wanted and a small inverter to run the TV whenever I wanted that on. Or just go and buy an inverter large enough to run the lights and TV at the same time. Tools would be off the generator.  I would consider spending extra on LED lights too; that will cut needed battery capacity. You can't have fewer than two, but LED's would make the charge last longer.

I'd try that for a few weekends and see how far down I discharged the batteries. They should not be discharged more than 50% as measured with a battery hydrometer, not by voltage. If I found myself dragging the batteries down past that in one day's use, I'd add two more batteries. Then I'd be able to choose a correctly sized battery charger. With 2 typical golf cart batteries in series a 25-30 amp charger would be good. With four of those batteries in series / parallel a 50 - 60 amp charger would be good.

My plan would have two different possible directions. One, would be to leave the batteries at the cabin and carry the generator back and forth. Use the generator and the external charger to recharge the batteries. I like Iota chargers; well made in the USA and they have a multi stage charge option with the IQ4 option. The 2000i could handle their 55 amp model.

Then I'd have a small PV panel and charge controller to finish off the charge and maintain the charge with a proper float while the cabin was left vacant like Shooter does. I did that too when we had an RV. I'd leave it all winter with no problems.


The second route would be to either initially or at a later date buy a larger panel or panels that could by themselves handle recharging the batteries on their own. That would mean more panels and a better charge controller. For the charge controller I'd seriously consider an MPPT type (because of the low number of sunlight hours).

My own way of thinking on the panels is to have the array large enough to recharge the batteries in a single normal day. That means more PV, more $$, but also means the batteries will spend less time in a state of partial change. But a smaller array would work at recharging the batteries in between uses. The batteries might not last as long. Sizing the array for the second option would depend on the number of batteries in use.


That's how I see it. Hope that helps. If I can attempt to clear up any details just holler. 

[considerations]

If you are thinking about an electric under counter apartment sized fridge....mine "surge starts" at about 200 watts for a few seconds then runs on 90 watts for about 20 minutes till it shuts off.  Does that cycle about every 3 hours..averaging 8 times over 24 hours. flyingvan is right about the ice cream...eat it fast....But, I have an apartment size freezer as well, so I get to keep ice cream on hand.    Same electrical load for the freezer, but it cycles at 85 watts, essentially the same as the fridge.

There are LED bulbs that have standard sockets, even long skinny LED bulbs for traditional flourescent fixtures...about half the watts of CFLs and the light is just as bright and more like incandescent, much more pleasant. Probably never have to replace them.  I replaced all of the bulbs in my house with LED bulbs. 

LED TV's...have to research each model, some say LED, but still use some flourescent lighting...the wattage label is the real proof. Plus, unplugging the darn thing completely when not in use saves watts because standby mode is a constant battery drainer.

[MountainDon]

I lean towards the "no large array" direction because of the statement you made in the OP about being worried about theft issues.

[containercabin]

Excellent info 'Considerations'! So I guess I can take my fridge usage number down a notch. This leads me to the next issue - the wife wants a fridge. Two options then:
Go with a small under the counter fridge like 'considerations' mentions and size it up with your numbers or do the chest fridge conversion thing. Anyone here tried it? http://mtbest.net/chest_fridge.html
supposed to be silly efficient.

BTW: is it ok to unplug the fridge when we leave? I heard you need to leave the door open.

Thanks for the info squirl. I will experiment with the bulb power. BTW - I always wonder why people here recommend LED's so much. Lummen per watt CFL wins... Not to mention price. http://4.bp.blogspot.com/_VyTCyizqrHs/TH0gG7EVVMI/AAAAAAAAI3s/wek0ogJNf_U/s1600/lumensperwatt2.gif

If you don't like the cfl light that is a taste thing but LPW cfl wins.

Don - I do want to run both lights and tv at the same time. I will get the larger inverter and I always prefer 'made in USA'. How much does each of those "fridge options" I mentioned change your recommendation for the system?

[considerations]

"is it ok to unplug the fridge when we leave? I heard you need to leave the door open. "

Yes, if you do not, you will likely spawn a host of Creatures from the Black Lagoon 

[flyingvan]

Pretty informative article about Kool-A-Tron coolers http://www.roadtrucker.com/koolatron/koolatron-12-volt-coolers-faq.html  They have a model that consumes 36 watts and a larger one that consumes 54 watts.  These thermoelectric units cool with peltier devices instead of pumping refrigerants around, and the best cooling you'll get is 40-45 degrees f below ambient temperature.  I had one at my building site---it kept drinks at the perfect drinking temperature

[UK4X4]

12v Fridge wise

This is presently the cheapest 12v-110V portable fridge with a Danfoss compressor- made in Italy

http://www.truckfridge.com/tf41.html

Edgestar can be found cheaper but chinese compresor- from compact appliance scratch and dent

Norcold is another cheaper brand

Other premium brands are ARB- National Luna-Engel to name the main players.

All of these will make ice and use a proper fridge compressor.

average usage per day means you'd need a 80watt panel on the better named versions and a 12V battery
the cheaper ones consume more energy and are less efficient.

I have an Engel- 7 years as a beer fridge and off roading travel fridge - never missed a beat - untill I plugged it into 220V

I now use a computer power supply and run on 12V as i blew the main board.

If I win the lottery I'll get a nat Luna aluminum for my next one twin door fridge and freezer

[containercabin]

Thanks UK.

I believe I can get a used chest fridge for 50-80$ and that plug in thermostat is 40$ shipped so this will be my best option. I will put it on rollers so I can keep it under the counter.

[Redcracker]

I am a member of the survivalpodcast.com. Search there and find answers to anything you could imagine about surviving off grid. Some of the most creative people ever! good luck.

[db4570]

MountainDon mentioned his propane fridge, and I know it wasn't one of your original choices, but it sounds like the best option to me. Solar I picture being inconsistent unless you're in a reliable high-sunshine area, plus expensive, and a lot of tinkering, and needing a big inverter, etc.

Since the fridge is probably the big power draw in your mix, which also has a startup surge, I like the idea of eliminating that right off the bat by going propane. Charge a big battery for a couple hours with your generator when you first get there to run the other stuff. Or rig it to charge from your vehicle during the drive up there. (I don't know what the TV draws. Might be too much to run on battery for long.)

You can even convert your Honda to run on propane for a couple hundred $$ so you never have to worry about fuel going bad, and having only one fuel to bring with you. FWIW.

David

[PorkChopsMmm]

We built and live in an offgrid cabin powered by solar and a generator. If this place is where snow occurs and/or there are common overcast conditions in winter (like where we are in Michigan) than you will most likely need to run the generator any way. We are running our generator nearly every day to keep our battery bank up to good charge levels -- we just haven't been getting enough sun in the day to charge the batteries enough. Not ideal and I will be making some changes and additions this summer.

Your needs are quite small excluding the fridge. Switching from CFL's to LED lights would bring down your loads even more. If I were you I would try to find a small used RV propane fridge and run that by itself. Then get 2 6V batteries, string them together for 12V, and charge them with your generator. That way the generator doesn't always need to be on wasting fuel and you can build up your solar system off of those batteries. Should be cheap enough to start.