So, we've been boondocking on private property just outside Phoenix since January 2, and we've been paying close attention to our solar power coming in and our power going out.
For our newer readers, here is a link detailing our system and how we came to have what we have: Our Electrical System - A Phased-in Approach. If you are new to RV electrical systems, you may not understand much of the rest of this entry. If you want to learn more, you can go to this page - RV Electrical Systems - which starts with the most basic information and gradually gets more complicated depending on how much you want to know and whether you are considering solar in the future. Warning: If you try to read it all at once it may confuse you even more or put you to sleep.
The short version is we have a built-in 5500-watt propane generator, 4 Lifeline 6-volt AGM batteries (600 amp hours), a Xantrex RS3000 sine-wave inverter/charger (3000 watts), and four 100-watt solar panels on the roof with a solar controller in our storage area near the batteries. The batteries and inverter were installed in 2007, and then we added the solar panels and solar controller in 2008 once we understood everything better.
Since we haven't changed anything since 2008 (except for replacing the batteries in 2013 and replacing all our lights with LEDs), we were curious as to how everything was holding up. It seemed to be doing okay, but it wouldn't hurt to do some easy testing.
Our Electrical/Solar System Monitors
Below are our system monitors - the Xantrex inverter/charger system control panel (SCP) is on top, and then we have our Trimetric 2025 (the current model is the 2030), and our Solar Controller monitor.
We use the Xantrex SCP to turn the inverter on and off. As it is an inverter & charger, the functions work independently so we can also use it to turn the charger function on and off (but we always leave the charger on). When in "invert" mode it tells us the voltage of our batteries AND how many amps are being used in total by the inverter and anything else that is plugged in that the inverter is powering via the batteries. That's what an inverter does - it takes the 12-volt battery power and "inverts" it to 120-volt AC power so that it can be used to run items that can be plugged into regular electrical outlets without running a generator or using "shore power".
The Xantrex SCP also tells us what charging mode we are in. It has a three-stage charger to prevent the batteries from being over-charged, and the stages are "bulk", "absorption", and "float". When running the generator, the charger will charge at its maximum rate until the batteries are charged to 75% of their capacity - that's "bulk" mode. The charger is programmed for the type of batteries we have (AGMs) and the number of amp hours of capacity we have (600). It's very important that your charger (whether it is an inverter/charger or a converter which most towables have) is a three-stage charger AND that it is programmed for the right type of batteries as different types of batteries are charged at different rates. In other words, if you replace regular wet-cell batteries with AGMs, you have to re-program the charger to handle AGMs or you will kill them.
Once the batteries are charged to 75% (according to our inverter/charger manual), then the mode changes to "absorption" in which case the amount of charge going into the batteries from the generator is reduced. Sometimes, we'll let the generator run for a few minutes (maybe up to a half an hour) in this mode, but generally, we turn the generator off and let the solar panels get the batteries fully charged. Because the charge is going in at a slower rate, but the amount of generator fuel used is the same, using the generator to charge the batteries becomes less efficient. And if we ever let the generator run until the charging mode goes into "float" (we don't), then it would be even less efficient because the charging rate slows way down in the "float" mode. "Float" is more of a "maintenance" or "trickle" charge.
We always want to try to get our batteries back to full charge as much as possible, and because of the inefficiency of doing that with the generator (it could take several hours due to the three-stage charging), solar is the best way to do that while continuing to park off-grid.
The second monitor in our line-up, the blue one, is our Trimetric battery monitor. The Trimetric is connected to to the batteries via wires that are also attached to a "shunt". The "shunt" interprets information from the batteries which is then displayed on the monitor. The Trimetric will tell us the number of "amp hours used" out of our 600 of available capacity. By pushing a button we can also get our battery voltage, the current "net" amps going in or out of the batteries, and the current status of the battery charge as a percentage (the ratio of amp hours available to total amp hours of capacity). In order to keep the batteries lasting as long as possible, we don't want to let them get below 50%.
The bottom monitor is our Solar Controller monitor. The solar controller "controls" the charge going into the batteries from the solar panels. It can boost the charge but, like the inverter/charger which controls the charging of batteries by the generator, it also acts as a three-stage charger to protect the batteries from being over-charged by the solar panels (which can happen). It uses the modes "bulk", "taper", and "float" and also tells us what mode we are in as the batteries are being charged by the solar panels. In addition, it displays the number of amps the solar panels are producing at any given moment and provides battery voltage as well.
The battery voltage is provided on all three monitors and they always match (occasionally one reading may be off by a tenth of a volt).
So, by using the combination of monitors, we always have a pretty good idea what's going on and can manage things as necessary.
Today's Inverter Testing
With the inverter on, we had the following plugged in: Two Samsung energy efficient TVs, two DirecTV DVRs (which use a bit of power as they re-configure upon start-up), our laptops (charging), our phones (charging), our Verizon Broadband Modem, our Verizon JetPack (charging), and our Lambright electric recliners. We were using almost 18 amps of power per hour. So, we started unplugging stuff to see how many amps each item was using.
We could garner that information from either the Xantrex inverter monitor or the Trimetric.
Actually, we started by turning off the main AC breaker and just turning on the inverter so that nothing else would be using power. The inverter alone was using 4.8 amps of battery power. When we talk about "amps being used" it really means "amps per hour".
Surprisingly, using our laptops while they were being charged was costing us another 7 amps with Linda's older 15-inch laptop using about 4 amps by itself. The laptop amps depend on whether or not they are open, closed, charging, or fully charged. They, of course, use the most when they are open, being used, and are charging.
The remaining six amps included about 1 - 2 amps of "phantom draw" (also called "parasitic draw") that comes from things like the clock on the microwave and other minuscule draws that add up. Most of the rest of the amps were from our two DVRs and TVs. So, we were able to pinpoint some power hogs and we'll manage those better.
We unplugged the bedroom TV and DVR since we never use those when boondocking, and we unplugged the living room TV and DVR so they won't have any draw during the day and then we'll plug them in at night when we use them. We got our amps down to under 10 and half of that was the inverter itself.
So, it looked like our 10-year old inverter/charger (which is no longer made) is still doing what it is supposed to be doing. Of course, we keep the inverter turned off most of the time when we are boondocking, but when it is on, the less battery draw we have, the better.
When the inverter is off, there is virtually no draw on the batteries. We do have 1.5 - 2.0 amps of "phantom draw", but there is no other drain on the batteries unless we turn on some lights. The LED lights draw about 0.1 amps each, as opposed to our old incandescent bulbs which drew about 1.0 - 2.0 amps each. And when we turn on the water, our water pump uses 2.0 - 3.o amps. When we say "uses" that means that's what it would use over over an hour, but since we just run the water pump for seconds at a time, it actually uses only fractions of amps.
Today's Basic Solar Testing
Next, I went up on the roof and cleaned the solar panels while Linda watched the solar monitor inside. We immediately gained 2 amps of solar input per hour just by cleaning the four panels with a wet towel.
We were getting in between 16 and 17 amps per hour at the peak time of the day around noon. So, we'll get anywhere between 12 - 17 amps from about 10:00 a..m to 3:00 p.m. assuming there are no clouds at this time of year at this location.
Then I threw a towel over each panel. Each time I did that, the total amps going in went down by 4 to 4.3 amps. So, we were getting in about 4 amps per hour for each panel. That was good news as it meant all the panels were functioning and producing about the same amount.
A 100-watt solar panel in peak sun should be getting in about 6 amps per hour. However, that assumes optimum sun. In the winter a panel that is flat on the roof and not tilted will lose 30 - 40% due to the low sun angle. The 6 amps would be for a panel at the perfect tilt angle toward a low winter sun OR a panel that is flat during a higher, overhead summer sun.
Our panels are flat and we don't tilt them, but they are on a section of roof that is slightly pitched. And currently we are parked so that the panels are ever-so-slightly pitched toward the lower sun, so the 4 - 4.3 amps per panel seems about right.
So, let's say we get an average of 14 amps of solar for five hours a day - that's 70 amps that our batteries are re-charged each day under perfect conditions .... this time of year at this location. We probably get in another 10 - 20 amps total in the morning and late afternoon. So, as long as we don't use anymore than 80 - 90 amps per day, our batteries should get back to full charge by just using our solar.
Of course, we tend to use more than that, especially during this time of year when I'm watching a lot of college basketball. So, we typically have to run our generator once a day for an hour or maybe twice a day for a half hour each to put the bulk charge into the batteries. And then we can let the solar do the rest. If we have cloudy days, the generator may have to pick up more of the workload.
In the summer, when we're getting in 6 amps per panel for a good six hours a day, we'll get nearly 150 amps of charge each day from our solar panels, and we've gone a couple of weeks without ever turning on the generator. Though it would be nice to have a couple hundred more watts of panels, we probably haven't done it because the panels we have, plus just a little generator time, tend to get us through most of the time.
It hasn't been five years yet since we replaced our Lifeline AGM batteries, but they seem to be holding a charge really well. I expect at least a few more years out of them.
So, that's our solar system review with some simple testing. For being 10 years old, everything is working great.
Parking off-grid is a matter of understanding your systems, and those that become boondockers tend to know their RVs better than those that always park with hook-ups. Through experience and learning the knowledge and confidence increase and the opportunities and freedom expand in this wonderful life we call full-time RVing.