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RVing message boards => Tech Talk => Solar => Topic started by: schoolsout2 on February 24, 2017, 06:12:54 AM

Title: What can I run?
Post by: schoolsout2 on February 24, 2017, 06:12:54 AM
I recently purchased a used MH that has a solar array on the roof.  The former owner installed it.  I was told it is 1kw.  I have 6 house batteries and a 2800 watt inverter.  I wonder what I can run and for how long.  Is this 1kw/hr? At 12 volts is it putting out 83 amps?
Title: Re: What can I run?
Post by: prfcdoc on February 24, 2017, 06:22:40 AM
That's a pretty impressive system. A little more information would help. Are the batteries 6 volt, in 3 pairs or 12 volt? I would guess 6 volt but with that much solar panel it's feasible that they're 12.
Title: Re: What can I run?
Post by: schoolsout2 on February 24, 2017, 06:49:55 AM
They are 12 volt.  There is the 100 w panel that was original and 6 150w that were added with all the additional hardware.
Title: Re: What can I run?
Post by: Gary RV_Wizard on February 24, 2017, 07:20:59 AM
The panel size has little to do with what you can run.  Basically the solar panels are a battery charger and you "run" off the stored energy in the batteries. So what you can run and how long depends on the amount of charge in the battery bank at any moment. The battery amp-hours are the limiting factor on that, so you want to know the total AH of those 6 batteries, and monitor how well the solar charging keeps them charged, i.e. the percentage of full charge, known as SOC (State of Charge).

A lot of solar panel watts basically means you can charge the batteries more quickly when the sun shines, but the direct solar power (that 1kw) is seldom consistent enough to power things without the battery as a buffer.

The 1 kw is a rate, so yes it is 1 kw/hour IF (and only if) the sun shines brightly on the panels from directly overhead for the entire hour.
Title: Re: What can I run
Post by: schoolsout2 on February 24, 2017, 07:44:21 AM
Thanks for the confirmation.  If I understand it correctly, the panels will charge the batteries faster since there are more of them, but I am limited by the amp hrs of the battery bank and of course the sun.
Title: Re: What can I run?
Post by: prfcdoc on February 24, 2017, 09:40:14 AM
Since they're 12 volt batteries the AH are additive. Hopefully the batteries are all the same because it's not desirable to have batteries with different AH in the same group. When you add those together you get the total AH of which you can safely use about 50% without recharging. Any more than that and you can damage your batteries. There's a lot of information in the forum library about batteries and electricity usage if you need more guidance.
Title: Re: What can I run?
Post by: Gary RV_Wizard on February 24, 2017, 10:54:02 AM
Think of your batteries as a water tank. Water pours in one side (the charging) and runs out the other side (the house electrical load, direct or via inverter). The amount on incoming and outgo varies, of course.  You can take more out than comes in, but only for a limited time. The size of the tank determines the amount of cushion between "in" and "out", i.e. the time limit.

If you are drawing less out than is coming in, you are in effect running off the solar panels, even though the load is wired to the batteries. That probably happens in peak sun periods.  Some of the time, though, you will be drawing more out than is coming in. In fact, there will be zero incoming for much of the time, so there is a continuous net loss even though the load may be small.
Title: Re: What can I run?
Post by: Kevin Means on February 24, 2017, 02:27:46 PM
We have the same solar setup on our Tour (six 160 watt panels) and here's what I believe you're going to find. Your six panels will significantly reduce the time you need to run your generator, but your house-batteries are going to get deeply discharged if you rely on solar alone. Your residential fridge is the primary reason. How far north or south you camp will also have a lot to do with it.

We initially had the same battery setup (six 12 volt AGMs.) According to the battery manufacturer (East Pen) those batteries are rated at 105 AH (each.) We also probably have the same (or very similar) appliances (I.e. consumption.) Here's what we found while boondocking in our Tour (We boondock a lot.)

When starting out with a full charge on a sunny winter day (the season solar is relied upon most) our panels would keep our house-batteries fully charged until about 3:00 PM. Then they'd discharge throughout the late afternoon, evening and morning hours as we used power. In the morning, our battery-monitor would indicate a SOC of about 60%.

The batteries can survive deep discharges like that for awhile, but the more often it happens, the more it will shorten their lives (And those are expensive batteries!) Our solar panels would have the batteries fully recharged by about 1:00 PM (on a sunny day) and keep them charged until about 3:00 PM, at which time the discharge cycle would repeat.

I didn't want the battery-bank discharging so deeply, so I added two more AGMs. Now the deepest discharge we see in the morning is about 75% - usually closer to 80. That's plenty of power to cook our breakfast in the microwave and brew a pot of coffee in our 12 cup coffee maker - all on battery power. I wouldn't have attempted that with a 60% SOC.

After adding the two additional batteries, our solar panels, which were all flat-mounted at the time, had the batteries fully recharged by about 3:00 PM, so the system was well balanced. I have since installed tilting mechanisms for the solar panels, and now the batteries are fully recharged by about 12:30 - 1:00 PM.

Title: Re: What can I run?
Post by: schoolsout2 on February 25, 2017, 02:41:28 PM
Thanks Kevin, that is great information. Now I wonder if you have 2 macerator toilets?  If so how fast does the black tank fill up?
Title: Re: What can I run?
Post by: Kevin Means on February 25, 2017, 08:10:44 PM
Yes, the 42QD is a bath and a half, and we have two macerator toilets. Our 51 gallon black water tank is the first thing to fill up when boondocking, not only because there's two electric toilets, but because the half bath's sink also drains into the black tank. I'm not sure where the kitchen sink drains, but it's so close to the half bath's sink that it might also drain into the B/W tank.

Our 105 gallon grey water tank rarely has more than 30 or 40 gallons in it - even after several days of boondocking. The grey tank capacity in later model Tours was reduced to 71 gallons, but that should be adequate. I wish I could reverse the black and grey tank capacities in our coach, but since that would be a plumbing nightmare, I think I'm going to put in a dump valve and just tie the two tanks together.

FWIW, when our daughter camped with us (she's in college now) we found our 90 gallon fresh water tank to be barely adequate for a week of boondocking. When it's just Cyndi and I, 90 gallons is fine. In later models, Winnie reduced the fresh water tank's capacity to 85 gallons, so it may be more of an issue for you, depending on how you camp. I ended up installing a second 25 gallon fresh water tank, which has really helped us extend our boondocking trips.

Title: Re: What can I run?
Post by: schoolsout2 on February 26, 2017, 08:40:21 AM
The black tank is the main issue.  We do Habitat for Humanity builds and often have power and water.  Having to dump every 4 days will be an issue.  I will check the plumbing diagrams.