A very nice site with lots of links to descriptions of solar energy, solar power projects, etc, and it's written up so that young people can understand the terminology. Good source of material for school science fair projects, scout badge work, girl guide badge work just to name a few. This suggestion was sent to me and I's like to say thanks to the contributor Barbara H.
Microsec R@D (Victoria BC Canada) is a company which has been involved in some relatively cutting edge technology. My friend Ian wanted a photovoltaic system for his residence but did not want to go through the expense of replacing a bunch of batteries or cells every 7 to 10 years. On doing a little research he found nickle-iron batteries being manufactured in China. He also discovered that they did not have components such as lead or cadmium in them which are very toxic to the environment. One surprize was that nickle iron batteries have existed for many years and that the first automobiles , which were electric, used nickle iron batteries. Nickle iron batteries are very robust and can last fourty or more years. Ian pointed out that nickle iron batteries were used in mines and that most of the batteries which have not been damaged are still in service. They are a float type battery like the average automobile battery and so need to be topped off periodically with distilled water. With modern chemistry that may be a thing of the past pretty soon too. It's not difficult to build batteries with catalyzing agents to recover hydrogen and oxygen back into water as is done with AGM lead acid batteries. The point is that nickle iron batteries do look to be a good long term energy storeage solution for people off the grid.
Do-It Yourself Photovoltaic (Solar) Panel Construction
O/K here's some suggestions on how-to make your own el cheapo photovoltaic panels. Read it all before jumping in with both feet. It’s not rocket science but it does require a careful approach
Tools needed:
Small soldering pencil
Saw for cutting plywood and backing to size
Side cutters and pliers
Voltmeter
Misc screwdrivers etc
Electric drill and bits
Length of 1/8” dowel or length of 1/8” welding as a temporary spacer
Materials Needed:
36 each - Photovoltaic (PV) cells (they are approximately ½ a volt each. They must all be the same size and same type. There are several types of cells and each type has its own characteristics. There are amorphos ones and they are a type which you may find in flexible PV arrays. I have one which folds up and stowes away in a back pack. They are not particularly efficient but they are durable. Then there are the polychrystaline silicon PV cells or arrays and monochrystaline cells and arrays. The polychrystaline (sometimes called multychrystaline) is the type you may have seen that look likea bunch of crystals, some say look like shattered glass. The monochrystaline cells are slightly more efficient, slightly more expensive, and the surface of the cell looks uniform.Either one of the latter will do for your PV project but don't mix the types. Be aware that some vendors on eBay often send out a mix of cells. Not a good idea. One place you may see amorphous silicon cells is in roofing. The efficiency quoted for the panels is from 3 to 6 percent and the quotes are for a 20 year life span. That is for the southern and central US. Amorphous silicon cells have been used in projects both Canada and in other countries such as Japanon a trial basis.
One very interesting use of thin amorphous PV panels is for building heat. All PV cells heat up in direct sunlight and that is a problem because it does cut down on efficiency. Several buildings have had south facing walls covered with amorphous cells with an air gap behind. Power from the cells runs circulation fans that push air up through the gap to a header at the top where controllers divert warmed air through ducts into the buildings on cool days.
Polychrystaline Cell with tabbing wire run across the middle
Monochrystaline Array of PV Cells
Flexible Amorphous Silicon Material
Get extras, you will break some accidentally. The cells I’m referring to are available thru places like eBay. I just saw one outfit selling batches of three amp cells at 36 for forty dollars on eBay. That would make a panel capable of putting out around 40 watts on a bright sunny day. Note that there is quite a bit of junk on eBay when it comes to this so it’s buyer beware. Before putting down your cash on Pay Pal contact the vender and see what they have to say about quality. Also check what others have had to say about the vendor by checking the customer feedback.
1 or more rolls tabbing wire with solder. Tabbing wire is also available thru eBay.
The cells must have a tab wire run across the back and across the front. You’ll notice that the material of the cells is laid down in stripes from end to end and there are very thin shiny conductors between those stripes. It’s those thin conductors which make contact with the active layers of the cells. One polarity is on the front and another on the back. The tabbing tape is very thin and very flat. You need to run a tab strip across the cells in two places. Select a spot about an inch from each end and solder the tab strip across the cell at right angles . That way you have two possible routes for current to flow. If you accidentally miss making contact with one of the cells conductive stripes all is not lost, same thing if you get a crack in a cell. You need to do the same on the other side. You will also need to extend the tab wires out a few inches beyond the edge of the cell because you will need to connect to the next cell (series string of cells). Note that you may be able to buy cells pre-tabbed from a source on eBay (read the advertising literature – fine print – carefully). In that case some of the work has been done for you. The tab wire is still handy to have to interconnect cells because it is thin, flat, and not as likely to cause breakage as a thick round wire would if tucked behind a cell. The tabbing wire is presoldered and just needs to be sweated into place with a small soldering iron. Don’t use a soldering gun, not adequate control. It’s like soldering egg shells, that delicate. If you were never able to build balsa wood airplanes without breaking the small pieces then this may not be for you.
Liquid solder flux for electronics – not Kester solder paste. This is just to aid soldering the tab wire to the connections on the front and rear of the cells. Apply it with a needle by drop or fine syringe to the tab wire as you go. This takes time and patience. Use a small fan to blow away fumes from the heated flux so that you aren’t inhaling it.
1 Shottkey power diode of sufficient current and voltage. The PV array will require one diode between it and the charge controller to prevent back flows of current at nightif a charge controller is not used, When a small panel is used to keep up a charge on a large battery a blocking diode is usually not necessary. When a charge controller is used the internal electronics are adequate for preventing reverse flow at night. Even without a charge controller or a blocking diode back flow from a battery into a small panel is not enough to be a concern according to literature available on the web. If you have series parallel strings of PV arrays then you may generating higher voltages than 12V (48V, 120V, etc) then it may be useful to put a blocking diode in each string to prevent possible destructive back flow into a string should that string become blocked by a shadow.
Here's ones that I purchased from eBay (five for $6.30 US):
Here's a link to a data sheet that shows you the pin outs and ratings. Note that these particular ones are duals. Two diodes on one heat sink. I purchased them for a different project but they are fine for this one too. Quite inexpensive. Just remember that electrons flow from negative to positive. If you look at the schematic of this diode assembly you will see two arrows pointing to a short flat line. Electrons flow against the arrow. That is they enter the pointy end and flow to the back. If you turn it around you will discover that the current will not flow, like a one way valve.
The Schottky diode is preferred over a silicon power diode because it has a fraction of the voltage drop loss in conduction than a silicon one (about .15V compared to .7V) every little bit helps. Besides that the cost of a Schottky diode is very little more than that of a silicon diode so why not eh! In this case you could make use of both sides of the diode assembly. On one side you could have a solar array and on the other side a wind charger. It’s often done that way commercially because when the sun is in hiding the wind is often blowing and vice versa.
Mounting board to mount PV cells on (must be sealed against moisture). Do not use plastic like ABS. It has a high coefficient of expansion, likely will bend and break any cells attached to it. One fellow used perf board as a mounting and it worked fine. Just be sure to seal it up well with a moisture resistant sealant and or paint. Make sure it’s thoroughly dry before attaching cells to it.
Showing tabbing wire on the back of some cells. Note that they are in series with each other just as if you were wiring up flachlight batteries to get a higher voltage.
Tabbing wires attached to the front and back of PV cells
PV cells tabbed and mounted to perf board with dabs of silicon calking. Note that the perf board is sealed and covered with white paint.
Thanks to my good friend VA7AYE for the above three photos shot during his trial by fire constructing a couple of PV panels. One thing that he discovered is that it's not a good idea to solidly fasten PV cells to a plastic backing, especially if that backing has a high expansion coeficient. It can cause flexing that will snap the cells into one or more pieces. They are quite unforgiving, don't stretch or bend.
Glass or plastic cover to protect cells – I used a pane of glass from a discarded sliding door that had been replaced by thermopane doors. Lots of that sort of thing available as people upgrade their older homes. While searching on the web I found a site extoling the virtues of encapsulating an array of cells between two layers of plastic, the same stuff you may use to preserve ID cards. I suppose it would cover the cells but you still need a stiff backing to protect the cells from cracking.
Plywood backing board to give the assembly some strength (3/4” plywood may be necessary for large arrays and thinner plywood for smaller arrays). You don’t want the panel to twist or seriously warp as that would cause the cover glass to shatter and the cells to crack.
Aluminum or plastic edge cover to prevent moisture getting by the glass. Could be angle aluminum or plastic. Aluminum stands up well to the UV in the sun whereas most plastics break down but are cheap to obtain.
Silicon caulking to seal edge cover to the glass and to the sides of the backing board and also to glue the PV cells to the backing board. It can also be used to bed the aluminum edge cover to the glass and edges of the plywood.
White gloves (don’t touch the surface of the PV cells with bare hands/fingers because the oils and acids will destroy the coatings and reduce the PV cell output)
Charge controller to control the charge going from the PV arrays to the battery. The lead acid batteries generally take about 13.8 volts and the 36 cell arrays can put out close to 20 volts. The charge controllers knock the voltage back in various ways depending on their design and there are several designs. If you are using the photovoltaic array for powering up communications equipment whether for transmit and receive or just receive you will want quiet power. I have a PWM controller and it uses “Pulse Width Modulation.” It was cheap and effective but during peak charging hours there is a whine on the power that comes through the speakers. This can be knocked way back by inserting block filtering between the charge controller and the battery. It’s simply a choke and one or two filter capacitors but the choke which is in series with the power must have low resistance so that there is not too much voltage drop across the internal resistance.
The MPPT (Maximum Power Point Tracking) charge controller is the shining star of today's PV systems. It’s more expensive than the PWM type but gives you much better output from the solar panels over a whole year. Basically what it does is convert the incoming voltage and current from the PV panels to high frequency AC and then back into DC to charge the batteries. From what I have seen there are two classifications, digital and analog and the digital ones have additional benefits and higher efficiency. A microprocessor, in the MPPT unit, watches the voltage available from the PV panels and it also watches the battery voltage. It adjusts the charging to suit both. If the sunlight falls off due to cloud then the controller will boost the voltage so that the output is effective at putting some charge into the battery.
In the case of my PWM (pulse width modulation) charge controller when the panel voltage drops below the battery voltage no charge comes in. The MPPT controllers are much more expensive than the PWM controllers but obviously they do much more. In the winter you can get an increase of 30 to 40% or more because of the up conversion on those cloudy days we normally get. It's a matter of getting what you pay for. A company in Washington State, Outback, make some top end ones. Morningstar also makes some MPPT's. Morningstar also makes some of the PWM type and they are useful too as an economical start to putting a PV system together. I use one with our setup in our camper. The thing about that is that it only gets used in the summer and only has one PV array. It's, therefore, not worth the extra cost of an MPPT for that application. I've only mentioned a couple of brands but there are many other good ones.
http://www.outbackpower.com/pdf/specs/flexmax.pdf
http://www.morningstarcorp.com/en/home
All cells will be attached together in series or series parallel arrangements and that should be done by using the tabbing wires to jumper them together. You probably will be getting 3 or 4 amp cells. If you build an array like that then the smaller tabbing wire will do. If you choose to parallel up several cells to give more current then you will need to choose a heavier tabbing wire but beware that the heavier tabbing wire will be tougher to manage when soldering across a cell.
There were various suggestions about the sides. Aluminum angle about 1/8" thick and at least 2" on each side would probably be my choice or better yet - "L" channel that's 1/2" on the front and 2 inches on the side. . One of the suggestions I read to make use of steel studs. Not sure how that plays out and in my area with west coast rain forest climate. There would need to be serious painting or the PV panels would succumb to rust.
If your cells have not been tabbed yet then go ahead with that very carefully. As I mentioned they are fragile as egg shells when they have no backing for protection. Use the pre-soldered tabbing wire to connect the thin contact strips together. Those are the shiny metallic ones that run end to end on the cell and they are about 1/8” apart. Leave a couple of inches of tabbing wire on each side of the cell to allow you to connect to the next cell. You need to do that to both sides of the cell and I would suggest offsetting the front foils from the back foils a quarter inch or so to reduce the chance of shorting them together.
The next strategy will be to determine whether to multiple cells together in parallel for more current or whether to achieve the same by multiplying whole arrays together. What I mean is that you could build a large array with, say, thirty six groups of three cells strung together (108 cells) to achieve around twenty volts and around 12 amperes or you could build three 36 cell arrays and then parallel them together to achieve the same thing. I lean toward having three separate arrays. That way the smaller tabbing wire works and if one array needs to go off line for some repairs it can. In either case only one Schottky diode is required.
When your cells are ready to be installed you will need to glue them to a backing board. As I mentioned under supplies another friend used peg board with success. He put a single dot of silicon seal dead in the middle of each cell as he laid it down. Remember that these cells have a polarity and when you connect them in series the foils on the top of one will need to be soldered carefully to the bottom of the next one. If you are careful you should be able to keep the in-between spacing down to 1/8”. One chap suggested using a piece of 1/8” hardwood dowel as a spacer. You stick the cells in place and then move the dowel on to the next position. The idea is to try and make a tidy job and by having uniform spacing that can be achieved.
You should have a square array of 6 strips of 6 cells for a total of 36 or 18V. You could as easily make a 4 X 9 panel if the glass and backing or your own design layout dictates that. A sliding glass door (mine) has glass panels about 27" X 75". Using a pane of glass that size a person could lay out three arrays of cells on the one sheet. That would create a total possible 140 watts out of the charge controller (really is not 12V but 13.8, typical of automobile power with the engine running). Not bad for something that may cost you under $200 if you have access to recycle material to help out with your project. Commercial panels of that much wattage are generally smaller and lighter but we are saving bags of money so no complaints now.
I suggest painting the backing plywood board with something like white epoxy paint as a sealant both front and back and sides or maybe some white marine paint. White paint will not absorb as much heat as other colors. Make sure that it's thoroughly dry before fastening the PV cells to it. Also make sure that there are no thick wires or lumps that will hold up a cell. Ideally they should lay as flat as possible (or they will break when you lay the glass in place.).
Once the cells are glued to the backing, but not yet set, you can lower the glass onto them. When the glue has actually set then you can fasten on the aluminum edging. You need at least 2" or more on the side to fasten supports to. Also you need to apply a good caulking around the sides to keep water out and bed the glass so no water leaks in from the front. If there is any opening it must be on the bottom to let out any moisture or condensation. Alternatively you could put a 1/4" spacer all around the outer edge of the plywood backing so that the glass does not come in contact with the PV cells and reduce risk of cracking one which may be sticking up for nsome reason.
What then? You need some way to support the panels whether it be on your roof or out in your yard. I have a panel, a commercially made one, and it’s mounted to the roof of my Trillium trailer. It took a lot of soul searching to decide just how to do it. The big question in my mind was whether to mount it totally horizontal or to design it so that it could be tilted directly into the direction of the sun. I eventually settled on the simplest solution, I mounted it flat. It’s much more robust than it would have been if it were able to be pointed. It was not a bad decision either. The panel has been able to gather sufficient sun light to keep our deep discharge battery up for all the time we have been on the road.
Further to that and my previous concerns, I had wired my truck and camper so that when my truck engine was running a solenoid relay would close and supply power to the camper battery to charge it up while we were on our way. Eventually I disconnected the charging system from the truck and the single 70 watt panel has been adequate for our needs ever since.
Preferred Battery Type
The only improvement I am seeking to make is to replace the battery in the camper with a sealed AGM (Absorbed Glass Mat) 12V deep discharge battery. I use one in my house for my ham radio needs and it does a great job.
Down side of AGM batteries – they aren’t cheap. I bought a 110 Amp 12V one a couple of years ago and it cost me a around $130. I recently purchased one that was considerably smaller and it’s price was almost the same as the big one. Cost of metals like lead have gone up. Anyway, the AGM battery is the way to go. No vents spewing noxious fumes or explosive gasses. No maintenance. Reliable. Seems a no-brainer. I was told that the AGM batteries seem to have also taken over the market formerly held by gel-cell batteries.
PV Panel Mounting
More about mounting of panels. If the panels are meant to be up all year round then you need to take steps to secure them very well. The wind is probably responsible for destroying more PV panels than little boys with baseballs. Think of a car door in windy weather. Sometimes the wind can rip a door right out of your hands. If you have deep pockets you can purchase commercially made aluminum support systems for the panels or if your pockets are shallow you can still buy pressure treated 4" X 4" posts and make up a sturdy structure.
You will need to make concrete supports in the ground with steel plates coming up above ground that can be drilled and fastened to the posts or go to a large lumber yard and they will probably have ready made supports but they are a lot more money than doing it yourself. Go to a metal recycling place and look for sturdy 1/4" or 3/8" steel plate or angle iron with at least 2" sides. I have done this with fences and it provides a long life, the post being protected from moisture, mold, and bugs they would otherwise have to contend with in our soil on the wet coast of Canada. I suggest that you make two plates for the posts, one for each side. You can cut them with a hack saw (darned hard work) or a metal chop saw or an angle grinder with metal cutting particle blade/disk. Drill two holes in them with a 9/16" drill and then drill the sides of the bottom of the post. I suggest buying some 1/2" galvanized redi-rod and some galvanized nuts.
You could buy ready made galvanized carriage bolts but with redi-rod you can cut it off to exactly the right length. Once the plates are bolted on dig holes for the footings of the posts. Where I live we usually dig down to clay and then go down to around a doot and a half and maybe 8 to 10 inches wide. If you are on gravel or sand then you would need to broaden out to maybe 2 feet square and only a half a foot. It's a support, you don't want to sink or blow away. I generally line the top few inches of a round footing hole with something called Sonatube. It's cardboard tube used for concrete work and once the concrete has cure you can peel it off and it looks like a professional has been there.
You will need some pieces of lumber and a few nails and a capenters level to support, (vertically, and with the wood a couple of inches above the concrete) the post and get it square. Once that is done you can pour your concrete. The concrete can be posthaste which you mix in a wheelbarrow or a big tub with a shovel, normally used for planting posts, or you can get some Portland cement and gravel and mix up your own. You just add water and stir until it's a homogeneous mass. Pour it down the hole and smooth off the top. If you have done things correctly the wood of your post should be an inch or two above the concrete. When the concrete is set (give it at least a week, maybe two). You should be able to remove your temporary supports and with any luck the support posts won't fall over.
Let me know if you come up with some procedures or materials that improve on the construction of home built PV panels. I will add them on to here, blog style so that others can benefit. I have seen several organizations advertise how-to books on the web and I would much rather see instructions for free, if not to build then to a least learn and share knowledge.
Lead Acid Battery Desulfation Pulse Generator
Lead acid batteries have a slight problem. If you over discharge them or let them sit long enought they will discharge themselves. It's just the nature of the chemistry. If they become sulfated badly enough it's hard to impossible to get much use out of them. The sulfation tends to become products that fall to the floor of the battery or are coatings on the battery that refuse to go back into solution and become part of the electrolyte. The electrolyte being made up of sulphuric acid and water. As more of the electrolyte becomes sulfates the battery loses capacity to do work.
Some clever people have come up with designs for special electronic equipment that is designed to desulphate batteries and there are a lot of claims for having great successes. Here is a link to a page for making your own.
Flexible Amorphous Silicon Material
