Shed project

mlail · February 2010

Hi all,

I have started a project where I will end up with a PV powered shed. This is informal and I have gathers some numbers. So what I am going to suggest is that I provide a list of components that I have and I am asking the readers to suggest configuration and layout of the units. Keeping in mind this is a small shed that I use as a small (very small) shop.

My electrical use:
1 - dual 40Watt shop light
1 - dual 75W spot lights (150 W total, only runs based on motion and for 1 minute).
A skill saw based on repairs. Low usage.
Various battery wall warts for charging, lights, drills,... (each)
15W soldering pencil ...

Optional usage:
1 PC (turned on once per week for 3-4 hours). I'll have to lookup the specs at home.
2-3 fans - I'll have to lookup the specs at home.

Equipment that I have today:
2 Sharp 80W 12V solar panels
1 - 15W solar panel (I think this needs to be sold)
2 Xantrex micro-Inverters 800W 12Vdc in
1 Duracell 400 W inverter
1 Xantrex C35 Charge Controller 12 or 24Vdc capability.
4 - 15Amp breakers (salvaged from UPS)
Various switches used to disable power to devices
1 - 4 breaker Square D box
2- Concord 104 Ah AGM batteries
3- panel meters
1 - panel amp meter
2 junction boxes (home made) used to combine UPS batteries that are not listed for use here.

OK, I hope to cut the shed off the grid and the batteries will be dual propose. If we loose power during snow storms that rarely happens, I can use the and an inverter to keep the frig running. Maybe so lights if needed. For those who are thinking that this is a hodge-podge of stuff; yes it is and its purpose was to tinker with, learn, and see if I am really interest in expanding to a real system.

I use the shed and tool 2-3 times per week. The solar panels are mounted on the shed roof but if time allows I was thinking about using a pole mount to attach the panels with a tracker from Redrok.com (because they are cheap). However, that might be in the summer before I have time to build a pole mounting contraption.

What do you think, series, parallel...?

I've really enjoyed reading everyones posts!

thanks
mlail

niel · February 2010

Re: Shed project

you'd have no choice but to parallel those pvs as the controller is not an mppt downconverting type. i doubt that what you have listed here will totally answer the question on whether it will run what you need unless you know the usage in terms of watt hours. a killawatt meter can get you a running tally of your usage and then a better idea of what is needed to power it can be addressed. in any case i do think you will need more, but i can't say exactly without more to go on.

mike95490 · February 2010

Re: Shed project

If the batteries are 12V, I would consider building up a 24V system. To spin up that saw, you will need a larger inverter. What's the power label on the saw say? It's likely a universal motor, and won't care about mod sine vs. pure sine, but as you step into the 24V world, may as well go for pure sine, in the 2,000W catagory. (I guess that would start the saw).
Saw's have huge startup surges, and a 24V system would deal better with the amps involved, with less loss.

dwaller · February 2010

Re: Shed project

I have a black and decker circular saw that is rated 10A@120V (1200W?)

That's a pretty big draw you are using 4% of your battery reserve (assuming a 24v system) running the saw for 5 minutes. Ideally you want to keep your batteries at 75% or above, so that would actually cut into 16% of your usable reserve, not including the losses that you incur from the inverter.

Disclaimer: My math may be wrong here, I would appreciate if someone with more knowledge would step up and correct me if necessary.

niel · February 2010

Re: Shed project

dwaller,
i'll put what you said into another perspective. when you draw 10a from 120vac the power from 12v dc minimally needed to provide that would be 100a. add to that losses incurred in conversion and and your draw rate exceeds the full capacity rating of the battery which is 104ah in this case. ideally, the draw should be no more than what the charge rate would be for most batteries or 13%. the battery capacity will drop when drawing at higher rates making the whole scenario worse. if it goes higher it should be only for very short time periods. that battery is an excellent battery, but it will not cover those loads even on a short time duration.

i wanted the op to know his loads first and then we can discuss the rest. i did indicate that what he proposed would not be enough for his loads adding further that he already purchased this meaning it is a ready, fire, aim scenario again. fear not as he can buy more, but it is an economics question if he will afford what is really needed when we help determine what he needs.

mike95490 · February 2010

Re: Shed project

That's why a fresh 24V system might work. That 10A AC is now only 50A @ 24V.

niel · February 2010

Re: Shed project

mike,
you are right as that makes it draw about half of the battery capacity being there's 2 batteries, but still no good. that isn't his only load either and what his watt hours will be is still all yet to be determined. if he goes with a better saw it could be a 13a draw and the start surge is murder in any case. we know he needs more, but what isn't known exactly yet.

mlail · February 2010

Re: Shed project

The saw pules 15 Amps at surge with 8 Amps no load, or 1418 Watts surge and 900 Watts no load.

The saw stays on the grid and I reevaluate the plan. I need to work out the PC's use next.
K-O-W Amps K-O-W Watts
1.45 running 2.49 surge 165 running 207 surge

I was going to attach my usage spreadsheet and Visio diagram but neither Visio or Power Point files are recognized by the upload utility.

My thoughts on setup is to run both panels in Parallel, same with the batteries because this will increase my run time on everything else.

So here are my other thoughts, PV to junction box, to charge controller. Place a switch and breaker between the panels and the charge controller. After the charge controller place another switch and breaker with a connector to allow me to disconnect the batteries from the system. Tie in the batteries again in parallel.

One more try with a jpg file

mlail · February 2010

Re: Shed project

mike90045 wrote: »

That's why a fresh 24V system might work. That 10A AC is now only 50A @ 24V.

But what are the 15 Amps @ 110v AC if I use 24Vdc? That would also mean a new inverter because my inverters are all 12vdc

niel · February 2010

Re: Shed project

you can still go with 12v, but the wires will need to be larger to handle the high currents that will flow.

your diagram looks nice, but it won't power all that you need.

BB. · February 2010

Re: Shed project

mlail wrote: »

But what are the 15 Amps @ 110v AC if I use 24Vdc? That would also mean a new inverter because my inverters are all 12vdc

Assuming the worst case battery voltages/wire drop and average inverter efficiency, the maximum current for various battery banks would be:

15a * 110 vac = 1,650 watts
1,650 watts * 1/10.5 volt dead battery * 1/0.85 = 185 amps on 12 volt bank
1,650 watts * 1/21 volt dead battery * 1/0.85 = 92 amps on 24 volt bank
1,650 watts * 1/42 volt dead battery * 1/0.85 = 46 amps on 48 volt bank

-Bill

mlail · February 2010

Re: Shed project

Well I've got to stay positive about these things so it appears for now that the computers are out too. Becke t o the lights and some small battery chargers. Maybe even some occasional low end things. Also it sounds like I need more batteries another inverter.

Suggestions that I have read would be to increase my battery bank voltages. Other than charge times, is it helpful to have a higher voltage inverter? Remembering it is a shed.

Also my battery cables and inverter cable are 0/2. I originally didn't think that I needed 0/4 for lower demands. Now I see that my demands are not necessarily low demand.

As I can see the math is what drives all of this. That is why you are always referring to it.

Any other things that I should consider? Thanks

niel wrote: »

you can still go with 12v, but the wires will need to be larger to handle the high currents that will flow.

your diagram looks nice, but it won't power all that you need.

BB. · February 2010

Re: Shed project

Unfortinatully--a higher voltage battery bank only makes the DC wiring easier and a little bit cheaper. It does nothing to reduce the size/cost of the solar array and battery bank (for same useful loads):

Your options as I see them:

Bury a 120/240 VAC 15-30 amp direct burial cable at least 18" deep from the house to the shed and install a small sub-panel for power. If the house is off-grid too--add the panels and, eventually, extra battery bank/inverters to the home power to support shed power.
Build a small solar + battery shed system for lights and radio (small loads). Use an extension cord or genset for larger loads.
Build the large solar PV off grid system and add a bath, kitchen, and living area--because your spouse will have you living out there for spending all o that money.

-Bill

mlail · February 2010

Re: Shed project

BB

LOL, that was good. The wife already complains that I spend too much time in the shed. I tell her that if I had a bigger garage or basement, I wouldn't be in the shed so much!

Since I already have buried cable to the shed, and a sink I will utilize both systems!

In the next house (if the market ever pick back up) or by 2016 I will add PV and Solar hot water panels to the house. Until then I am doing a little here and there to lean and improve on the shed further. I only wish I had a place for all of the stored crap (stuff) that takes up most of the shed.

Now I have to asked a real ignorant questions, don't laugh too much! Is it safe or possible to connect two inverters to one battery bank? I have two of the 800 W micro inverters. I bought one and it was busted so the company sent me a replacement. They never asked for the bad one back so after a few months I fixed it... Now I have two.

Also, is there a place that people use to sell just solar stuff? I know that I could use Craig's list or ebay but I was just wondering if there is such a place as I described?

Thanks again for helping!

BB. · February 2010

Re: Shed project

Yes, you can connect multiple inverters and charge controllers to a single battery bank. The limits of how much current you can dump in or take out of the bank still apply and "power is power" (2x800 inverters running same loads as 1x1,600 inverter etc.).

For selling--you are welcome to post a "For Sale" posting the general topics area. Must be non-commercial/personal solar equipment/one time sale and only regular posters may make a for sale thread (I sort of let that Telco AGM battery thing slide--sounds like it may be a nice deal and recycling batteries has a place in everyone's heart here). Recommend that you "negotiate by PM or emails" and post when the item is no longer available for sale.

Price wise--EBay type sites do seem to draw out the bidders. Otherwise--I cannot offer anything else.

-Bill

Shed project

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