Small solar shed installation

System · November 2007

So I have a few questions and I was hoping someone could help me out (real questions are in the last 2 paragraphs).

I am planning on building a shed under my deck next summer or the following to replace a corragated metal shed under there that I hate. The construction won't be a problem, I have done framing and lots of construction either on my own house or on friend/family members houses. I've also done a fair bit of electrical work.

Now what is stumping me is choices.

My plans are to do a very small capacity system to handle powering a couple of CFLs, either 7 or 11w in the shed for light and I may also decide to do a 30w CFL flood light to give light under my deck (walk out basement) for working as doing 'dirty' work like using my table or circular saw in my work shop in the house is verboten (to hard to clean up).

The shed roof would have a north west exposure giving me direct sunlight from mid april till mid october, primarily when I would need light in the shed or under the deck (not often I would need to get into the shed during the winter time). The deck itself is only partially shaded by the house and even on Dec 21st it still gets at least 30 minutes of direct sunlight along the stop of the steeps heading to the ground.

My thoughts were to mount a small solar panel on the railing for the steps as it receives direct sunlight for part of the day no matter what time of year and mounting a small solar panel on the roof of the shed as it receives at least 2-3hrs of direct sun in the summer time (and the steps would receive about 4-6hrs of direct sun in the summer time).

Now here is where I am having problems. I would prefer the setup to be inexpensive and I don't need a lot of power.

My original thought was (2) 5w panels, a charge controller and a 12v lead acid battery of about 22ah capacity. I figured that would give me about 8hrs of power for 22w draw and 75% discharge on the battery. I am having a hard time finding 12v+ panels near 5w of a resonable (well, to me) price. I did find some 3.2w 8-10v panels that would be fine for a 6v system and I have been thinking of going that way.

Now my thoughts are this. The two panels connected in parallel to the 6v charge controller and the charger controller connected in parallel to (2) 6v batteries. What is stopping me, I guess because I can't wrap my head around it is...if I connect the batteries in parallel to the charge controller, can I then connect the batteries together in series to get the 12v I would need for a 12v electrical system?

My guess is yes, but I am having a hard time thinking about it at the moment (I guess I could have made this a very short post, but I felt like sharing my plans as well).

Thanks!
-Matt

mike95490 · November 2007

Re: Small solar shed installation

Wire the panels in series to get 12V and use 12V controller/batteries. Going the 6V route is just wrong in my opinion. 12V you can use automotive adapters and you can find lots of 12V yard lights, but not many 6V ones.

Mount the panels where they will get sun year round, as a poorly charged battery is prone to freezing and rupture. You are more likely to use light on shorter days too. (maybe)

Make sure your charge controller is adjustable for the type of battery you get (gel cell/AGM) and 50% discharge is all you want to pull out of the battery, not 75%.

System2 · November 2007

Re: Small solar shed installation

Thanks for the info. The biggest reason I wanted to go 6v with the two panels in parallel is that the one on the shed will see sunlight for a much smaller period of the day/year then the one that is deck mounted, so if one of the panels is in shade the system would still be getting current.

I would just go in series with the panels and use 12v charger and battery, but my wife is a limiting factor on where I can mount the panels. I have a location scouted out that will fit a single panel up to about 24"x10" on the railing that is semi-out of sight, but still receives direct sunlight and I can mount just about whatever I want on the shed, but the shed is shaded 24hrs a day for part of the year and I am having a hard time finding 12v+ PV cells in the low wattage range for a resonable price in weather proof housings.

icarus · November 2007

Re: Small solar shed installation

A quick thought.

Try not to build a system that routinely draws your batteries down 75% The life cycle will be severly shortened. I suggest that you read the following, http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

It is very educational.

Icarus

System2 · November 2007

Re: Small solar shed installation

Great info on the link, thanks.

I had figured a 75% discharge maximum as that would start dropping the battery voltage low enough to make a noticable impact on voltage. Hopefully I will never discharge it that low.

With a little poking around I am thinking a pair of 6v 12ah batteries, but I may go a little larger. That gets me 144w/hr of capacity and I had been figuring a maximum of 75% discharge, so 108w/hr...and a 22w drain gets me close to 5 hours of maximum life before I hit 75% discharge. Since I won't be using the shed as a workshop, and simply for storage I am hoping I won't ever be using the lighting in the shed for more then 15-30 minutes on the high side, which gets me a minimal of discharge.

If I do decide to setup a CFL flood I might be looking at as high as a 30w drain (I am assuming I would only be using the exterior flood, and not the interior lights at the same time) so that would be maybe 3 1/2hrs to hit the 75% discharge mark. Again I can't see many cases where I would ever use the lighting for that long. If it is full dark at 8-9pm I might be working outside for an additional 1 to 2 hrs. A more likely flood light would be around a 23w CFL which gets me back up near 5hrs of maximum life.

I would rarely be using the system in the winter time, certainly not to power a flood light. Even if I am only assuming 4hrs of direct sunlight on one panel and 2hrs on the other panel that should be around 18w/hr minimum charging per day on sunny days in the summer, and I am expecting more like 25 to as much as maybe 30w/hr of charging per day.

So can anyone help on the battery setup? Charge controller connected to each battery (positive and negative terminals) and then the batteries connected in series. Should it work? I am thinking yes, but I want to make sure I am not missing anything.

Thanks.

quid_non · November 2007

Re: Small solar shed installation

Hi Matt!
I've had good luck with these relatively inexpensive amorphorous 15W panels and controller:

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200263174_200263174

They likely won't last as long as the "big guys" for for getting started and keeping to a budget they are quite good. If you go to e-bay, you will wil find some decent deals on up 45W systems, very similiar to the ones in the link.

Also - using conventional fluorescent tubes and hardware from Home Depot, I built a great 40W system using this electronic balast:

http://powerstream.com/

Total system cost less than $35, is sufficiently bright, works GREAT and consumes about 1.7Ah!

Here's to the sun!
Best
Wayne

n3qik · November 2007

Re: Small solar shed installation

I have 2 sets of these:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90599

They are a little bigger that you stated, but may work. Plus you get two 5W CFL bulbs. The down side is if the kit has that tan controller, it's junk.

System2 · November 2007

Re: Small solar shed installation

Thanks for all of the information everyone!

I spent a good part of yesterday mulling it, doing research (including reading everyone's posts) and talking to my wife. I think what I am going to do is pole mount (close to the ground) a single 5w solar cell at the base of the steps down from the deck. This will make it mildly inconspicuous as it is right by a bush so it doesn't just stand out. I'll hook it to a 12v regulator and a 22ah lead acid battery. I am then thinking I will go with a pair of 7w flourescent bulbs in the shed and a 23w flood light outside of the shed (haven't decided if I want to make it motion sensing or not). I have managed to find a 5w panel for a resonable enough price (actually through this site's store front) for about $62 and is a fairly small size (the unisolar 5w).

I'd love to go larger on the solar cell, but I want to make it as inconspicuous as possible.

The downside and things I will need to look for is, due to its exposure it won't receive direct sunlight all day long (or most of the day). The best exposure is probably pointing it west with about a 70 degree inclination on it so that it starts getting sun at around 10am or so (even if it is very little due to the high incidence angle of the light) and will receive steadily more light until around 2pm or so and then reducing light until the sun is shaded by the row of townhouses to the west of mine at around 8pm (on the longest day of the year). I think that will maximize the light gathering and should get me around 10hrs of sunlight on the longest day of the year, probably averaging to about 6hrs of really good direct sunlight.

On the shortest day of the year the solar panel should still get some sun exposure, but it will be short since my house shades it a lot of the day, maybe 30-60 minutes of total sun exposure.

I am planning on checking on Dec 21 or around it when the weather is good and see what kind of sun exposure I get on a few spots around there, if the exposure turns out to be worse then I think I may lobby my wife to let me set the panel on the corner railing of the deck where I know it will receive a bit more light, especially in the winter.

Small solar shed installation

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