Need help, What battery do i need?

NathanS

I just got a 45watt solar panel kit and have no idea what battery to get.

This is the kit I got: " http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90599 "

I know i need a deep cycle lead acid or gel battery. I just don't know how big of a battery i need. Are these batterys measured in mah?

Please let me know what battery to get, some links would be nice. I would also like to buy it local.

I have heard car batterys are no good, is this true?

Cariboocoot

Re: Need help, What battery do i need?

Oh no! Another one!

Can you send it back and get your money refunded? HF's 45 Watt "solar kits" are a joke. Not a funny one either.

Now let's start with the beginning: why do you want solar power? In other words, what do you hope to do with it?

As for your battery question; yes, ordinary car batteries or even "Marine/RV Deep Cycle" are not suitable for solar power usage. They aren't built to take the repeated continual discharge/recharge cycles and will fail prematurely.

Batteries for solar application are measured in Amp/hours (20 hour rate usually). For example, a 200 A/hr 12 Volt battery will supply 2400 Watts for one hour, or 100 Watts for 24 hours - MINUS the limits of depth of discharge (DOD) - it is not recommended that batteries be drawn below 50% of capacity and less is better. Thus 200 A/hrs is in practical use no more than 100 A/hrs. Then there's compensation for loss of efficiency in the system.

You have to determine what you want to do before you can decide what sort of invert/battery/panels you get.
Otherwise, your 45 Watt panel isn't capable of recharging a lawn-mower size battery much less running a load. The best it could manage under ideal conditions would probably be a 50 Amp/hr battery.

I hope you're not out too much money. And remember; we're here to help!

icarus

Re: Need help, What battery do i need?

FYI:http://forum.solar-electric.com/showthread.php?t=5495

Tony

niel

Re: Need help, What battery do i need?

btw nathan, mah is milliampere hours and you don't want that unless your goal is to recharge aa nicad or nimh rechargable batteries. for the record, 1000mah equals 1ah. from feedback i've read on the hf solar kit indicates it may give about 1.25a or so and the battery would range between 9.6ah and 25ah if that's so.

NathanS

Re: Need help, What battery do i need?

Whets so bad about the kit I bought. It was $160 and it sells on Amazon for like 370.

I paid extra for a 2 year warranty buy the sales guy mad it should a lot different than the paper that came with it does.

I just got this to experiment with and maybe power some stuff.

So is the a battery at batteries plus i should get. I guess i need to get a 10ah -20ah battery?

Please just tell me what battery to buy. If i should really take the kit back then show me where i can get something like it but better that doesn't cost much more.

RandomJoe

Re: Need help, What battery do i need?

The main problem with those kits is that they greatly exaggerate what you can do with them. As long as you understand you will NOT be running half your house off of it, they can be fun to play and learn with. There is also a problem with the panels, they are quite optimistic with their ratings. A few people have actually had good success and gotten near the 45W rating, most get nowhere near it.

And finally, the "charge controller" they supply is very crude. It basically just connects the panels directly to the battery until the voltage reaches a preset point, then disconnects until the voltage falls to another preset point. I found mine went way too high - right close to 15V - for my AGM battery. Might have gotten away with it for a flooded lead-acid battery, but didn't want to damage my (expensive!) AGM. I wound up buying a replacement controller from NAWS, and it works just fine with the panels.

Oh, almost forgot - at least with mine, there's a reason HF has a note to disconnect things after dark. The panels had no blocking diodes, when the battery voltage fell the controller "switched on", and I watched (on the WattsUp meter) current flow *backward* into the panels! Could have run the battery down overnight had I left it all connected. A better charge controller (like the one I replaced the HF one with) prevents this, or at the very least add a blocking diode to the panels.

I started with an HF kit, knowing full well what it is and isn't, so wasn't disappointed. My panels only give me about 20W output, to give you an idea of the ratings...

I used a 100AH AGM battery with my panels. That's right up to the top end as far as what the panels could possibly hope to keep up with, but my goal was to have only very shallow discharges on the battery for longevity, as well as have some reserve (that I would have to make up for by other means) in an outage. I used a "WattsUp" meter to watch power in and power out, found I could replace roughly 9AH per day with my panels. So I just made sure I used that much or less. Which was tough - that's not much power! On occasion I topped up the battery with a power supply from my ham bench.

I still use the HF set, even now that I have a much larger array of nicer panels. It makes for a handy battery-charging set to keep my collection of smaller AGM batteries ready to go.

icarus

Re: Need help, What battery do i need?

NathanS wrote: »

Whets so bad about the kit I bought. It was $160 and it sells on Amazon for like 370.

I paid extra for a 2 year warranty buy the sales guy mad it should a lot different than the paper that came with it does.

I just got this to experiment with and maybe power some stuff.

So is the a battery at batteries plus i should get. I guess i need to get a 10ah -20ah battery?

Please just tell me what battery to buy. If i should really take the kit back then show me where i can get something like it but better that doesn't cost much more.

What is "so bad" about HF panels is that for 45 watts you are paying $3.66/watt! AND the performance doesn't meet specs.

So if you are looking for something else, try here:http://sunelec.com/ The Sun panels can be had for $2.38/watt, for a reputable, reliable panel.

I believe ( and I may be wrong) but I think the HF panels are amorphous panel whose performance (even it's limited performance) will drop off ~20% in the first year.

The reality is that the HF panels are an overpriced, over hyped toy. Will they work for simple experiments, sure, but for the same price you can by a "real"panel and do real work.

What irritates many of us on this site is that too many people have learned from expensive experience the limitations of this and other POS hardware. It is a shame that people keep getting away selling such junk,, but I guess that is the system we have,, where hype sells better than performance.

I always advise folks here on this forum that there are some very smart folks here,, folks that have forgotten more about Pv, Re, electrical engineering etc. than most of us will ever know. The great beauty of this forum is that the rest of us can chose (or not!) to use the advice of these folks so that we don't have to reinvent the wheel at each turn.

By all means play with your HF panel. It may turn you on to what Pv can (and can't) do, but be prepared to spend some more money soon, because you will be disapointed.

Good luck, keep in touch and welcome to the forum,

Tony

BB.

Re: Need help, What battery do i need?

"Irritates ... us" is probably too strong of term...

We have all made mistakes in our lives--and hope that we can help others avoid making the same ones.

I really feel bad for people that buy this based on vendor statements--and then get an $$$$ surprise.

On the other hand, Harbor Freight and others, many times, are the first exposure that many get with solar--so it is an educational experience (which usually costs money anyway).

We are here to help--because we want to help (by-product is that NAWS gets some commercial exposure too--this site is 100% paid for by NAWS).

-Bill

niel

Re: Need help, What battery do i need?

btw a good pv you don't need to pay extra to get a 2yr warranty as most are rated to 20 and 25yrs without paying for an extra warranty.
if you wish to keep what you have and buy a battery then you could get one of those batteries at batteries plus or shop around as you may find a cheaper one elsewhere. remember that for these batteries that you don't want to drain it dead as this will deplete capacity and shorten the battery lifespan. go no more than halfway.
i also would suggest that you further read up on things here to help educate and familiarize yourself with some of the ins and outs of solar. i will not scold you or anything like that, but it was your not knowing of these things that allowed you to buy into the hf stuff so read to make better decisions in the future. if your solar application is critical for something then time is of the essence and ask us our opinions, otherwise read and if you have questions along the way we are still here to ask.

icarus

Re: Need help, What battery do i need?

Bill,

"Irritates ... us" is probably too strong of term..."

I agree it is a bad choice of words. When I suggest that it "irritates us" what I mean is that it is a source of irritation that there is still a plethora of shoddy stuff out there ,, and that through no fault of their own, folks like Nathan spend money that might otherwise go to good Pv stuff,, potentially leaving them with a bad taste in their mouths regarding Pv.

I didn't mean to suggest in any way that I (or anyone else) was irritated at Nathan (or anyone else). It is an irritation at HF, Ebay junk etc. I hope that clarifies my point,, no offense intended.

Tony

BB.

Re: Need help, What battery do i need?

Tony,

I know that it was not your intention...

-Bill

Cariboocoot

Re: Need help, What battery do i need?

We don't like to see nice people like Nathan bilked of their solar $ by outrageous claims like HF contention that you can run a TV off their 45 Watt panels. Maybe you can, if it's a small set and the program isn't very long. If they didn't say things like that, implying it's capable of operating significant loads, it wouldn't be so bad. Good experimenter's start, especially for $160 (HF lists it at $299 I think).

Of course there are worse 'deals' out there: look at Canada's own Canadian Tire;
http://www.canadiantire.ca/AST/browse/Green/EnergyConservation/RenewableEnergy/PRD~0111830P/80W%2BSolar%2BPanel.jsp

(Short version: 80 Watt panel for $759.99 CD$ - about $650 US)

To get back to the Original Post: Nathan, what is your solar goal?
We may fly off the handle from time to time and definitely get side-tracked, but we are here to help! :-)

NathanS

Re: Need help, What battery do i need?

ok, well I'm glad I Know I bought a piece of shit.

If someone could direct me to buy something better for around the same price let me know.

The worst part is that I still have no clue what battery to get and that was my original question.

I got this solar panel to "have fun" I got it to try something new. I do not own a house so I cannot build a solar empire on a roof.

I was hoping this set could power my computer monitor, but I don't even know how much power it eats up.


Please advise me on a battery to buy and when I want to get some real solar panels I will talk to you guys first.

PS. I may try to get my money back on the warranty, the salesman made it seem like I could drop it and they would replace it. The paper that I got makes it seem like it has to be a defect... I don't like things like this.

icarus

Re: Need help, What battery do i need?

Sorry for your disappointment.

The reality is, as has been suggested often before,, one has to do the math. That is you have to start with your loads and work backwards to find the battery/Pv system that fits the load. So for example it doesn't mean much to ask,,"What kind of battery do I need to use with this panel?"

A proper question might be, "I have 45 watts of panel,, what can I run for how long with what battery?" Or, "I would like to run my lap top for 4 hours a day, what kind of panel and battery would you recommend?"

In the real world,, by my rule of thumb,, with a battery based system, you can count on About 1/2 the name plate rating of a good Pv panel, multiplied by the number of hours of good sun. Normal good sun rarely exceeds 4 hours per day.

So for example,, 100 watts of panel might be thus: 100/2*4(hours)=200 watt hours/day. So in this example, you could run a 50 watt lap top for ~4 hours.

All loads have to be expressed in both watts and time. One without the other means little. I suggest that for ~$20 you buy (or borrow) a Kill-a-watt meter. This simple meter will allow you to plug in your stuff, and it will tell you how many Kwhs it uses.

After you total all your loads,, you then can figure out how to power them. That said,, battery based Pv systems will run about double the cost of a Grid tied system.

Good luck, keep in touch

Tony

Cariboocoot

Re: Need help, What battery do i need?

FYI: Extended warranties on anything are almost always a waste of money.

Now, let's see what we can salvage, shall we?

In reality, your 45 Watt panel given 5 good hours of sun would probably produce about 135-150 Watts in a day.
It's maximum output current, according to HF, is 3 amps, which is barely enough to keep ahead of self-discharge on even small batteries. Let's be optimistic here and say there's enough power to re-charge a 50 Amp/hr battery.

At first, you'd probably pick an AGM because there are plenty of small ones that would fall into that A/hr range. BUT, since the charge controller is definitely not a three-stage type (and is probably only a 'high voltage cut-out') the AGM isn't a good choice; they are very picky about how they're recharged so in the end you'd be throwing more money away. AGM's are pretty pricey per A/hr compared to a flooded cell.

So what about the standard type used in most solar apps? They're too big; basically 200 A/hrs and up.

In this case I'm thinking you should break the rule and see how cheaply you can get a small 'Marine/RV' battery from Wal-Mart or similar (trolling motor battery). This will work for experimenting, it's just not going to have a long-life because they can't take the repeated charge cycling.

Now, what will you run with it? Have you got an inverter, or are you looking to use it as a renewable 12 V source? There are many 12 V devices available from RV supply.

And hey, it's still cheaper than a college education, right?

Second opinions are always welcome.

Slappy

Re: Need help, What battery do i need?

NathanS have you seen the "u-tube" vids on those panels, Some people actually get some use out of them. And a couple shows their battery bank in the vid as well. Just type in solar panel in the search bar of u-tube.:cool:

NathanS

Re: Need help, What battery do i need?

SO i am looking for an rv battery and just choose how much juice i want it to hold. How much will this cost?

I have a 200watt inverter but it says i need a 300 watt inverter.

I am not even sure what i will use this for. I want to see how much power i will get first.

This is all just for some fun, I think im going to ask for the extended warennty money back so it will only cost me 160 no matter what happens.

Could someone direct me to a good battery i could buy at wal-mart?

BB.

Re: Need help, What battery do i need?

A 50 AmpHour battery is probably the maximum you can charge with that array... You can go larger, but that will mean you may have to use a 120 VAC battery charger on occasion to recharge at times.

RV batteries are not great deep cycle batteries--but you may not find good Deep Cycle batteries in the smaller capacities. If you find an RV or trolling motor battery in that size range--it will probably last 1-3 years of reasonable use.

Getting accessories like a Kill-a-Watt meter, DMM, good quality hydrometer (for non-sealed batteries), will give you a good start.

Secondary equipment that is very handy, but hard to justify... For a small system, a Watts UP or Doc Watson cumulative Amp*Hour/Watt*Hour meter is nice. For bigger battery banks/systems--a true Battery Monitor. Cumulative meters are pretty much required to know what is going on with sealed/AGM batteries.

Inverter wise--One of the best 12 volt ~300 watt True Sine Wave inverter is the Morning Star one. Not cheap, but much better than the MSW (modified sine/square wave) inverters. For playing around with your first system--had to justify the cost--but really is worth it.

The recommended maximum discharge level of 50% gives you:

50 AH * 12 volts * 0.50 = 300 Watt*Hours useful storage capacity.

A 300 watt inverter is really a lot of load for a 50 AH 12 volt battery... Ideally, the best average load would be in the 30-120 watt range (C/20-C/5 amps). You could pull 300-600 watts for surge current--but it will be a stretch to get an hour of 300 watts (for very many charging cycles).

To recharge your 300 watt*hours of your battery bank with the 45 watt panel... Assuming good summer weather you get ~5 hours of "full" sun per day... 2-3 Amps...

50 AH * 50% / (2.5 amps * 5 hours of sun per day) = 2 days to recharge

Of course, if you sun/average current is less, then it will take longer to recharge.

-Bill

dwh

Re: Need help, What battery do i need?

NathanS wrote: »

I am not even sure what i will use this for. I want to see how much power i will get first.

Not much. It's been explained already that you can expect to harvest maybe 150 watts a day - 30 watts from the panels X 5 hours a day of *good* sun.

If your monitor draws 50 watts, you can expect to run it for maybe 3 hours.


So you need a battery that can hold 150 watts. But draining a battery all the way will kill it - you might do that 10 times before it's wasted.

Better figure on draining it halfway - then you need a battery that can hold 300 watts.

300 watts divided by 12 volts comes to about 25 amps.

So you need a 25 amp/hour DEEP CYCLE battery.

Which is pretty much ultra-dinky. Like - wheelchair battery dinky...

Here's a 26ah (amp hour) wheelchair battery:

http://www.batteryweb.com/wheelchairdetail.cfm?Model=UB-12260

NathanS

Re: Need help, What battery do i need?

SO i just need a deep cycle 25amp/hour battery. If i tell a guy at a battery store that he will know what i need?

Can i expect to have a battery hold a weeks worth of poer tou use later?

BB.

Re: Need help, What battery do i need?

25 to 50 AH 12 volt battery would work...

It will take ~1-3 days in the summer to recharge your battery. In the winter it may take 2 - 6 sunny days.

What do you mean by "have a battery hold a weeks worth" of power?

Do you mean store 7 days of sun shine, or to power something for 7 days * X hours per day?

-Bill

dwh

Re: Need help, What battery do i need?

NathanS wrote: »

SO i just need a deep cycle 25amp/hour battery. If i tell a guy at a battery store that he will know what i need?

Depends on the guy and the store I guess.

Can i expect to have a battery hold a weeks worth of poer tou use later?

The more you want to store, the bigger the battery you'll need.

The 25 amp hour battery is the size for 150 watts per day of drain/recharge.

If you want to store a week's worth, then 25 amp hours x 7 = 175 amp hours.

But batteries self-drain as they sit, and they need a minimum amount of charging just to keep up with their self-draining. If the battery is too big, then that little HF kit won't put out enough juice to even keep it from self-draining.

And if you DON'T give it enough juice to keep up with the self-drain, then it won't last very long.

NathanS

Re: Need help, What battery do i need?

I was thinking i wanted the battery to hold about a weeks worth of charging.

So can you give me a range of what i shough get depending on how much i want to spend.

Also I am looking for a RV battery right? Is that the cheapest wat to go for such a small system.

Cariboocoot

Re: Need help, What battery do i need?

Some further elaboration:

These panels will have difficulty staying ahead of the self-discharge rate of even a small battery - and the larger the battery, the greater the self-discharge rate.
Also, batteries like to be charged at a certain minimum amperage in order to reduce the effects of sulfation - resulting in a longer battery life. This is generally agreed to be 5%-13% of the '20 hour' Amp/hr rate; i.e. a 25 A/hr battery would prefer being charged at a about 1.25 - 2.5 amps. The 3 amps available to you would be capable of charging and keeping up a 50 A/hr battery at best. Such a battery would lose approximately 0.5 A/hr per day +/- depending on how it's made so it's guesswork. The fully charged battery after a week of sitting would be down to, say, 45 A/hrs - which is still not bad.

So you could get one battery for each day of the week, charge them separately, and take the cumulative losses.

I'd suggest something in the lines of a Group 24M* like an Interstate HD24-DP or similar. Others may have their own suggestions. Sorry if there are too many different, yet equally correct, answers to what seems like a simple question. Engineers nearly always see more than one solution to a problem, then spend eternity working out which one to go with.

And just so you know we're not perfect either: I got up to dead batteries this morning because some idiot (me) left something on all night that he shouldn't have.

It's another bright, sunny day in the Cariboo - and the generator is running.

*The 24M would be the largest I think you could get away with. The smaller choice would be a U1 like an Exide STU1DC40.

icarus

Re: Need help, What battery do i need?

Nathan,

I'm sorry, but I think you are missing an essential element! As has been suggested before,, asking what kind battery to buy to "hold a weeks worth of charging" is sort of backward. With out load information "holding a weeks worth of charging" is a pretty nebulous question.

If at it simplest, your question is "with this panel sitting in the sun for 7 days, what is the maximum ah capacity battery I could keep charged"? I suppose that you can figure your net solar gain into the battery in the week minus the self discharge and other system loses and say you can keep a battery of Xah charge.

But the first time you decide to use the battery to do some "work" even if it is "playing around" work the equations are all thrown askew. One answer would be if you were going to run a couple of LED bulbs for 4 hours a day, as opposed to using a 50 watt lap top 4 hours.

It seems that the "right answer" for you now, would be to go buy a $100 tolling motor "deep cycle" battery and start playing with it. I wouldn't buy any fancy agm or anything else. You will in all likely hood turn your first battery into scrap metal with in a fairly short time. (This is not a personal indictment, for all of us have done it!) Get a good hydrometer, which is the only way you will be able to gauge battery state of charge, and start playing.

I suggest that you read the following links :http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
http://www.batteryfaq.org/

Remember, checking battery voltage to deduce battery condition is not a good method. At the very least, battery voltage should be checked with the battery at rest, ideally after several hours of not being charged nor loaded. Too many people put (including myself) have put a voltmeter on the battery and seeing it read 12.8 vdc think that it is "fully charged" not realizing that it is on the Pv being charged. Take it off the Pv and let it sit for a while and the voltage might be any where from 12.7 on down! The inverse is also correct. You check the voltage and it read 12.1 and you pour on the charge, then you realize that it is running X load, removing that load might reveal a much higher state of charge.

Good luck, keep asking questions and enjoy your hobby. Many here started just where you are,

Tony