laugh, but please help :) system for IL

System · February 2007

I used the link below to calculate # of panels, etc.

http://telemetryhelp.com/solar_power_sizing.asp

i am truly confused. this system will power a 'hermit' cabin...a 12v fridge (30wts), along with a few lights and the small (.4 amp) fan for the composting toilet. the heat/on demand hot water are propane. i was looking at 300 amp hour batteries (the sealed gel, as these must be inside the cabin in a loft) I would also like to run my laptop with a direct 12v plug in for charging the battery.

was going to add an air-x wind turbine into the mix (400 watts/12v) as well.

i'm in northern illinois...and a complete newbie to all of this. the panels must be roof mounted. the air-x will go on the roof as well.

can someone give me some idea if the calculator above is correct? according to it, to have a 5-day backup and power only the fridge would take 6 of these batteries, and a ton of panels....I assumed I'm doing something wrong?

sigh...this cabin is completely off grid and i need to figure this out :-D

System2 · February 2007

Re: laugh, but please help

system for IL

I got a good laugh using the calculator. It opined my requirements to 2.5kw pv panels (only about $30K installed) and 4450amp hours of battery capacity, 3 days with 7.5kwh per day. :-o I am living with a lot less than that. I'd suggest looking around at other calculators which are bound to show up recommended by some of the very knowledgable people on this forum.

Cruise some to the threads in the forums and you'll pick up a lot of usefull information from other folks. Enjoy! Don't forget some sort of generator as the sun don't always shine and the wind don't always blow, am I right?

ralph

System2 · February 2007

Re: laugh, but please help

system for IL

good to know i wasn't the only one taken aback by the calculations.

i've been perusing the posts, and i'm learning a lot. but i have many questions inregards to batteries, etc.

1.) are the gel batteries the only ones that can be stored in a vented loft?
2.) is using a 300amp/hr battery excessive?
3.) is the air-x at 400 watts worth the $ -- we do have fairly good wind, i thought it would help.
4.) what brand panels are people using? we have LIMITED roof space, so i was looking at panels rated 200 watts +
5.) anyone know of a good consultant for our little project?

niel · February 2007

Re: laugh, but please help

system for IL

1> no they aren't as you can get agm batteries.
2> i couldn't say without knowing specifically your power usage for every item and the length of time used. i would venture to say that if you're looking for a 5 day backup that you are most undoubtedly underestimating the current capacity needed. do know you don't want to use all of the battery capacity or 100% dod as this will kill the battery. double it as batteries should not normally be drained beyond 50% dod.
3> i never thought the airx to be worth it as the better ones are 1kw or above. if you do get it though don't mount it on your roof. wind generators have a good deal of vibration so save the roof for the pvs.
4> you could consider most of the pvs being sold by our host as popular, but which are most popular i couldn't say. i do know the 12v kc130 is popular as indicated by many pv users feedback and that it is about the highest power 12v pv. that is a 12v pv and you're next point indicated 200w+ pvs and they are generally 24v pvs. most will have a similar range of efficiency to them, but the more efficient they are, the higher they generally cost for the same power. btw, thin films are low efficiency and therefore you need alot more room for them for the same power. one more point is the battery system voltage you will use if it's different than the pv system voltage then you will need a controller that can downconvert the voltage and these are so far always an mppt controller. use a battery temperature sensor being the batteries will be high aloft where temps are generally higher.
5> quite a few people here are good at advising. advice is cheap here, but it's not always in line with what you want. ultimately it is your decision on anything. now if you want a local guy, then you'll need to look a solar installer up yourself. this could be found in the back of homepower magazine(get free copy on their site) or your telephone book.

System2 · February 2007

Re: laugh, but please help

system for IL

thanks! i didn't know agm's were safe inside. had asked for a consultant because i know i'm ignorant of so much that i didn't want anyone using up too much time without compensation...but free/cheap advice is always great!

ok, so before i can do much more i take it i need exact usage/storage requirements? as i'd said, above and beyond the 30wt fridge, and the 6wt fan everything else is 'gravy' a light or two...all 12 volt. the fridge and fan run 24hours (i know the fridge cycles on/off but not sure how to calc for that)

glad for the advice on the air-x, and will probably nix the idea for now...we can always add it later.

i guess with my limited knowledge, it's difficult to even ask the right questions!
i just want enough storage for 4-5 days of no sun. and roof mount panels only.

sign me 'lost in illinois' :?

niel · February 2007

Re: laugh, but please help

system for IL

before we venture to even guess at things here, i'm very curious of the make and model of this 30w frig. the only time i've heard of cooling that low in watts is with a peltier device and that would be a very small frig indeed not to mention inefficient. now the lights aren't free or next to nothing either. you must know the wattage and for how long each of them are to be on. compact flourescents are best and are available for 12v use. leds are another option as they are good night lights. most cfls are 115vac as i'm sure you've seen them in the stores. though the fan usage may be small you need to add that too. think even if it runs only 2 minutes per use(don't really know) and you use it say 10 times a day for 5 days this is now 100 minutes of use with .4amp and 12v. .4x12=4.8wx1.67hrs=8whrs. add more for more people or usage. laptops too can draw over time. i'm not sure of the current consumption of yours though. it may list the current and/or wattage or you may have to look it up elsewhere. the goal would be to supply your daily needs and a bit more for those cloudy periods. without a more precise estimate of the power used you can't come close to knowing what you need.

System2 · February 2007

Re: laugh, but please help

system for IL

i calculated the watts for the fridge at 30 (2.5 amp/12 volt, ampsxvolts=watts) it's a undercounter tiny fridge...all we have room for.
http://www.3rivers.net/~cmac/r-2.htm has the description/specs
i calculated the fan to run continuously as i'm not sure of the cycle on it.
i'm researching the requirements of everything else right now.

Brock · February 2007

Re: laugh, but please help

system for IL

That's weird 2.5 amps at 12v? I have never heard of a draw that small for a fridge. Even a pelter portable unit will typically draw over 5 amps at 12v. Just looking at that fridge, if it were a 120vac unit I might guess 2.5amps or 300w total while it was running. Without knowing more about what the loads are in wattage and how long they run it will be hard for us to guestimate what you might need.

I would second the idea of NOT putting the wind genset on the house. I was in a house once that was like that and it reminded me of when our washer was on spin with a slightly unbalanced load, sort of a slow rumble or shaking, but it never stopped

System2 · February 2007

Re: laugh, but please help

system for IL

i contacted the company about the fridge...the 2.5 amps is running. they tell me it will cycle 60/40 at a 4amp surge/draw for the compressor. so, that changes things a bit

i am awaiting email from the same company regarding the LED 12 volt options i have, although more expensive they are so meager in their energy use I thought it would be worth the investment -- especially since we are talking 3 lights, not a huge house alotment. 1 bath, 1 living area, 1 kitchen task light.
they also discussed my laptop power, and suggested (they are sending me specs) a 12v converter plug for my current power source. I have a Sony VAIO, but cannot find power draw info on it -- anyone else have this brand?

crewzer · February 2007

Re: laugh, but please help

system for IL

Montat,

Comments

The calculator is seriously flawed… pass on it. The fridge compressor may be a “swing” compressor. 4 A at 60% on and 40% off = 24 hrs/day x 60% x 4 A = 57.6 Ah/day. That’s the same as 57.6 Ah/day / 24 hours/day = 2.4 A.

(Gu)estimiated Energy Requirement

Clumping the fridge, the small fan, a laptop (85 W?) and some lights together may result in a daily energy requirement of 1,500 Wh. Assuming no inverter, VRLA batteries and overall summer system efficiency of ~75%, you’ll need a system rated for 2,000 Wh/day.

Environment

Average summer insolation (April – September) for the Rockford, IL area on south-facing PV array tilted up at ~27 degrees (+ roof slope?) is 5.0 hrs/day of “full” Sun or better. This suggests that you’ll need an array rated at 2000 Wh/day / 5 hrs/day = 400 W STC.

See: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/94822.txt

Unfortunately, winter insolation falls as low as 2.3 hrs/day average. This suggests you’ll need an array rated at 2000 Wh/day / 2.3 hrs/day = 870 W STC.

PV Module Suggestions (tentative; see below)

For a 400 W array: Two each GE 200 W modules, wired in parallel.
See: http://store.solar-electric.com/geel200wasop.html

For an 870 W array: Five each Evergreen 180 W modules, wired in parallel
See: http://store.solar-electric.com/ev180wasopa.html

Charge Controller Recommendation

Get an OutBack MX60 along with its optional remote battery temp sensor and be done with it.
See: http://store.solar-electric.com/outpowmxmp.html

Batteries

If your net energy requirement is 1,500 Wh/day, that’s 125 Ah at 12 V. Allowing for three days of autonomy and limiting discharge to 50%, you’ll need a 12 V battery bank rated at 125 Ah/day x 3 days / 50% = 750 Ah. For five days of autonomy, you’ll need 1,250 Ah.

The size 8D AGM 12 V battery is rated at ~250 Ah. You’d need three wired in parallel for 12 V x 750 Ah, and five wired in parallel for 1,250 Ah.

See: http://www.mkbattery.com/images/lagm.pdf

A 400 W STC array will struggle to recharge a 12 V x 750 Ah battery bank, but an 870 W array should be able to keep up with a 1,250 Ah battery bank.

Alternate “Balanced” Solution.

Mounting PV modules on a roof and parallel to the roof slope can result in excessive power generation capacity in the summer and insufficient capability in the winter. An alternate approach is to install the array at a steep angle (I.e., latitude + 15 degrees). This reduces summer production, but it increases winter production, resulting in a better balanced and more cost-effective system for year-‘round use.

Increasing the array tilt to ~57 degrees would improve the worst case winter month insolation by ~22% to 2.8 hrs/day. Plugging this into the discussion above, you’ll need an array rated at 2,000 Whr/day / 2.8 hrs/day = ~715 W STC. This array size would be a good match for the 12 V x 750 Ah battery bank.

Based on the 1,500 Wh/day energy assumption and installing the array at the steep angle suggested, the following configuration is worth considering:

Four each Evergreen 180 PV modules wired in parallel
One each OutBack MX60 charge controller
Three each 12 V x 250 Ah size 8D AGM batteries wired in parallel (good for ~ 3 days autonomy)
Misc fuses, breakers, wire, etc.

HTH,
Jim / crewzer

Roderick · February 2007

Re: laugh, but please help

system for IL

I could never laugh at someone who comes with a sincere request, especially since I'm a novice, myself.

I'm not used to thinking in terms of snow, since we rarely get any here, but the high tilt may help your array to shed snow in the winter. Apologies in advance if I've made an incorrect assumption about your climate. And if you go with high tilt, I'm sure you'll use something strong enough to withstand the maximum winds in your area.

My observation on Winter in my climate (San Jose, CA, lattitude 37) is that the cold temperature offsets the low sun angle and short day. A clear day in winter would have given me more kWh than a clear day in Summer, if the array was tilted optimally for each. However, the real trick is getting a clear day. The overcast skies are what really kills winter production. Do look at the nrel data to see actual historical insolation for your area. Or even better, if there's another cabin with PV nearby, ask that guy what he or she gets in Winter vs. Summer...

System2 · February 2007

Re: laugh, but please help

system for IL

the evergreen 180's you mention say they are for grid tied systems...stupid ? #5009:
does it make a difference? is it okay to use in an off-grid situtation?

and, would adding one more panel make sense if i have to stay flat with the roof?

System2 · February 2007

Re: laugh, but please help

system for IL

evergreens are great for offgrid too. (and their stock blessed me with a nice week for a change)

crewzer · February 2007

Re: laugh, but please help

system for IL

The Evergreens are sometimes labeled for on-grid use due to their unusual voltage specs (~23 Vmp, as I recall). The MX60 controller doesn't care (within limits, of course). It'll take the "extra" module voltage and convert it into extra charging current.

Outback's official array power limit for the MX60 used with a 12 V battery bank is 800 W STC. However, the output current can be user set as high as 70 A, so, as a practical matter, it can unofficially handle an array of up to ~900 W STC or so for 12 V applications.

If you have to stay with the roof pitch, using five ~180 W STC PV modules instead of four should work (per the discussions above), assuming the pitch is ~correct. The "flatter" array will require more maintenance: cleaning off leaves, snow, pollen and misc. environmental debris.

HTH,
Jim / crewzer

System2 · February 2007

Re: laugh, but please help

system for IL

thanks for all the help

I guess now I'm just puzzled about the fridge. It is the biggest watt-hog (I can always charge my laptop as I drive) and I wonder if there are alternatives to the fridge I selected? I want to stay 12 volt and tiny...

any suggestions for a more efficient fridge to use?

and MATTL: i'd love to hear more about your 17watt pc!!!! i'll be needing a new computer about the time the house is built, might as well shop for something that uses less.

System2 · February 2007

Re: laugh, but please help

system for IL

well, it's only a web server for a small (2 actually) website (my sig and my business). it also functions as a nice little "always on" internet station for my wife. it's a tad slow for everyday use but is perfect for the web server

heres some info on how i converted my regular desktop pc to run on 12v (more than you probably want to know but...):http://www.wind-sun.com/smf/index.php?topic=1493.0

your best best is get a laptop. the one im using is a low end compaq (is my second one of the same design, i love the small size) bought in walmart for $700(inc'd 2 yrs extended warranty), i bought another adapter to charge it directly off the 12v solar. acceptable performance , low power & cost .
http://www.laptopical.com/rohs-green-laptop.html

something based on intel core 2 duo processor is fast and dynamically adjusts power, still that is top of the line and a slower model like mine uses much less power. i have basically the same as this but with more ram: http://www.pcmag.com/article2/0,1759,1825173,00.asp
actually i can tell you exact charging/running power if you like

crewzer · February 2007

Re: laugh, but please help

system for IL

I guess now I'm just puzzled about the fridge. It is the biggest watt-hog (I can always charge my laptop as I drive) and I wonder if there are alternatives to the fridge I selected? I want to stay 12 volt and tiny... any suggestions for a more efficient fridge to use?

Something like this might be an alternative: http://www.wind-sun.com/smf/index.php?topic=1073.0 You might need to run it from a small-ish true sine wave inverter (NOT an MSW inverter).

HTH,
Jim / crewzer

System2 · February 2007

Re: laugh, but please help

system for IL

those sundanzers' are sooo expensive!!
i havent looked into these but the name and brand i came across recently. be interested what people find out.
i do know that my washer/dryer all in one research led me to equator as the TOP rated energy efficient unit. its an italian brand but i read alot of online reviews regarding failures so i bought my lg . anyhow this fridge is equator i note http://www.usasolarstore.com/pages/prodtourpages/apps.php
they seam to have a clue as to efficiency. the brands and models i found for maximum efficiency in a washer/dryer are NEVER for sale in any of the big outlet stores for some reason. you really have to shop around, and compare reviews and warranty if possible. and then some of the guys here have BUILT stuff!!

crewzer wrote:

I guess now I'm just puzzled about the fridge. It is the biggest watt-hog (I can always charge my laptop as I drive) and I wonder if there are alternatives to the fridge I selected? I want to stay 12 volt and tiny... any suggestions for a more efficient fridge to use?

Something like this might be an alternative: http://www.wind-sun.com/smf/index.php?topic=1073.0 You might need to run it from a small-ish true sine wave inverter (NOT an MSW inverter).

HTH,
Jim / crewzer

crewzer · February 2007

Re: laugh, but please help

system for IL

Forget the Sundanzer... I was thinking about a small chest-type freezer set up to run a fridge. For example, the Kenmore 5.0 cu. ft. Manual Defrost Chest Freezer (Sears item #04616512000 Mfr. model #16512; $170) is rated at 242 kWh/yr ... that's just 663 Wh/day, a bit less than what montat's current fridge requires (~720 Wh/day). It would use a lot less energy if reconfigured as a fridge... I think Jay got his 7.2 CF freezer down to 240 Wh/day -- about 1/3 of the calculated for montat's fridge.

Do the math... The cost of buying the freezer, thermostat/controller and inverter should easily be recovered in savings from a smaller PV energy system.

HTH,
Jim / crewzer

System2 · February 2007

Re: laugh, but please help

system for IL

we don't have room for the chest or the sundanzer

i am considering going propane on the fridge...we'll have the tank there anyway for the heater and the on demand hot water.

it would certainly cut our PV system WAY down, but i'm just not sure -- i guess we could start with the propane fridge, and if it doesn't work out switch back to the 12 volt and add on to our system.

any users of propane fridges on the forum?

BTW -- i need the 'big' processer on my laptop...do a lot of graphics work....i'm just going to do my best on energy when i buy my next laptop.
and i'll probably buy a spare battery for it. i'm online at least 3-4 hours per day, so i MUST keep that in mind.

System2 · March 2007

Re: laugh, but please help

system for IL

Being a person who likes to be on line. How will you connect in your "hermit cabin"? Satellite? If so that must be added to the equation. I have assumed you are off grid.

System2 · March 2007

Re: laugh, but please help

system for IL

We've used the Dometic refrigerator/freezer in our RV for 10 years and it has been 100% relaible and a very modest user of the propane and practically no 12v. I wonder why more people don't use them?

laugh, but please help :) system for IL

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