Newbe here

[TJay]

My wife and I are Embarking on a solar journey for Wisconsin camp site, We have Ordered a small system from a local Wisconsin Business, To keep the cost with in our budget We will be doing most of the work ourselves, Guessing we will have a few questions along the way, Excited to hear what you guys have to offer,

[littleharbor]

Welcome TJay.

Can you tell us what your goal is here? One mistake many people make is buying a "kit" before they have any idea what they really need, based on their daily loads.

The proper way to approach off grid solar is to, first, identify your loads, next determine how much battery you will need to cover your loads. Generally you plan for 2 - 3 days of battery capacity without going under 50% discharge. Based on your battery amp hour capacity you would like to be able to produce 10 % of that with your solar array. This % can go as low as 5% and up to about 13% depending on whether you are say weekend only or heavy daily users. So for example if you have a 350 amp hour, 24 volt battery bank you want to be able to charge at 35 amps.

There is lots of good information to be found in the "stickies" located at the beginning of the Off grid topics page. Enjoy your learning experience here. There is a lot to learn.

[TJay]

Well I guess our main goal is to start small so we don't go broke and add later, For now we have a camper and a shed on the property, So we had the local solar company come out and figure up what we need to run what we got, We ended up ordering two 325watt panels, 1 mppt Charge controller , 1 sw 2500 watt Inverter 1 li-ion battery 4kwk@24 volt thats it for now, my next step is to build a panel ground mount, we are putting the panels about 150 feet away from the camper so they are in sun light all day not blocked by any trees, Battery and controls will be mounted inside the shed, All this should start in the next few weeks, Looking forward to it, never been around solar or even been up close to a solar panel, Should be fun,

[SunEagle]

At a distance of 150 ft you will need to perform a voltage drop calculation to properly size the wires between the panels and charge controller. Unfortunately you will find that wire to be big & expensive. Good luck.

[TJay]

At a distance of 150 ft you will need to perform a voltage drop calculation to properly size the wires between the panels and charge controller. Unfortunately you will find that wire to be big & expensive. Good luck.

Hey that would bring up my first question, What are you guys running for underground cable, When I build a house hooked up to the grid for 100 amp service I will pull a 2/0 wire and for 200 amp will do a 4/0 Now this solar only figures to 30 amp which would only be a 10 wire But Im sure this system will tripple when we build a cabin on it so should I just pull a 4/0 right away or do you use something totally different for solar, when I asked the local solar guy he said he usually just does a 2 gauge wire which is good for 100 amp. Like I said this is all new to me as you can probably tell ha,

[SunEagle]

Hey that would bring up my first question, What are you guys running for underground cable, When I build a house hooked up to the grid for 100 amp service I will pull a 2/0 wire and for 200 amp will do a 4/0 Now this solar only figures to 30 amp which would only be a 10 wire But Im sure this system will tripple when we build a cabin on it so should I just pull a 4/0 right away or do you use something totally different for solar, when I asked the local solar guy he said he usually just does a 2 gauge wire which is good for 100 amp. Like I said this is all new to me as you can probably tell ha,

The voltage drop should be less than 2%. If you wire your panels in series you generate the highest voltage they can generate but without knowing your panel specs I can't tell you what your stating voltage will be or how much it needs to be at the charge controller. If you were only 25 feet I would say you need to just worry about the total amp requirements for those panels but at 150ft voltage drop is a bigger concern.

There are a number of VD calculators on the web. Just make sure you find one for DC solar panel 2 wire system.

[Sunking]

Hey that would bring up my first question, What are you guys running for underground cable, When I build a house hooked up to the grid for 100 amp service I will pull a 2/0 wire and for 200 amp will do a 4/0 Now this solar only figures to 30 amp which would only be a 10 wire But Im sure this system will tripple when we build a cabin on it so should I just pull a 4/0 right away or do you use something totally different for solar, when I asked the local solar guy he said he usually just does a 2 gauge wire which is good for 100 amp. Like I said this is all new to me as you can probably tell ha,

That is not going to work. 2 AWg is more than safe for 100 amps but you have over looked or unaware of LOW VOLTAGE. With a 300 foot Loop or 150 feet 1-way whichever way you want to look at it with 100 amps will loose 5 volts. Not much of a problem at 120 volts as that is roughly 5% of the power. Problem is your 325 watt panel is 37 volts and you will loose that same 5 volts or 12% of your power and voltage. Not enough voltage to charge a 24 volt battery. Surprise surprise.

You want to keep the voltage loss to 3% or less. That requires 250 MCM copper cable that cost roughly $6/ft and you need 300 feet. Lastly your panels and controller have no means to terminate a cable as large as your wrist, nor do you have the tools or skill to work with it.

Here is chart to show you what you are up against. Use the 3% column. Note 2 AWG is only good for 15 amps at 130 feet.

If you want a Calculator use this one. For the voltage use the panel Vmp voltage, and for the current use the panel Imp. Example for the 325 watt panel

Conductor = Copper
AWG = 4 AWG
Voltage = 37
Number of Conductor = Single Set
Distance = 150 Feet. 1-way
Load Current = 10 Amps

With 4 AWG you loose 2% voltage (.75 volts) and power.(6.5 watts)

[Sunking]

without knowing your panel specs I can't tell you what your stating voltage will be or how much it needs to be at the charge controller..

325 watt panel should be roughly 37 volts Vmp. Barely enough to charge a 24 volt battery. He says it will be lithium. Good luck with that.

[SunEagle]

325 watt panel should be roughly 37 volts Vmp. Barely enough to charge a 24 volt battery. He says it will be lithium. Good luck with that.

If the OP wires 2 of those 325w panels in series then the total voltage would be somewhere around 74volts and around 9 amps. With that information they should be able to calculate their wire size but as you pointed out if that wire is really big then being able to terminate it at the panels and CC becomes a problem.

[Sunking]

If the OP wires 2 of those 325w panels in series then the total voltage would be somewhere around 74 volts and around 9 amps. .

Correct and that is why MPPT controllers are used to get voltages up. But the length still poses challenges. If you uses a quality MPPT controller like Midnight Solar or Morning Star., he can use up to 3 panels in series, and a No. 2 AWG will be fine at 9 amps. But the minute he is forced to Parallel the panels because either his controller cannot handle 3 panels in series or he needs more than 1000 watts with an 80 Amp controller, the 2 AWG will not work out so well.

As I have said thousands of times, with low voltage and meeting 2 to 3% voltage loss, current capacity of conductors is not an issue. I mean by code you use 12 AWG with 2 parallel strings is plenty safe for for 18 to 20 amps, but completely useless if the distance is more than 15-feet one-way. At 150 feet you would loose 9.5 volts or roughly 25% of his power and voltage. Not a problem if the voltage is say 200 volts or higher. Huge problem at 37 volts.

Now everyone knows why utilities use high voltages up to 1,000,000 volts, and why low voltage suks.

[TJay]

Im sure we will get something figured out It looks like alot or solar system I see in wicsonsin are more than 100 feet from the house, I would perfer it that way anyway I like having the trees around us, And the comment by sunking (He says it will be lithium. Good luck with that.) I catch hell from the airplane guys everytime I install an Earth X in a plane as well, I like them you can keep your lead acid batteries, Thanks for now,

[SunEagle]

Im sure we will get something figured out It looks like alot or solar system I see in wicsonsin are more than 100 feet from the house, I would perfer it that way anyway I like having the trees around us, And the comment by sunking (He says it will be lithium. Good luck with that.) I catch hell from the airplane guys everytime I install an Earth X in a plane as well, I like them you can keep your lead acid batteries, Thanks for now,

I was just trying to point out that having your panels a long distance from your CC requires you to keep an eye on minimizing your voltage drop which usually requires bigger wire then anticipated.

I hope it all works out for you.

[TJay]

[QUOTE=SunEagle;n348850]

I was just trying to point out that having your panels a long distance from your CC requires you to keep an eye on minimizing your voltage drop which usually requires bigger wire then anticipated.

I hope it all works out for you.


Thanks, Sun Eagle I know im getting super excited here Hoping to start on it on Memorial weekend Ill post in after that,

[neweclipse]

What about another shed/cabinet at the sunny panel area?...Then you could send 120VAC to the first shed instead of the 37VDC.