How Much solar to Add??

Last winter with Roy in mind, I took the 8-D down to 12.1v resting and put a 220w system on it. I think it tickled it for the 5 hours of brilliant sun available that day, under charge it got up to 13.1v. The panel had only replaced half what was taken out and that was close to 1-1 watt- AH.

So to me it's a watt to AH ratio that will get the job done in a worse case scenario. We run 2w per AH and never have had a issue. The normal weather has been 6 hours of sun in the morning and cloudy afternoons, so my charging has to be done early on. It's easy with a 2-1 ratio and the panels tracking.

So rule of thumb is a good place to start but in the end it is your thumb that rules. Set up for your situation and needs.

If it happens that your daily AH consumption is 120AH, and you have a bank of 240AH, then yes, you will be needing to do 50-100s every day. You can only do 50-90s with gen/charger so you need solar.

How much solar it takes to get 120AH a day "depends" (latitude, location, time of year, panels flat, tilted, tracking, etc. not to speak of how long you run the gen in the morning before turning it all loose on the solar) but say you have that much solar.

You are now at the so-called magic rule of thumb one for one solar/battery ratio IF---somehow you can get 120AH a day out of 120w solar (have to be in a tracking contraption in the summer down south)

So you buy two more batteries to get you by when the sun fails to shine for a day. You still use the 120AH but now you only need to do 75-100s every day. Same solar does that, no change there.

But now you are no longer obeying the rule of thumb! Yipes! You only have half as much solar as you are supposed to have for that much battery! Oh no, you are going to die! Never mind your solar is still doing the 120AH daily that you use.

Lets take a poll,...
How many believe even 1/3 of whats in the post below :)

wintersun wrote:
Ideally the batteries should not be drawn down more than 50% before being recharged. With 240 Ah that means a draw down of 120 Ah and for that 100 Watts or solar panel is all that is needed. I have that and the two 100 Watt panels recharge the batteries in only a few hours and the rest of the day are not doing anything. The rule of thumb of 1 Watt solar for every 1 Ah or battery to charge was on right on the money for us.

A heater fan is not an energy hog by any means. The fridge and lights are what tend to draw the most current. Upgrade the tungsten lamps to LED's and you can reduce their energy consumption by 90%.

By all means install a Trimetric or other digital charge meter so you will know exactly how much your systems draw in a 24 hour period.

If you add more than 200 Watts of panel output you should add more battery capacity to your bank as well or the extra output will not provide any additional benefit.

Hi,

Led's on EBay that have a voltage controller are on the order of $3 each including shipping. I do not see that as expensive.

LEDs can be had extremely inexpensive any more. Most are under $2 a unit or not more on ebay, usually with free shipping.

Wintersun,

Thats helpful. We rarely utilize the lights and I have been researching LED but they aren't cheap. Still I will eventually replace them. It was on my mind about the batt's being full and generating to much power for no purpose so I don't want to over size and pay out alot that I dont have to. I'm not concerned about clouds or shade as we always toat a genny and we will be downsizing to the lighter 2000's. I have begun researching 300 watt kits that are also easily expandable. So if its not enough I will add a panel. I do fortunately have a lot of real estate on this roof.

Thanks for the input!

Ideally the batteries should not be drawn down more than 50% before being recharged. With 240 Ah that means a draw down of 120 Ah and for that 100 Watts or solar panel is all that is needed. I have that and the two 100 Watt panels recharge the batteries in only a few hours and the rest of the day are not doing anything. The rule of thumb of 1 Watt solar for every 1 Ah or battery to charge was on right on the money for us.

A heater fan is not an energy hog by any means. The fridge and lights are what tend to draw the most current. Upgrade the tungsten lamps to LED's and you can reduce their energy consumption by 90%.

By all means install a Trimetric or other digital charge meter so you will know exactly how much your systems draw in a 24 hour period.

If you add more than 200 Watts of panel output you should add more battery capacity to your bank as well or the extra output will not provide any additional benefit.

Well now I'll say what I really thought,...dumb question.
Perhaps I should have answered,....
"300 watts" Its enuff for me, so it should be enuff for you ! :)

In reality, 300 watts will be plenty for me in AZ, but I'm not sure 1200 would be enuff here on the coast in Oregon.

Give him a break, he's only been here 10 years.

True

He could have searched and spent much time finding info that related to his personal situation or as he did, give us something to talk about. :)