Basics of Solar Power
Lots of people are intrigued by the idea of free electricity from the sun, but it all seems so mysterious they become paralyzed by fear of the unknown. I understand, because that’s exactly how I felt in the beginning. You know the old saying “Necessity is the mother of invention,” well that applied to me. I parked for long periods of time in the desert and ran out of power because my batteries weren’t being charged by the alternator. Since I was in the desert there was an abundance of sun but two things held me back: 1) fear of the unknown and 2) lack of money. So I set up a budget where I set aside $50 a month for solar panels and started studying the web to understand how they worked. I still don’t understand how the panels turn sun rays into electricity, but I discovered that setting up and installing a system is extremely easy. If you can strip and crimp wires, you can install a solar system. Let me show you how. In this article, we will take a look at the basic of solar power, and in a future article we will look at the installation.
As you can see in the above diagram there are really only 3 essential components to a solar system: 1) Solar panel 2) Charge controller 3) Batteries. A fourth piece is the inverter to get power out of the battery, so we will take a quick look at it also.
This is my solar setup. I have a 55 watt and 135 watt Kyocera solar panels and a BZ250 mppt controller, charging a pair of Trojan T105 golf cart batteries. You don’t have to buy everything all at once. I started with a small panel, an inexpensive controller, and used the battery I had on hand, and added to it as I could afford it
Solar panels come in a large variety of shapes, sizes and configurations. At the low end there are cheap panels like the Sun Force 60 watt kit or Harbor Freight 45 watt kit. These are cheap because they are older, less efficient technology. They produce less power for their size than do more efficient panels, which is very important if you live in a small vehicle with limited roof space. They also only come with a 5 year warranty. Most big name-brands offer at least a 20 year warranty, so that tells you something about their quality. If they are all you can afford, then they are worth buying, but my recommendation is that you buy a name-brand panel from a reputable dealer who can help you if you have problems. My first system I bought from Solar Mike at Slab City which I installed myself. I paid more because he charges retail, but I wanted someone who could help if I needed it, and it turned out I did. I had some questions with the installation and Mike was extremely helpful so it all went very smoothly. That little extra money was well spent. When I upgraded my system with a second panel, I was very comfortable with solar power, so I mail-ordered the panel to save some money. I bought it from Northern Arizona Wind and Solar and had it delivered by UPS. When I went to install it I had some questions so I called them and just happened to talk to the owner of the company. It was a new panel that he wasn’t familiar with, so he got a screwdriver, opened up the junction box of a panel on the sales floor, and talked me through the installation. I bought the panel because of their great prices but I will buy from them again because of their great customer service. Chances are you may need some help with your first installation, so that’s why I recommend a name-brand panel from a reputable dealer.
One of your first questions will be what size panel should you get. My answer is simple: buy the biggest you can afford. This is one instance where more is very much better. Size your system for the worst case. For example, there is much less sun in the winter than in the summer, and cloudy/hazy days also reduce your power output. So plan ahead so that on a hazy winter day you have an adequate amount of power and then you will have extra in the summer. You will probably be limited by the amount you have to spend and the room on your roof. The bigger the panel, usually the less they cost per watt, but they can be so large it’s hard to fit them on your roof and they are harder to handle. Panels larger than 135 watts are designed to be used exclusively on house installations, so they are quite large and can’t be shipped by UPS, they must be shipped by truck. That makes shipping much more expensive. My 135 watt panel cost $30 to ship UPS, but a 205 watt panel would be over $100 to ship by truck. Also, large panels must meet NESC code standards and all come with something called MC4 connectors. It’s no problem to wire them into a 12 volt automobile system, but it costs a little more. You have to buy an MC4 extension cord and cut it to get to the negative and positive wire inside (if you cut the cord coming out of the panel you will void its warranty). A 135 watt or smaller panels is designed to work directly with 12 volt systems and will come with a junction box that makes it very easy to wire. A 135 watt panel is probably the ideal balance of all factors. The roof of some vehicles is so convoluted there is nowhere to put a solar panel. In those situations you can leave the panel uninstalled, and carry it inside the vehicle and set it out to charge when you are parked using quick connectors to connect it. Finding a place to store the panels can be hard, so some people use flexible panels for easy storage (see story here).
Solar panels come in different voltages. The majority are around 17-19 volt to be wired into 12 volt systems. But many have a higher voltage to be wired into 24, 48, or 36 volt systems. The higher voltage systems are more efficient so actually work better, but they require a charge controller that can handle that voltage and step it down to 12 volt. They are usually more expensive (I recommend the BZ500 mppt controller for larger 24 volt systems) but they are so much more efficient that they are worth the cost. Just like you can wire two 6 volt golf cart batteries together in series to make them 12 volt, you can wire two 12 (actually 17) volt panels together in series to make them 24 volt.
Here’s the bottom line: For most of us in small vehicles, you probably want to buy a 135 watt (or whatever size you can afford and will fit), 17 volt panel and wire it to a 12 volt controller. I buy Kyocera because they are a huge, trusted Japanese company that will always be there if I need warranty work in 20 years.
After the solar panel has created the power, it is connected by simple positive and negative cables to the charge controller. The charge controller changes the voltage coming from the solar panel to work for the battery. So if it is a 17 volt panel, it steps it down to 12 volt. It also constantly monitors the state of the battery to send it the most power it can without doing harm to the battery. An empty battery can take much more power all at once than an almost full one. For example, a 225 amp hour deep cycle battery at 12.2 volts is 50 % discharged and can easily handle 20 amps of power coming in. But a battery at 12.55 is nearly full and can probably only handle 1-2 amps of power coming in. The charge controller monitors the charge of the battery and reduces it as it fills. If the battery is at 100% charge in the middle of the day, but the solar panel is still producing power, the solar controller will cut out the charge entirely so no power is going into the battery. Then if you turn on a light, drawing 1 amp, the charge controller will then let in 1 amp of power so the battery remains at 100% charged. This is called “Floating.” The battery is full and just floating along. There are three features you want to get in a controller if at all possible: 1) MPPT 2) digital display 3)adjustable float point.
- I strongly suggest you buy an MPPT controller. That stands for Multi Power-Point Tracking. Let’s say you have a 17.4 volt panel that is charging a battery that should never be charged above 14.4 volts. That means there is a 3 volt difference—where does that power go to? The controller takes the 17.4 volts, steps it down to 14.4 (or whatever the battery will take at that moment) and the 3 volts are simply lost, they aren’t available to charge the battery. An MPPT controller is designed to step down the voltage, but at the same time increase the amps, so all the power the panel is making gets into the battery. You can expect at least 25% and as much as 35% more power into the battery with an MPPT controller. It’s a much more complicated subject than that, but that’s it in a nutshell. An MPPT controller used to cost you quite a bit more, but now they are so common you shouldn’t pay a premium for one. Even if it costs more, it’s worth the cost.
- I also recommend you buy a controller with a digital display of the voltage of the battery. That way you can always know at a glance the exact state of your battery. It’s important you avoid discharging the battery below 12.2 volts, because that is 50% discharge, and going below that does minor damage to the battery. Most controllers also have a switch that lets you change the display from the voltage of the battery, to the amps that it is putting into the battery. That can be very handy knowledge to have.
- A third feature you want to have in a controller is the ability to set the float point of the controller. Most controllers come from the factory set to float at 14.4 volts. But some batteries are designed to float at a higher voltage, in that case you want to be able to change the float point.
The gold standard for small systems is the Blue Sky Energy, 2000E (see picture below). It is MPPT, does everything you want it to do, and is extremely reliable. It costs about $230 and is well worth it. When I bought my system, that was simply more money than I had to spend, so I bought a BZ250 MPPT controller, made by BZ Products, for $109 from Solar Mike, it comes with a 5 year warranty. He said he sold many more of the Blue Sky and almost never had them come back with a problem. But he had sold a lot of the BZ250 and some, but not many, had come back with problems, but the manufacturer fixed them. The bottom line was he recommended them if you were on a tight budget. He said he was using the BZ500 MPPT controller to run his 24 volt office and it had been working fine for a long time. That was 2 years ago and I have been entirely satisfied with it. My reasoning was that this was just a starter system, (I could only afford a 55 watt panel) so this controller would work fine until I could afford to add more panels. When the system grew I would have to upgrade to a larger controller anyway and then this one would go into storage as a back-up. I did add a 135 watt panel a year later, and I am completely happy with my current system, so I probably won’t add any more panels. Because the BZ controller still works great, I’m glad I saved the money.
Once the solar panels have created the power and the controller has regulated it, we need a way to use it in our daily lives. Not only that, but what are we going to do when the sun goes down, which is when we need power the most? That’s where the batteries come in. They store the power and let us draw it overnight. Here’s a quick overview of the different types of batteries:
- Starting Batteries: When you lift the hood of any car you will see a battery that is used to start the engine. In the battery world, they are sprinters, they come fast out of the gate, giving everything they have, but then they tire out quickly. It is designed to provide a very large amount of power on demand when we turn the key and the starter spins. Because it is connected to the alternator, the assumption is that it will always be charged, and rarely discharged, so they don’t have to hold their power for very long. If you have ever left your lights on and come out the next day and the battery was dead, that battery was discharged. Starter batteries are very intolerant of being discharged. If you run it dead that way more than 5-7 times, the battery will be ruined and have to be replaced.
- Deep Cycle Batteries: In the battery world, deep cycles are the marathoners. They are designed to provide low amounts of power constantly for the long haul. They are specifically designed to be tolerant of discharges. A discharge is considered when the battery is 50% discharged. On a 12 volt battery, a full charge is 12.7 volts, and a 50% discharge is 12.2 volts. Each discharge is called one cycle. A good deep cycle battery can be cycled (discharged) up to 500-1000 times. But remember, the fewer times you discharge it, the longer it will last. If you cycle it every night for a year and a half, you may have to replace it after only 1 1/2 years. If you are careful and only let it drop below 12.4 once a month, it might last 10 years. A partial discharge doesn’t count as a cycle. If you only draw it down 25% to 12.4, that isn’t a full cycle and the battery will probably last twice as long. So if you can afford it, the best thing you can do is size your system so there is enough power to seldom draw it down below 12.4. Golf cart batteries are a good example of a deep cycle battery. They are designed to be charged overnight, then to have a constant, low drain all day, then be recharged at night again. The battery bank in the golf cart is designed so that in normal use it will only draw down to 12.4 volt in order to get the maximum life out of them. They are commonly used in RVs and called “house” batteries because they operate your household needs like lights and appliances.
- Marine Batteries: In the battery world, these are the decathaloners. They try to do everything well, but not great. They are a hybrid of starting and deep cycle. I replaced the starting battery of my Ford F150 with one, and it has worked fine. Many people use them for their house battery, and often they work great. Personally, I think you are better off in the long run by buying a battery dedicated to one purpose, not two. A golf cart battery, treated in the exact same way as a marine battery, will last much longer, more than offsetting anything extra you may have to pay to buy it.
- Golf Cart Batteries: A high-quality golf cart battery is the ultra-distance runner of the battery world. It is designed to run 100 mile cross-country races. It starts running, and just keeeepsss going. Since that is what we want out of our house batteries, it is the perfect choice for us. The one confusing part is that they are 6 volt, instead of 12 volt. Don’t let that bother you, it is no big deal! It does mean you have to buy them in pairs so you can wire them together in series so that they become 12 volt (see diagram at end of article). The confusing part is that when you wire them together, the voltage doubles, but the storage capacity stays the same. For example, my Trojan T105 is rated at 225 ah at 6 volt. When I wire two of them together in series so that they become 12 volt, they are still only 225 ah. When wired in series, the voltage doubles, but the amp-hours remains the same. On the other hand if, I wire a 105 ah 12 volt battery in parallel with a second 105 ah 12 volt battery, they are still 12 volt but the amp hours doubles to 210. When wired in parallel, the voltage stays the same but the amp hours double.
- Lead-Acid, Wet Batteries: The majority of batteries are lead-acid. That means they have caps on top that can be unscrewed and you can look inside to see the plates and the acid solution. It’s very important to keep an eye on the water level of these batteries and add distilled water (and only distilled water!) whenever they get low. I suggest checking once a month until you learn your batteries and then adjust it to fit their water usage. When deep cycle batteries are charged at a high rate, they discharge hydrogen gas which is both toxic and explosive. For that reason they must only be used in an open area, or if used in an enclosed area, they need to be vented to the outside. Having said that, let me admit I have always broken this safety rule. For over 9 years I have had lead-acid batteries in my little camper homes (usually under my bed) that were not vented. The risk is real, but in my opinion very low. They only vent hydrogen when being charged at a high rate. If you are using solar to charge, the rate won’t ever be high enough to cause them to vent hydrogen. Again, this is risky and almost universally you are told not to do it. If you choose to do it, you do it at your own risk!
- AGM Batteries: This is a construction method of making batteries using Absorbed Glass Mat in them. Their huge advantage is that they are sealed and don’t need to have water added, nor do they discharge hydrogen. That means you never have to check them or worry about venting them. In fact you can store them on their side or even upside down. That makes them very attractive in the small size of a van because you can put them anywhere they fit and not give them another thought. I have a friend who has breathing problems, and she bought a pair of lead-acid golf cart batteries for her van and on the drive home from the store she developed breathing issues. She turned around right then and took them back and exchanged them for AGM deep-cycle batteries, she didn’t have any breathing issues with them. They are great batteries except that they are much more expensive than lead-acid. If you can afford them, they are the best choice.
Nearly everything vandwellers will need power for will either be 12 volt, or 110 volt. Getting power to the 12 volt items is easy. They are either hard-wired onto the battery, or they use a cigarette lighter plug for power. But how are we going to power the 110 volt items that use regular wall power from our house? For this we need an inverter. It is a simple device we wire to the positive and negative posts of the battery, and it turns the 12 volt power coming out of the battery into 110 volt power. They almost always come with 2 wall outlet plugs to plug things into. To have power, you just connect it to the battery, turn it on, and plug the 110 item into it, and it works. There are two types of inverters, Pure Sine Wave (PS), and Modified Sine Wave (MSW). The difference is in the quality and purity of the power they make. Some items are very sensitive to the quality of power and require a PSW inverter, but the vast majority will work fine with a MSW. Pure Sine Wave inverters are much more expensive, so I suggest you buy a MSW and use it. If you ever find an item that requires a PSW, then you can spend the extra money on it.
And that’s it! I hope this demystifies solar power for you because one of the very best things you can do is install solar panels. You will love the free, silent, abundant power, and the earth will be so much better off with one less person using coal or some other fossil fuel to create power.
This is the battery bank of a friend of mine who lives in an RV. He has 480 watts of solar panels charging 8, golf cart batteries. He never runs out of power, and rarely cycles the batteries below 12.4 volts.
This diagram shows how to wire two 6 volt batteries in SERIES so they become 12 volt. I think it is very helpful to set the batteries together just the way you see them here. One advantage is that you need a shorter cable (2 gauge is best) to connect the positive and negative posts of the batteries. But a much bigger advantage is that the two posts that you are going to use to connect all your 12 volt items are separated from the other posts that are still 6 volt. You must use only the 12 volt posts! Connecting a 12 volt item to the 6 volt posts will damage it!