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Old 10-03-2016, 12:18 PM   #1
Mini-Skoolie
 
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Need help with solar / house power system

Hello all,

I am looking for some help with my solar / battery power system. I recently ordered the Renogy 600w solar kit, and now I want to make sure I get correctly corresponding batteries and inverter setup. I was thinking somewhere in the range of 300-500 AH battery bank and 1,000 - 2,000 watt inverter charger.

One thing that is confusing me in all this is the "battery / Charging Current". I noticed on the 60 Amp Renogy MPPT charge controller it says "Rated Battery Current: 60 Amp". But on batteries such as the VMax Charge Tank it says "Charging Current: 10-35 Amps. Are these two rating relevant to each other?

Nowhere in my many hours of researching have I read anything about pairing charge controllers to batteries. Perhaps I am reading into this too much? Really hoping that my solar selection has not limited my battery options?

Are there similar concerns for sizing up the inverter to battery bank?

Thanks!
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Old 10-03-2016, 01:03 PM   #2
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Originally Posted by WhiteWhale View Post
Hello all,

I am looking for some help with my solar / battery power system. I recently ordered the Renogy 600w solar kit, and now I want to make sure I get correctly corresponding batteries and inverter setup. I was thinking somewhere in the range of 300-500 AH battery bank and 1,000 - 2,000 watt inverter charger.

One thing that is confusing me in all this is the "battery / Charging Current". I noticed on the 60 Amp Renogy MPPT charge controller it says "Rated Battery Current: 60 Amp". But on batteries such as the VMax Charge Tank it says "Charging Current: 10-35 Amps. Are these two rating relevant to each other?

Nowhere in my many hours of researching have I read anything about pairing charge controllers to batteries. Perhaps I am reading into this too much? Really hoping that my solar selection has not limited my battery options?

Are there similar concerns for sizing up the inverter to battery bank?

Thanks!
A 60A MPPT charge controller can provide a maximum of 60A into the batteries, regardless of battery system voltage. If you have a 12V battery system it can provide about 888W (60A x 14.8V); if you have a 24V battery system it can provide twice that wattage at the same 60A maximum current.

A 600W PV system will not usually produce 600W of electrical power - it will typically produce a maximum of about 3/4 of that under most conditions, i.e. you will see about 450W from the panels most days. 450W divided by 14.8V battery charging Absorb voltage (needed for Trojan T-105 batteries in a 12V system) is about 30A, less the CC's own inefficiencies that will drop its output to just under 30A. In other words, your 60A CC is able to be powered from a lot more than 600W of panels. I have two Morningstar TS-MPPT-60 CCs that are each fed by 1020W of panels, and each CC charges four golfcart batteries in series/parallel at about the maximum recommended charge rate 0f 13%. FLA deep-cycle batteries should ideally be charged at between 5 to 13% of their 20-hour Ah rating.

Don't forget to keep all your DC cables short and fat to minimize voltage loss under load. If you need further good advice, it's worth your while to read the Northern Arizona Wind & Sun forum - there's enough expertise and experience there to answer any questions you may ever have.

John
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Old 10-03-2016, 01:47 PM   #3
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Originally Posted by Iceni John View Post
A 60A MPPT charge controller can provide a maximum of 60A into the batteries, regardless of battery system voltage. If you have a 12V battery system it can provide about 888W (60A x 14.8V); if you have a 24V battery system it can provide twice that wattage at the same 60A maximum current.

A 600W PV system will not usually produce 600W of electrical power - it will typically produce a maximum of about 3/4 of that under most conditions, i.e. you will see about 450W from the panels most days. 450W divided by 14.8V battery charging Absorb voltage (needed for Trojan T-105 batteries in a 12V system) is about 30A, less the CC's own inefficiencies that will drop its output to just under 30A. In other words, your 60A CC is able to be powered from a lot more than 600W of panels. I have two Morningstar TS-MPPT-60 CCs that are each fed by 1020W of panels, and each CC charges four golfcart batteries in series/parallel at about the maximum recommended charge rate 0f 13%. FLA deep-cycle batteries should ideally be charged at between 5 to 13% of their 20-hour Ah rating.

Don't forget to keep all your DC cables short and fat to minimize voltage loss under load. If you need further good advice, it's worth your while to read the Northern Arizona Wind & Sun forum - there's enough expertise and experience there to answer any questions you may ever have.

John
Thanks John. I appreciate the response. I'm still a little lost when it comes to the charging rate. How does one accommodate the ideal 5-13% ah charging rate? The last thing I want to do is ruin my batteries with the incorrect charging rate. And will this rate change based on the size of the battery bank I use? In a nut shell, I'm trying to figure out what batteries to get for this system.

Thanks!
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Old 10-03-2016, 02:39 PM   #4
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If for convenience you assume a 10% charge rate, your 30A charge current from the CC would nicely charge a 300Ah battery bank, which is a little more than two golfcart batteries in series and parallel (they would produce about 225Ah at 12V). Four batteries would be towards the low end of the recommended charge rate with 600W of panels. Why not get some more panels? As long as their voltage matches what you already have, they should play well together.

John
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Old 10-03-2016, 04:27 PM   #5
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Great, thanks! Theoretically we could go to 800 watts with this kit but not sure we have the rooftop real estate. We will see how things go. Can always expand later. Thanks!
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Old 10-03-2016, 05:30 PM   #6
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I had a 10kw generator picked out to use on my bus, think now I might be better off investing that thousand dollars into my solar bank, that way I don't p!$$ off my neighbors by running a noisy generator, not to mention the savings by not having to buy gasoline/diesel/propane to run it.
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Old 10-03-2016, 07:59 PM   #7
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I had a 10kw generator picked out to use on my bus, think now I might be better off investing that thousand dollars into my solar bank, that way I don't p!$$ off my neighbors by running a noisy generator, not to mention the savings by not having to buy gasoline/diesel/propane to run it.

You mean your battery bank you don't run off solar you run off the battery's. Unless you have 4500 watts of solar and tracking system on it plus your in texas or mexico and its just blistering hot out. your always going to want a Gent set. There so versatile out of the box. They have 110 and maybe 220, there governed to run the load required so there very efficient. if you use a propane one like I do there is never any work to be done to them because there is no fuel to plug up a carb . propane can set for 100 years and still be as good as the day you got it. Solar is good for boon docking your running a led light to read abook and your running your full size fridge at 6 amps and you only need a couple deep cycles. plus if it gets cloudy you can start the bus fro an hour and top off the batterys and go back to quite. Home depot sells a propane gen set its green. they sell them on ebay as well. I have had one on my boat for years now. it just works perfect and starts every time. plus if anything ever happens to it i can go return it and get another one any where in the country. Just my thoughts on solar. its just not quite here yet. $1 a watt that you can only get .5 of awatt on a great day for 5 hours? battery storage in lith ion is so expensive tesla can't even afford it. Think small loads and try not to use an inverter if you can. pull right off the 12 volt batterys. Serious solar plans and thousands of dollars changes the whole game.
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Old 10-03-2016, 08:28 PM   #8
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Well yeah.... I just lumped it all together and called it solar bank. My water pump will run off 12v, water heater can run 12v/120v/LP, looking at a 3 way fridge as well but that's for down the road... tank heaters go 12v/120v. So the inverter would only be for loads that are 120v only.

This is the genset I had picked out:
Duromax 10,000-Watt Dual Fuel Electric Start Portable Generator

I can probably find a cheaper one elsewhere if I look around but at a minimum I want 10kw with a 50 amp outlet to plug my shore power cable into.
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Old 10-03-2016, 09:20 PM   #9
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I have 480 watts of solar, a 60 amp MPPT controller going to four 6 volt 230 ahr batteries in series/parallel for a 12 volt bank. I modified an upright freezer from HD to make it a more efficient fridge running on 110ac. I have a 2000 watt pure sine inverter and I love it all.

To monitor the batteries I use a victron BMV-702 and it works great. On a sunny day mid-afternoon, i've seen 440 watts of power reaching my batteries. Most partly cloudy days I average about 350 watts for six or seven hours. My panels are "house size" 96 cell panels (2) and I mounted them flat... not screwing around with tilt.

If I wanted to power a 40ft RV and all the accessories you might find on one, I would need that 2k system. But with what I have, I can handle the fridge, computers, cell phones, lights, pumps, coffee pot and cook on an induction cooktop. Mind you, I will be frugal but I think I can get along fine with what I have.

I plan to boondock and if I run low on power or hit a stretch of rainy weather, I'll plug in somewhere or find a campground with power. I personally don't want to use a gen set.

Best of luck!

Ross
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Old 10-03-2016, 09:41 PM   #10
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Alleycat, for what you're doing you could easily get away with solar and propane. Skip the gennie. They're loud and obnoxious.

The three big typical electrical draws for any house are the water heater, electrical range and air conditioning. The only one of those that makes sense to run off of a generator is the AC, which you didn't list as a load.

Running a water heater or range from a generator is a silly affair. You get this great fuel (gasoline or propane) that creates loads of heat, then you waste 90% of the heat to produce a bit of electricity, then you send it across wires that waste more energy (line loss) to produce more heat at the end... Same thing with a water heater. Just burn some propane for gosh sake!

A reasonable solar system would suit you well. I run my small fridge year-round off of 600w of solar panels and a 455Ah battery bank. Both have paid themselves off several times over compared to the cost of a generator and the required fuels. My lights always work, my pumps always work, my fans always work, my stereo always works. I can run a miter saw off of my 2000w inverter. Heck, I even ran a cement mixer off of the inverter! Mind you, it was a beautiful sunny day which helped keep things running along.

Despite what naysayers be sayin', the cost of solar has come down to an incredibly reasonable price. It took 1.5 years for my solar to make sense over a generator. That ain't bad. By no means do I have endless energy, but even living up north there is ample sun to make it worthwhile. I dunno.. it was an easy choice for me.
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