100 sq ft cabin needs solarpower pack

System · April 2011

I would like get input on designing a portable solar power pack for a 100 sq foot cube cabin as shown below.

http://www.carre-detoiles.com/index_uk.html

It's french design cube cabin rented out to tourists.

We're thinking that the basic elec load would be

4 cu ft ref
2 CFL bulbs at about 6 hrs a day
a 30w LCD tv for about 6 hrs a day
a netbook at about 15w for 6 hours a day.

We did some rough calcs and roughly came out with a rough shopping list.
We're all new to this so please bear with us.
1) Kyocera 135w panel = qty=3 to 4
2) Xantrex c60 controller
3) 6v trojan lead acid batteries paired in 2's for 12v= qty=6 to 8
4) Sine wave inverter - please suggest
5) Misc hardware. I know we forgot something so please help us.

Budget is a concern.

We want the unit to be portable and mounted on a garden cart as below

http://www.amazon.com/Northern-Industrial--48in-L-1400-Lb-Capacity/dp/B0007CTMX2/ref=sr_1_20?ie=UTF8&qid=1301957771&sr=8-20

We want to build like a mini dog house on top of the cart - the panels to rest on the roof, batteries in one compartment, controller/inverter in another. Plan is to seal everything from the elements and at the same time vent the batteries via a mini chimney.

With the whole system on wheels, our dream is to be able to move it from one cube house to another if not in use.

From the AC out of the inverter, the plan is to have an 10/3 wire with an L5-30 female connector at the end. The AC input of the cube house would be an L5-30 socket. SO when somebody is using the house, we roll the SOlar power pack and plug it to the house.

Is this too ambitious, doable. Again thanks and please feel free to suggest anything that can make it a doable project.

icarus · April 2011

Re: 100 sq ft cabin needs solarpower pack

Well, it is a simple series of eauations.

Take your loads,, and convert them to watt/hours:

Guessing at a 4 cu ft fridge, 250 wh
2 CFL buls, 15*2=30*6=180 wh
30 watt TV * 6= 180 wh
Netbook 15*6=60 wh
Total wh= 670 wh

A general rule of thumb,, take the nameplate rating of the PV, divide by 2 to account for all cumulative system loses, then multiply that by 4 to represent the number of hours of good sun one can reasonably expect to have per day on average over the course of the year.

So your proposed 4 135 watt panels might look like this: 135*4/2=270*4=1080 watt/hours,, so your three or four panels would be about right. Your batteries, 4 T-105 Trojans would yield ~ 450 ah of power, or ~ 5.4 kwh if you were to draw them to zero. A daily draw of 670 wh would be ~55 ah, or just about 10%.

Bottom line, you want panels that will charge in the 5-13% of ah capacity, and you want a battery that you can draw ~ 20% per day, leaving ~ 3 days without having to run a genny.

So you can decide how to fit the hardware in. As I often cite as an example, we draw 5-800 wh per day. We generate that from 400 watts of PV, into 450 ah of T-105 battery.

The second rule of Pv/Re is that people over estimate their solar harvest at the same time they under estimate their loads, leading to a double whammy of not enough capacity.

The third rule, is that loads almost always grow with time.

Good luck and keep in touch,

Tony

Suresine 300 inverter, fuses, both DC and AC,

Photowhit · April 2011

Re: 100 sq ft cabin needs solarpower pack

I do most of my living in a 160 sq foot cabin, and have for some time, I have lots of opinions, rather than Ideas.

If this is for the tourism trade, your in trouble, some people will just not understand, think hair dryers and hot plates...

C60 is likely over kill, a C40 should be fine, for summer use likely there would be little advantage to a MPPT.

A 400 watt system is marginal for a fridge an any extra modest load, in a year round situation. A battery bank larger than 400 amp hours in a 12 volt would be lopsided. unless it was used weekend only/Summer only (longer days more dependable solar charging, in most areas)

In a small area, with people who understand solar, it is doubtful you'll have near that amount of lamp use, very likely you'll have more incidental loads, MP3 player, phone chargers, etc.

In my brothers year in France, he found that people food shop every day, so perhaps you could just have an available ice box.

Not sure how far your likely to transport this, and given your moniker, a bike trailer might work as well, though 4 6 volt batts will run 200lbs. For that load you'd want a framed trailer, one with support on either side of each wheel, they are out there, I've hauled fire wood in a winchester trailer of similar design, with out a problem, it'll likely support 400lbs.

Cariboocoot · April 2011

Re: 100 sq ft cabin needs solarpower pack

In addition to Photowhit's weight concern, remember that four panels will be about twelve feet long by five feet wide. Not an easily transportable assembly. They don't like to be flexed in any way; breakage is possible.

Even a small refrigerator can have large start-up current. That one is an unknown factor which needs to be reasoned out some way.

Otherwise, without the 'frige you're just under 500 Watt hours per day: about 36 Amp hours @ 12 Volts. Very reasonable, if you can actually regulate consumption there. A refrigerator can easily use 2X that, especially in hot weather. They're not consistent in their power consumption. Based on my experience with my own full-size refrigerator, one set of the 225 Amp hour batteries would just barely make it. Having a smaller unit doesn't equate to a likewise reduction in power consumption.

Sorry this is all sounding negative. It certainly can be done; you just have to watch out for these potential pitfalls before you step in them!

100 sq ft cabin needs solarpower pack

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