newbie, example first system review

11 Posts
Dec 27, 2008 10:33 pm
newbie, example first system review

I'm looking at the cost of creating a solar system to providing light for a small barn.  I've done the calculations generally following the book "Photovoltaics--Design and Installation Manual".  And I have estimated some very general costs from the alt-E store.  I want to make sure my calculations are correct, and that the costs seem to make sense.  It seems that it is very expensive to create a system for even a relatively small system. I would appreciate any feedback along with any suggestions to simplify the system.  One I'm aware of is to just run everything off the 12 V battery and skip the inverter, but I have included it for now.

Example to provide lighting for a barn: a total of 100 W (multiple CFL bulbs) for 2 hours a day (200 W hrs) in central Massachusetts (December Peak Sun Hrs/Day = 2.8 ).

For a 12 V battery:
(200 W hrs/0.9 inverter efficiency)/12 V = 18.5 Amp hrs
Battery Amp hrs capacity = 18.5 * (2 days automonony)/0.5 discharge limit = 74 Amp hrs

Array size:
(18.5 Amp hrs/0.8 battery efficency)/(2.8 sun hrs/day) = 8.25 Array peak Amps
2 modules of 4.5 peak amps each could be used

Controller size:
4.83 short circuit current * 2 modules * 1.25 = 12 short circuit amps
Controller array amps = 15 Amps

Inverter size:
100 Total AC watts for 12 V DC system

In this example:
TOTAL COST = \$1350

220 Posts
Dec 28, 2008 12:34 am
Re: newbie, example first system review

hi brian,

looks like you nailed those calculations. right by the book (page 117-118) of the manual. i would recommend this manual to everyone. i think they are a bit over optimistic with the battery efficiency of %80 though, i find it closer to the %60 mark. we may want to go a little bigger with the bank and round up from that 74ah to a standard 100ah battery.

you may be a bit high with that \$900 for pv, altE has 100-120watt modules for around \$600 but we can go through that "extra" \$300 with mounting/wiring etc.

and i agree "It seems that it is very expensive to create a system for even a relatively small system." the plus is the satisfaction of seeing the system up and running. i predict you will be adding on in no time!

best regards,

11 Posts
Dec 28, 2008 10:31 am
Re: newbie, example first system review

Thanks for the feedback.  I think you are right, I do plan to add a basic system soon.  I just wanted to have my calculations double checked.  I might scale it back a bit to start.  I agree, it will be nice to have it all set up, and to be learning all about these systems in the process.

11 Posts
Dec 29, 2008 10:04 pm
Re: newbie, example first system review

For the system described above I'm looking at the following parts. I've tried to oversize most of the parts so that I might add to it at a later point without replacing everything.  I put a couple options for the battery and inverter.  The main price difference is in the two inverters, I'm not sure why they are so different. Any feedback would be appreciated.

Battery:
http://store.altenergystore.com/Batteries/Batteries-Sealed-Agm/MK-8A27-AGM-92-Ah-20-Hr-AGM-Battery/p3832/

-or-

http://store.altenergystore.com/Batteries/Batteries-Sealed-Agm/Universal-Ub121000-12V-100Ah-20Hr-Sealed-Agm/p4163/

Solar Panel:
http://store.altenergystore.com/Solar-Panels/100-to-149-Watts-Solar-Panels/Kyocera-KC130TM-130W-12V-Solar-Panel-w-J-Box/p2403/

Inverter:
I'm not sure why, but the Samlex is half the price and more Watts than the Exeltech.

http://store.altenergystore.com/Inverters/Off-Grid-No-Utility-Needs-Batteries/10-to-299-Watts/Samlex-150W-12V-Pure-Sine-Wave-Inverter/p1043/

-or-

http://store.altenergystore.com/Inverters/Off-Grid-No-Utility-Needs-Batteries/10-to-299-Watts/Exeltech-125W-XP-125-12-12V-Inverter/p528/

Charge controller:
http://store.altenergystore.com/Charge-Controllers/Solar-Charge-Controllers/Pwm-Type-Solar-Charge-Contollers/Go-Power-Solar-Charge-Controllers-Pwm/Go-Power-Solar-Charger-with-Digital-Amp-Meter/p4477/

220 Posts
Dec 30, 2008 05:40 pm
Re: newbie, example first system review

hi brian,

it looks like you are serious about going ahead with the system plans. much of your design is going to depend on the pv module location. that is.. the wire distance from the array to the controller. lets say for example your barn is orientated with its four corners north, south, east and west
and we can mount that module on the south corner at the proper angle and obtain a full solar window all year long there (see fig.3-5 and 3-7 pages 33 thru 36 of pdim) high enough so that we avoid head damage. and have our charge control setup inside that corner of the building only ten feet away. or a more conventional roof top mounting with the controller 50 feet away. lets look at those wire run examples for 10 feet vs 50 feet in this example. (see table 9-5 pg 97)when we look at the voltage (%2) drop tables for 8amps at 12vdc we see we are good for 12 feet with #10awg and need #4awg for 49 feet. thats not too bad, but lets say next year we would like to add on and max out that 25amp controller. we can do that no problem with #6awg at ten feet but would need no less than #2/0 awg cable for that 50 foot run! so brian, i ask.. how does your site survey look?

depending on the above lets look at some of the components to build this system. first off that kyocera module. i love the new look of that d.blue line and i'm getting so i can spot them at 100 yards. never had my hands on one yet, but looks good and is a proven cell poly/multi. vs thin film. looks like this line should be around for a while. (i would double check when ordering) also has a friendly j box vs sometimes difficult techno wacko connectors. nice aluminum frame..not much to not like.

gotta go for now.. check out chapter 7 pages 73-82 and check out this link.
http://store.altenergystore.com/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Blue-Sky-Solar-Charge-Controllers-MPPT/Blue-Sky-Solar-Boost-2512i-25A12V-3-Stage-Charg/p4618/

also consider,

http://store.altenergystore.com/Meters-Communications-Site-Analysis/Meters-Battery-Monitors/Ammeters-Voltmeters-Battery-Monitors/Bogart-Engineering-Tm-2020-Trimetric-Meter-Battery-Monitor/p254/

there may be some real big advantages to going with mppt with this setup.

more latter, dave

4 Posts
Dec 30, 2008 09:18 pm
Re: newbie, example first system review

Hi Brian,

It's great to hear that you are doing this.  I am working on an identical project for a small chicken coop.  I only need a few hours of artificial light a day for half the year.  My budget is a lot smaller than yours--if I pay too much my chicks will be laying golden eggs, so to speak.  Two suggestions that I have: first is to use LED lighting.  It is far more energy efficient than CFL's even, and they come in DC models as well as AC, so you can eliminate the inverter.  I found one at a local camping store with fairly good light output at 12V 250 mAmp, and it came with a DC adapter.  Second is to check out RV lighting systems.  They can still be fairly pricey, but cheeper than your plan. I'm ready to buy my hardware, but am hung up on how to wire it altogether.  Good luck with your project!

Becky

11 Posts
Dec 30, 2008 10:18 pm
Re: newbie, example first system review

Thanks for the suggestion on the MPPT controller.  It sounds like it might be a better option in terms of efficiency. I originally selected the PVM controller because I had read it was the standard type of controller and less expensive.

I had also considered a battery monitor, but wasn't sure how necessary it was.

As far as my site.  One side of the barn faces directly south.  The roof on this side of the barn is sloped at approximately 45 degrees.  My latitude is 42.5 degrees, so this is close to optimal.  I'm thinking the roof would be the best option because of the potential of shade at the ground level from some trees.  However, putting it on the ground might make the installation much easier. I also don't like the idea of having to make holes in the roofing material.
Either way, the length of wire should be relatively short.  The barn has a second story loft, so the cable from the panel on the roof to the controller could be kept close to 10 feet.  Or if there is spot at the ground level without shade I could also run the wire into the barn at less than 10 feet.  So, I think the wire runs can be kept short.  I didn't mention the wiring in my earlier post, because I still need to do some more exact measurements once I decide exactly where to place everything and then determine the wire gauge.

Thanks for the help.
« Last Edit: Dec 30, 2008 10:32 pm by Brian Papa »

11 Posts
Dec 30, 2008 10:31 pm
Re: newbie, example first system review

Hi Brian,

It's great to hear that you are doing this.  I am working on an identical project for a small chicken coop.  I only need a few hours of artificial light a day for half the year.  My budget is a lot smaller than yours--if I pay too much my chicks will be laying golden eggs, so to speak.  Two suggestions that I have: first is to use LED lighting.  It is far more energy efficient than CFL's even, and they come in DC models as well as AC, so you can eliminate the inverter.  I found one at a local camping store with fairly good light output at 12V 250 mAmp, and it came with a DC adapter.  Second is to check out RV lighting systems.  They can still be fairly pricey, but cheaper than your plan. I'm ready to buy my hardware, but am hung up on how to wire it altogether.  Good luck with your project!

Becky

Thanks Becky.  I had originally considered running everything as 12V DC, but finding 12 V DC lighting, switches/outlets, etc. and the cost didn't appeal to me. I thought it would be easier to just use the regular 120 V AC powered stuff I already have along with an inverter. In the end, I'm not sure which is more cost efficient or the better way to go.  I suppose its a case by case decision.

I'm actually building a small chicken coop myself.  I had originally started reading about solar power thinking I would just use it in the coop as you describe.  For now, I've decided to look into the larger system I have described.  Good luck on your system too.

220 Posts
Dec 30, 2008 11:38 pm
Re: newbie, example first system review

looks like you lucked out big time with the roof slope and orientation. nice when things work that way..

"I had also considered a battery monitor, but wasn't sure how necessary it was."

brian, i suggested the monitor because i am sold on the idea of seeing exactly whats happening to every piece of equipment and every variable in the changes that occur throughout the charge and discharge cycles, as the clouds roll by and the temperature changes, as the loads are switched on and off. you can get a real feel for whats occurring and why. this is in itself the most excellent tutor i have encountered while playing with all this renewable equipment. chances are that you will never outgrow this monitor and my hat goes off to anyone who can. also if you trade that \$112 controller for the \$165 mppt version you are giving up that limited display info from the go power pwm unit..and we all like to look at some pretty display.

some thoughts on a battery choice..now this is my opinion only so take it as such. those expensive agms are super choices..but, may i suggest that you start out with an el cheapo marine deep cycle "hybrid" battery as a disposable learning tool? at fifty bucks for a group 27 battery you can't go wrong. and if we kill it within six months i bet we get more than a fifty dollar education from the experience. i know of people that can kill a battery in six weeks! i also know of folks that can make them last for ten years! experience and knowledge will make you one of the folks in the latter group.

also with an inverter choice..thats alotta clams for a dinky little micro inverter. i would be tempted to go the el cheapo route there as well. something like a \$40 throwaway 400watt modified sine wave unit. the thinking here is you will most likely grow out of that 200ish watt pure sine wave inverter and 100ah battery bank very quickly when you see what you have done and what you are capable of.

on that note- i would strongly reccommend one of the classes there in hudson ma. you are a candidate for that pv 302 class imho. (jumping ahead of those first two courses)

http://workshops.altenergystore.com/PV-302-Intermediate-Photovoltaic-Design-and-Installation-Sat-Feb-28-Mon-Mar-2/e57/

if you look into this class, double check with the instructor for a waiver to take the advanced class without the basics classes. (looks like you have all that covered)

cheers, 73 dave

11 Posts
Dec 31, 2008 12:18 pm
Re: newbie, example first system review

Thanks once again Dave.  I've been thinking about taking the class for a while.  I definitely wouldn't want to spend a bunch of money only to realize I made some mistake or didn't know how to set everything up.
Of course, its another expense. I suppose I could start with a smaller panel and battery and then add a second battery/panel later on to offset the cost.
I'll look into it further and give some more thought to the system.  Again, thanks for all your suggestions and help.

-brian

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