It’s the middle of the summer and what better time to talk about off-grid solar power. The days are long and the sun is bright. Lots of power to harvest for sure. However, you are never running anything directly off the solar panels. All of that incoming power is stored in your batteries. The power you use always comes from the batteries. If it is bright and sunny, you can use a lot of power before your batteries will start to drop.
Typical batteries used for off-grid systems are of the flooded lead-acid variety and these do require maintenance. How often they need it is dependent on usage; we use our system everyday. If you have a summer cottage and are only there for few weeks during the year, you can do maintenance less often.
The main form of maintenance involves adding distilled water to the batteries’ cells. We’ll talk about that in a minute. The first maintenance I want to talk about, which is less common, is keeping things clean.
As you can see from this first picture, the terminals where the cables are connected have large amounts of blue corrosion. This needs to be cleaned as corrosion increases the resistance in the circuit and this is bad when you are trying to maintain a certain level of voltage to your system. In this case, I hadn’t cleaned the terminals since we had initially installed it, which is almost three years.
There are anti-corrosion compounds you can get, and I did get some for this job, but I should have obtained some shortly after doing the initial install. That ended up being on of those things that got pushed way down on the to-do list apparently.
In any event, armed with my battery terminal cleaning spray, steel wool, a rag and a screw driver, I scraped and scrubbed, polished and rubbed until the copper was once again visible on the terminal cables.
I should mention that is highly recommended that you shut off all main breakers in your system before attempting this. Additionally, you need to be very aware of what you are doing. Closing the circuit across the terminals on the same battery probably won’t do you much harm (it’s only 6 volts), but it will kill your battery really fast. If you still have all of your batteries connected together and managed to short-circuit them (in my case, that’s 8 batteries at 6 volts each, adding up to 48 volts) that not only will probably cause a fire, but it is enough to give you a really serious health risking jolt. Be careful.
Take your time, don’t be rushed and pay attention to what you are doing. Simple enough. After you’re all done, it should look something like this.
Now we’re going to talk about the regular maintenance, the one I do once a month: topping up the cells with distilled water. For this job, we’re going to need a few things to make our job easier.
First, of course, is the distilled water.
This is a 4L (slightly more than 1 US gallon) jug. This time of year, in the middle of summer, I can go through almost a full jug with one refill. During the winter, that same jug will last 3 fillings. The batteries are much more active during the summer and they don’t like the cold.
Incidentally, I should mention the sound the batteries make. This isn’t something one thinks about a whole lot when thinking about batteries and solar power. If your batteries are doing well (and it’s not below freezing) you will hear lots of pops and fizzles, kinda like a cross between a low simmer on the stove and the sounds a healthy horse’s gut makes. If you don’t know what that sounds like, I’m sure youtube can help you.
Moving on in our tool list we have an empty, well cleaned yogurt container.
Next up is one of these fancy thinga-ma-jigs. It’s actually a hydrometer and it measures the density, or specific gravity, of liquids. In this case, this one is intended for testing flooded lead-acid batteries. You can also get hydrometers that test how much alcohol is in your wine and beer, for all those wanting to start their own home brewing.
Last, but not least, a working noggin lamp. Some people just call them head lamps. To each their own.
The head lamp is essential because you’re going to have both of your hands busy and you’re going to need some light to look into the cells of the batteries.
The process is really quite straight-forward. I fill the yogurt container with distilled water. I use the hydrometer to suck up a bulb’s worth of water and gently squirt it into each of the cells until they are full. Nothing too complicated, but I’ll give you some justifications for using this method.
First of all, having the distilled water in the yogurt container and not in the jug just makes it easier to fill the hydrometer. Leaving the water in the jug and trying to suck the water out of it directly just becomes more of a pain the more empty the jug becomes.
You could use a funnel and just pour the water into each cell, but then you’re going to have to stop a lot, pulling the funnel out each time to see if it’s full. You don’t want to overfill it. Using the hydrometer allows you to have great control over how fast you are filling the cell and, with the use of the noggin lamp, shows you how much is in the cell at any given moment.
Here is a close-up picture of one of the battery cells open.
From that picture, you can’t really tell how full it is. The bubbles help a bit, but I tell you now, it’s not much easier when you’re actually doing it. So, how do you know when it’s full? Good question.
If you look at the opening of the cell, it has around 2cm (3/4″) of plastic forming a cylinder down to the liquid, with a vertical cut in it. You can see that in the picture above.
The way I have been filling my batteries, I do it until the water just kisses the bottom of the plastic. This way I can easily see when I’m done and I don’t need to sit there trying to judge if it’s actually 3mm (1/8″) from the top, which is next to impossible.
I did take pictures of a full cell, but they all turned out blurry, unfortunately. I included one anyway, as you can still see how the water is just touching the bottom of the cell’s opening.
You also may be wondering about that hydrometer. It’s main purpose isn’t to fill the cells; it’s for testing the health of your batteries. If you suck up regular water with the hydrometer, the little arrow indicator will be at the bottom.
Ironically, pointing at the “water” setting. If, on the other hand, you suck up the liquid from the battery’s cell, it might look something like this:
My charge controller said the batteries were at about 96% when I took this reading so that matches. I will mention that this type of hydrometer isn’t the most trustworthy as all it is, is a float inside the plastic housing; not super accurate for sure. However, what you really want to check is consistency across cells in the same battery and across the batteries as well. If you test all of the cells and you find one that is way off compared to the others, then something is up with that battery. It’s usually best to test your batteries when the charge controller says they are at 100% so you know they should all be full. Also, don’t do your cell testing after you just added more water to them, as the readings will be off. Do your testing first, then start adding more water.
That’s the end of our lesson for today, boys and girls. You can now all be happy battery maintenance experts.