As I noted earlier in this series, there are many items to consider when making a purchase of panels and batteries. Chief among these is weight and size. An 85 Ah Gel Cell will weigh in at around 70 pounds. A 125 W panel will weigh in at 26 pounds with dimensions of close to 5′ x 2′. These are not very portable.
We can break these things down into smaller units!
For example, I noted that I needed 30 W of solar panels and a 21 Ah battery to power my Elecraft K2 for a 24 hour period. This is actually a small battery and small panel, however, as the size of the solar array and battery bank grows, and trust me – once you get hooked on this stuff it will, you will really appreciate it more if it is made of smaller units.
My first solar panel array consisted of five 5 W panels, giving me 25 W total of solar power to feed a battery. The five panels were chosen because they were small and that made them a lot easier to transport. I ran all of the outputs in parallel. This means I connected all the positive leads together, and all of the negative leads together, then fed the battery this way.
You can do likewise with your batteries. Having two 12V at 85 Ah batteries in parallel is a lot easier to move around than one 12V at 170 Ah battery! Trust me on this. I have a 155 Ah battery in my basement and the thing weighs in at 125 pounds. That is not easy to move around.
Again, parallel means to hook positive (+) to positive (+) and negative (-) to negative (-). Hooking them in series (positive to negative to positive to negative) is not advisable, as that will increase the voltage. We want to increase the current instead.
Now that we are generating power, and storing it, we need to hook up our chosen devices. The easiest way to do this is to just make sure everything uses 12V! Remember, we can go +-15% usually and be okay.
But what about things such as charging up cell phones? My iPhone charges off of USB, for instance. So, I have a 12V car adapter I purchased that is made for charging the iPhone and iPod. That works really well. All I did was wire in a cigarette lighter plug into my battery bank, and charge away.
You can also find some other things out there that are a lot more fun than the cigarette lighter adapter thingy (which, personally, I hate). I will leave it to you to find the way to do this, as the number of possibilities is limitless here.
So, that’s pretty much it!
I urge everyone to try playing around with solar electricity generation. It is simple, cost effective, and it will continue to make electricity for you for many many years to come.
Tags: battery bank, Solar, solar array, solar panel array, solar panels, solar powerYou know what the weather is like where you live. You know approximately how many hours of sun you get during the day. Combine this knowledge with the size of you battery bank and you will start to get a picture for what size your solar panels need to be.
We determined earlier that I need at least a 22 Ah battery to power the one radio I need powered over a 24 hour period. However, something I did not mention earlier is that this number is misleading. Keep in mind there are periods that I do need to sleep. During these periods I will have the radio turned off. It will not be drawing any current off the battery. When it is daylight, the battery itself will be charging.
Again, we really need to keep these things in mind. Sometimes we are drawing power from the battery, sometimes we are charging the battery, sometimes we are doing both.
We know that the radio I am using draws, on average, 750 mA/hour. Therefore, we need to put 750 mA/hour back into the battery to keep it at a full charge. Since there is a time that there will be no daylight, we have to adjust for that.
The easiest way to adjust for non charging times is to look at an almanac for your city and look at the amount of daylight available on the shortest day of the year. At my location, that is around December 21. I found a number of sunrise/sunset calculators via Google, and the one I happened to pick is located here.
For 2009, it shows December 20 as the shortest day, with sunrise at 7:33 AM and sunset at 4:58 PM. Doing some math that gives me about 9 1/2 hours of daylight for charging. Not too shabby! I do not really care about any other days of the year – I want to look at the worst case scenario, so that’s why I have picked the shortest day.
Now that I know this, I know what I am up against. I will consume 18 Ah of current. I have 9.5 hours to replenish. So, I need to charge the battery at a rate of 18/9.5 = 1.89 A/hour to keep a full charge on the battery.
Way back when there was this German guy named Ohm. He came up with a law that showed how current, voltage, and resistance were all related. Along the way, power got thrown into the mix and it was found that power, in watts, is equal to the voltage times the current. Or, written out, it would be P = E * I. Some people like to change E and I around, so the formula appears as P = I * E. See? This formula is now as easy as PIE to remember!
By knowing any two of the values, we can quickly find the third value.
‘To find the current in Amps, or I, the formula becomes I = P / E.
To find the voltage, in Volts, or E, the formula becomes E = P / I.
And finally, as mentioned above, to find the power in watts, or P, the formula is P = I * E.
Now we start getting into the fun part of the whole thing. We know from above that we need to put 1.89 Amps into the battery to keep it charged on the shortest day of the year. That’s all fine and good, but solar panels are not specified by their output in amps! Actually, they are, but the current in Amps is shown at the specific voltage output of the panel.
For instance, I found a BP Solar panel with the following ratings:
This means this particular panel will put out 16 Volts when connected to a load – in this case a battery – and is sized to be a 10 watt panel. By using the formula above, I = 10W / 16.8 V, we can see that we will get .59 Amps out of it, or 590 mA.
You may also see designations talking about Voc and Ioc. These are ‘O’pen ‘C’ircuit voltages and currents. For a common 12V gel cell, something with a Voc up to about 21 volts would be okay. This particular BP panel above would be something we would want to look at. However, it is a bit on the small side. This can be good or bad depending on your needs.
Remember: As long as the voltage going into a rechargeable battery is greater that the float voltage of the battery, the battery is going to charge. Just don’t overdo it by shoving 30V into a 1.5V battery! A few volts over and you are okay. Going hog wild will get you into trouble.
Tags: hours of sun, solar panelsWe last left off by sizing our battery bank. Now it is time to size the solar panels.
This is probably the most critical part of the system. It is, after all, the thing that will charge your batteries! If we do not size it correctly, we will end up with dead batteries a lot of the time. If you are okay with that then fine. However, if you are running something that you consider to be of a critical nature, you will want to make sure that you have sized the panels.
As I have noted previously, I have been playing with solar panels for quite a while now. Since 2001, to be exact. I bring this up because I have seen and heard a lot of, well, let me be honest here, a lot of REALLY stupid things.
Taking these one at a time:
We can’t use solar power because of where we live – we don’t get enough sunlight
Nothing could be further from the truth on this one. Even on the cloudiest of days, my solar panels typically put out 75% of their rated capacity, and this is worse case! Solar panels are also used the world over, from deserts to the arctic. The trick here is to size the panels and batteries accordingly! Think about it. At the south pole, where it is dark 6 months out of the year, and light the other six months, you can easily use solar power. You just have to make sure that your battery bank is sized correctly to supply all your needs when it is dark. You also need to make sure that your panels are sized correctly so they can charge the battery bank when it is light. It does not matter what part of the globe you are on – you get daylight and you get darkness.
This panel that plugs into the cigarette lighter of my car is actually doing something useful
Yes, it is. It is providing enough power to keep the clock running. Maybe.
This is an instance of what I consider selling snake oil. Usually these panels are only putting out a few milliamps of current. This might be enough, as I noted, to keep the clock in the car running, but it is NOT enough to make any real difference.
I have seen people actually try to use these very small panels to power large things. Trust me, the power one of these puts out is not enough to even keep the battery supplied with a float voltage. People tend to want to rely on them for one reason and one reason only – they are cheap. The first thing you must realize is that doing solar right is not a cheap thing to do. Small panels like this DO have a use, but not in this case. If you are considering this method of powering lights and radios, you should stop reading now, as nothing in this document will help you.
I tried solar power and it was a waste of money and time
I hate to say it, but obviously you were not doing solar properly! Yes, solar power is expensive. It is very expensive when compared to using electricity from the grid. Currently in my area, electricity is delivered at the rate of around 14 cents for every 1000 watts. A solar system like I have built has cost me close to the $7.50 a watt range. That is a huge difference! However, my goal is to be able to be without grid power for many many days and still operate my amateur radio station.
But another thing to think about is life of the panels. I spend $7.50 a watt up front. That panel will be able to generate power whenever it is daylight for the next 30+ years. Some of the first panels that were manufactured in the early 1970s are still going strong today.
So, yes it is expensive up front, and the return on investment is a long way off. But being able to have electricity any time without the need for to rely on an outside source far outweighs the price in my situation.
You have to have some fancy contraption to point the panels at the sun
No, you do not. You could come up with something to do this if you wanted, and you can spend lots of money doing it. You will see a benefit by way of higher output from the panels if they are pointed directly at the sun, but you will also be generating power even if they are stationary. The cost of these pointing devices is quite high. There are times when you would want to employ a device such as this, but the system I am using is not one of these cases.
That will never work
It sure does! As I noted, I have been using solar power for quite a while now. I have never run out of power. I live in a location where I was told “we can’t use solar power in this part of the country because we don’t have enough daylight.” I was told I had to have “some fancy contraption to keep the panels pointed at the sun.” And I have been told time and time again “that will never work.” Yet it does. And very reliably, I might add.
Tags: battery bank, solar panels, solar powerMany moons ago I decided it would be fun to run my amateur radio station off of solar power. What started off on a small scale, quickly became overkill in some respects. However, I have had nothing but success from the endeavor.
My main goal in doing this at that time was to just run one low powered radio for at least a 24 hour period, with no interruption. Today, I am powering two radios with the goal of having them operate continuously with zero downtime because of no power. I also have a lamp, and am able to charge the batteries on two hand-held radios – all on solar power, and all for free. Well, kind of free.
If you decide that you want to undertake a project like this, you first need to sit down and figure out what you are wanting to power 24-7. Although this article applies mainly to ham radio, you can apply it to other things as well. For instance, a good place to start might be powering your cable modem and WiFi access point. Since those two devices are normally left on all the time, they would be a terrific starting point – but you will have to do some other things besides hooking up a panel to them and expecting them to work.
As a matter of fact, hooking up a panel to them would most likely result in their destruction. This is something that will be addressed later. So, for now, we will just be focusing on my solar powered ham radio station.
Any system like this needs a plan. As much as you might want it to, throwing together a batter and a solar panel is NOT the way to do things.
The first thing you MUST do is figure out what your needs are. The radio I first used was an Elecraft K2. The K2 has very low power requirements – 12V @ 1.5A for 5W output when transmitting and 12V @ 400 mA when receiving.
Now, one could hook up a solar panel directly to the device one wants to power, but this would be bad for the device. Solar panels very seldom put out 12 volts – the are most commonly putting out 18V and in some cases 24 and 48 volts, depending on the size of the panel. Most 12 volt devices have an operating zone they can tolerate of about 15%, so a 12V device could actually operate at (12 * .15) = 1.8, or somewhere in the 10.2-13.8 volts range.
But here is another kicker – a lot of things are designed to be operated in a car. The car electrical system may say it is 12 volts but in actuality it is 13.5 volts. This gives us a slightly larger operating range of +- 2.02 volts, or, 11.5 to 15.5 volts. It is best, however, to keep this voltage at around 13.7-14.2 volts. You will see why later on.
For now, we are wanting to try and figure out what kind of load we are going to be putting on the panel and try to size our solar panel accordingly. It would be really easy to just go buy a 150W panel and be done with it. But, we would end up spending money we probably do not need to. Add to this the physical size and weight of a 150W panel and you will probably want to do otherwise as well, especially if you are planning on taking your panels out to the field.
In my case of using the K2, I figured that I would be drawing 1.5A around 30% of the time. I spend an awful lot of time listening instead of transmitting. However, to be safe, I went ahead and figured out the system at a 50% load of 1.5A. I would rather have too much available to me than not enough, especially since if there were some emergency communications event going on, I would need to have my station running 24/7 for up to two weeks. Maybe longer even, if conditions so dictate.
Now that I know I am going to require 750 mA continuously (1.5A * 50%), I can now size the battery I will need. Why a battery? Because the sun does not shine 24/7, no matter how much I want it to! I will need my battery to supply 750 mA constantly over a 24 hour period.
The battery I will choose is what is commonly referred to as a Gel Cell. These are sealed maintenance free batteries. They are NOT car batteries, which are actually junk and are not able to do what we need them to. If you are thinking “I will just use a car battery!” think again. You will have ZERO success doing this. You must use some sort of a deep cycle battery. A gel cell is a perfect battery to use for this application.
One word about batteries before we continue much further. Batteries are extremely dangerous things. You are probably not going to be shocked by them (you can be, but not with this type of system), however it is extremely easy to do something really bad and start a fire or cause an explosion. When you are working around any type of battery, remove any jewelry you have on. Make sure nothing can come in contact with the battery terminals and cause a short. If you do cause a short, run like hell because something bad is about to happen. Do NOT take any chances with these things. I am very serious about this, and you should be too.
With that warning out of the way, we are now ready to start doing some more cypherin’…
Tags: amateur radio station, batteries, elecraft k2, solar panel, solar panels, solar power