RV Solar Series: Which first, solar or lithium?

RV Solar Series: Which first solar or lithium? My install could have been done, either way. There are good reasons to put in better batteries first and there are good reasons to install solar panels before upgrading the batteries. I learned lots of things that I wouldn’t know had I done both at the same time or had I done lithium batteries before I installed solar panels.

Was the solar install a mistake or should have we installed lithium batteries before solar? 

We already had a good battery, in-fact three years ago, it was the best we could hope for, and it came with our RV without any additional expense.  The question was how to keep it charged.  We discovered on our first big trip to see the total eclipse that keeping the battery full was a daily effort.  Last year when we were boondocking and gathering data for our solar install, we measured our usage every day and recharged using our generator.  This year we had solar and it makes a big difference in re-charging, assuming sunshine.  As you could see in previous articles if the sun doesn’t shine we have to turn our generator on to recharge our battery.

Theory is part of the scientific process. What would have happened if we didn’t get solar but instead (spending lots of money) first installed a big lithium battery bank and used the generator to recharge?  Well were going to have to stick with theory only rather than the scientific process. Since I already installed solar I can’t test the theory.  At least we won’t be able to, perhaps you might test it, but I’m not going to give up the solar just to test the theory.

It also depends on how you camp.

We want to be independent of electrical power for extended periods and we live in the RV full time.  So for us, we have been building as we go, adding incrementally.  What if instead, you were only using the RV for pleasure trips. Maybe you camp during the summer for a few days at a time?  Or, what if you were living in the RV but moving more frequently?  Or perhaps, what if you lived in the RV but only a few days a year were without shore power?  For each of the above circumstances, the answer might be different.

For us, if we had a big lithium battery that would go four days without depleting the charge, in the summer, and then we started our big generator, without solar, we would only have to run our generator for a recharge every few days.  

Numbers, how about some numbers: 

Ok, we started our solar quest with the goal of creating 250 amp-hours per day, 100 amp-hours used at night and 150 amp hours while being awake.  If we wanted only to recharge every four days we would need a battery bank of 1000 amp-hours. (I have friends with 10 lithium batteries, total weight 300 pounds, 1000 amp hours)  At the end of the four days, our battery would be empty.  Then at the end of the four days, we would have to run our generator to produce for more than eight hours to replace the energy used over the four days.  This assumes a 120 amp per hour charge rate.  Of course, you could go with about 300 amp-hours of lithium and run the generator about two hours a day, rather than eight hours after four days.

If instead of having a 120 amp per hour recharge rate you could have a bigger charger hooked to your generator (our generator big enough to do this) and you could recharge lithium batteries at an even faster rate.

Compared to lead-acid batteries, the lithium battery would be recharged in eight hours, lead-acid batteries given the same capacity isn’t even a practical comparison because this would be about 1200 pounds of lead.  (remember a lead-acid battery bank can only be discharged to half before they incur damage, even if it were possible to carry an extra 1200 pounds of lead in your RV, it would take almost two to three days to recharge because lead-acid doesn’t like to accept a charge at anywhere near as fast as lithium.  

What about the vacationing camper.

Then the big lithium battery answer isn’t so obvious unless you want to first talk about weight savings. Quick recharge rate still applies, and weight savings is even more important in a lightweight RV. So lithium batteries recharged quickly on a small generator also makes sense.  

What if your camping style included shorter four-day stops, followed by one day at a location with shore power.  If you had a lithium bank big enough, (I have friends with 10 lithium batteries, total weight 300 pounds) you would not need solar or a generator.  Instead, you just stop and recharge every four days.

For us, it is about balance

Since we have enough solar to replace our used amperage on a daily basis (assuming sunshine) we don’t need ten lithium batteries.  We can also recharge with our generator.

How Much Lithium

So the next question for us is not only lithium but how much lithium. If I only wanted to replace our lead-acid the answer is easier, but when I assumed expanded use of electricity the answer isn’t as obvious. Three lithium batteries would double our battery capacity, in theory, I could then bridge oneor two cloudy days and get a full recharge on the following day. My 700 watts of solar could recharge a full two days of discharged lithium due to the faster recharge rate, but the same solar is equal to one full day of discharge on lead-acid. While it is “topping off” the battery in the float stage I have lots of extrasolar power in the afternoon to do other things with, but that is not the subject.

Air conditioning?

Six 100 amp lithium batteries would be able to bridge multiple cloudy days or could do something that was beyond my belief only one year ago.  Air conditioning is not outside the possibility, especially if I double the solar panel array. With twice the solar and a high-efficiency air conditioner, the solar might just be able to keep up with the electric demand, while the sun was shining.  Or with the same six lithium batteries, we could have air conditioning when we were sleeping at night.

I am at the end of the worst solar day that I have experienced in the RV.  Totally I collected 900-watt hours of energy. If my panels were one hundred percent efficient I should be able to create 700-watt hours in a single hour. Typically I create much more than twice that amount each day.  As you can tell from the numbers, it was a very cloudy, rainy day. If I had twice the solar array, today I could have created 1800-watt hours today and had full lithium on a cloudy day.

Now that is something to think about.

Update: June 27, 2020, In our new RV we installed a new lithium battery before we installed solar. To make a long story much shorter both are important. But what we didn’t fully understand was that a lithium battery is much easier to charge than our old lead-acid battery. Here is part of that story. Hybrid Mongrel Battery and Massive Electric Bucket

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