Cabin Off Grid Design Part 1 - Total Watt-Hours

SunJammer

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.

SunJammer

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.

SunJammer

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.

littleharbor2

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.
https://www.homedepot.com/p/Hampton-Bay-12-7-in-120-Watt-Equivalent-Oil-Rubbed-Bronze-Integrated-LED-Flushmount-with-Etched-Linen-Glass-Shade-AD160-BR-B/205472541?MERCH=REC-_-PIPHorizontal1_rr-_-205127893-_-205472541-_-N

BB.

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

SunJammer

good to know little harbour thank you. This is the kind of feedback I’m looking for.

Estragon

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

petertearai

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 .

SunJammer

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?

BB.

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

mike95490

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

Estragon

Personally, I like both toast
and coffee. They aren't "BAD LOADs," they're choices.

littleharbor2

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.

SunJammer

BB I’m looking forward to the battery bank discussion - just not there yet. First step is define watt hours / day.

Photowhit

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

Estragon

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.

SunJammer

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.

SunJammer

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.

mcgivor

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.

Photowhit

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...

BB.

Sunjammer has a map link to his location in the first post.

https://www.google.com/maps/@46.0043467,-80.8826988,12z

Bill

SunJammer

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.

wellbuilt

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.

SunJammer

Yup a propane stovetop like that might be a better choice

Dave Angelini

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

SunJammer

What great feed back thank you everyone.  I'll open a new thread now continuing the design.