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foxdud
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# Posted: 2 Oct 2013 15:01
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I had a quick question I was hoping someone could help me with.
I have 45watts of solar on my cabin roof with a 10amp solar controller and 4 deep cycle batteries totaling 368ah
How many more panels would I need to keep my batteries topped off?
I am only running 2 lights a small fridge during the day (we unplug the fridge at night) and maybe a few hours of tv time over a entire weekend. 1000w power inverter to run the lights and fridge and a 400w inverter to run the tv.
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MtnDon
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# Posted: 2 Oct 2013 15:09 - Edited by: MtnDon
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Depends...
1. on how much power has actually been drawn off. Best way to measure is using a hydrometer and using the specific gravity.
2. on what the "good" sun hours per day are. That is best taken for the worst time of year that the cabin is used.
My gut feeling is you may need at least 5 times as many watts worth of panels. But that depends on #1 and 32 above.
Also depends on how many cloudy days in a row frequently happen and if you want/need to recharge those several days worth of use all in one day.
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foxdud
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# Posted: 2 Oct 2013 15:22
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I'm thinking that my solar charge controller can only handle 10amps which I think would be around 120 watts of panels? So right now that would be my max until I get a new system and move this one to the workshop. I will have to supplement with the generator to charge the batteries.
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cman47c
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# Posted: 2 Oct 2013 15:26
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The fridge will be the killer. As has been discussed here previously, there are several models that could be used for solar but it appears that you are using a 120 VAC model fed from your 1000W inverter. Even if the lights and fridge only are using 500W(12 hours per day would be almost 500 Amp-Hrs), this is an enormous 12 VDC load for your batteries per day. Your batteries will be drawn down in less than a day and only recharged(assuming 5 hours of good sunlight) at a rate of about 20 Amp-Hrs per day so unless you are not there for a month, the batteries will not cut it with this amount of solar. As MtnDon said, to do this would require much more solar panel capacity.
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foxdud
Member
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# Posted: 2 Oct 2013 15:32
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It is a very small fridge I'll look at the specs and post it here.
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foxdud
Member
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# Posted: 2 Oct 2013 15:51
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If I'm right this refrigerator uses about 75w at start up and then around 35w while running
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MtnDon
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# Posted: 2 Oct 2013 16:57 - Edited by: MtnDon
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Quoting: foxdud If I'm right this refrigerator uses about 75w at start up and then around 35w while running
The energy guide annual average use figures would give something to compare to. It is hard for the average person to accurately guess the number of hours the unit actually runs.. A metered figure would be superb. Google kill-A-Watt meter if you don't have one. .. Also is it a compressor type or a thermocouple device? Small under the counter ones can be either. Thermo- are the worst.
Quoting: foxdud my solar charge controller can only handle 10amps which I think would be around 120 watts of panels?
approximately. The charge controller will have a maximum amperage, a maximum voltage and a maximum wattage specified.
If adding a panel(s) to what you have it is best when adding panels in parallel to keep the voltages within 10%.
Check the Isc rating for the panel you have. Subtract that from the maximum amperage rating of the charge controller. The result is what you can add in terms of the Isc rating on the panel to add.
Then check the rated wattage of the CC. Subtract 45 from that and you have the maximum wattage of any panel you can add.
Also make sure none of the panel Voc voltages exceed the max voltage rating of the CC
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basewindow
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# Posted: 3 Oct 2013 00:49
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What voltage is your system going to be? 12v I assume. What type, voltage and configuration (series/parallel) are your batteries?
You really need to define your electrical loads before you do anything. Get a kilowatt meter and check what that fridge uses over 24h of real use.
Having said all that in general you need enough panel to charge your batteries at somewhere between 5-10%. So in your case something between 360w (minimum) supplying about 18amps per hour and 600w supplying about 30+ (About right), for your 368Ah of battery.
You will need a new Charge Controller or Solar Regulator rated to whatever Amps your panel array produces. An MPPT type will be more efficient than a PWM, but will cost you more.
As stated the fridge is the killer. Is it a part time, holiday cabin or full time? If it's only weekend and holiday use go with a gas propane fridge. If you are set on electric, get a new modern energy efficient model and a PSW (puresine) inverter.
LED for lighting and LED TV.
If I were you, I throw that 45w panel and buy some bigger ones. Panels are relatively cheap, where batteries are expensive.
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foxdud
Member
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# Posted: 3 Oct 2013 03:35
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My system is 12v
Batteries in parallel.
Fridge is new from Walmart.
Charge controller is brand new and I am planning on installing it this weekend it is a PWM controller.
My cabin is only a weekend getaway.
Kilowatt meter seems like a good investment.
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cman47c
Member
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# Posted: 3 Oct 2013 08:10
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If the fridge is 35W running, your system may be OK. If you only use the system on weekends and leave the batteries charge while your away and you do in fact turn the fridge off at nite, your batteries should easily last a weekend and recharge until the next visit.
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foxdud
Member
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# Posted: 3 Oct 2013 09:26
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Thanks all for the help.
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basewindow
Member
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# Posted: 8 Oct 2013 21:27
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The batteries will easily last a weekend, no problem.
The problem is getting them back of to 100% SOC as quickly as possible. Leaving batteries at less than 100% SOC for more than a few days can cause problems with sulphation and rapidly decrease your battery life. Your 45w of panel just isn't going to cut it with 368Ah of battery. At best you might get 3Amps out of that panel and at an average of 4-5 good sun hours you're only putting back perhaps 15Ah at very best per day. Not good.
If you want to be replacing expensive batteries every 1-2 years fine. As I said PV panels are relatively cheap and last a long time....
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foxdud
Member
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# Posted: 9 Oct 2013 03:26
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I got the new controller hooked up this last weekend and im only pulling in at best 0.4ah and 13.5w looks like im going to have to cut a few trees. also I was wrong on the amount of AH I have. It's 380ah also another question is I have 2 flood acid batteries and 2 gel batteries should I set the controller to FLD or GEL?
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basewindow
Member
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# Posted: 9 Oct 2013 04:00
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What is the Ah of each individual battery?
I wouldn't be mixing batteries of different Ah and especially different type and construction.
Flooded Lead Acid (FLA) usually have different charging parameters to GEL or AGM.
On each battery it should have written the charging parameters for Bulk (usually some thing like 14.3-14.6v), Absorption (a bit lower), float (bit lower again) on it somewhere.
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Dillio187
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# Posted: 9 Oct 2013 11:34
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+1 on what base said. You should not mix battery types like that, it's just asking for trouble.
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Truecabin
Member
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# Posted: 9 Oct 2013 12:13
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if one of the battery types tells the charge controller to shut off the other battery type will never get a full charge this is almost certain to happen
one battery bank cant have 2 types it cant work
the only way to get full charges is to have all batteries in the bank as equal as possible and even if they are same types you can run into trouble with cabling problems or corrosion
you think you are gaining capacity but the pair that cant get a full charge is sitting there wasted it cant put out a fraction of its capacity and your actually losing by shortening the life of the pair thats not getting a full charge
its like rowing a boat with 4 people where two are only floating there oars with the water your better off letting them swim
separate the types and use one type in your shop
you can buy a 100w panel for $130 delivered and a 2nd charge controller is not so much.
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foxdud
Member
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# Posted: 9 Oct 2013 17:50
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I have 2 brand new 101ah deep cycle batteries from walmart and the 2 gel batteries are used but in good condition they were freebies one is a 86ah and the other is a 116ah so Im thinking I should ditch the two gel batteries and use them for core's on two more new Walmart batteries?
Also based on the fact that im only getting 0.4ah and 13.4w would it be better to get a new panel even bigger than 100w? My charge controller can only handle 10amps but im no where near that now with what im bringing in.
Here is my full set up right now...
solar panels... http://www.harborfreight.com/solar-panel-kit-45-watt-68751.html
Charge controller... http://www.amazon.com/Amp-Volt-Solar-Charge-Controller/dp/B00CXVB9AO/ref=sr_1_1?ie=UT F8&qid=1381354982&sr=8-1&keywords=10+Amp+12%2F24+Volt+PWM+Solar+Charge+Controller+-+I ncludes+Remote+Meter
Batteries... http://www.walmart.com/ip/EverStart-Group-Size-24DC-Marine-Battery/20531540#Specifica tions
Power Inverter... http://www.harborfreight.com/1000-watt-continuous2000-watt-peak-power-inverter-60704- 9815.html
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foxdud
Member
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# Posted: 9 Oct 2013 18:01
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So in a nutshell how much more Panel do I need???
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Steve961
Member
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# Posted: 9 Oct 2013 18:30 - Edited by: Steve961
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A common rule of thumb for panels is for the charging rate to be 5-13% of battery size. That would be somewhere between 328 to 853 watts of panels for you.
In my opinion, for your battery bank size, you'd be much better off, both functionally and monetarily, starting from scratch with different panels, charge controller, and possibly even inverter. With the four batteries you will have, you should give strong consideration to a 24 volt battery bank. This would be two parallel strings of two batteries in series. This will allow for more efficient charging, more even discharging, and easier upgrading in the future.
In addition, you're reaching the level where a MPPT charge controller would be beneficial. This would also allow you to purchase lower cost/watt (i.e. ~ $1/watt) grid tie panels in >200 watt sizes and run them in series for higher voltage between the panels and charge controller.
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Dillio187
Member
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# Posted: 9 Oct 2013 21:10 - Edited by: Dillio187
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to echo what Steve said, your 10 amp charge controller is about the right size to charge 1 single 100ah 12V battery (if able to by having enough solar panels connected to it)
Your single 100W panel can probably only provide 4-5 amps of charge when the sun is shining directly on it perfectly, so this means your setup is about right to charge a 40-50ah battery.
As you can see, you are significantly undersized in both the panel and charge controller department.
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