Boondocking without solar, we have done that before but never have we done it this easily. Our battery system is holding us into the second day without recharging so it has met the design goal of two days without sunshine. We now have thirty days of off-grid camping (so far this summer) to prove that not only is boondocking without solar possible, but that boondocking with solar is going to be easier than ever before. In Idaho, our longest run without outside power was eleven nights in a row.
Big Battery – Big Generator
Our average consumption overnight is more than double that of our previous RV. I can blame that directly on our huge residential refrigerator. (this is nothing new) The refrigerator is more than double the size of our previous refrigerator. It runs on electricity that we hold in our battery bank. We now have more than 850 amp hours of battery and our measured overnight consumption is between 10-14 amps per hour. It has been a little less than ten but never more than fourteen. This includes the refrigerator, CPAP, and heat.
If we were to, and we don’t try to, maintain the same consumption during the day as we do at night, this would mean that we would consume 240-336 amp hours every twenty four hour period. If we started with a full charge, we would have empty batteries in 2.5 – 3.5 days. However, we don’t live that way. During the day we use lights, computer and the microwave without regard for the effect on our battery bank. Today while boondocking without solar, we (Tami) cooked two batches of scones in the oven only using only battery power. Before now we have been too timid to try and cook in our electric oven without running our generator. For me, using the microwave from the battery was test enough. The impact on our state of charge was immediate and obvious, but it worked, and then we recharged later with the generator.
Here is a link to the description of my battery system. Massive Electric Bucket
I’m sure I mentioned it, but in case it wasn’t clear, our year 2008 factory-installed solar collectors don’t do anything other than shade the roof. I didn’t expect much, they were too small to begin with and completely unable to contribute much of anything. Right now we are planning our big roof shade (solar) that will be able to (almost, maybe, time will tell) charge the battery while running the air conditioner. That will be the ultimate test when boondocking without solar.
Here is a link to our post describing our stay at Nason Creek. Two parks and a forest
Air Conditioner from the Battery
We will test run the air conditioner from the battery bank soon, I promise. I just need to rewire so that the air conditioner will be fed from the inverter. Right now, to run the air conditioner, I need to start the generator. I started buying parts last week to make this change.
Why would I want to run the air conditioner from the battery?
Well other than to prove that I could do it; I can think of three circumstances that it would be so very nice.
First, sometimes when we are boondocking it is quite warm at bedtime — air conditioning would be great. We wouldn’t want to run the generator at bedtime because of the noise, both for us and for any neighbors.
The second time would be when we are driving. Right now to get extra cooling for the RV, we run the generator — so that we can run the air conditioners while we are driving. Our dash air conditioner, since it is a long distance from the engine, does not work very well. Different RVs and different RVers have different needs, running our air conditioner while driving may not be a need, but sure would be very nice.
The third time we could run the air conditioner is in the afternoon when the battery is full or nearly full. Air conditioners if run at full blast (does not usually happen unless in extreme heat) then each air conditioner would nearly drain one battery in one hour.
So how many batteries — to run an air conditioner?
This answer is simple, each of my batteries, will run one of my air conditioners for more than one hour.
I have nine batteries so I should be able to run one air conditioner for nine hours. Each of my batteries holds about 100 amp-hours of energy, multiply this by the voltage, which is nominally 12 volts per battery, and I have 1200 watts available to use. My air conditioners consume about 900 watts per hour to run. So each battery is able to run one air conditioner for 1.3 hours it is empty.
When we get the solar installed, the solar should be able to run one air conditioner at full blast with no drain on the battery. (assuming the solar was producing adequate input)
One of my design goals was to be able to run my air conditioner all night long when sleeping. All my calculations say that this should not be a problem. We will see next week how that works out.
So how much solar — to run an air conditioner?
Each 100-watt solar panel should produce about 100 watts of energy per hour (in lab conditions). Thus, to run an air conditioner that would draw 900 watts of energy over the period of one hour, you would need 900 watts of solar panels. This would equal the consumption of the air conditioner. Any extra electricity would then go to recharge the battery bank.
Here is a link to our post describing our stay in Northern Idaho. Stunning beauty in Northern Idaho
However, as a caution, you need to understand that solar panels don’t live in a laboratory; they live on your roof. Thus, even if we hit peak output on the solar panel, we don’t expect to be able to hold peak output for very long. Instead, I expect each panel to produce about 500-600 watts per day over a period of eight hours. Each panel should produce about 75 watts per hour. Therefore to hit break-even on running an air conditioner, you would need 1200 watts of solar. You need lots of solar and a big on the battery. Soon–very soon.
When do we run the generator to recharge?
We have been running our generator to recharge the batteries at the same time as the air conditioner is needed to keep the house cool. This is what you do if you are boondocking without solar. Our generator is able to run both air conditioners and at the same time, recharge the batteries and keep the refrigerator cold.
How low did we go?
We have tested our batteries to failure, but don’t intend to repeat that mistake. Our one test was good enough for a lesson learned.
How low did we go? — All the way to the bottom. We used our lithium batteries all the way to failure.
(Not really total failure, but rather inverter cut off. Since our lithium batteries only purpose is to power the inverter; if they are so low they can’t do that, then that is failure).
As you can see from the charts on August 8, 9:08 am we drained our battery bank to the 850 amp “limit”. It is not that the battery was unable to deliver more power, but the limit was hit because the inverter declared a halt to the test.
We also discovered that our automatic generator start wasn’t going to protect us from being dumb (it didn’t work).
I have been using the word test, incorrectly, because if this was a test I would have had much better data, and been watching more closely. What happened is that at 6 am the batteries were ready to charge and I didn’t do that. We used 773 of the available amp-hours during the previous day and night. Two days before, I had started using the lithium battery to recharge the lead-acid batteries. Thus my energy use was higher than normal. Even then my energy draw from the lithium batteries was eighteen amps per hour for the previous eight hour period. That morning I was clicking away at the computer. Then after Tami got up, we turned on the microwave our inverter said enough.
In theory, I already understood what had happened, but now I had experience to go with the theory. Here is the deal with lithium batteries, volts mean nothing until they mean everything.
For a complete description of how Lithium Batteries work here is my previous post on that subject. Ten Lithium Battery Myths and Answers
- August 7, 10 pm, 629 amp hours used, 12.93 volts
- August 8, 6 am, 773 amp hours used, 12.69 volts
- August 8, 9 am, 847 amp hours used, 10.12 volts
As you can see the voltage for the last three hours was in free-fall. We had useful energy until we used it all. The final nail in the coffin was starting the microwave which is a large immediate demand and caused the sudden voltage drop. Previously we had already “tested” down to -867 but the inverter wasn’t hit with a large load while the battery was at a weak state of charge. So, where is the bottom? That day the bottom was at 847, on another day, the bottom was somewhere below 867. Perhaps the bottom is more than 900. I don’t intend to find out.
What did we do?
As you can see from the charts, we started the generator and charged back up to an acceptable state of charge and didn’t hit -773 amps early in the morning ever again. If we had solar, (and assuming we had sunshine that day) we would have never found the bottom. My plan is for the solar is to deliver about 500 amp-hours per day into the battery and that will keep the battery at a higher charge level, rather than visiting the bottom. Transferring energy from the lithium to the lead-acid batteries all night long was a mistake, but it did make starting the generator easy.
Here is a link to our post describing our stay at Tally Lake. Montana Remote