Need to power 320 watts for about 10 minutes a day....

[motochris]

Just built a horse shelter and hay storage area and am tossing around the idea of running a small "off-grid" type solar system to power lights for feeding at night. I have a total of 320 watts of combined CFL and LED lighting thru the building. Currently running it off a small generator.
I figure daily usage...the lights will be on for an average of 10-15 minutes maximum (more like 5-10 minutes), with maybe once or twice a month being on for 30 minutes or so. I figure beyond that... I can always fire up the generator if needed, or to run higher draw items and such.
What can I get away with as far as panel voltage and battery size? My first guess was a single deep cycle battery and a 400-600 watt invertor would do it, with maybe a 35 watt panel to recharge in the day. I have considered the Harbor Freight setup... but thought maybe building a bit better quality setup from the start would make sure I was happy.
I'm in an excellent solar area now, high desert area in California... we are sunny 340+ days of the year. Easy 7 hours of good sun everyday. No shade anywhere near this structure.
Any help appreciated!! Chris

[Sunking]

Easy 7 hours of good sun everyday. No shade anywhere near this structure.
Any help appreciated!! Chris

That does not mean you get 7 Sun hours per day.

You will need:

100 watt solar panel
12 volt 100 AH battery
10 amp charge controller.

[motochris]

That does not mean you get 7 Sun hours per day.

You will need:

100 watt solar panel
12 volt 100 AH battery
10 amp charge controller.

Your numbers are right about where I was thinking other than the panel voltage.... why 100watt vs. say 50watt?
If I draw on average 60 watts per day, wouldn't even a 35 watt panel at say 5 hours of charge time (175watts- losses) suffice? Not arguing..just wondering if I'm missing something?
I figured the Morningstar SS-10L would work for my controller. Do you think I'de need a true sinewave invertor to keep my CFL ballasts in good shape?
We actually get about 10 hours of sun, 7 hours of good sun. I have a PV system on my home that was sized with having 5 hours of productive sun and it puts out more than we planned on due to our sun time. For sake of discussion we can plan on 5 hours if you prefer.

[Sunking]

Your numbers are right about where I was thinking other than the panel voltage.... why 100watt vs. say 50watt?
If I draw on average 60 watts per day

Never said a word about panel voltage. With 320 watts for 30 minutes per day is 160 watt hours. In addition if you are using an inverter you can bump that up to 200 watt hours per day.

Like I said just because you get 14 hours of sunshine per day does not mean you get 14 Sun Hours, more like 5 at best in summer.

For battery systems you cannot use summer sun hours. You have to use winter months of December and January which in your area is down around 3 Sun Hours per day.

Secondly using a PWM controller cuts your efficiency down to 50%. So 100 watts x 3 hours x .5 efficiency factor = 150 watt hours. In summer you will get twice that if you used it, but it is winter you have to design for.

Secondly 320 watts on a 100 AH 12 volt battery is one hell of a load. Be sure you use a AGM battery with such a large load on such a small battery. Battery systems typically run at the C/20 discharge rate where C = th ebattery amp hour capacity. So for a 100 AH battery 100 AH / 20 H = 5 amps. At a 320 watt load on a 12 volt battery you will be drawing 30 plus amps out of the battery. Mr Peukert will punish you severely for doing that and turn your 100 AH battery into a 60 AH battery.

[motochris]

With 320 watts for 30 minutes per day is 160 watt hours.

I said 30 minutes maybe once or twice a month at most(realistically...that hasn't happened yet at all). The lights are currently used 5-10 minutes a day. Enough time to throw hay to 3 horses. All other chores are done in the daylight. That would give me 53.33 watt hours correct?
Bump up the amount you said on the invertor and we are at 103.33 watt hours.

From the sounds of it, a 100 watt panel will be more than enough including the efficiency loss of the controller. I wasn't aware they were that bad off.
I'm guessing even 75 watts would suffice, but the price difference isn't enough to bother with.
I actually plan to use my 2 deep cycle batteries from my RV, as it doesn't get used enough now and the batteries tend to go bad with it sitting so much. I don't know the specs on them other than they are both 12v Walmart brand. They should be fine with the current draw.
Thanks for the edumacation!

[Sunking]

You can probable get away with 50 watts, but winter months maybe a problem.

[motochris]

You can probable get away with 50 watts, but winter months maybe a problem.

Yea and winter is when I need it. Summer time it's still light enough to feed without lights at 8pm.
I'm pricing around 75-100 watt panels right now. Looks like [...] had some great deals but are all sold out.-- here's 120watts for only $148.80 [...]
onsidering this one-- 80 watts- [...]

r as the charge controllers being so poor on efficiency....are there better ones that aren't alot of cash?

Worse part about this whole thing... I'm only doing it as it just sounds like a cool project. I could trench and run electricity out to the horse shelter for less than it would cost to do this. (Heck, I could just keep using the generator...it's only about $3-4 every 5-6 weeks in gas.)
It just sounds like a good project to get my feet wet, as I have an "off-grid" cabin that we have no power at, but I want to eventually have a small system up there.

[Sunking]

As far as the charge controllers being so poor on efficiency....are there better ones that aren't alot of cash?

Yes a lot better called MPPT, but for a small system it can be justified. It is less expensive to just add more panel wattage. You can buy a 10 amp PWM controller for less than $50, where as the smallest 15 amp MPPT controller for around $200.

Let's say you need to make 200 watt hours per day, and winter Insolation is 3 Sun Hours.

For a PWM controller you need a 135 watt panel and a 10 Amp PWM controller. Panel cost roughly $250, plus a $50 PWM 10 amp controller for a total of $300.

For a MPPT controller you need a 65 watt panel and a 15 amp MPPT charge controller. Panel cost around $117, and controller around $200 for a total of $317.

You just have to work the numbers to see what is the most economical route. Once you get up around 150 to 200 or more panel wattage is the cross over point where MPPT becomes economical. Once it gets up around 500 watt or more panel wattage MPPT controllers offer huge cost advantages.

[john p]

Why use an inverter ???. Just use 12v LED lamps . no inverter losses. and more than adequate light from say 10x 3w LEDs total draw 60w. (MR16 )replacements.. use std MR16 bases...that is a lot of light ,and will cover a large area.from very little battery draw. Mount them as high as possible or diagonally to get as long a throw as possible.
You most likely wont need 10 ,,,6 may be adequate.

[motochris]

Why use an inverter ???. Just use 12v LED lamps . no inverter losses. and more than adequate light from say 10x 3w LEDs total draw 60w. (MR16 )replacements.. use std MR16 bases...that is a lot of light ,and will cover a large area.from very little battery draw. Mount them as high as possible or diagonally to get as long a throw as possible.
You most likely wont need 10 ,,,6 may be adequate.

Main reason...too late. I've already done the lighting in there. 6) T8 8ft bulbs in the main area, 2) 20w CFL floods in the hay storage area and a 9 LED light on the outside for light to load/unload. It's got a couple outlets and switches..... basically FAR too late to change it now.
I originally didn't plan to do this, I planned to just run elec. from the house. I've been running off a generator for the last month while taking care of some other things and the idea of a small off-grid type system popped into my head about a week ago.

[motochris]

Yes a lot better called MPPT, but for a small system it can be justified. It is less expensive to just add more panel wattage. You can buy a 10 amp PWM controller for less than $50, where as the smallest 15 amp MPPT controller for around $200.

Let's say you need to make 200 watt hours per day, and winter Insolation is 3 Sun Hours.

For a PWM controller you need a 135 watt panel and a 10 Amp PWM controller. Panel cost roughly $250, plus a $50 PWM 10 amp controller for a total of $300.

For a MPPT controller you need a 65 watt panel and a 15 amp MPPT charge controller. Panel cost around $117, and controller around $200 for a total of $317.

You just have to work the numbers to see what is the most economical route. Once you get up around 150 to 200 or more panel wattage is the cross over point where MPPT becomes economical. Once it gets up around 500 watt or more panel wattage MPPT controllers offer huge cost advantages.

That's good to know. I'll definitely want the MPPT controller at the cabin.... I'll have to toss around the cost/benefit for this project.
Are the MPPT controllers better on the batteries than a PWM controller? Meaning the batteries stay in better overall condition? If so, that would probably sway me that direction for this project too. Not to mention not feeling the need to upgrade later if I wanted more panels/wattage.
Got a recommendation on one?

Also... got any leads on panel suppliers that I should look into?

[john p]

All the gains of MPPT chargers over PWM chargers for small under 500w panel systems are mostly theory .. you never get the claimed gains in most cases. You just pay a lot of extra cash for the charger.
You will always notice that you never see side by side working examples of MPPT gains over PWM chargers. You are always given the theory only..
Having tested at least 100 MPPT and PWM chargers (expensive and cheap ones)I have found the gains are about 5 to 15%. Many MPPT chargers produce no more power into your batteries than PWM ones do. This is especially true when the battery/ies are above 90% charged. Under thse conditions the MPPT part usually does nothing.
Here is one example . but it is only one very well tested example .. of a high priced MPPT charger compared to a Chinese copy of a old well known American PWM charger.. 3x 80 w 12v panels in parallel PWM charger days production 78ahr into the batteries
3x 80w 12v panels in series MPPT charger days production 81 ahr into the batteries

different types of battery/ies and depth of discharge would alter these figures. but it does give some idea of what you can possibly expect.

On systems of panels above 1000w the good MPPT controllers win by a big margin. But you need to use a top of the range controler to achieve that.

[Sunking]

Are the MPPT controllers better on the batteries than a PWM controller? Meaning the batteries stay in better overall condition?

No MPPT are just more efficient.

PWM is very easy to understand, and the acronym is a dead give away as to how they operate. PWM = Pulse Width Modulation. They are nothing more than an electronically controlled switch. They are either on (short circuit or closed), or off (open circuit). There efficiency is anywhere for 10 to as high as 90% completely depending on how well matched the source (panel) to the (load) is. If you use standard 12 volt battery panels the efficiency is 66%. PWM works by modulating the on/off pulse width from 0 to 100%. They are used to regulate battery chargers, and speed controllers for series wound DC motors like you see in golf carts and heavy drag line coal digging shovels.

The reason they are so very inefficient is because they are a SERIES regulator. Which simply means the input current roughly equals the output current minus what the device needs operate.

So lets assume you have a 12 volt battery which is 50% discharged and you have a standard 12 volt panel rated for 100 watts. A standard 12 volt panel has a Vmp of roughly 18 volts @ 5.5 amps. But here is the problem, a solar panel is a current source, not a voltage source. If you take that panel and directly connect it to the battery (as would be the same as the PWM CC charging @ 100%) the panel only supplies 5.5 amps at the battery voltage, not the panel voltage. So if that battery is say a 100 AH 12 volt battery at 50% DOD the battery voltage is roughly 12.2 volts. 12.4 volts x 5.5 amps = 67 watts. The controller is not burning off the missing 33 watts, in fact it is only consuming just a few watts. What has happend is the panel impedance is not matched to the battery impedance. The low batery impedance has pulled the voltage down below the maximum power point.

MPPT is a different animal. It is a true DC-to-DC voltage converter using a current buck/boost switching mode. It takes the 18 volts @ 5.5 amps, and converts it to 12.4 volts @ 7.6 amps. It up converted the current and down converted the voltage inversely proportional just like an AC transformer would do.

[john p]

The theory behind MPPT chargers is good.
In using real ones the results are not so good in most cases..
Cheap MPPT chargers are usually no better than PWM chargers and in some cases LESS effecient.
Good ones are far too expensive for the gains on under 1000 w systems Its cheaper to buy a higher output panel/s
The gains that are claimed are theory. much the same as the rating on panels.
You are living in a dream if you expect to get 225 w from a roof mounted 225 w rated panel..
In general even the manufacturers have doubts about the long term reliability of MPPT chargers and most give shorter warranties compared to PWM ones. So what is the consumer to think??
Its almost impossible to find proof of gains of MPPT chargers ,If you ask the people telling you how good the gains are by comparison tests they have done.the answer is nearly always the same, NO I have never done a comparison test ,and have no documented results to show you BUT I know they are better. hmmmm

[motochris]

OK, scored a good deal on Ebay for an SS-10L. It's on it's way now. Trying to decide between 3 different panels.... hoping you guys might have some input.
Looking at a Solar Cynergy 80watt (mono) , CNBM 90watt (mono) and a UL Solar 85watt (poly). All are roughly the same price shipped, the CNBM is the only one UL listed as far as I can see.
Just wondering if one brand seems to be more reliable than another. Can't find much info on the CNBM, the Solar Cynergy got some badmouthing a few years ago but not much recently. The UL Solar..again, not a ton of info but not alot bad that I saw.
Any input appreciated...