my solar plan

[cleb]

This is my first post... been lurking and reading for a little while. I am in the process of building a off-grid cabin. I have already purchased an inverter but everything else is still up in the air.

I am mostly looking for lights but other things like radio, maybe a small tv, fan for composting toilet(not on all the time) will be used

The cabin is on the edge of an old field. To get enough light I figure I need to go 50' or more mount the panels. because of this I was looking for a solution so as to not have to use large gauge expensive wire. This got me looking at mppt charge controllers to go from larger voltages down to 12v.

I have the plan as it sits now on a web page here : http://web.mac.com/chris_bordeleau/BethnChris/Solar_Power.html

I will be adding photos and such as things progress. Right now the cabin shell is complete (built by local Amish) I will be finishing it up this year.

also for batteries My initial plan is for two then to add two more next year.

any comments and suggestions would be helpful. I have been reading alot but I know I have holes in what I have read. Some things I am questioning are the fuse/breaker/wiring requirements at each stage (between PV Panels & controller, battery & controller, battery & inverter and inverter & panel)

Thanks in advance for any help

[12vman]

Hi cleb..
I was looking at your panel hook up.. I have questions..

Do you have a link to the exact panels that you plan to use?

Connecting panels in series does increase the voltage but the total current will be as one panel. I understand your point of saving money by using smaller wire but wire is cheaper than panels. You're losing 2/3 of your possible charge current connecting them this way with a 12 volt system..

"I am mostly looking for lights but other things like radio, maybe a small tv, fan for composting toilet(not on all the time) will be used"

You can do all of these things without an inverter and I would suggest doing so in a small system like you describe. It's a lot more efficient to operate items direct from the battery, if possible, than through an inverter..

I was looking at this (http://sunelco.com/documents/wireloss12volt.pdf) line loss chart and figured at 50' you would need 2/0 wire to stay below a 5.00% loss between the charge controller and the panels. This chart shows a one way loss so you must double your charge current to get the proper wire gauge..
~Don

[cleb]

thanks for your response.

I know I could have stayed DC only but for a couple of reasons I wanted to go right in a do AC... I found a decent inverter for a good price and figured having AC available would make my family more comfortable.

I am also thinking of leaving a DC circuit in the house but so far have found little information about wiring this up.

for the panels themselves I was looking at the ones here : http://sunelec.com/Distributors_/Solar_Panels/body_solar_panels.html

They have a couple at $4.00 per watt. they are the photowatt pw100 & pw110. I found the detail page here : http://www.photowatt.com/fileadmin/pdf/modules/pw6-110.pdf

now like I said my reason for running them in series was that if I ran the in a 36 volt setup I could use much cheaper #8 awg wiring.

It was my understanding that the MPPT charge controllers where then able to step the back down to 12 volts while creating the max charge possible. Another assumption of mine would be when you brought the 36 volts down to 12 volts you would be creating increasing amps. here is an example using best case no loss inefficiencies or lines losses taken into account.

so the panels in question are 16.7 volts @ 6 amps. in a series they would be 16.7*3 = 50.2 volts @ 6 ampts = 300 watts

now with the MPPT controller it should take it back down to 12.5 volts @ 24 amps

Now I know those numbers are best case and in real life would be much lower but I was just trying to get the idea down... please let me know if I am incorrect about how the MPPT controllers work.

thanks

[12vman]

For what I've read..

I don't see any advantage with going 3 times the charge voltage, IMO. If you were to add another panel and gauge your wiring towards a 24 volt basis between your panels and the controller, this might be a better approach. (2 in series and then parallel the 2 sets)

Personally, I'm not real convinced that this type of controller has all of the advantages as they state. Maybe it's because I'm from the old school.. ???

Ohm's Law has never let me down. Nor has line loss charts. I don't see this type of controller being magical in any way. I've never seen one up close. The only way that they could achieve what they say is by using some sort of transformer in circuit which would provide a small loss within itself. And the fact that there is no direct connection to the panel is another issue with me.. (As for the common)

I'm open for debate about this. Maybe I'll get enlightened.. ;)

It's a fact.. When 2 panels are connected in series, the voltage is doubled but the potential amperage is as 1. The same as batteries..

The current (amp) load is dependent on the capacity of the panel. Current is what adds amp hours to a battery, not voltage. Charging a battery with a higher than normal voltage at a lower current equals a trickle charge in my book. A good deep charge requires plenty of current when needed with the voltage tapered towards the end of the charge cycle so not to boil the batteries to death..

To me, the connection between the battery and the panel is very important. The wiring must be able to carry the current to the controller. If the battery is down, it needs all of the current it can get from the panel at the begining. As the battery charges, the internal resistance drops which allows the voltage to rise. This is where the controller comes into play. It controls the voltage to a set level so it doesn't boil the battery to death and diverts the unneeded current to some kind of load. (internal or external)

Your panels will produce plenty of voltage to fully charge a 12 volt battery without connecting them in series and provide real current but the wire issue comes into play... again.. :P

I still say wire is cheaper.. Even cheaper than one of those fancy controllers.. ;D

Here's (http://www.blueskyenergyinc.com/solarboostreview.htm) some stuff that I read about MPPT..
~Don

[cleb]

thanks for you opinion... I will really appreciate it... I will do more digging on these controllers and crunch numbers on the cost / benefit of each approach...

one clarification... using a MPPT charge controller does not charge the batteries at increated voltage... the way I understand it is that it modulates the voltage to what it thinks is the most charge it can produce. So if the batteries are 12 volt it will charge at a slightly larger voltage (say 14 volts) while increasing the amps... so ohms law is still in effect... From what I understand they are 90-95% efficient but make up for any losses by being able to use more of the available power.

thanks again

Cleb

[12vman]

I use the C-40 (http://store.altenergystore.com/Charge-Controllers/Solar-Charge-Controllers/Pwm-Type-Solar-Charge-Contollers/Xantrex-Solar-Charge-Controllers-Pwm/Xantrex-C40-40A12-48V-Charge-Controller/p2070/) on my set up. It uses PWM technology that has been proven to extend battery life and provide a deep charge..

I just don't understand how they give the battery more current when it isn't there to start with.. ???

I can understand a longer charge period because of the higher voltage potential but the current thing is another story.. ;) (Old Schoolitus?) ;D

Anyhow.. Good luck in your venture. Choose wisely and don't try to save too much money on short cuts. Do it right from the start. You won't be sorry 10 yrs. down the road..
~Don

[jott]

I read that link that 12v said he read, this is my thoughts on what they are saying, based on my knowledge of electronics and electrical engineering. I have limited experience with small solar power systems and know nothing of this company.

Basically it sounds like this box has a DC-DC converter in it to go from the high voltage to low. If you put in 24V at 15A (nominal) it will charge your battery at 12V 30A (nominal). They are saying that they can charge your batteries faster because when the panels are cool the output voltage is higher they convert that higher voltage power to a lower voltage but with more current.

So if an array can put out 10A at 17V (170W) then the charger puts out maybe 12A at charging voltage.

I would say that this is a better way to use the power from your array if this companies claims are true. But I see no reason they could not do what they say. So it comes down to will this cost less then going with bigger wire. And do you think this is a quality product form a quality company

Good luck let us know how it works out.

[12vman]

Thanks, Jott. That puts it into a better perspective. This reminds me of a switching power supply. (Transformerless)

I've dealt with switching power supplies many times in my career. I've see them fail many times too. I've replaced them with a good 'ol transformer/bridge rectifier type and the problems go away.. (Switching supplies create noise too..)

If this is the case, I don't think I'd trust them. The theroy is good but how long will they last? Lots of extra parts for a simple job, IMO..
~Don

[jott]

Yes that’s why I was saying you have to trust the company. They could make a box that is bullet proof and it could be the best thing ever. Or it could be a piece of junk that will die in a year or two. Inherently more parts means less reliability in a single path system.

[12vman]

Great discussion.. ;)

I believe that there's a bit of "Hype" in the advertising also. Fact is that the "Box" isn't going to produce any more current than what the panels can deliver. Possibly a little less with the additional losses of the complex circuitry it uses..
~Don

[cleb]

so Sam's clubs had a visitors day today and I picked up a couple of the everyready 220 ah 6v batteries...

for the dc connection between the batteries and the inverter I was figuring on putting a fuse and a breaker on the line but I am not sure what size.

and for the ac in from the generator what size fuse and breaker should I use?

thanks

[Anon001]

I have to add my two cents. I am certainly no electrician, but I am 100% off grid and have been for 10 years. I will make you one promise. With a system as small as yours, you will come to regret not having more DC loads and using the inverter less.

Another thing to consider.....what happens when the inverter goes out? It is electronic and can fail. If you use DC lighting with 12V compact flourescents you will always have lights in the event your inverter fails.

You batteries..... not just any 6v battery will work. They must be "deep cycle". However, if they are for marine or rv applications, they will be worthless in a solar application. The reason being is that they say "deep cycle" but are a hybrid and not a true deep cycle. The only true deep cycle 6V batteries on the market are golf cart batteries. (Other than high dollar solar or other specialized batteries.)

When I built my cabin, I ran two separate "electric systems". Everywhere I wanted an electrical outlet, I placed two boxes... one is DC and one is AC. They are all labeled. I knew to bite the bullet on cost because it would be easier than trying to add later. I have a DC fuse box and I have an AC breaker box. I can plug the breaker box into my inverter or into the generator. I used the electrical cord from an RV.

I get the impression you haven't studied nearly enough. If you are worried about making it easier on your family, you won't be happy with it and as small as you are making your system, you won't be able to provide enough power for a family.....maybe for one individual, but not a family.

Keep updating. I studied solar for many months before I ever began to look at any distributors or equipment. Like another reply on here, I too, use the C-40 with the digital readout. I wouldn't give it up for anything. LOL

The best advice I can give is to part with the money to buy the book "The Solar Electric Independent Home Book". I learned more from it than from anything else I read. It explains many of the issues you have asked about.

Good luck.
Paul

[cleb]

thanks for your response...

the batteries I picked up where everyready deep cycle golf cart batteries. I had read about them on a couple sites as being the best bang for your buck for small systems. total cost for both batteries was about $150...

I have been looking at this for a couple of years... but for the last six months I really got moving. I cleared the area I built in, I have built the cabin and am now ready to wire it up. I am hoping to have it mostly ready by this summer sometime.

I am planning on doing a DC run and outlets in each room. I will also have some DC backup lighting. The reason I was not going with DC CFL for the main light was that for the price of the DC CFL's I was able to buy my xantrex inverter.

I will be running an outlet(or inlet :)) from my generator to the AC in on the inverter which can charge the batteries and run the house AC. In the event that the inverter fails I could for a time re-run the generator in to the main AC panel to supply the house if needed or use a charger off the generator to charge the batteries (one other option I am looking at is building a DC generator from a car alternator and a lawn mower engine)

when i said make my family more comfortable I was hoping to allow for devices that I may not be able to get a DC equivalent. I also figured while I have the walls open it made sense to wire the place for AC (basically the same thing you were thinking).

I also have kerosene and white gas backup lighting... I would figure that use of these would be in the winter when I would be the only weekend occupant.

Winter use is mostly just to check on the property, remove excess snow from the roof ( we get about 200" a year ), clear any downed trees from the trail in and check that the well on the property (run on grid with another dwelling my father in-law uses) is not frozen up (uses 100 watt light in the well to keep it warm)

Thanks for the recommendation on the book... I just ordered a copy.

[Anon001]

Another thing that some of the solar or alternative energy distributors recommend is to not go with one central light fixture per room. They recommend using "task" lighting which is strategical placing smaller wattage lighting in specific areas...... For example: one over the kitchen sink or over the food prep.... a floor lamp with small wattage bulb next to your favorite chair where you read, etc. you will actually use less energy with your lighting. I use almost all DC compact flourescent bulbs with the exception of a desk lamp that I have an AC CFL bulb in....but all I do to change it is to swith the bulbs. LOL

Good luck.

[cleb]

thanks... I was planning on putting several working lights in each room, either using lamps or fixtures that use pull string. so if I put a switch in the room you could turn off individual lights. then also having a DC backup in the main rooms.

oh course the plan is very much a work in progress... I am going to be building a testing board at home in the next couple of weeks to try everything out (test components before going out to the cabin)

just need to figure out the fuse sizes... seeing as I ordered that book I am betting it has some details.

thanks again

[12vman]

Some ideas that I used concerning D.C. wiring..

When dealing with low voltage D.C., you must always keep the line loss factor in mind. Loss is caused by resistance and that equals wasted energy..

I have a "Buss", or a main power run along the ceiling the length of the house. (Rebuilt Mobile Home) The length is about 45' from end to end. I have my battery/controller at one end as close to the panels as possible. The buss is connected to the battery through a 30 amp fuse. (I'll never pull more than that through the buss at any one time) In case of any kind of short, that fuse will open and kill whatever I have connected to it without burning up any of the wiring anywhere. Any of the wiring that I use as drops to any point that I need power will handle at least 30 amps by gauge and length. Any higher current loads (central inverter, pumps, ect..) is connected as directly to the battery as possible with as short as runs as possible.. (Fused Accordingly)

To make my power drops, I use split bolts that will fit the 2 ga. wire. I skin the insulation off, put the bolt on and stick in the wire that I'm using for the drop and tighten it up, and wrap the connection with electrical tape. (No codes around here for low voltage.. ;) ) I've never had a connection fail..

The method to my madness is I could connect 20-30 amp load at th opposite end of the house without much line loss. I'm assured that any drop that I install will be provided with the maxium current it needs. (Which is usually under 5-6 amps.) The reason for gauging all drop wires to 30 amps is in the event of any shorts at any drop point will open the main fuse first before the wiring starts to smoke and burn..

With the power bus being located in the center of everything saves on wiring. The power drops can be made with smaller wire, (10-14 ga., Depending on the length) just so it will handle the current of the main fuse you decide to install..

Of course, All outlets are fused at the outlet itself and any item plugged into it, smaller than the main fuse. (My outlets are at 15 amps each) If I have an issue at an outlet, It'll open that fuse first or the fuse connected to the item and not kill the whole house. It also aids in finding the problem faster..

Another thought.. If you plan to install any permanent room lights in the ceiling, use this idea to save on wiring..

I run the power directly to the fixture to save length. I then install a relay at the fixture for the "Switch" circuit. I then use phone wire from the relay to the wall switch to operate the relay. The relay uses milliamps to operate so the phone wire will handle that circuit. Phone wire is much cheaper than the wiring necessary to connect the light up in the conventional way. (Power to the switch, up the wall, to the fixture) 8)

And to be more frugal, I will end up doing this when I finally get to the point of finishing this place up.. LOL.. A bit outdated but the theroy is there. I used this before I rebuilt the roof.. It does work.. ;D

http://minifarmhome.proboards25.com/index.cgi?board=building&action=display&thread=153 &page=1

[jott]

To find your fuse size use ohms law. I=P/V where I is current(amps), P is power(watts), and V is volts.

If you have something that uses 100watts that is its power usage, if it works on 12Volts you have everything you need to know. 100W/12V=8.33Amps once you have the current needed to power the device size the fuse or breaker to the next size bigger maybe 10 or 15A. Then size your wire for the current that the fuse or breaker is rated for. Make sure that all the fuses and breakers you use are rated for DC current an AC breaker may not open with DC and can lead to a fire.

[cleb]

so I am now looking for info on wiring the dc outlets (my book I ordered is still not in). I was planning on using 240 volt heavy duty outlets for the dc outlets. for wiring these outlets do I need to run a ground? There is a pretty big difference between 10/3 wire and 10/2 wire so if I can save some money here I will... if not I won't....

also do I really need to use 10 gauge here... the longest run will be under 50 feet from the breaker box. I am planning on using no more then a fan, radio or maybe a ham radio in the future on the DC circuits. I am planning on running one run to were I am going to put the refrigerator incase I go with a dc model instead of a propane one.

thanks

[12vman]

Cleb..
It's important that you design your wiring to the job that you want to do. It's not a guessing game by no means. You need to know how much current that you're going to use at any point that you want an outlet and gauge your wire to carry that amount of current..

This (http://sunelco.com/documents/wireloss12volt.pdf) wire loss chart will help a lot.. (Read the fine print at the top.. One way run..) Think of a car stereo hook up where the ground is the body/frame and you are only concerned with getting the positive connection to where you need it. You must double your current amount to get the proper wire gauge..

By looking at the chart, your 10 gauge wire at 50' will only carry around 2/2.5 amps and stay below the 5% loss level. That isn't going to operate much..

IMO, the best way to overcome this is to plan for a large sized (gauge) buss somewhere centrally located of everything that can handle large current loads and make drops or connections from it to keep the wire runs to your outlets as short as possible..

Another option is to place your battery in a centrally located area of your house. This would keep the runs shorter than trying to make runs from one end of the house to the other..
~Don

[12vman]

To add..
You don't need to have a ground wire for the 12 volt stuff.

And I would highly suggest using stranded copper wire.. Not aluminum..
~Don