Solar: If you had to chose...more batteries OR more panels?

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gruzzy47

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Jun 29, 2015
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Would you rather have 400 watts of panels and two deep cycle batteries (225 amp hours) OR 200 watts of panels and four deep cycle batteries (450 amp hours). 

I've got space on the roof for the panels, no problem, but I'd have to do some serious rearranging to add two more batteries.  I'm leaning more towards 400 watts of panels. 

My thought is that 200 watts of panels runs the risk of not keeping all four batteries charged enough. 
 
My thought is that if I had a generator, I would go with more batteries, but if no generator, I would go with more panels, but the second option would limit your power available.
 
The unknown factor here is your normal power consumption. Without knowing that we're just guessing at what would be most helpful. If you find that you're often running your house-batteries down overnight, more battery capacity would probably be more beneficial than adding more panels. If your batteries normally have a healthy charge in the morning, you're probably fine as you are.

Adding additional solar panels can be wasteful if your battery-bank doesn't have enough AH capacity to store all the energy generated by the panels. It's a three way balancing act - AH capacity, charging capacity and consumption. You really have to look at all three. We're big fans of solar, because we do a fair amount of boondocking, but solar is oftentimes hit or miss - depending on the weather and camping environment. In most cases, I think RVers could benefit most by installing more batteries.

Kev
 
Give you a feel.

My stick and bricks is powered on 400w of solar, 4000w inverter and 820amp/hours of batteries. I've been this way for over 20 years.

As for the RV I'm a mere 45w solar, 1,200 watts inverter, and 2 standard 12V deep cycle batteries. My power requirements are fairly basic for the RV.
 
The keys to the choice are your daily power consumption and the typical amount (hours) of sunlight where you are. The solar panels aren't really a direct power source - think if them as battery chargers. You need enough batteries to supply your daily power consumption needs, including some reserve for rainy days. One small panel will charge a huge battery bank if it gets enough hours of direct sunlight. More panels will gather more solar energy per hour, of course, but if there are 7-10 hours of good sun most every day, you probably don't need a lot of panels (watts) to get a full charge.

In general, then, more battery amp-hours is more useful than more panels. At the extreme, lots of panels and little or no battery is all but useless: you generate lots of power but have no way to store it, so the excess power is wasted. Conversely, a large battery can store lots of energy, even if charging is relatively slow.  The right balance between the extremes is the combination that stores at least as much power as you use every day, and replaces that same amount on a typical day of solar charging.
 
Keep in mind that discharging batteries below 50% state of charge can result in significantly shorter battery life.  So, a 120 amp hr battery would be good for 60 amp hrs on a consistent basis.
 
I would do both in this order.

Matched set of batteries.
Add solar panels as you have the budget.

A 100 watt panel is about 110 bucks on amazon if you have prime.

That being said I would go for the batteries first.

 
The "Achilles heel" of all solar systems is sun light.

Put several cloudy and stormy days with a long winters night and you may wish you spent the solar panel money on more batteries and a wind generator.

I live in California and they keep telling us that it may even rain here !

More batteries is what I want, I'm going to convert one of my storage compartments to a second battery compartment.
 
A lot of info is needed before making choices for a system. What do you have now, what does it do or doesn't do, what kind of conditions do you face are all things to consider.

Extra panel is great for not so perfect conditions if your batteries last long enough for you now. It takes a lot of extra solar to provide for your needs when it is overcast. Extra battery holds you over in bad weather longer but without enough solar, it's easy to fall behind on a big bank.

Look for what you need for the answer.
 
gruzzy47 said:
Would you rather have 400 watts of panels and two deep cycle batteries (225 amp hours) OR 200 watts of panels and four deep cycle batteries (450 amp hours).

As already stated by others, I would calculate my average overnight power usage (worst case) and how much power I expect from my solar panels on a less than optimal day and go from there.  I prefer to have enough stored power to last a couple of days and created a battery bank to achieve that.  Charging that bank from solar is highly dependent on the "sunshine" that is "available" to you.  I spend most of my time in the southwest so there isn't a shortage of power available. If I were somewhere else, it might be advantageous to have an unusually large PV array to capture as much power as possible (in the low light/short day scenario that is common).

I would also go with 6V batteries and not 12V "deep cycle" batteries.
 
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