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LastOutlaw
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# Posted: 8 Sep 2014 13:48
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I ran the info from the 300 watt panels I want to buy into the MNKID SIZING TOOL. Didn't come out good with a 12 volt battery bank. In fact it didn't come out good with a 24 volt battery bank either.
Here are the results:
PV Array
Rated PV Array Power: 900 Watts
Anticipated Array Power @ 104F: 839 Watts
Rated PV Array Current: 8.01 Amps
Battery Charging Current @ 14.4 V: 62.5 Amps
VMP (Maximum Power Point Voltage) : 112.38 Volts
VOC (Open Circuit Voltage): 138.36 Volts
VMP @ -10 F°: 136.8 Volts
VOC @ -10 F°: 158.4 Volts
MNKID Selection
Max Operating Voltage 150
Max Non operating VOC (HyperVOC) @ 12V Nominal Battery Voltage 162
Maximum Number Of Modules In Series 2
Max Allowable Output Current Per KID
Based On This Current Configuration 30
Max Allowable Wattage Per KID
Based On This Current Configuration 432
Present PV Array Wattage Of This Configuration 900
Design Check
Max VOC MARGINAL
(HyperVOC)
Temperature The KID Will
Enter HyperVOC 26.6 F°
Array Power (Wattage) EXCESSIVE
KIDs Required 2.1
NOTE: MidNite Solar recommends a second controller be added after 1.2
WARNING: MidNite Solar makes no representation, warranty or assumption of liability regarding the use of the String Calculator. This tool uses data provided by other parties (such as PV module specs) and makes calculations based on assumptions which may or may not prove to be valid.
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LastOutlaw
Member
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# Posted: 8 Sep 2014 13:51
Reply
So, Im guessing that I have to run a 48volt battery bank and buy a new 48 volt power inverter in order to run the MNKID with three 300 watt panels?
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MtnDon
Member
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# Posted: 8 Sep 2014 14:57 - Edited by: MtnDon
Reply
OR,
-- panels with lower output
-- a different charge controller; Classic series for example
How much battery capacity do you need to run your power requirements? Amp-hours @ what volts, or watt hours.
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LastOutlaw
Member
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# Posted: 8 Sep 2014 16:53
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Still working on that number MtnDon.
Crucial items so far are an ac unit at least in the night to sleep in the hot parts of the year and maybe a converted chest freezer once i get one. Possibly a couple lights at night.
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MtnDon
Member
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# Posted: 8 Sep 2014 17:02
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Work on the loads you must run as well as what would be nice to have.
Don't worry about the CC or the panels or any other hardware until you know the power consumption in watt-hours for a typical day. Then the battery capacity can be determined. Next the solar panel capacity and finally the CC. The inverter size will depend on the maximum at one time watts.
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LastOutlaw
Member
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# Posted: 8 Sep 2014 17:25
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Hmm. well I plugged in the data for the classic series and it wants a classic 200. That unit looks great but at $850 that won't be happening. I'm getting close to the end of the solar funds allocated plus a few hundred. Still have wire and connectors to buy after panels and CC. I'll keep working on it until I get it right. Hopefully at some point in the near future we will be trying to be there on a full time basis.
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LastOutlaw
Member
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# Posted: 8 Sep 2014 17:43
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Quoting: MtnDon Work on the loads you must run as well as what would be nice to have.
Very hard to come up with that number before we are running it. I'll try to work up some serious numbers on my next trip up there.
Power needs will be higher in the summer for sure though.
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MtnDon
Member
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# Posted: 8 Sep 2014 18:41 - Edited by: MtnDon
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I realize it is difficult to come up with an accurate estimate. I've been down that road.
The danger is if you guess, or take someone else's advice "...here's what I have...", it is you and your family and nobody else who might find themselves short on something; too few panels, too small or too large a battery bank, a CC that can not take anymore PV power, etc. etc. There are many ways to go wrong. Too small a panel array and too small a battery bank are the leading two, strangely followed by too large a battery capacity for the PV array used.
It may be that for the budget allotted you are trying to do too much; the battery and pv panel capacity needed being larger than the budget.
One of the best online forum resources for PV is http://forum.solar-electric.com/forum.php? Anyone who is puzzling about building an alternative energy system and getting it right owes themself a visit over there. IMO.
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LastOutlaw
Member
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# Posted: 8 Sep 2014 20:48
Reply
I realize that MtnDon, I appreciate all the help and info that you and Ruggles have thrown into this thread. It is a lot of good info and advice.
While i appreciate it, I would never hold anyone responsible for my choices. Those are mine.
I also realize there is a very large learning curve that goes with all of this and as you all have helped me to realize, there are also a number of different ways to go about this.
I know I will need to run the loads I have and build and adjust the system to fit my needs.
You may be right, I may be trying to get more than my budget allows. That does sound like me...lol.
All part of the learning curve...lol.
I see that those 300 watt panels are out of stock now and not expected to be back in stock until Oct first so they are out of the equation now.
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groingo
Member
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# Posted: 9 Sep 2014 11:57
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Just my two and a quarter cents worth, for years now I have been racking my brain with a similar question to go or not to go with solar and the key ingredient for me has been to take electricity out of the equation where ever possible, look for viable alternatives either in appliances or in many cases just the way you do things and always question (do I really need that or could it be done different and better). Myself, I constantly re evaluate how I do things and find simple is better.
When all else fails you make (THE LIST) that shows the Pros and Cons, if the Cons outweigh the Pros you need to re think but most of all you need to be completely honest with yourself....ambiguity is not your friend and can wind up costing you.
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LastOutlaw
Member
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# Posted: 9 Sep 2014 13:04
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Honestly...there isn't much choice. Either we suffer through the summer in 100+ degree weather or we make AC happen. Either we make a way to keep our food cold or we make ice runs every 2 or 3 days. I don't see a propane fridge as a viable/affordable solution so that leaves a chest freezer conversion on battery and solar/generator. Winters won't be as large of a power demand with a wood burning stove and a propane heater for backup.
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MtnDon
Member
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# Posted: 9 Sep 2014 14:27
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Quoting: LastOutlaw Either we suffer through the summer in 100+ degree weather or we make AC happen.
Does that mean day and night are hot and maybe humid? Or do the evenings cool off? If like many high altitude places in the SW it cools off at night A/C can be done without mostly. If the wall / ceiling insulation is sufficient that is easy.
If a little A/C is needed during the day when the sun shines it can also be relatively easy to run a mini split A/C; in small cabins that can even be done with a window unit. But evenings need to cool down naturally unless the battery bank is Large.
If it is hot 'n' humid all day and through the evening then A/C becomes a challenge. IMO, then the only viable option is a mini split. And a good top of the line one with a SEER above 22. Even then the battery bank may need to be Large. Large battery banks mean Large solar arrays as the batteries need to be full again before the A/C demands of the next day need to be met.
Fridge: how big do you need? There are a variety of small through larger ones that use a Danfoss compressor and run on 12 to 24 volts. They are about as miserly as you can get on electricity. Not all brands are equal even though they may use the same basic compressor and control module. Some are built with better condenser systems than others.
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LastOutlaw
Member
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# Posted: 9 Sep 2014 14:57
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Sometimes it cools down after midnight and if we can run a few hours at bedtime to cool the room and bypass the humidity we can get by.
There are a few cabins in the area that run AC off batteries then recharge each evening around dinner time by running a generator for a few hours.
I can do this too but would like to generate from solar as well. If the wife has a lot to do inside the cabin in the afternoons she would need AC then, but it could be run from the generator while recharging the battery use from the evening before if solar can't keep up.
Im looking at possibly using a chest freezer conversion fridge. From what I have read this is very feasible with a minimal draw. Still researching this though and it may change in the near future.
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