# Cabin Off Grid Design Part 1 - Total Watt-Hours

Registered Users Posts: 19 ✭✭
My background is electrical engineering, so I have a decent grasp of electrical theory and concepts in the practical world.  I have zero experience with solar, however I've spent a lot of time shopping and reading.  But have purchased nothing.  So let's start with my power consumption estimation first.  The Cabin would be Here.  Stove cooking and water heating will be propane.

1) QTY 1 - Solar powered fridge - Between 525 and 1100 Wh/day  depending on size.  Groceries will be far away so I'm thinking designing from more towards 1100 Wh is a good idea.
http://uniqueoffgrid.com/category/solar-appliances/ is an example of what I am thinking.

2) QTY 2 - CPAP machines - 8 hours per day each, 60 watts continuous each, 120 watts for QTY 2, yields 960  Wh/day

Lighting - Difficult to estimate - Advice  welcome.  The cabin is about 500 square feet and there are two small outbuildings at about 100 square feet a piece.  Additionally the ability to run 4 modest flood lights would be great since unloading / loading of boat may take place at this property during nighttime.  I want to design for 3 hours per day of typical use of all of the lighting.  I'm thinking allocating a 500 DC watts worth of invert er power to power my LED lighting which would run at 120VAC.   My indoor 120VAC lights I run in my on grid house are less than 10 watts, so assuming inverted efficiency of 85% would allow for 200 watt at 120VAC.  So back to my DC Wh/day would be 500 watts * 3 = 1500 Wh/day

Water Pump - Difficult to estimate - Advice  welcome.  There is currently a water tower there with a tote up top, and so it's possible to run with this all by itself and to fill it with a gas lift pump periodically.  I've also considered using the tote at ground level feeding an 12 VDC RV booster pump.  I've also considered using a 12 or 24 VDC motor to fill a bladder pump, and finally I've considered using an inverter to drive a max 15 amp 120VAC water pump.  For sizing, I'll consider the last option:  15A * 120VAC * 15 minutes per day of continuous pumping  and considering an 85 inverter efficiency yeilds 530 Wh/day.

Vent Van - The cabin will need rapid ventilation in the evening to cool - I envision a squirrel cage type fan, ~ 10A, 120VAC for 15 min max, typical inverter efficeincy as above.  352 Wh/day

Coffee percolator, toaster - 15 min max per day total @ 15A * 120VAC * 15 min 530 Wh/day.

Grey water Pump - equal to the water pump lift and volume, so assume 530 Wh/day

Power tools, cell phone charging, vaccume, Laptop charger - 530 Wh/day

TV - 100 Wh/day

OPTIONAL - UV water treatment 1200 Wh/day

TOTAL Wh/day

I welcome any suggestions.  This forum looks great.

• Registered Users Posts: 19 ✭✭
I forgot to post my totals here.  My range is between 5557 and 7332 Wh/day depending on if I calculate the lower fridge consumption with no UV system, or with the higher fridge consumption and optional UV.

I'm going to hold off on writing the kind of solar array I'm thinking of and the batteries, because to do that It would be like the tail wagging the dog.  I'm also not opening discussion on the gas powered DC charging options.  I'm trying to keep the discussion on track with the first step which is estimating Wh/day.
• Registered Users Posts: 19 ✭✭
I have made a mistake on the lighting.  I had revised the numbers to 200 watts for 3 hours of lighting per day after talking to a friend in the busiess but did not revise the 1500 watts of power down to 600 DC Wh/day.

So revised totals are now 4.7 to 6.4 kWh/day.
• Solar Expert Posts: 1,111 ✭✭✭✭
edited July 25 #4
What are you figuring to use for lighting? LED lighting could be less than 200 watts unless you are really lighting up the neighborhood. Here's a 120 watt equivalent ceiling fixture that uses 17 watts. These are bright lights. a couple in the kitchen illuminate really well.  The warm white LEDs are not at all harsh like the cool white ones are.

2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

edited July 26 #5
Is the cabin seasonal usage or full time off grid.

Roughly, near what major city (hours of sun per day). [sorry, missed the "here" on my phone]....

I would suggest that you look at 3.3 kWH per day for energy usage. Use other fuels for cooking, hot water, heating, etc.

3.3 kWH per day can be pretty close toa near normal electric life with lots of conservation. Especially if not full time off grid.

Energy usage is a highly personal set of course choices. But, in general, conservation is much less expensive than generating your own power.

First guess is off grid solar+backup genset is around \$1-\$2 per kWH. About 10x the cost of utility power.

Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 19 ✭✭
good to know little harbour thank you. This is the kind of feedback I’m looking for.
• Registered Users Posts: 3,037 ✭✭✭✭✭
The location seems to be around French River PP in Ontario. If so, you may want to check with the local health authority about water issues generally in the area, and maybe get your specific source tested by them before deciding on remediation. I'm on Lake of the Woods, north and west of there, and find filtration works fine. Not far away in a different waterway (so doesn't affect me), there's a nasty mercury issue going back decades. It can be very local, and remediation really depends on the issue being remediated. UV won't affect mercury, for example.

A couple of wrinkles to throw into the load calcs. 120vac loads will go through an inverter, with variable losses. Some loads (eg water pumping into a gravity/water tower storage) can be done as an opportunity load when "excess" solar power is available) are cheap/free. Others (eg CPAP, which presumably runs only at night), are expensive. Running a big inverter for a 180w load, for example, might actually require more like 250w with losses. OTOH, if you have storage capacity in the water tower and grey water systems to just pump when the sun shines and batteries are nearly full, those loads don't really count. Like Bill said, highly personal choices. FWIW, my system is designed for ~3kw/day, but by timing loads with weather, it actually runs more like 5-6kw/day in summer by running things like the septic lift pump when weather permits.

Also like Bill asked, it will matter a lot if you'll be there in late fall/winter.

For unloading the boat in the dark, I'd use red LEDs. They don't take much power vs floods, and don't kill night vision, so you can see the bear coming for your groceries
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Solar Expert Posts: 366 ✭✭✭
lots to consider  ... for me  i started at 12 volts , best to go to 48 volt system straight off . Consider a inverter fridge , keeps everything simple. Water is best [if you can ] gravity ... means 24 hour water with pumping when you chose .
2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . victron battery monitor . 24 volts 450 ah surette batterys . off grid  holiday home
• Registered Users Posts: 19 ✭✭
I really like eveyone’s Input. However if possible - Please help me on the estimation on the KW hours per day, and then I will size the panel array and rest of the system accordingly.

Does anyone think any of the power estimations on a per day basis are out in left field?
If you are going for 5+ kWH per day, you are probably looking at a 48 volt battery bank (for optimum wiring/system design).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 8,029 ✭✭✭✭
1) outdoor nighttime illumination.  Green is shown to preserve night vision better than red.  Red was used because established photographic darkroom practices at the time.

2) Coffee  & Toast   BAD LOADS, very high power, and 10 min will suck your batteries dry - so you have to build a huge system to feed these.
Maybe use a dedicated mod sine inverter for these loads, and only turn it on as needed,  the idle power through the day will consume more than the appliance

Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Registered Users Posts: 3,037 ✭✭✭✭✭
Personally, I like both toast
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Solar Expert Posts: 1,111 ✭✭✭✭
edited July 26 #13
Brew your coffee and immediately transfer it into an insulated carafe. works great, doesn't waste power keeping your coffee hot.. The coffee stays tasting like fresh brewed instead of burnt hotplate coffee as well.

2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

• Registered Users Posts: 19 ✭✭
BB I’m looking forward to the battery bank discussion - just not there yet. First step is define watt hours / day.
• Solar Expert Posts: 4,768 ✭✭✭✭
Somewhere there is a discussion about coffee making, I'm not a coffee drinker, so what do I know... But I agree with the premise that a small load repeated is better than a large load at once.

So if you want to make coffee and toast, do it at separate time, not running the 2 loads at the same time. Also look for a small coffee maker and run it 2x if needed. This one uses 650 watts and makes 5 cups of coffee, it's just the first one I found. 10-15 minutes at 650 watts, call it 180 watt hours. My toaster runs 700 watts and takes about 10 minutes. so another 150 watt
hours.

https://www.amazon.com/BLACK-DECKER-5-Cup-Coffeemaker-DCM600B/dp/B001NXC5YC/ref=sr_1_6?s=home-garden&ie=UTF8&qid=1532569415&sr=1-6&keywords=6+cup+coffee&dpID=41zVZhXzruL&preST=_SY300_QL70_&dpSrc=srch

If you try to run them at the same time, you need to worry about the draw on the battery bank, if you have a 12 KWh battery bank and you are drawing 1500 watts (combined with inverter load) You are drawing at about a 8th of the amp hour battery capacity. So in reality you will be using perhaps as much as 25 % above the load since the battery bank is effectively smaller at high draws. (Peukert's law)

https://en.wikipedia.org/wiki/Peukert's_law
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Registered Users Posts: 3,037 ✭✭✭✭✭
Your numbers seem reasonable as a first approximation. Nothing strikes me as totally wrong, but that's only my opinion as someone who lives off grid with my own set of choices. Yours may be different.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Registered Users Posts: 19 ✭✭
Very interesting. Makes sense - I typically don’t run both toaster and coffee maker at the same time here on my grid connected home either.

Seems to me my ~500 wH/day is reasonable.
• Registered Users Posts: 19 ✭✭
Thank you estragon this is the kind of feedback I’m looking for for the first part of my design step.

Tomorrow I plan to post on the next design step. Should be fun.
• Solar Expert Posts: 2,422 ✭✭✭✭✭
edited July 26 #19
Keeping with the OP's request to focus on loads, as long as the calculations are done conservatively, establishment of a baseline is the most important step of system design, think of anything that you may have forgotten to include, washing machine was not mentioned , neither was inverter self consumption, the latter can be a jack in the box if not factored in.

1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank
900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
• Solar Expert Posts: 4,768 ✭✭✭✭
So will this be a year round home, or seasonal use? Did we get your location? I'll run some numbers on a system to fit your needs tomorrow...
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
edited July 26 #21
Sunjammer has a map link to his location in the first post.

Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 19 ✭✭
I’m going to start another thread shortly after I complete my watt hours estimation.

No washing machine planned.

Regarding the jack in the box - I plan on a 1.5 multiplier.
• Solar Expert Posts: 330 ✭✭✭
This pot cost me 15 bucks it makes a large tasty cup of coffee in about 3  minutes
All stainless steal .
I used it on my wood stove all winter.
Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
• Registered Users Posts: 19 ✭✭
Yup a propane stovetop like that might be a better choice
• Solar Expert Posts: 4,137 ✭✭✭✭✭
Anything is possible these days Offgrid. Sometimes having a budget for the power system makes it easier to design.
You live in a very challenging area. If this is full time you will have challenges. Good Luck
"we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
http://members.sti.net/offgridsolar/
E-mail [email protected]

• Registered Users Posts: 19 ✭✭
What great feed back thank you everyone.  I'll open a new thread now continuing the design.