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Small home solar system question.
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Batteries have a characteristic called Internal Resistance. So as you increase the current drain on a battery, the voltage folds back or put another way goes lower as the current increases. For FLA deed cycle batteries the maximum current you can draw is about C/8 to C/10 before Voltage Drop becomes a problem C = the battery Amp Hour capacity. So a 50 AH battery can only deliver about 50 AH / 8h = 6 to 7 amps before the voltage starts to crash. So a 12 volt battery powering a 1000 watt inverter will need to be able to deliver roughly 85 to 90 amps. This is why I said in my first reply you need around a 500 to 600 AH battery to run the inverter effectively.
Try this experiment. Take a hair blow dryer and plug it into the inverter and see what happens. Be careful because if the inverter can run the blow dryer, your wring from the battery to inverter can easily catch fire if it is under sized. It takes a # 4 AWG copper wire to safely handle 90 amps.MSEE, PEComment
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Well, I finally got it all installed. I ended up with the basic Harbor Freight solar kit, a 1000/2000 inverter and a 115 AH CostCo deep cycle battery. The first day the reading on the charge controller went 13 - 13-4. Today I see it is reading about 12.6. I assume this is reading the state of the battery. So, what parts of this setup are going to give me trouble? Di I need a smaller battery? Or a smaller inverter? If I read the leads coming in from the solar panels what should I see? They are the three 15 watt panels. So far I am not impressed but I haven't really put it to a test yet.Comment
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basic Harbor Freight solar kit, a 1000/2000 inverter and a 115 AH CostCo deep cycle battery. So, what parts of this setup are going to give me trouble? Di I need a smaller battery? Or a smaller inverter? If I read the leads coming in from the solar panels what should I see? They are the three 15 watt panels. So far I am not impressed but I haven't really put it to a test yet.
Lets start from working backwards at the inverter. You have a 1000 watt 12 volt inverter. To run that inverter up near full power requires 85 to 100 amps from the battery. Actual amount depends on the inverter efficiency. For a flooded lead acid battery to deliver that much current require the AH rating to be at least 8 times higher so that means your battery should be at least 85 amps x 8 hours = 680 Amp Hours and your battery is only 115 AH. So what will happen if you try to run loads more than 175 watts, your inverter will trip off-line from under voltage. Your battery can only realistically supply a 200 watt inverter.
Now to your battery, charge controller, and panels. To properly charge a 115 AH battery in any meaningful amount of time would require you to use 190 watt panel with a 15 amp PWM charge controller. You have a panel wattage of 45 watts with a shunt controller that can only support about a 20 to 40 AH battery.MSEE, PEComment
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OR, cut your battery capacity in half. And use a smaller inverter with smaller loads. We're kind of back to square one of the thread, so you'll need to make some choices on which direction to go. Oh, do yourself a favor and ditch that on/off non-temperature compensated shunt regulator, and get a decent charge controller while your battery is still relatively new.Comment
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Dear Sir
hope that we can give you better suggestion for your smaller off-grid solar kit .
1: currently there are two kinds of battery which is so popular for off-grid solar kit,
one is called lead-acid battery, the price is not so much, the price is about USD1 for one Ah, so if you buy 100AH, the price is about USD 60/set if you buy them directly from the manufacture.
but you need to care it so much.
if your solar system is not so large, you also can choose car battery, which also can reduce your whole cost., just you need to put water into it.
another one is called gel battery, which is called maintenance free battery, but the price is a little higer.
the price is about USD 134 for 100AH.
2: how to calculate the battery.
if you do not use the speical software to calculate them, you can calculate them by formulate.
1kwh: 100AH battery.
if your solar panel watt is 1000w, your local effective suntiime is 4 hours, so the total power is 4kw.
so you can choose 4sets 100AH Battery.
meaning that your solar panel ( 1kw ) can charge the battery with 400AH full in one day.
hope that you can understand soonRead Forum Rules. No advertising in signatures.Comment
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Dear Sir
hope that we can give you better suggestion for your smaller off-grid solar kit .
1: currently there are two kinds of battery which is so popular for off-grid solar kit,
one is called lead-acid battery, the price is not so much, the price is about USD1 for one Ah, so if you buy 100AH, the price is about USD 60/set if you buy them directly from the manufacture.
but you need to care it so much.
if your solar system is not so large, you also can choose car battery, which also can reduce your whole cost., just you need to put water into it.
another one is called gel battery, which is called maintenance free battery, but the price is a little higer.
the price is about USD 134 for 100AH.
2: how to calculate the battery.
if you do not use the speical software to calculate them, you can calculate them by formulate.
1kwh: 100AH battery.
if your solar panel watt is 1000w, your local effective suntiime is 4 hours, so the total power is 4kw.
so you can choose 4sets 100AH Battery.
meaning that your solar panel ( 1kw ) can charge the battery with 400AH full in one day.
hope that you can understand soonRead Forum Rules. No advertising in signatures.Comment
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For small projects, I personally like the Morningstar series. Either a Morningstar Sunguard 4.5a if you don't plan on expanding beyond what you have now, or perhaps a Morningstar 6 or 10ah Sunsaver. Both are temperature controlled and pwm. I don't use the "load" terminals, and run my loads directly from the battery. Steca is another manufacturer. There are cheaper ones out there that may have serious QC problems, or are counterfeits.
The C/20 calculation is about 5% of a batteries capacity, which is usually the bare minimum needed to do a practical charge, and for FLA's takes into account the minimum needed to overcome internal resistance and just charging fast enough to beat sulfation. Many shoot for at least 10 percent, so realistically if I were to support that battery with no load considerations taken, you'd need 12 of those HF panels for that 112ah battery.
With currents lower than C/20, you may obtain a surface charge that quickly goes away when any sort of load is placed upon it.
The problem with the crop of videos with HF panels attached to a large battery is that it *seems* to work initially, but all are running in deficit-charge scenario. What would really be interesting is doing a "where are they now" followup. Most likely the batteries are trash and have moved on to other things and disappointed with solar.Comment
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Looks like I was tripped up by the "bigger is better" way of doing things. Thanks for all the advice.Comment
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No problem - trust me, I've been there. I even went so far as to build my Harbor-Freight (Sunforce) kit, one panel $$ at a time! I stopped when I reached three. I switched to a good charge controller when I killed my battery quickly using the included on/off 7a shunt controller. I started with a known good fresh battery too.
You bring up a good issue - the HF panels are amorphous, so they are about 1/3 larger or more than an equivalent crystalline panel. So they look impressive, but if you were to bring home a single 45w crystalline panel you'd be amazed at the size reduction, and perhaps thought that just based on size, it may not be enough. I think size of the amorphous is somewhat deceptive for new users.
At any rate, my HF panels are doing great duty for my smaller stuff. No they aren't heirlooms or best in class, but they do the job adequately - once I sized the load / battery capacity requirements.
One thing you could do is just plan on not using any more than say 25% of your Costco's battery capacity - which is always a good idea no matter what, even though you are under the 5% (C/20) minimum recommended charge current rating of the battery overall. With a good charge controller, you might just get away with it enough to keep your interest up even if you don't always reach 100% charge.
The good thing is that nobody seems to get their first battery perfect - so it makes a great "sacrificial" learning battery. Unfortunately, I've sacrificed more than one, but at least I'm not testing the waters with a really expensive Concord, Odyssey, Surrette or the like and crying when I kill it.Comment
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Forgot to mention - I also cheat by having an ac-powered battery charger for those times when I run out of solar insolation hours to do the job, or wake up to find myself with a discharged battery and a week of rain coming. I don't like my batteries sitting around discharged for more than a day - even the little 5ah battery gets treated as if it was an expensive 500ah Rolls-Surrette.
Like having a decent multimeter on hand, I also think that having a battery charger is also requisite. I've used Battery-Tender products, and lately have been playing with NOCO Genius chargers. Iota makes some really serious chargers too. I tend to size the charger capacity much the same to meet at least a C/20 minimum charge rate.
I try not to use it, but will put a charger online to save my batteries if weather conditions go bad.Comment
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Interesting discussion, I have learned alot. If I hook up a battery charger to kee the battery up will it hurt my solar panels? Seems some of the current will be fed into the output from the panels.Comment
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When it comes to chargers, you may want to make sure you don't use a dumb automotive charger. At least shoot for something that has a bulk / absorb / trickle stages and at the proper voltages. Temperature compensation is a big plus.Comment
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