Help me finish my setup and opinions.

MNdiyguy

Here's my story:

I have been in the process of building my "dream garage" on a semi-remote 26 acres in Carlton County MN. I have been at it for about 12 years ,from buying the land, having the building shell put up, hydronic heat and concrete,wiring, insulating. sheetrock, on a do as  I have time and can pay basis.

The Power COOP wants $15000 to run power to the site, + $25 a month for the honor of having them there whether I use them or not. I have been living on a 4000 watt max Chinese generator. I live about 30 miles away from this property, I do not live there, however I do have a camper that works well for summer use for when i don't go home.

My "dream garage" is nothing fancy, 40x60 14 ft ceiling split into 2 30x40's, a heated workshop and cold storage,1200 square feet per side.

I will be retiring in a little over 2 years and be living on a fixed income. I am a equipment mechanic by trade and hope to fund my hobbies in said garage by doing a lil wrenching on the side other than my own projects once I retire.

I am really unsure of my future power needs, I know in the winter I will need to run a genset no matter what in the dark season here in MN.
This winter when I was working with all the things I "need" my usage from a Kill a Watt meter off the genny was reading 400 watts , but I don't have the hydronic set up yet and am unsure what that is going to draw opposed to the 75000btu propane unit heater. I have a gas powered welder and air compressor. 

What I have bought so far for my system;

12 180 watt 24 v Chinese poly panels with plans to buy 4 more for a total of 2880 panel array.

Related power	180W
Open Circuit Voltage(Voc)	44.89V
Maximum/Peak Voltage(Vmp)	35.16V
Short circuit current (Isc)	5.49A
Maximum/Peak Current(Imp)	5.12A
Output Tolerance	±3%
SLA Battery Voltage	24V

All Magnum Energy system,  4024PAE Inverter,,
ARC remote
mini enclosure/wall plate
Pt 100 100 amp charge contoller
BMK
AGS
non Magnum 6 string combiner box
3 Midnight lightning supressors for the diff voltages
been working on getting that.wired up.
and considering/tryng to come up with the $ for a Honda 7000is generator, mine's got a rope. (opinions welcome)

Spring has sprung and I can start building the array mount and trenching in wire, and here is where I need assistance.doing the math, finding the maximum # of panel/strings, thinking 4x4, wire size,it will be  about 30 ft from the combiner box to the controler and also some assistance with my decision with a battery bank. I am considering 12 l 16  2 volt Trojans for a 1100 amp hour, or 8 6 volt l16 Trojans for a  740 a/h 24 v bank,within 4 feet of the controler, will I have enough panel for that, or enough battery for the panels ?

I look at all those letter over letter formulas and my head starts spinning,(not to mention trying to comprehend the electrical code 2014 for solar). I can daignose troubleshoot and repair 24 volt systems on modern equipment, but no matter how much I read I have smoke coming out of my ears with this. I am a jack of most trades,master of none, but I am finding I am not an electrical engineer whatsoever!

Let's hear it, I can take it!

mike95490

$15K is not a bad install for grid power.  You can't get a decent off grid system for that. (unless you are a dyed in the wool hermit that thinks 1 candle is great.)

If you are going to install off grid battery, go with a 48V bank.
Or at least ASK BEFORE you buy stuff,   Unless you can get a refund, you are stuck with paralleling 24V battery banks.

vtmaps

I am considering 12 l 16  2 volt Trojans for a 1100 amp hour, or 8 6 volt l16 Trojans for a  740 a/h 24 v bank,within 4 feet of the controller

Avoid parallel batteries... thus twelve 2-volt batteries is the way to go... but I don't like those Trojans.  Those 2 volt batteries are actually three 2-volt cells in parallel.  Three times as many cells to check and water.  Trojan does make a true single cell 2-volt battery in their industrial line.  

mike95490 said:
$15K is not a bad install for grid power.  You can't get a decent off grid system for that.

If you are going to install off grid battery, go with a 48V bank.

I agree with both of those points. 

Regarding Mike's second point:  If there's any chance you will run power tools, vacuum, laser printer, microwave, or other large loads, you would be better off at 48 volts.

In a 24 volt system, even if you have adequate storage capacity, you may run into unacceptable battery voltage sag with large loads.  This is because of the battery internal resistance. 

A battery's energy storage capacity depends on how much lead and electrolyte it has.  For any given amount of lead, the battery can be designed with fewer, thicker plates, or with more plates that are thinner.   When cycled, the battery with fewer thicker plates will last longer.  The battery with thinner plates will not last as long, but its plates have more surface area and thus the battery has less internal resistance. 

The point is that if you are using thick plate batteries, you may have unacceptable battery voltage sag with large loads.  Under those circumstances you might be better off at 48 volts.  By the way, cold batteries have more voltage sag.

One of the attractions of AGM and LiFePO4 batteries is their low internal resistance, but each of those batteries has other problematic issues.

--vtMaps

Photowhit

While I DO NOT agree with the "can't get a decent off grid system" statement, and the "Hermit with 1 candle" is just silly! I cooked a pizza, did a few loads of laundry, and heated 30 gallons of water yesterday and I forgot to light a candle!

I would agree that 48 volt is the way to go! The only reason I'm at 24 volts is I had purchased the battery for a smaller residence and had to move.

I'm pretty happy with my system and if I ever get around to buying an inverter, I might go with the Magnum you spec'ed. and I think I'd be around $10 K after federal tax credit.

I would first suggest seeing if you can exchange the 24 volt inverter for a 48 volt. I would use those exact words with the seller. Let them know it's unused and a mistake, might even let them know you have other needs...

I would consider a forklift battery, they require a bit more maintenance, but the cost per Kw over the lifetime of the battery is quite better and likely cheaper for the stored Amp hour to start with.

I would suggest that the cost over your lifetime, if you are 63-65 the cost over your lifetime vs grid connect at $15K might be about the same. You will run the genny in Minnesota! so you will have added expenses.

You don't know your loads yet, but you will want and array that can deliver a minimum of 10% of your batteries Amp Hour capacity, at 20 hour rate (this is tricky as forklift batteries are typically rated for 6-8 hours and large case batteries for solar, often at 100 hour rate) Solar arrays typically deliver about 75% of their labeled wattage. So to calculate the array to battery bank, you can reduce the array to amps it can deliver. a 4000 watt array, will deliver about 3000 watts normally, 3000 watts divided by 48 volts will give you about 62 amps delivered, so would support about a 620 amp, 48 volt battery.

Photowhit

Forgot to say, you might see if there are 3rd party options for running the power across your property.

BB.

I too would suggest that $15,000 installation + $25 per month ($300 per year) connection charge is "not bad". And I would suggest that if you ever want to get a building loan/get old and unable to do as much later in life/sell the property--That $15k is not the "worse" "investment".

But enough of that--To see if I can help answer some of your questions assuming you have what you have (note, many of the answers for 24 volt system vs 48 are about the same (i.e. 4x 12 volt batteries in series for 48 volts vs 2x 12 volt batteries in series, then 2x parallel strings gives you the same storage "roughly" the similar system costs). However, your choices can have dramatic effects on installation and maintenance issues.

You have 12x180 Watt solar panels--I like to have a "balanced" system design (loads -> define battery bank -> Solar array size). But since you have the panels, lets size the battery bank (note, I will do 24 volt battery bank, but you can do 48 volt battery bank with 1/2 the AH rating). suggest 5% to 13% rate of charge, with 10%+ rate of charge for full time off grid power (and 10%+ if forklift/industrial batteries):

• 12 x 180 Watt panels * 0.77 panel+controller derating * 1/29 volts charging * 1/0.05 rate of charge = 1,147 AH @ 24 volt battery bank (minimum rate of charge)
  
• 12 x 180 Watt panels * 0.77 panel+controller derating * 1/29 volts charging * 1/0.10 rate of charge = 574 AH @ 24 volt (nominal rate of charge)
  
• 12 x 180 Watt panels * 0.77 panel+controller derating * 1/29 volts charging * 1/0.13 rate of charge = 441 AH @ 24 volt (maximum "cost effective solar charging rate")
  

Assuming you look at a 574 AH @ 24 volt "nominal" battery bank--What kind of power could you get from such a battery bank. For flooded cell batteries (usually cheaper and more rugged than SLA--Sealed/AGM type lead acid batteries):

• 574 AH * 24 volts * C/20 hour rate * 0.85 AC inverter eff = 585 Watt AC load @ 5 hours per day/night for 2 days (50% battery discharge)
• 574 AH * 24 volts * C/8 hour rate * 0.85 AC inverter eff = 1,464 Watt AC load for ~3 hours or so (maximum continuous discharge rate to 50% Battery State of Charge)
• 574 AH * 24 volts * C/5 hour rate * 0.85 AC inverter eff = 2,342 Watt AC load for minutes to maybe 1 hour load (max load on battery bank)
• 574 AH * 24 volts * C/2.5 hour rate * 0.85 AC inverter eff =4,684 Watt max AC surge load (starting well pump, etc.)

And then there is how much power per day you can "harvest" from your solar array... By Season, fixed array:
http://solarelectricityhandbook.com/solar-irradiance.html

Duluth
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 43° angle from Vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.54	3.79	4.46	4.85	5.03	5.03
Jul	Aug	Sep	Oct	Nov	Dec
5.29	4.99	4.20	3.38	2.59	2.18

If you toss the "bottom" four months (need generator), then that gives you Feb as your "break even month" (may need a genset or not depending on weather/loads):

• 12 * 180 Watt * 0.52 off grid system eff * 3.79 hours of sun per day (Feb) = 4,257 Watt*Hours of AC power per average Feb day
  

So--That is an example of a "balance system design" and its capabilities.

Some of your other questions...

You should be able to put three panels in series--Four panels may be a bit much (I don't know anything about the new Magnum MPPT charge controller--I would have to read the manual on array configuration).

You probably want around 60 to 120 Amps of 24 VDC charging current for a ~574 AH @ 24 volt battery bank.

Your Magnum inverter can output 105 Amps @ ~29 VAC, a genset running the inverter at maximum power should be around:

• 105 Amps * 29 volts * 1/0.85 charger eff * 1/0.95 Power Factor * 1/0.80 genset derating = 4,714 VA rated genset (approx)

A Honda em4000sz has been used by a poster in Minnesota successfully. Note this will support 120/240 VAC and the "sx" has the electronic engine/fuel controller (no manual choke needed).

Choosing a good generator
Demonstration of Generator Support

Of course--You may have needs for a large genset and two (small+large) generators may be your solution. Fuel choice--Propane, diesel, gasoline--In cold weather, may not be an obvious choice (i.e., gasoline seems to be easier to start in cold weather?). I live in California--So don't take my suggestion as the "correct answer" here.

-Bill

vtmaps

BB. said:

Assuming you look at a 574 AH @ 24 volt "nominal" battery bank--What kind of power could you get from such a battery bank. For flooded cell batteries (usually cheaper and more rugged than SLA--Sealed/AGM type lead acid batteries):

• 574 AH * 24 volts * C/20 hour rate * 0.85 AC inverter eff = 585 Watt AC load @ 5 hours per day/night for 2 days (50% battery discharge)
• 574 AH * 24 volts * C/8 hour rate * 0.85 AC inverter eff = 1,464 Watt AC load for ~3 hours or so (maximum continuous discharge rate to 50% Battery State of Charge)
• 574 AH * 24 volts * C/5 hour rate * 0.85 AC inverter eff = 2,342 Watt AC load for minutes to maybe 1 hour load (max load on battery bank)
• 574 AH * 24 volts * C/2.5 hour rate * 0.85 AC inverter eff =4,684 Watt max AC surge load (starting well pump, etc.)

MNdlyguy,  in terms of energy consumed, 500 watts for 5 hours is the same as 2500 watts for 1 hour... each is 2500 watthours of energy.  

But your battery doesn't see it that way.  The larger your draw (watts), the lower the capacity of your battery.  That is what the Peukert factor is about.

In Bill's numbers that I have quoted, notice that you can draw 585 watts for 10 hours (to get the battery down to 50% SOC).  But if you draw four times as much (2342 watts) you cannot do it for one fourth the time (which would be 2.5 hours).  Bill has incorporated the Peukert factor into his estimates of the run time.

BB. said:

You should be able to put three panels in series--Four panels may be a bit much (I don't know anything about the new Magnum MPPT charge controller--I would have to read the manual on array configuration).

Those panels have a Voc Vmp of 35 volts...  On a 24 volt system you will get better performance with the panels configured with a string length of 2.  Three in series will work well for a 48 volt system.

BB. said:

Your Magnum inverter can output 105 Amps @ ~29 VAC, a genset running the inverter at maximum power should be around:

• 105 Amps * 29 volts * 1/0.85 charger eff * 1/0.95 Power Factor * 1/0.80 genset derating = 4,714 VA rated genset (approx)

Yes, but.... If the OP has a 574 ah battery (as per the quoted example), then 105 amps is too much charging current.  If the OP buys an 1000 ah battery, then 105 amps is just right.

--vtMaps

BB.

I believe the magnum has programmable output current limits. Programming for ~57 amps would be 10% rate of charge.

Going over 13% rate of charge with a standard lead acid deep cycle flooded cell battery runs a chance of overheating the battery.

I like remote battery temperature sensors back to the charge controller to limit the chances of thermal runaway at higher charging current.

Anyway, this is a high level rule of thumbs design to give you a high level estimate of system sizing and performance.

Still lots of details to worry about.

-Bill

sanitariu

For these money you can get Lifepo winston batteries and good controllers like electrodacus. For the rest of the money just put panels panels panels and nothing more. You will have no moving parts, use panels even for heating and be easy 20-25 years at least. Do not go for lead acid batteries !