TOR here: Our good friends at Idaho Preps were kind enough to write a guest post on the topic of simple solar systems. They sell some solar items but really just wrote this because they had done some research already on a topic I was talking about and wanted to help out. They called this a basic overview but it seems pretty comprehensive to me. That might speak more to my minimal knowledge on the subject than anything else. Anyway, enjoy.
The premise of a solar electric system is using the sun's energy through solar panels to charge batteries, then using the energy stored in the batteries to power needed electric devices.
This will be a very generalized, very basic overview. You can use this as a rough guide to calculate costs and gain a basic understanding of the setup of a solar electric system. But before you jump into building a system, please gather more information. At the end of the article, I've listed three books I found on Amazon that have very good reviews. I have not personally read any of these, but the reviews of these books make me confident that they contain worthwhile information.
We will create an example system to help illustrate how much power you need for various devices. Our example system is an emergency backup system, only used when the power is out for whatever reason. This system will be substantially smaller than an off-grid setup for a cabin or retreat.
With any project the first step is planning. Ask yourself some questions:
-What devices do you want to power?
-How long do you want to power the devices?
-How quickly do you want to recharge your battery bank?
-How much money can you throw at this project (a solar project can be stages to avoid large cost upfront)?
-Where will you put the panels and the battery bank?
Let's go through each of these.
What devices do you want to power?
In our example, we would like to power a laptop, cell phone charger, small battery charger (AA, AAA, etc), a few lights, and a few other small miscellaneous devices. When you are calculating devices, try to overestimate, of course it is better to have too much power than not enough. This is your basic figure used to calculate your inverter size and to a lesser extent how many panels and batteries you need to start out.
How long do you want to power the devices?
In our example our power emergency will last two days. Your goals will be different and this will mostly effect the size of your battery bank. Again, more is better so overestimate this as well.
How quickly do you want to recharge your batteries?
In our example, we only have a two day power emergency and this is a very infrequent event, so charge time is not that big of a concern to us. If you were living off grid, charge time would probably be your most important factor. This effects the size of your solar array or how many watts worth of panels you will install. One other thing to keep in mind here is that depending on where you live and the amount of usable sun you receive at your location you charge time may be dramatically different than the example. There are charts on the internet that will give you a rough estimate of how much power you can expect from your solar panels at your location during different times of the year. Here is a map of the US and it's solar irradiation http://lib.store.yahoo.net/lib/yhst-21796510175022/Irradiation.pdf
How much money can you throw at this project?
The nice thing with solar systems is that they can grow over time. Once you have a single panel, charge controller, batteries and inverter, you can simply grow the system. Add more panels, add more batteries, at a certain point of solar output you will split the batteries and add a second charge controller. If you get a large enough install you might look into a second inverter. At that point you would have essentially two complete systems which have the benefit of failure protection as well as power capacity.
Where will you put the panels and the battery bank?
This can be a tough decision. The panels will need a good view of the sun, the exact angle and cardinal direction of the panels will vary depending on your location on the planet, but essentially you want the panels in full sun as long as possible per day. Panels are fragile, so they need to be protected from falling tree limbs, kids throwing baseballs, etc. Your batteries need to be protected from the elements as much as possible. I've seen quite a few different installation methods for batteries from small sheds, to underground root cellar type vaults. Cold greatly effects batteries and if possible having the batteries in a controlled temperature would be the best. Some batteries emit gases when charged, you need to research this and be aware of the potential hazards.
Our example system
For our example we only need to power a few devices for a few hours each for two days and again, we're not really concerned with the recharge time.
First we need to calculate the wattage and usage of the devices.
Laptop - 50W for two hours each day
Cell phone charger - 25W for one hour each day
Small battery charger - 10W for four hours each day
Lights - 25W for four hours each day
Misc - 25W for two hours each day
Now we do some simple math to come up with watt hours, which is a key number in battery sizing calculations.
50W * 2 hours = 100Whr
25W * 1 hour = 25Whr
10W * 4 hour = 40Whr
25W * 4 hours = 100Whr
25W * 2 hours = 50Whr
So our total watt hours for one day is 315Whr
Multiple this times 2 days 315* 2 days = 630Whr
We want to be able to supply 630Whr of power from our battery bank.
A handy page for doing these types of calculations (and for system design in general) is here:
http://www.advancepower.net/advcalc.htm
Parts
In general these are the parts we will need.
-Solar panels
-Charge controller
-Batteries
-Inverter
-Misc cables and connectors
Let's go through each of these.
Solar panels
There are three types of materials that panels are made from:
Monocrystalline Silicon Panels
Monocrystalline panels use crystalline silicon, a basic semiconductor material. The way to identify whether a panel is Mono or Poly is simple. A Mono panel has individual cells. A Poly type panel is solid with what looks like flakes of silicon pressed together. . Monocrystalline panels are typically 15-18% efficient, meaning that for every unit of solar energy that hits the cell, the panel can convert 15-18% of this energy into electricity. These panels are usually more expensive.
Polycrystalline Silicon Panels
Polycrystalline, or multicrystalline, photovoltaics use a series of cells in place of the single large cell used in monocrystalline panels. These panels are the least expensive pv panel available today. The drawback to these panels is that they have lower efficiency rates at 12-14% efficiency.
Amorphous Silicon or Thin Film Panels
Thin-film panels are the lowest efficiency of any current photovoltaic technology at 5-6%. The primary advantage of thin-film panels lies in flexibility.
Each type of panel has its purpose. The Monocrystalline are more expensive, but with higher output. The polycrystalline are easier to make and therefore cheaper, but with lower output. The thin film panels are pretty new, and are great for portable use, their output is very low, but the ability to roll them up and take them with out more than makes up for the low output. For our experiment we are going to pony up the cash and go for the good stuff, monocrystalline panels.
Using the system calculator I mentioned above (http://www.advancepower.net/advcalc.htm), our example system requires only one panel. The calculator was pre-configured with the data for a Kyocera KD135GX-LP solar panel, so we will go with that one. There may be others with better output, better warranties, etc. Your research can determine the right panel for your situation.
Charge controller
The charge controller not only keeps your batteries charged, it lets you know the status of your battery bank (charge level), and it prevents over charging of the batteries, which is a critical function. Over charging will shorten battery life and can lead to batteries overheating, bursting, spilling acid everywhere, and other nasty things. I have used the Xantrex brand in the past, so we will go with the Xantrex C35. This charge controller can support up to 35 amps at one time. Our single panel can only reach a max of 7.6 amps, so this is more than capable of handling our system with room for expansion.
Batteries
Our calculator was pre-configured with the battery data for an Interstate L-16. This battery is very popular for solar and wind power applications and is a great choice. It is fairly expensive and for this type of backup system (vs an off-grid system) I would probably not recommend this battery simply due to cost. You can find the "golf cart" type batteries for half the price per Ah (amp hour) as the L-16. The downside of the golf cart type battery is that they take up more space (L-16 is very space efficient), and their lifespan is shorter (3 to 5 years for golf cart, 5 to 7 years for the L-16). You can use any battery for your system in a pinch, but for longevity you must use a deep-cycle battery and if you are spending money, you are better off to pony up for a good quality battery. Do a little research on the battery and you can save quite a bit of money over the life of your system. One other note on batteries, there are many places that use battery backup systems for computers, telcom gear, etc. Some of the places have strict rules on the life of the batteries. If you play your cards right you might be able to swing free batteries of excellent quality. They may be near the end of their stated life, but will still have plenty of capacity and if they are free you can double or triple your needed capacity and be confident that you still have the power storage you desire. Some places to check for batteries are hospitals, telco companies, cable companies, and any company with large computer systems. For our example I am going to use a generic gel-cell 12V battery I found via a quick google search. One of these batteries will have just enough capacity to run our system to our requirements. Deka MK Battery Sealed Gel, 12V, 86.4Ah, Group 27 8G27DT-DEKA
Inverter
You have a choice when designing the system, depending on how many and what type of batteries you buy, your system can be 12V or 24V. 24V is more efficient especially at longer cable runs. I personally like 12V systems because you can take advantage of the 12V in your system to directly power devices that require 12VDC, in this way there is no power loss from the conversion of 12VDC to 120AC. Many small electronic devices run off transformers that convert 120VAC to 12VDC. You want to bypass this transformer and go straight to your bank of batteries if you can. If you don't bypass the transformer this is the flow of power, 12VDC batteries run to an inverter to make 120VAC then into a transformer to go back to 12VDC to power your device. This is extremely inefficient. When shopping for electronics, take into consideration what voltage the device actually uses. You can see on the transformer itself what the output voltage is. Also, when experimenting with plugging devices directly into your bank of batteries, you need to come up with a way to safely connect those devices and distribute power. I like the idea of using car cigarette lighter adapters wired to plugs that connect to the device. Also you need to be very mindful of polarity, you can destroy electronics if + is connected to - .
Beyond that however there will be devices you want to use that are 120VAC, for this you need an inverter. As with the charge controller, you get what you pay for here and spending more money will gain more efficiency (to a point). Again, Xantrex is a respected company in this field and I have used their products with success in the past. Inverters are measured in Watts, so you will use the number you came up with during the planning stage to determine how many Watts of 120VAC you need to supply. One other note, be sure that you use high quality, large gauge cords if you need to run extension cords off of the inverter, use the largest gauge cords you can so as to avoid voltage drop (and inefficiency) through the cable. For our example we will go with the Xantrex XPower Inverter 1000, it's simple, has good reviews, and has more that enough capacity to power our simple system.
Misc
There are many ways you can connect your system and just as many ways to physically lay out your system. Cable runs will vary, depending on your charge controller or inverter you may or may not need additional circuit breakers or fuses. There is always an unseen part that is needed.
Costs
Let's add up our various parts and see what we come up with.
Charge controller - Xantrex C35 - $125
Battery - Deka 8G27DT - $250
Inverter - Xantrex XPower Inverter 1000 - $125
Misc - cables, fuses, terminals, panel mounting supplies, etc - $150
Total cost - $650
So for around $650 (those prices include shipping) you can have a single solar panel setup with a single battery that can power quite a few devices for several hours over two days. Where I live in southern Idaho, it would take about three days to charge the battery from completely empty. That's not too bad. If you built the system in the right way, this system could even be portable.
Books
Here are three books that I found on solar electric systems that have favorable reviews on Amazon.
http://www.amazon.com/Got-Sun-Solar-Renewable-Grid-Tied/dp/0965809870/ref=sr_1_7?ie=UTF8&s=books&qid=1261622983&sr=8-7
http://www.amazon.com/Easy-Guide-Solar-Electric-second/dp/096718911X/ref=sr_1_33?ie=UTF8&s=books&qid=1261623057&sr=8-33
http://www.amazon.com/Solar-Electricity-Handbook-2009-Photovoltaic/dp/1907215018/ref=sr_1_1?ie=UTF8&s=books&qid=1261622983&sr=8-1
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