|A rare sunny day during the long northern winter. The leaning pole-brush is used to clear snow from our solar panels.|
In last week's post I talked about calculating your power needs in order to appropriately size your future solar power system. In this post I will finish walking you through the process of choosing different components for your system and give a few tips on shopping for them. If you haven't read part one yet, you can see it here. Before we go any further I am going state the following one more time;
I should also mention that there are multiple methods of putting these systems together. Many people suggest, for example, that you begin by first sizing your battery bank. Others start with the panels. Many of us on a budget take various parts and pieces as we find them at a reasonable price. While you are reading this, keep in mind, that before you start shopping you first need to have a good idea of what you're aiming for in the end. These are not necessarily step by step instructions, they are simply written in a way that make the most sense to me. I am about to drop a load of information on you, so I suggest you grab a pencil and paper, a calculator and a cold beer (or other soothing beverage of your choice) and settle in. Don't worry though, solar energy is fun!
|Looking at the backside of our solar panels. I made these tilting panel mounts to gain solar efficiency.|
Alright, so hopefully you have figured out how many watts of energy you will need to produce by using one of the calculators I mentioned in part one. In this post, I will use the data from my own system as an example. When I put my energy use information into the calculator it stated that I would require 414 watts(w) of solar power to support my energy use. This number is a minimum. So I know that I am aiming for at least 414w of solar panels for a 12 volt (v) system. There is no harm in having extra solar panels, you will simply be able to charge your batteries faster . The maximum size of the panel or group of panels (called an array) is limited, however, by the amount of power your charge controller can handle. We will talk more about this in a bit.
Today, there are loads of solar panel choices in many sizes. Panels are rated in terms of watts (the maximum power they can produce) and volts (in simple terms, the speed or pressure at which the power is delivered) click here for a simple explanation of amps, volts and watts. For most systems of the size we are talking about, the options are usually limited to 12v or sometimes 24v. I will talk about the advantages of a 24v system later, for now just note that you can easily build a 24v system using 12v panels but not the other way around. Lets assume that we are shopping for 12v panels. We need to find a panel or a number of 12v panels that add up to at least 414w for my system. Currently, any panel over 250 watts is so large and expensive they wouldn't make sense for my application (on a moving vehicle). So, I know that will I need more then one panel. The really nice thing about solar panels are that many are rated to work efficiently for over 25years and they are virtually maintenance free. This means that they are great candidates for buying used. I found two of mine used on Craigslist for a third of their retail price, the others were given to us from a friend who had them sitting in storage for about 10years. When looking at used panels you can test that they work by using a volt meter and placing the panel in the sun. If you don't know how to do this, find a friend who does, or have the seller demonstrate it for you. If the panels are generating any power at all, and they don't show any physical damage, it is likely that they will work just fine. There are many reputable panel manufacturers out there, but I don't know enough about them to make any recommendations. I suggest that you do your homework by comparing reviews, contacting companies etc.
For my project I ended up with two 125w panels (made by Kyocera) and four 50w panels (by Arco). Since they are all the same voltage (12v) you can simply add their watt ratings which gives me a 450w solar panel array. According to the calculator, this should provide plenty of power to cover my energy needs even in the depths of a cloudy northern winter.
Solar panel placement:
This is another important aspect to consider. Solar without the sun is obviously worthless, so if you want to get the most from your system (and why wouldn't you) follow the following guide lines.
-Choose a spot with good southern exposure (assuming you live in the northern hemisphere).
-Avoid shading as much as possible. Even the shadow from a single leaf or antenna can decrease a panel's output by 50%!
-Locate the panels in an area where they can easily be cleaned and cleared of debris/snow.
-Tilt 'em if you can. You can find the optimum solar panel tilt for your location and season here. You may purchase tilting panel mounts, or if you have a few tools and some creativity DIY!
|Our batteries are housed safely in this vented compartment outside of our living space.|
So, we have established that solar panels can take energy from the sun's light and convert it into electricity which we can then utilize for our household needs. But what about when the sun goes down or is hidden by dense clouds. Batteries serve as our energy pool. We can add to the pool whenever the sun is out and then pull from it, whenever we need it and in what ever quantities are necessary. There are many options for battery types and sizes. You may only need one battery or you may need a group of connected batteries called a battery bank.
The batteries we are going to discuss contain sulfuric acid which is a highly corrosive substance that can burn your skin and eyes. Always where safety glasses and chemical resistant gloves when handling batteries. The acid will also turn cotton clothing into Swiss cheese even after they have been washed (learned that one the hard way), so don't where your favorite designer jeans. When charging, the chemical reaction inside of the battery produces highly flammable and potentially explosive gasses if it is allowed to accumulate. For this reason, they should always be placed in areas that are well vented to the outside. NEVER intentionally or accidentally connect the positive and negative ends of a battery (or series of batteries) directly to one another because they will short circuit causing a spark and possibly a shock, fire and/or explosion. It's a good idea to use tools with insulated handles for this reason. Finally those suckers are seriously heavy so (repeat after me) lift with the knees! Read this page for more info.
For most solar applications it is suggested that you use deep cycle batteries. A deep cycle battery is different from a car battery in that it can be discharged to a low rate many times without doing damage to the battery. Car batteries are only designed to give a large surge of power for a very short period of time, just enough to get the engine turning. While car batteries are often measured in CCA cold cranking amps, a good deep cycle battery should have an amp hour rating. Amp-hour (A-hr) ratings are useful for solar applications because they give you information on how long your batteries will last when fully charged.
There are two different types of batteries I suggest using for this type of system, they are Flooded and Absorbed Glass Mat (AGM) batteries. Here is a quick run down of the pros and cons of each.
Pros: -Longest track record for this kind of use
-Significantly cheaper than AGMs for same sizes (A-hrs)
-Available in larger sizes (A-hrs) then AGMs
Cons: -More maintenance required
-Must be housed in a well vented area
Pros: -Don't need to be vented
-Can be placed on there sides
Cons: -Very expensive!
-Lower amp-hr ratings can make large battery banks cumbersome.
I am going to assume that for a lot of you DIYers, like me, cost is a concern. For that reason I would recommend using flooded batteries. They are plenty expensive already ($100-$400 each) and the maintenance is not really a huge burden. Basically you just need to keep an eye on the water levels which generally means checking about one time per month and adding distilled water if the cells (individual compartments of the battery) are low. Keep the terminals clean and equalize the batteries routinely. Equalization is basically applying an occasional controlled over-charge to the battery, which when done at the suggested intervals and voltage keeps the battery healthy. This operation will require a charge controller with equalization capabilities. Read this article from countryside magazine for more info on flooded batteries.
Battery Life Span: The reason that deep cycle batteries are good for solar is that they have the ability to be discharged (or drained) almost completely and then regain a full charge. Just because they can do this does not mean that you should do this. The more deeply you discharge a lead acid battery (Flooded or AGM), the shorter the overall lifespan becomes. Look at the chart below from the data sheets for the batteries we use. A "cycle" represents discharging the battery and then recharging it one time.
|Copyright Trojan Battery Company|
|Our two 6v batteries connected in a series to make 220 A-hrs at 12v|
Sizing a battery bank (my way):
There are tools available online to size a battery bank, but I have found that they are usually designed for large scale projects with very large battery banks and they take into account a plethora of factors that aren't always that easy to estimate. I found that many of these calculators suggested a battery bank twice as large as the one we are currently using without a problem. This may possibly be because these sites are often also trying to sell you batteries. For a small scale design like the type we are talking about, I have a suggestion for a simple method that I think will work well for most people. Its probably a good idea to speak with a solar electric supplier for a second opinion. I have had great luck dealing with the friendly people at Backwoods Solar for both questions and supplies.
My simple (and unscientific) method goes like this; Take your energy needs (remember the daily amp-hours calculation from the solar panel calculator?) and divide this number by .15 . In my example, my predicted energy use was 29.5 A-hrs when divide by .15 equals 196.6. This number is the absolute minimum battery amp-hour ratting I should start with. The number .15 represents a daily discharge of 20% on average with 5% built in for system inefficiencies. Some days you will likely go beyond the optimum 20% discharge if you have a series of cloudy days or on days when you use more than average energy. To be more conservative, divide by .1. This suggestion is only a starting point for those of us concerned with saving some cash. Many of you may want to expand your battery bank. This can easily be accomplished in the future provided you have the space for additional batteries. Too many batteries can be a problem though. An important part of battery maintenance is making sure that you fully charge your battery bank on a regular basis (at least once a week for our batteries). The larger your battery bank is, the more power it will require to reach a full charge. When we started, we purchased a 440 A-hr. battery bank which worked great in the summer. As winter came and the sun disappeared we were no longer able to fully charge our batteries. At the risk of damageing them all, we ended up dropping down form four batteries to two batteries which halved our amp hr capacity. This solution solved the problem, but we had already spent hundreds on two extra batteries that we could not support.
The general rule of thumb is that the amp rating of your panels should provide between 5% and 13% charge of your total battery bank amp-hours. So if you have a battery bank of 220 A-hrs 5% (220 x .05) is 11 and 13% (220 x .13) is 28.6. Therefore the solar panel's potential amperage (which we discussed in the solar panel section) should be between 11 amps and 28.6 amps. If you live in a very sunny climate 5%-8% may work fine, but for cloudy northern areas like hours aim for 10%-13%.
Finding the batteries:
Now to learn from another one of my mistakes. I would highly recommend that you avoid buying used batteries. I know that the retail price of new batteries is hard to swallow, but at least you know that you are starting with a battery that has never been damaged and has a potentially long lifespan (if you treat it well). Not having the knowledge that I have now, I originally purchased four high quality deep-cycle batteries used from a private party. The price was half that of buying them new, so I thought I was getting a lot more bang for my buck. When I made the purchase, the batteries were only a year old. The water levels looked good and the seller claimed that they had been well maintained. When I hooked them up to the system, they just didn't seem to hold a charge very well. I didn't really know what was normal since this was my first experience with solar power. A couple of months later a friend who did have experience with solar helped me to test the cells using a hydrometer. As it turned out, two of the four batteries were badly damaged and a third one was slightly damaged. Having even one damaged battery in your bank will eventually bring the others down as well. Buying new protects you from another person's poor maintenance (whether they know it or not) and new batteries often come with some kind of warranty. The one exception to this is buying used or reconditioned batteries from a reputable battery dealer. If you still insist on bargain hunting the used market, at least bring a hydrometer and know how to use it.
Like solar panels, batteries come in a variety of voltages from 2v to 24v and beyond, but the most common sizes for a small system are either 6v or 12v. Also similarly to solar panels, you can link batteries together to increase the battery bank voltage and/or it's total amp-hrs. Connecting batteries in a "series" will increase the bank voltage while linking them in "parallel" increases the bank's A-hr rating. There is an illustration of this on the Trojan Battery website. I also recommend that you watch this helpful video. These concepts are the same for solar panels. Connecting a panel array in parallel will increase the the total amperage, while connecting in a series will increase its voltage. Check out this video demonstrating these concepts.
|Our charge controller made by Blue Sky Energy.|
The next piece of the puzzle is finding a charge controller that will fit your system. A charge controller, in the simplest terms, receives the energy produced by your solar panels and sends it to the batteries in a safe and efficient manner. The limiting factor in choosing a controller is the maximum amount of power input that it can handle. The controller's maximum input will be your solar panel's total potential output. The simple way of finding panel output is dividing your total panel watts by the panel voltage. For example a 12v panel array with 300 total watts would give you 25 amps. In reality, it is highly unlikely that you will ever achieve a charge this high do to environmental factors and system inefficiencies, but it gives you a conservative estimate to work with. It is important to find a charge controller's maximum input information in it's the specifications since different controllers are rated in different ways (they may also use different methods for finding total solar panel amperage). You can always go with a larger controller and this may be good idea so that you will have room to easily expand the system later if you want to. The only sacrifice is the cost. Charge controllers come at many price points from less than a $100 to many thousands. What you are paying for is its handling capacity, quality construction, customer support and the versatility of its features. In most cases, I am a huge advocate of keeping things simple, but in the case of charge controllers I believe that bells and whistles are a good thing. Having greater capabilities will maximize your systems efficiency, give you more options for panel voltages and battery types, and maximize your batteries life span. I wont get into the details of all feature options, but here is my opinion of the features you should look for in a solar charge controller.
Bare Minimum: -Automatic 3 stage charging capability (Bulk, Absorption, Float)
- Battery Voltage display (you could use a separate meter for this also)
Better: -Equalizing function (For Flooded batteries only)
- MPPT (Maximum Power Point Tracking) for maximum charge efficiency
- A display or remote display that accurately measures amp hrs and battery capacity (with shunt)
Best: -Capability to use temperature compensation (with a temperature sensor)
-Capability to set charging parameters specific to your battery
-Capability to divert extra unused charge to axillary batteries or other loads
-Capability to utilize and convert multiple voltages (i.e. 24v from panels to 12v battery bank)
|A remote display like this one gives you important information and controls for the system.|
When I was living in Portland, I was lucky enough to find exactly the type of charge controller I wanted used on Craigslist. This is probably a rare event though I'm afraid. You may be able to find used controllers on eBay or from a solar parts dealers. Use caution when buying a used controller because they are complex and highly sensitive pieces of equipment. If they have not been handled properly, they could easily have been damaged.
We have arrived at the final basic component in designing your solar energy system! Wiring is a piece of the puzzle that is often overlooked but is just as important as all the other parts. There is nothing complicated about the wires themselves. In general, you will be using stranded copper wires for all Direct Current (DC) connections, which applies to everything he have talked about so far. Stranded wires are made of many small copper wires (strands) twisted together like a rope and then coated in a plastic insulation. The important part of wiring is choosing the correct size (or gauge) of wire for the application. In the USA gauges are usually marked as AWG (American Wire Gauge) preceded by a number. A larger number represents a smaller width of wire. 18 AWG is about the width of a cotton string while 8 AWG is closer to the width of a pencil. Once you get to 0AWG the larger sizes just keep adding 0's. Car battery, cables for example are often 00AWG. They are sometimes marked 2/0 which is pronounced "two-aught". This abbreviated chart should help;
|See the entire chart at www.powerstream.com|
The thing that we are most concerned with is choosing the correct wire gauge that can handle the amount of current we need and deliver that current without losing too much voltage by the time it reaches it's destination. Voltage is lost from a wire due to electrical resistance. This phenomenon is called voltage drop. Larger wires have less resistance and therefore will carry a current further with less voltage drop. When sizing wires from your solar panels to your charge controller and from the controller to the batteries, you should aim for a voltage drop of less then 3%. Try this online calculator to size your wires. Set the acceptable loss to 3%, the system voltage to 12v, enter the maximum output of your solar panels in the Amps section, and the total length of cable you will need to reach the batteries via the charge controller. When you hit calculate you will have your gauge. (Note: you should run smaller wires to connect your panels together in an array and then to a junction box. Run the larger wires the rest of the distance to the other components). The longer the distance you have to run the wire, the larger the wire will need to be. Therefore you should try to locate all of your system components as close together as possible. This is also why having a charge controller that can switch between 12v and 24v is useful. The higher the voltage the lower the resistance. So, if solar panels are setup for 24v you can use wiring half the size of the 12v system. Change the calculator to 24v and see what happens. Copper wire is expensive enough that if you must run wires a long distances (say over 20 ft or so) it could easily be cheaper to upgrade your charge controller instead of buying huge wires for that length. Don't forget you will need to plan on running two wires (positive+, and negative-) between components. If you are going to use a large inverter (over 300 watts) you will need to purchase even larger wires that can handle large loads. My 2000watt inverter required 0000AWG to handle the potential of drawing over 300amps for six feet. The cables alone were more than half the cost of the inverter! These are all things to consider.
|The monster under our bed. This is what our entire system looks like.|
Note the giant inverter cables going through the floor to the battery bank.
A few notes to end with:
This is a whole other can of worms that I am going to leave to someone else. There is a good article and video about inverters found on the West Marine website. I will say that adding an inverter to your system will add substantial cost. Don't forget to add it to your budget. We started off with a small inexpensive portable inverter that plugs into a DC outlet (cigarette lighter) for small appliances and then upgraded to a larger hardwired inverter when we could afford it.
I am not going to provide any specific information on the installation of components since each system will be different and specific to the components you choose. Good components will come with clear installation instructions that you must follow exactly. Always use fuses where instructed (generally there should be a fuse on any positive wire connected to the battery) and use different colored wires to differentiate positive, negative and ground wiring. Make sure that all connections are tight and that wires are secured in safe locations. Installation is not overly complicated, but it does requires great care and attention to detail so as not to create risk of fire or doing damage to yourself or the equipment. Some warranties may require professional installation to be valid. Remember, if you do not feel 100% confident, ask an expert. I am not an expert btw.
Finding tools and miscellaneous parts:
If you choose to embark on this mission, you will quickly find that hardware stores and electrical supply stores often have very limited supplies and knowledge of DC electricity aside form the basic tools you will need for cutting and splicing wires. Auto parts, welding supply and battery stores will do a bit better especially with larger gauge wire and connectors. They also may be able to make custom battery cables with crimped ends for you. For other specific parts and pieces you are probably best off ordering directly from a solar supply store such as Backwoods Solar.
I know that many of you are going to wonder about the cost of such a project. There is no good general answer. Somewhere between $200 and $200,000. How's that for an answer? I can say that the system I built and have described here was in the $1500 ball park. It was constructed utilizing mostly used parts, buying the same parts new would have put it closer to $2500. But this was just for our very specific situation. I guarantee yours will be different.
Well then! That should be enough to get you started. Now, get out there and research other websites, read books and articles, talk to people who have solar experience and most of all, have fun setting up your new system and generating free renewable energy from the sun!
For even more specific info on these same topics, check out HandyBob Solar. It is kind of one long jaded rant, but it is loaded with specific information and real world experience. This blog is where I got much of my solar power education.
The site marxrv.com also has some good info. Definitely check out builditsolar.com for all kinds of cool solar DIY projects and info.
As I mentioned before, I am not am not a solar power expert or professional, but I will try to answer any general questions pertaining to this post to the best of my ability.
Return to DIY Solar Energy (Part 1)
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Thanks so much for that information. We aren't close to installing a solar system, but I would love to in the future. A couple questions, when you move your bus at speed, are your panels secure enough, or will they be temporarily removed, or do you not plan on being at highway speed ever? With regards to the need to fully charge your battery bank once a week, would it be difficult to set up a way to do this with a generator? Lastly, have you looked at small wind turbines? I have always thought a small turbine on a moving vehicle would be fun, although I realize you guys don't move your skoolie much. Thanks again.
Thanks for the questions HD. The panel mounts are designed to lock into a flat position (as if they were bolted to a roof rack) we have driven the bus many 100's of miles at 60mph (which is as fast as the bus will go) with no issues at all. You just need to be weary of those low underpasses and drive-troughs! You can absolutely use a generator to charge your batteries. Some inverters have a charger option to make this very simple. We just really like not having to deal with it, not to mention the cost of a generator and all the gas adds up quickly. Small turbines are starting to show up on RVs but they aren't really designed to be used while moving. The wind resistance would just make the engine work harder and burn more fuel which kind of defeats the purpose. Thanks for following the blog!
Thanks for linking up to The HomeAcre Hop! Great info! I shared this on facebook and sent along to hubz to share on his sustainable energy page :)
Keep up the great work!
Thanks for hosting Lisa. Please share the link to the this sustainable energy page. I would love to check it out.
Here is the link to the facebook page I mentioned :)
Cool side note, he will be writing articles about the tech side of sustainable energy on Engineering.com in March:)
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