Off-Grid Planning

[Tobit]

How do I plan a proper size array and battery bank when I really don't know how many AH/day I will be using.  I cannot compare to what I use now because my lifestyle will be changing drastically.  After decades of dreaming, I finally have a piece of land in the mountains, on a southern slope, where I will be moving to live an off-grid existence.  I have no clue how to calculate the items, such as battery chargers, I will use very intermittently.

My daily insolation goes from a low 2 in December/January to a high of 6 in summer.

In or near my shed, I will have:

2 x 19.2W 12v lights (1.6A draw each, usage unknown)
1 x Water pump for shower (4.4A at 12V) - used for 20 minutes/day maybe twice a week
1 x USB charger for cell phone (draw/usage unknown)
1 x USB charger for tablet (draw/usage unknown)
1 x 120VAC Battery charger for AA/AAA NiMH batteries (draw/usage unknown)
1 x 120VAC Battery charger for 18V cordless tools (draw/usage unknown)
1 x Sundanzer Fridge (114W/day at 89.6 degrees F)
1 x Sundanzer Freezer (280W/day at 9.6 degrees F)

My shed will draw more power than my cabin. In my cabin, I only plan on having a 4.4A water pump and my shortwave radio (800 mA draw, unknown usage). Lighting will be candles and oil lamps.  Fridge and freezer will naturally run more in the summer than the winter.

Any thoughts on how to calculate array size?  Many thanks in advance.

[vtmaps]

How do I plan a proper size array and battery bank when I really don't know how many AH/day I will be using. 

Unfortunately you need some hard numbers to design a power system.   It's a bit like designing a roof... you tell me how many lbs per sq ft the roof must support, and I will tell you what size rafters to use. 

Other questions... do you have a generator?  What about laundry?  Power tools? 

You mention a shed and a cabin... Are the sundanzers in the shed?  Does the shed get cold in the winter?  That may be a problem with the sundanzers... they don't work properly in ambient temperatures that are near their internal temperatures.

--vtMaps

[Tobit]

do you have a generator?  What about laundry?  Power tools?  You mention a shed and a cabin... Are the sundanzers in the shed?  Does the shed get cold in the winter? 

I have a generator to run big power tools as needed during construction.  These are the really small sundanzers, they will mostly be in the shed along with most of my water storage so the shed will have some insulation and could likely be unplugged in the winter time (freezer moved outside).  The shed, if I insulate it well, should stay just above freezing during the winter.

Since I live alone, I will hand-wash clothes.. air dry.

The issue I have are my small rechargeable devices such as cell phone, tablet, and cordless tools.  I also have no clue how long I will use the water pumps.  I suppose I could fire up the generator to recharge the cordless tools but I'd rather not. 

[Tobit]

I punched 446WH/day into a calculator based on my big three items (radio, fridge, and freezer) and an insolation number of 4 and this is what it recommends.



So I am thinking of 400W of panels and ~200 AH battery bank (4x6V for 24V) and use a KID controller.

[Rybren]

You'll want ~10% rate of charge for the batteries, so for a 200AH 24V battery bank, you'd want enough panel to produce 20A.  400W of PV won't do it for you.

FWIW, at my off-grid cabin, I have a 232AH 24V battery bank and I have 840W of panels. 

[Tobit]

I think I am going to go with 2x275W Solarworld Mono panels.  I found a seller who has them for $1.27/watt and he can ship two of them to me for only $25.  With the KID, I will have some expansion room to add one more 275W panel in series if I ever need to grow the system.

[zoneblue]

Living a basic life off grid isnt rocket science. Most folk have a baseline set of needs, pumps, lighting refrigeration, tools of various kinds be they kitchen, DIY, computer etc. Unless your budget is radically constrained id encourage you to aim a little higher. Anyway once you have refrigeration in your load budget you really need to start planning in the 2000-3000Wh per day territory. That means more PV.

[zoneblue]

Heres an basic example load budget in the 3000Wh/day ballpark. You can tweak it your your lifestyle easy enough. Unless you relish a cave dwelling hermit type of life, too much less isnt going to be much fun. YMMV.

[Tobit]

yeah zone, you have a lot of things listed that I will not have:

laptop will be replaced by a tablet (I only use my computer these days for web, email, photo sharing)
desktop computer
stereo
tv
washing machine
telephone (I haven't had a landline in over a decade, cell phone lifestyle only)
girls toys?  (I will be living alone, no kids in my future)

So yeah, you can call me the cave dwelling hermit type.. it's fairly accurate.  I only need a few essentials which I listed in my first post.  Thanks for sharing though.

[Tobit]

I'm probably going to go with this inverter for 120V battery chargers (NiMH AA/AAA and cordless tools).  I've done a lot of testing with my various chargers with a Kill-A-Watt today and 125W will be fine and will likely not see much use:

Exeltech XP125 24-Volt 125 Watt Sine Wave Inverter

http://www.solar-electric.com/xp-125-24.html

[Rybren]

In your OP, you mentioned a number of 12V loads, yet you are discussing a 24V battery bank and 24V inverter.  What are your plans for converting the 24V to 12V?  What distances are involved for the 12V/24V runs?  If lengthy, you may want to rethink running anything 12V and just stick with the AC, even if you'd need a slightly larger inverter.

[Tobit]

In your OP, you mentioned a number of 12V loads, yet you are discussing a 24V battery bank and 24V inverter.  What are your plans for converting the 24V to 12V?  What distances are involved for the 12V/24V runs?  If lengthy, you may want to rethink running anything 12V and just stick with the AC, even if you'd need a slightly larger inverter.

As I wrote in my OP, everything will be in or near the shed.  I really don't think I have many 12V devices.  The Sundanzers will run great at 24V.

The lights were a typo, they are LED lights with variable input voltage all the way up to 30VDC.  They will be run in the shed with the battery bank.

The water pump for the shower will also be in the shed.  Shower will be just outside the shed on the southern wall.  The pump is the only thing that is 12VDC and I will use this buck converter. 

The USB chargers are simple circuits and I believe there are several 24V ones on the market.  If not, they are easy to build.  I have some electronics knowledge having been a HAM for 30 years and have built several of my own radios over the years.

Since I plan on getting all new panels for the shed project, I will put the 100W panel I already have on my cabin for the water pump and shortwave radio I plan for the cabin.

[Tobit]

Here is a nice little 7-24V USB charging circuit.  Put it in a simple enclosure and you are set.  This is only one example of many.  Cheap enough to have several spares yet I think they'd last a long time, the circuits are bloody simple.

http://www.ebay.com/itm/390830217452

Here is a four port model:

http://www.ebay.com/itm/200954463025

These are essentially the same type of circuits that your car charger you plug into your cig. lighter every day use.

[Westbranch]

For the sake of your lungs, you should seriously consider using LED lights, not candles or kerosene lamps.  good for a real emergency but not long term...

hth

[Tobit]

For the sake of your lungs, you should seriously consider using LED lights, not candles or kerosene lamps.  good for a real emergency but not long term...

Tell that to the Amish. *shrug*   My beeswax candles are smokeless and they are very non-toxic.  I have been collecting them for awhile from three different beekeeper friends.  I also use this lamp-oil which is much cleaner than kerosene.