Do I need a battery to run a simple fan from a 25w solar pane during the day?

[mattr33]

I'm completely new to Solar and I just want to set up a small solar system to use during the day while camping. My plan is to run a fan for one of those home made air conditioners that I see all over Youtube. I see that most solar setups need batteries but they're quite expensive and I don't need to use them at night. I know what I need to get started with my system as far as panel, inverter and charge controller if using a battery.

My questions:
Do I need a battery to run a simple fan from a 25W solar panel during the day?
Is a 25W panel enough or too much?
If I do need a battery, what are my realistic and economical options?

Thank you! Any help would be appreciated!

[PNjunction]

Hi Matt!

This is a pretty common question about running things without a battery, and only under certain circumstances is it practical. You'll need a battery-as-a-buffer. Which also means charge controller.

Do I need a battery to run a simple fan from a 25W solar panel during the day?

Ok, by simple lets assume a single-speed "trucker fan" that you invert into a bucket. Average power consumption here is .500ma or about half an amp per hour.

We need a battery as a buffer to pick up the slack when clouds, overcast, haze or whatever passes over. Otherwise your system will be unstable and you want air-con (such as it is) to be working well. The panel is still designed to provide most of the power, and just take a nibble here and there out of the battery when needed, and put back those nibbles.

Can the panel alone handle the trucker fan at 500 milliamps? Yes, provided conditions are perfect. We are still going to use the battery as a buffer.

Save this formula for future projects, the (P/I*E), aka (watts / current * voltage). Know any two and you'll get the 3rd.

How much current can a 25 watt panel provide:
25w / 18v = 1.388A

18v is the "OCV" of the typical "nominal 12v panel", and although it really varies from about 17-21v or so, we use 18 for middle of the road calculations.

So yeah, a 25 watt panel attached to a buffer battery powering a trucker fan that only draws 500ma will work during the day. And will pick up the slack when conditions aren't the best.

So how big of a battery? The other factor for any succesful solar project is knowing how much TIME you need the system to work when the chips are down. How about designing the system such that if some stupid dark cloud passes overhead for 2 hours, but it is still hot and sunny, you'd need .500a * 2 to come solely from the battery. In this case, that would be just 1A.

And you are camping. The easiest solution would be to over-engineer the project, but we're going to try and keep it real. If we plan on only 2 hours of air-con with no sun that would be no problem for say a little 5ah agm, where again if things are perfect, the panel would be able to provide the 500ma of power to keep the fan running, and also 500 milliamps of charge current to keep that battery charged when it has to serve duty as the buffer and be the main source of power.

I think a Morningstar Sunguard 4.5a charge controller would be perfect for this application. It is potted and there is nothing to adjust. Toss a 5 to maybe 7ah ups style little agm in the bag and away you go.

Have fun and if you can, send us some pics!







Is a 25W panel enough or too much?
If I do need a battery, what are my realistic and economical options?

Thank you! Any help would be appreciated![/QUOTE]

[SunEagle]

Hi Matt!

This is a pretty common question about running things without a battery, and only under certain circumstances is it practical. You'll need a battery-as-a-buffer. Which also means charge controller.


Ok, by simple lets assume a single-speed "trucker fan" that you invert into a bucket. Average power consumption here is .500ma or about half an amp per hour.

We need a battery as a buffer to pick up the slack when clouds, overcast, haze or whatever passes over. Otherwise your system will be unstable and you want air-con (such as it is) to be working well. The panel is still designed to provide most of the power, and just take a nibble here and there out of the battery when needed, and put back those nibbles.

Can the panel alone handle the trucker fan at 500 milliamps? Yes, provided conditions are perfect. We are still going to use the battery as a buffer.

Save this formula for future projects, the (P/I*E), aka (watts / current * voltage). Know any two and you'll get the 3rd.

How much current can a 25 watt panel provide:
25w / 18v = 1.388A

18v is the "OCV" of the typical "nominal 12v panel", and although it really varies from about 17-21v or so, we use 18 for middle of the road calculations.

So yeah, a 25 watt panel attached to a buffer battery powering a trucker fan that only draws 500ma will work during the day. And will pick up the slack when conditions aren't the best.

So how big of a battery? The other factor for any succesful solar project is knowing how much TIME you need the system to work when the chips are down. How about designing the system such that if some stupid dark cloud passes overhead for 2 hours, but it is still hot and sunny, you'd need .500a * 2 to come solely from the battery. In this case, that would be just 1A.

And you are camping. The easiest solution would be to over-engineer the project, but we're going to try and keep it real. If we plan on only 2 hours of air-con with no sun that would be no problem for say a little 5ah agm, where again if things are perfect, the panel would be able to provide the 500ma of power to keep the fan running, and also 500 milliamps of charge current to keep that battery charged when it has to serve duty as the buffer and be the main source of power.

I think a Morningstar Sunguard 4.5a charge controller would be perfect for this application. It is potted and there is nothing to adjust. Toss a 5 to maybe 7ah ups style little agm in the bag and away you go.

Have fun and if you can, send us some pics!

Is a 25W panel enough or too much?
If I do need a battery, what are my realistic and economical options?

Thank you! Any help would be appreciated!

[/QUOTE]

There are DC fans that run directly from solar panels without using batteries. They come in different wattage rating which provide different CFM outputs

Here is a 20 watt version sold by our websites owners.

http://www.solartown.com/store/product/solar-gable-20-watt-fan/

[mattr33]

Thanks!

Hi Matt!

This is a pretty common question about running things without a battery, and only under certain circumstances is it practical. You'll need a battery-as-a-buffer. Which also means charge controller.


Ok, by simple lets assume a single-speed "trucker fan" that you invert into a bucket. Average power consumption here is .500ma or about half an amp per hour.

We need a battery as a buffer to pick up the slack when clouds, overcast, haze or whatever passes over. Otherwise your system will be unstable and you want air-con (such as it is) to be working well. The panel is still designed to provide most of the power, and just take a nibble here and there out of the battery when needed, and put back those nibbles.

Can the panel alone handle the trucker fan at 500 milliamps? Yes, provided conditions are perfect. We are still going to use the battery as a buffer.

Save this formula for future projects, the (P/I*E), aka (watts / current * voltage). Know any two and you'll get the 3rd.

How much current can a 25 watt panel provide:
25w / 18v = 1.388A

18v is the "OCV" of the typical "nominal 12v panel", and although it really varies from about 17-21v or so, we use 18 for middle of the road calculations.

So yeah, a 25 watt panel attached to a buffer battery powering a trucker fan that only draws 500ma will work during the day. And will pick up the slack when conditions aren't the best.

So how big of a battery? The other factor for any succesful solar project is knowing how much TIME you need the system to work when the chips are down. How about designing the system such that if some stupid dark cloud passes overhead for 2 hours, but it is still hot and sunny, you'd need .500a * 2 to come solely from the battery. In this case, that would be just 1A.

And you are camping. The easiest solution would be to over-engineer the project, but we're going to try and keep it real. If we plan on only 2 hours of air-con with no sun that would be no problem for say a little 5ah agm, where again if things are perfect, the panel would be able to provide the 500ma of power to keep the fan running, and also 500 milliamps of charge current to keep that battery charged when it has to serve duty as the buffer and be the main source of power.

I think a Morningstar Sunguard 4.5a charge controller would be perfect for this application. It is potted and there is nothing to adjust. Toss a 5 to maybe 7ah ups style little agm in the bag and away you go.

Have fun and if you can, send us some pics!

[/QUOTE]

Wow, this was super helpful! Thanks, it's the best info I've gathered yet
I have some new questions based off of your answer:

What if I increase my battery to let's say 8-10ah, will that allow me to also charge electronics such as phone, tablet, laptop etc. as well as give me enough charge on the battery at night to run a small light for a couple hours? If not, what ah should I be looking for to pair with my 25w panel?

Also, is a 25w panel too much or too little to run the fan with the battery as a buffer?

And also is it too much or too little to run the fan as well as charge the electronics and charge the battery for a small light at night?

[PNjunction]

What if I increase my battery to let's say 8-10ah, will that allow me to also charge electronics such as phone, tablet, laptop etc. as well as give me enough charge on the battery at night to run a small light for a couple hours? If not, what ah should I be looking for to pair with my 25w panel?[/quote]

Ah, now we're getting a bit deeper into it. There are some really good threads here on much the same stuff, and it all comes down to three (four actually) when you want to do it right.

How much current / wattage does your intended device pull? I mentioned a trucker fan typically at 500 milliamps. If you go shopping for one, it might vary from 250ma to maybe 750, so our calculations are may be way off with a small battery.

In essence, use the P/I*E formula, Luke.

Also, is a 25w panel too much or too little to run the fan with the battery as a buffer?

It will run a 500ma trucker fan as discussed earlier. We can go larger, but how much lead are you willing to hump in a camping setup? What is your budget like for larger panels, and of course is going larger even practical for you? When we start adding loads like charging phones, tablets, and so forth, that may be hard to determine what battery you will need since we don't know how much current your devices need to charge to full, and for how many times they will be charged daily. So I'd be shooting in the dark until we know that much.

And also is it too much or too little to run the fan as well as charge the electronics and charge the battery for a small light at night?

Basically what we discussed above is only for a single speed trucker fan during the best parts of the day, and only 2 hours during darkness / heavy cloud.

Here comes another issue - Solar Insolation hours. The times when the 25w panel would actually be able to put out something near its rated current, is during these hours. Solar insolation hours are different than just sunrise-to-sunset, and center around noon. Now we have to know what geographical location you are going to use this in, and get the hours from that. I might get 5 hours centered around noon in the summer, but depending on where you are, that may only be 2 hours! (despite the fact that you can still "see" beyond these solar insolation hours)

So you see that to properly determine these things, we need to know pretty much exactly how much current /wattage your devices need to run, how long you intend to run them daily, and what your solar-insolation hours are before determining a real battery-capacity and panel combination pair to ensure full battery charging. Advanced users will plan for "winter hours" of solar insolation, even if they are using the system in the summer. This involves getting tools like Kill-A-Watt meters, multimeters, clamp-on ammeters and so forth.

If we don't know all these things, the best we can do is "wing it" and see what happens. That is usually expensive with either an under-designed system being a total technical waste, or an overkill system being a financial waste.

At this point we could probably wing it by suggesting an 80 watt panel, 10A charge controller, and an 18ah agm. Things are getting larger, heavier and more expensive by the minute, with no guarantee of working to your expectations.

I guess I'm saying you can do these things, but don't be tempted to bite off more than you can chew at this point. Lets see if you can get your youtube airconditioner working first.

[mattr33]

If we don't know all these things, the best we can do is "wing it" and see what happens. That is usually expensive with either an under-designed system being a total technical waste, or an overkill system being a financial waste.

At this point we could probably wing it by suggesting an 80 watt panel, 10A charge controller, and an 18ah agm. Things are getting larger, heavier and more expensive by the minute, with no guarantee of working to your expectations.

I guess I'm saying you can do these things, but don't be tempted to bite off more than you can chew at this point. Lets see if you can get your youtube airconditioner working first.

I hear you loud and clear especially your last couple sentences. I think I'll stick with the 25w panel and maybe a 10-12ah battery and charge controller and RV fan; I feel like twice the ah is safer than sorry and won't break the bank. Also, I can charge my electronics during the day on another Solar charger that I already have (16w solar charger with USB inputs as well as a couple Mophie juice packs) and besides, I need to unplug from my electronics and enjoy my camping! I'll be camping in the desert so there should be plenty of sun during that 5 hour time frame. But of course, I need to get that youtube AC going first I'll take your advice on that!

[PNjunction]

Right on!

These days, the solution you proposed with the Mophie's and the 16 watt panel was on the tip of my tongue when I was about to mention an Anker 14w with Anker batts. You'll do fine in that arena with your stuff.

Truthfully, unless one wanted to do it solely as a learning experience, using lead-acid for charging very small stuff like phones, tablets and so forth is just not worth the time, and many pitfalls arise which normally does not lead to a lot of knowledge they can apply to the larger aspects of solar systems.

The 12ah battery would be fine too. At this point, if it all doesn't work out you haven't blown your budget, but I've got a feeling you'll be having fun and learning in the process regardless.

[mattr33]

I'm seeing some pretty good prices on Amazon, is there a better source that might be more cost effective than Amazon?

Thanks again for all your help and insight, I'm definitely on the right path now and ready to buy.

[PNjunction]

I don't really want to get into a sales perspective, but I can say this: going the cheapest route is not always cost-effective.

For example, my best advice would be to stick to legitimate and hopefully authorized dealers with the major name brands. For charge controllers, this would be Morningstar, Xantrex/Schneider, Steca, Samlex, Midnite Solar, Outback and so forth. There are others out there that may be cheaper, but you are taking a chance that you'll be buying the product twice or more when you concentrate on the lowest price alone, and they fail down the line. Worse yet is that the cheaper units have much looser specifications, and even things very important in the lead-acid world such as temperature-compensation (different than just temperature over/under load).

Some are ok, but I wouldn't bet my life on them. For instance, my folding Renogy panel kit. CC is OK, but I wouldn't use it for any critical project where my job or life depended on it. I would upgrade to a higher-tier product.

For example, some inexpensive kits may contain charge controllers that are right from the 1970's tech-wise, (they are not even pwm!) work slowly, and are generally not good for your batteries. Back then, the idea was to just abuse a huge bank of batteries, and replace them often. That worked to an extent, but is wasteful.

The moral here is not to just jump at the cheapest - even in your little project. Give it a modicum of quality, and you'll be better off because you can actually learn from the good stuff, where the cheapest things leave you scratching your head when they smoke suddenly.

[lkruper]

I don't really want to get into a sales perspective, but I can say this: going the cheapest route is not always cost-effective.

For example, my best advice would be to stick to legitimate and hopefully authorized dealers with the major name brands. For charge controllers, this would be Morningstar, Xantrex/Schneider, Steca, Samlex, Midnite Solar, Outback and so forth. There are others out there that may be cheaper, but you are taking a chance that you'll be buying the product twice or more when you concentrate on the lowest price alone, and they fail down the line. Worse yet is that the cheaper units have much looser specifications, and even things very important in the lead-acid world such as temperature-compensation (different than just temperature over/under load).

Some are ok, but I wouldn't bet my life on them. For instance, my folding Renogy panel kit. CC is OK, but I wouldn't use it for any critical project where my job or life depended on it. I would upgrade to a higher-tier product.

For example, some inexpensive kits may contain charge controllers that are right from the 1970's tech-wise, (they are not even pwm!) work slowly, and are generally not good for your batteries. Back then, the idea was to just abuse a huge bank of batteries, and replace them often. That worked to an extent, but is wasteful.

The moral here is not to just jump at the cheapest - even in your little project. Give it a modicum of quality, and you'll be better off because you can actually learn from the good stuff, where the cheapest things leave you scratching your head when they smoke suddenly.

Did I read you were a battery hobbyist? I was looking at an ARB AC/DC fridge on Amazon where a buyer commented that it took 0.8 amps per hour to run @ 12v and that he used 24 NiMH batteries to run it for 5 hours. I looked at some of the RC battery packs and never realized that 20 2000 ma batteries would be so substantial.

Is this a good application for powering a DC fridge/freezer in a car when the alternator is not running? I see a Tenergy NiMH 12V pack for $23.92 with 10 AAs that adds up to 20AH.

[PNjunction]

Is this a good application for powering a DC fridge/freezer in a car when the alternator is not running? I see a Tenergy NiMH 12V pack for $23.92 with 10 AAs that adds up to 20AH.

Hah! No way unless it is just to build up geek street-cred. Again, how LONG do you plan on running it when the alternator is not running. 1 hour? 12 hours?

Anything can be done given enough time / money / thought. On the flip side, is it practical, or make sense financially when all is considered? Ie, would the massive amounts of Tenergy cells that you would need to buy be 10 times more than just using a small 12v agm tucked away somewhere?

Normally these are used in offroad / camping setups from a two-battery setup with an isolator between the two batteries. Usually hefty.

One has already spent $600 or more on one of these in the first place. Give it a good battery. Going cheap here is like drinking a diet soda after a 40000 calorie meal.

[lkruper]

Hah! No way unless it is just to build up geek street-cred. Again, how LONG do you plan on running it when the alternator is not running. 1 hour? 12 hours?

Anything can be done given enough time / money / thought. On the flip side, is it practical, or make sense financially when all is considered? Ie, would the massive amounts of Tenergy cells that you would need to buy be 10 times more than just using a small 12v agm tucked away somewhere?

Normally these are used in offroad / camping setups from a two-battery setup with an isolator between the two batteries. Usually hefty.

One has already spent $600 or more on one of these in the first place. Give it a good battery. Going cheap here is like drinking a diet soda after a 40000 calorie meal.

I can just see my Subaru Forester with a single panel on the roof, my ARB fridge in the back with my "house" batteries! I keep going back and forth on the ARB or Engel fridge and unfortunately it is not practical. I would like more room to store food than the 3.2 fridge/freezer in the cabin but don't want to crowd the kitchen. So instead we have a 50 quart Coleman cooler filled 1/2 with ice on the kitchen floor the entire time we are there and we "temporarily" crowd the kitchen anyway.

But my Coleman has wheels and fully loaded can get it down a 20% slope 40 feet from the car to the cabin with no problem. The ARB or Engel are heavier and don't have wheels.

I may just get a second fridge for the basement and call it a day.

[PNjunction]

No matter what the load is, be it an ARB fridge or a simple light bulb, one has to know the time factor of usage in addition to the current draw.

Once you have that, you may find you do not need a panel at all, just a simple battery. Ie, for an 8 hour picnic, a common 12-18ah little agm battery might do the trick for an arb fridge. To justify spending a grand to keep your drinks and sandwiches cold, you'd probably want to take a LOT of picnics. Everything is relative.