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.
Quote from: Tobit on April 28, 2014, 04:57:06 PM
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
Quote from: vtmaps on April 28, 2014, 07:55:47 PM
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.
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.
(http://i.imgur.com/8tYkEK9.jpg)
So I am thinking of 400W of panels and ~200 AH battery bank (4x6V for 24V) and use a KID controller.
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.
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.
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.
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.
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.
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
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.
Quote from: Rybren on April 29, 2014, 07:00:23 PM
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 (http://www.amazon.com/dp/B00C4QVTNU).
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.
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.
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
Quote from: Westbranch on April 29, 2014, 09:31:25 PM
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 (http://www.amazon.com/dp/B005CBWIMK) which is much cleaner than kerosene.
My 2x275W SolarWorld panels arrived the other day, very nice looking panels and they actually came in under quoted price by a few cents/watt. I think I am going to add one more which will be max for the KID CC. I'm going to start looking for some decent 225AH 6V batteries next.
vtMaps, sorry if it sounded like I was being overly stubborn on the Sundanzers. I am open to other suggestions as refrigeration and freezer are going to be my two largest power consumers. I don't want a huge battery bank and solar array but I do want to run quality batteries and the batteries play a major role in the cost. Since I found someone close by to my present location who can ship me panels for only $25, I will most likely be adding the third 275W panel to get me to 825W and a 24V 225AH battery bank sounds like it will play well.
I was looking at the Sundanzers because their smallest ones are 1.8 liter in size which is plenty for me. I also prefer chest style over front door. In fact, freezer size is more important to me than refrigeration. Other than keeping things like eggs, butter, and a few condiments cold. I don't see a need to get anything larger than 1.8 liters.
My climate is southern Missouri. Winter nights will get below freezing, down to 0 on a few occasions, but it usually warms back up to the low 30s during the days although last winter was one of the coldest in decades according to a friend who lives 2 miles from my off-grid location . The shed will have a fair amount of water storage in it so I plan to insulate it well and it may have a tiny wood stove for those rare nights it gets super cold. I could also always unplug the refrigerator during the night on those cold winters.
If there is something that'd be more efficient than the small Sundanzer freezer, I'm listening. Over on another forum, I think you are a member there as well, I heard about a Stecca 24V unit but they seem hard to find here in the US. Again, I will be living alone and only have my mouth to feed. I plan to hunt a couple times a year so vacuumed packed meat in my freezer is important.
Edit: Maybe go with a slightly larger inverter and a freezer like this http://tinyurl.com/ky296vt and a fridge like this http://tinyurl.com/lcnpkwt ?
Im still not sure that you have enough PV for a fridge and a freezer. Refridgeration is a hard task master. And when it comes to power use/efficiency, you either spend the big bickys on the fridge or you spend it on the rest of the system... to power less efficient units/inverter losses etc.
825W of PV cannot power a fridge and freezer unit?
Quote from: Tobit on May 04, 2014, 07:28:50 PM
825W of PV cannot power a fridge and freezer unit?
It probably matters "where" but for years I ran a full size fridge and 2 smallish freezers as base loads on 820 watts of panels. Seldom needed to switch to grid or charger. It did other stuff but mostly on an opportunity basis like running the washer.
Then this year with 2350 watts I have had stretches of 3 days of switching them to the grid from lack of incoming power combined with improper load management.
So it can be all over the map but anywhere reasonably sunny that seems it should be enough.
Just from here in my real world situation.
Tom
Quote from: zoneblue on May 04, 2014, 05:09:38 PM
Im still not sure that you have enough PV for a fridge and a freezer.
Tiny 1.8 cu. ft. fridge and 5.0 cu. ft. freezer I am looking at, kWh/year numbers from energy star labels:
240+260=500KWH/year 500/365= 1.37 KWH/day
825 watts x 4.9 hours (solar insolation average for Springfield MO) =4042.5 = approximately 4 KWH/day
Would appear I'd have plenty of PV buffer in the array, especially in summer when insolation climbs to 6. In winter, since they'd be in the shed, they'd hardly run if I keep temps just above freezing.
I could actually save energy by going with a conventional fridge/freezer combo but the fridge areas are much larger than I need with smaller freezers sections.
Some of those little fridges have the same size compressor of a larger refrigerator. True it may not have to run as long - but consider a larger refrigerator instead of those mini ones - the kind with manual defrost. You might be surprised it doesn't take too much more energy for the extra room you get - plus the much larger freezer section.
Also be aware that some refrigeration may not operate properly outside if it gets too cold. The refrigerator I am using a friend gave me - it had a bad cold control so I replaced it with one of the $15 digital ones you see on ebay and it works with very good precision now.
Quote from: ClassicCrazy on May 04, 2014, 11:36:29 PM
Some of those little fridges have the same size compressor of a larger refrigerator. True it may not have to run as long - but consider a larger refrigerator instead of those mini ones - the kind with manual defrost. You might be surprised it doesn't take too much more energy for the extra room you get - plus the much larger freezer section.
See, that's the thing. I don't need large refrigeration. I'm just one person who doesn't drink milk, soda, beer, juices, and use a wide variety of condiments and leftovers that need a lot of refrigeration space. I drink water, tea, and coffee. A freezer, on the other hand, is something I'd get more use out of and this 5 cu. ft. chest freezer I am looking at would be perfect. I just need an energy efficient way of keeping small things like butter and eggs.
Again, I'll be keeping my shed, where the freezer and reefer will be located, just above freezing as my shed will also be used for water storage.
Just a thought for low capacity cooling...
Try using an old fashioned "ice box" or cooler and swap frozen water in jugs into the cooler?
The up side of a freezer full of frozen jugs is it will run very little.
Based on you having a freezer anyway. Plus less equipment to fail?
Just tossing it on the wall to see if it sticks.
Tom
That ice box idea is a good one - well insulated box and a jug of frozen water will keep it cool enough. And as Tom says - easy to swap out a frozen jug from the freezer.
Yeah, that's a good idea Tom. It is definitely worth a try. I used to have an old-fashioned ice-box when I lived on a small sailboat and it worked quite well. However, the ambient temperature down in the cabin always seemed much cooler than outside probably due to being partly in the ocean.
I'll give it a go before investing in a fridge. Freezer and and old-fashioned ice-box. I dig it.
Quote from: Tobit on May 05, 2014, 01:13:28 PM
Yeah, that's a good idea Tom. It is definitely worth a try. I used to have an old-fashioned ice-box when I lived on a small sailboat and it worked quite well. However, the ambient temperature down in the cabin always seemed much cooler than outside probably due to being partly in the ocean.
I'll give it a go before investing in a fridge. Freezer and and old-fashioned ice-box. I dig it.
Might look at those extra thick styrofoam coolers they sell in summer for extended camping, several inches thick but likely need a box around them for long term use.
We used one with dry ice to keep bacon frozen that we bought vacationing in the west and kept it frozen for days on a hunk of dry ice.
I love the bacon selections out west much better than here in the corn belt where we have millions of hogs?
Tom
Ill say it again. Refrdigeration is a relentless load. Small fridges are as bad or even worse than bigger fridges because there is less room for insulation. Dont rely on published numbers, they are for certain optimistic "marketing" conditions that you may not find exist in your setup.
If you are willing to spend the bucks you can buy super insulated units, and then your minimum pv thing will work.
Its an exceptional fridge that uses less than 1000Wh per day and an exceptional freezer that uses less than 1500Wh/day. Worse case, for cheap off the shelf whiteware would be 3000Wh/day for both.
If you think you can consistently produce 3kWh/day from 800Wp pv you clearly live somewhere a lot more sunny that me.
Be careful to use realistic data, else your design will not satisfy. Living off grid with insufficent pv is a misery. And ... PV is cheap!
Quote from: zoneblue on May 05, 2014, 06:10:29 PM
If you think you can consistently produce 3kWh/day from 800Wp pv you clearly live somewhere a lot more sunny that me.
The weather is always a gamble but, based on insolation numbers, with 825W of PV, I am showing the ability to produce 95-104 kWh/month from March - Sept. at my location in southern, MO. I am also on a south facing slope of a ridge at 1400'. Drops down to 75 to 80's all other months but those are the coldest months anyway where the freezer will not run as much.
As I stated in my last couple of posts, I'm going to ditch the idea of a traditional fridge and stick with just a single 5.0 cu. ft. freezer and build a well insulated, old-fashioned, ice chest cooler for the small amount of items such as butter and cheese that'll need it. The fridge is still a relative modern convenience. I think I can live without it if I have a good freezer for making ice jugs.
Quote from: Tobit on May 05, 2014, 10:39:21 PM
The weather is always a gamble but, based on insolation numbers, with 825W of PV, I am showing the ability to produce 95-104 kWh/month from March - Sept. at my location in southern, MO.
Unlike virtually every other load off gridders have, a fridge in particular doesnt understand monthly averages, it runs 24/7, and the weather ... you know how she is, sunny one day rainy the next,...fickle, and batterys are expensive, so...
Quote
As I stated in my last couple of posts, I'm going to ditch the idea of a traditional fridge and stick with just a single 5.0 cu. ft. freezer and build a well insulated, old-fashioned, ice chest cooler for the small amount of items such as butter and cheese that'll need it. The fridge is still a relative modern convenience. I think I can live without it if I have a good freezer for making ice jugs.
Cool. Theres always room for simpler lives.
Quote from: Tobit on May 05, 2014, 10:39:21 PM
As I stated in my last couple of posts, I'm going to ditch the idea of a traditional fridge and stick with just a single 5.0 cu. ft. freezer and build a well insulated, old-fashioned, ice chest cooler for the small amount of items such as butter and cheese that'll need it. The fridge is still a relative modern convenience. I think I can live without it if I have a good freezer for making ice jugs.
But why live without a modern fridge? Modern fridge/freezer combos (fridge/freezer/cool drawer/crisper drawer etc) are just getting pretty darn efficient. Some years ago it was ELCOLD for freezers and various european low power fridges in the sub 300kW/hr per year that were very popular with RE people.
But now commercial units from the likes of Samsung/Miele/Gorenge are even lower power and have fridge/freezer capacity for 2 or 3 people (or 1 person and a decent supply of beer/bacon)
Even better now as ZB hinted at, PVs are just so cheap its easy to get enough power for a nice fridge/freezer.
My recommendation is get twice as many PVs to make 1600W or even more and just forget all the messing about with a separate freezer and polystyrene cool boxes etc and get a modern low power fridge/freezer. Just IMHO
dgd
(who recently bought a 506Kw/hr per year electric guzzling F&P fridge/freezer AND 55inch LG led tv 176Kw/H year so I can now have sufficient cold beer to enjoy a good 3D movie or Premier league football)
dgd How many watts does that big LED TV take to run ? I recently acquired a 42 inch LCD ( freebie) and the thing sucks 230 watts - but I have plenty of extra solar power so no big deal so far. I know the LED TV's use a lot less power.
CC,
This LG tv is normally about 90watts. It has power saving modes, really screen brightness, and I keep it on the medium power setting. On 'retailer demo' brightness its nearer 160 watts.
For comparison my fridge/freezer sucks 200 watts when compressing and about 30 when not.
dgd
Quote from: dgd on May 05, 2014, 11:09:50 PM
PVs are just so cheap its easy to get enough power for a nice fridge/freezer.
My recommendation is get twice as many PVs to make 1600W or even more and just forget all the messing about with a separate freezer and polystyrene cool boxes etc and get a modern low power fridge/freezer. Just IMHO
If it were that simple, we (off-grid) would all be doubling our arrays. Unfortunately, bigger loads don't just require bigger arrays, they also require bigger batteries.
I do agree that Tobit should get a modern low power fridge/freezer. That 1.8 cu ft Danby fridge consumes 827 wh per day (according to energy star label). That's HUGE for such a small capacity. Tobit can do much better (but not much cheaper).
--vtMaps
Quote from: dgd on May 05, 2014, 11:09:50 PM
But why live without a modern fridge? Modern fridge/freezer combos (fridge/freezer/cool drawer/crisper drawer etc) are just getting pretty darn efficient.
But why live with one if I don't need one? As I've said a couple times, I need more freezer space than fridge space. Modern combos have twice the fridge space to freezer space. The big fridge in my on-grid apartment is mostly empty, I currently have butter, some cheeses, a jar of mayonnaise, and store bought eggs because they are not farm fresh *. My freezer, on the other hand, has about 10 lbs. of vacuum packed deer meat and fish.
There are a lot of fruits and vegetables that do not require modern refrigeration. Eggs fresh from the hens also do not need refrigeration.
Find me a modern combo that has a 5 cu. ft. to 8 cu. ft. freezer and fridge space of 3 cu. ft. or less and I'm there.
Quote from: vtmaps on May 06, 2014, 03:46:46 AM
If it were that simple, we (off-grid) would all be doubling our arrays. Unfortunately, bigger loads don't just require bigger arrays, they also require bigger batteries.
I do agree that Tobit should get a modern low power fridge/freezer. That 1.8 cu ft Danby fridge consumes 827 wh per day (according to energy star label). That's HUGE for such a small capacity. Tobit can do much better (but not much cheaper).
But is he not at the planning stage for the new RE system? So battery sizes and pv array size is easy now to get right(er). Going too small to begin with can be a real disappointment when it's realised the battery capacity is insufficient.
Dgd
Tobit,
My logic on refrigerated space is that although you may not need extra space now you may find it useful in future. For example you may be able to trade for perishable food, dairy products etc.. Or take advantage of lower cost bulk food items from supermarket that need cold storing.
Since the upfront fridge cost should be near same as Danby and energy needed to run it is also near same then why not go with modern fridge/freezer combo?
Dgd
tobit;
I think I understand what you are trying to do.
Nothing wrong with "less stuff". Been there, done that. I remember a time right after I got discharged from the Army and wanted no "stuff" I did not absolutely need. Everything I owned fit in my pickup with a camper and I lived in that for a couple years.
Too old for that now and I have more stuff than I actually need but enjoy them now. Indoor plumbing, pressure water, etc all shifted into the necessities column as I aged.
I actually see both angles on this but you get to decide.
Bigger is probably better on an energy system. Far better to have it and not need it than need it and not have it.
On a good day I can argue either side of these solutions. Some times less is actually more.
Best of luck and glad to see you researching before you pull the trigger on things. I did not and ended up having to do a lot of upgrades due to knee jerk decisions. Like starting at 12 volts thinking vehicle and RV gear would be able to use it. Problem there is that stuff all is powered by an engine driven alternator so efficiency is non existent.
I could go on but that will drift off topic as others tell me I am silly.
Tom
Quote from: TomW on May 06, 2014, 09:02:39 AM
I think I understand what you are trying to do.
Think of this photo and add a shed on the southern side of the ridge for storing tools, my freezer, water, and running PV. :)
This isn't me in the photo but pretty damn close to how I want to spend the rest of my life.
(http://media.knoxnews.com/media/img/photos/2007/11/22/1123appy1_t607.jpg)
My new Amana 5.2 cu. ft. freezer arrived today for the woodstead. I wanted to buy it now for a couple reasons.
A) Price was right, only cost me $149.00 out of pocket
B) Energy star label reads 215 KWH/year which is one of the best I have seen.
C) No sales tax here.
D) I wanted to set it up in the garage over the summer so I could monitor energy usage to make sure I am sizing my solar array adequately. I figure it will be the largest energy consumer.
The downfall to this unit is it's external thermostat located on the front of the unit. This means the unit is only efficient in rooms that stay between 32F and 110F. However, this shouldn't be an issue since I will be locating it in my insulated shed, which I plan to heat to just above freezing in the winter so rain water stored inside the shed doesn't freeze. The other potential downfall is that some units like these need a high-quality and beefy inverter otherwise they have a hard time starting. There are a few ways around this but I don't plan to skimp on an inverter so hopefully I won't have an issue.
So far so good. Ambient temp this morning was only 50F degrees. I tried to watch the kill-a-watt closely when the compressor first kicked on. It seemed to draw ~200W but quickly settled down to 115W and, after a few moments, has been drawing a steady ~84W at .0.84A ever since. The compressor only ran for about and hour before it decided that was cold enough on the inside, at the number 3 setting, and turned itself off.
Next step is to get a thermometer in there and see how cold it is at the #3 setting. The manual states #3 should be 0F degrees and that number #4 and #5 on the dial are deep freeze modes.