Solar Batteries

How did you build your own solar panel? any pics? What will you be using the battery bank for? What type of batteries do you have? What's a VAWT?

VAWT = Vertical Axis Wind Turbine

Well essentially I started with the individual solar cells. I was able to buy several off ebay. (dimensions: 3.125" x 6" cells, 0.5V untabbed) I buy "untabbed" but you may want to buy "tabbed". Anyway, I laid them out on a scrap board I had then soldered them together in series. ( 0.5V/cell * 24 cells = 12V roughly) The picture is an in process pic and don't have any final pics this computer. Anyway, as I was connecting them together I put a dab of silicone on the back of each to get them to stay. Also I used my volt meter after every connection to make sure I was still getting voltage and that they were being connected properly. I will try to get some final pics but after connecting all 24 then soldering lead wires on and a diode I came back and built a frame around the board. On the frame pieces I cut out a groove in order to also slide a piece of plexiglass in before finishing. After I built the frame I drilled a hole for my leads and assembled the frame. On both the lead-hole and around the plexiglass I laid down a bead of silicone to protect from moisture.

I basically learned from this website: http://www.mdpub.com/SolarPanel/index.html

I took what he was showing and modified to my own ideas. At least it was a start. Also be kind when critiquing my work please.

FOO, Most of the DIY panels are made with 36. 3x6 cells.and you should try to aim at 18 volts to charge 12 deep cyl. batteries. Your panel dose look nice, but you shoudn't use wood.Try this. Make one like a thermopane window. Go to home depot and get 2 pieces of window glass 24 x 30. and enought of U chanel 3/8 inside dia x 1/2. to use as a frame.And some silica,that is used to remove moisture.they put that in pill bottles or clothes. Take and make 4 rows of 9 cells,[put these Very close together] or they wont fit in the glass.Take the 4 rows and place them on top of one of the glasses,wire them up,TEST them. On the first piece of glass face the Blue toward the glass,now put sctoch tape on the corners of the cells to hold them in place,take a piece of paper towel or something that will hold about 3 tea spoons of the silica,form a pouch and put the silica in it and seal the ends so the silica cant fall out,place the pouch on the back side of the solar cells.Now put a bead of silicone aroung the the whole outside edges, next put the 2nd piece of glass on top, use about 4 cloths pins on each side to squeese the glass together till it dries.Next cut the alum U chanel to fit the sides,Drill the 2 holes for the + and - wires in the u chanel, next put a bead of calk in each chanel and put then on the sides over the glass.You can tape these to hold them in place.These are pretty tough,but remember it is regular window glass,It can take alot of punishment, Well most houses have windows, right. But the panels will last very long with no problems,no water,no moisture.I have about 1500 watts of these panels now for 5 years.

The open circuit voltage for the lead/acid battery is 2.1v. i.e. 12.6v for a 6-cell pack. To charge the battery at a reasonable rate, you will need a voltage greater than this - typically between 14.2 V and 14.4 V, depending on temperature and manufacturer's recommendation. These voltages should be adjusted by −0.0235V/°C for temperature rises above 20C.

Charging too fast (higher voltages) causes the evolution of hydrogen (at anode) and oxygen (at cathode), which can be dangerous, but also wastes power and causes loss of water from the electrolyte.

your numbers (14.2 to 14.4 volts) are correct for a generator. For solar panels, the post recommending 18 volts is correct. Solar panel voltage needs to be a good deal higher than battery bank voltage. The issue is how much CURRENT you are shoving in the battery and the solar panels can only put out a finite amount of current. I prefer to use a lot of battery and not have to worry about overcharging so much. If overcharging is a concern and you don't want to stay "on top of it" (monitor it), get a charge controller.

Ok well I was getting ready to build a bigger panel and thought 14V would be a good target.

Thanks for that.

Now any discussion for some good batteries?

Unless I hear otherwise I will start buying some deep-cycle marine batteries for first go round.

This system (link) is a typical setup...You can expect similar values....The rate of charge needed (number of panels) will be dependent on the daily load, or hours per week, or whatever the power supply is going to be used for....

http://www.homedepot.com/catalog/pdfImages/07/079152c9-63b7-4682-844b-092ea37ea531.pdf

The battery bank then will need the storage capacity to meet the load(in watts) for typical usage, and the number of panels will be sufficient to replace typical daily usage...The unit must have the overcapacity to last without charging for several days(allowing for cloudy weather) and a minimum residual charge maintained in the battery bank, so as not to damage the batteries...so you need a low voltage cutout...This then may switch to an alternate power supply for uninterrupted service....

I got MY best deal by going with a reconditioned fork lift battery. The vendor had it sitting around in his shop for a month after the last charge and it showed the same voltage as you would expect for a new battery. in other words, the battery was literally good as new. it weighed 1400 lbs. My pickup did a serious squat when he put it in the back. I paid under 600 dollars and considered it one heck of a bargain. I think you will find bigger cells are a better deal. Don't forget, you will have to have more cabling if you use a bunch of little batteries like golf cart batteries which I would only use for small systems or mobile apps, like an RV. NAPA when I checked, had great prices on some big cells, brand new. Based on my own personal experience, I wouldn't try to build a battery bank so big that you can go for days without sunshine. Unless you can pare your usage down to next to nothing, you will spend a fortune on batteries. Better just have a standby generator if you are completely off the grid. If you can score a good Onan (one of the old ones that run at 1800 rpm) that runs off propane, you will do well. They are very efficient and last forever with proper preventative maintenance. Converting to propane isn't a big deal for any gasoline engine. You could rig them up to auto start.

You are doing some very interesting work.

To get the most out of your panels, you should consider wiring them for 16-18V. However, this cannot be directly wired to your battery bank because it will boil the batteries--it's 'way too much voltage to charge a 12V bank.

You need to consider investing in a "solar charge controller". Its a device that takes the power from the solar panels and converts it to the necessary voltages to properly charge a battery using a two or three step charging process.

The most up-to-date charge controllers are called "Maximum Power Point" (MPPT) charge controllers. They load the solar panel to its maximum output power...which is a combination of the output voltage and current from the solar panel. This is continuously adjusted as the amount of light reaching the panel varies throughout the day.

While the charge controller is manipulating the solar panels for maximum output it is also changing the voltage to a level that the batteries require for proper charging. Battery manufacturers will tell you what they recommend the maximum charging voltage to be. Since a battery is a chemical reaction, it is dependent on the temperature and most good charge controllers will have a temperature sensor that needs to be attached to the battery. This will control the maximum charging voltage--a cold battery will need a bit more voltage to take a full charge.

One other detail you should consider...your battery bank voltage. 12V is a little low for many applications. Check the availability of solar charge controllers and power inverters in 12VDC if you are aiming at making 120VAC power to reduce your dependence on the grid. It seems to me that these devices in 24VDC and higher are more common.

Hope this helps,

Jon.

I looked into this MPPT gizmos a few years back. They were spendy and I did the math and figured I would get more if I put the money towards more panels and batteries instead of the controller and passed on the controller. Hopefully the prices have come down since then. I think the CONCEPT is a great idea. Be careful of manufacturer's hype. I would recommend look for real user reviews. There is also the possibility that you could buy a controller for X amount of power and then expand your system to exceed the controllers capacity and that would suk

I know a few guys that like Nickel Iron batteries. One is working on some sort of platinum thingy to prevent them evolving hydrogen. One is (was?) trying to make them from scratch. Edison made them but I think a big battery company bought the nickel iron battery company around 1970 and shut it down. Whats his name (talk show host with big chin) Jay leno has a working car with its original nickel irone battery in it.

Anyway the great thing about them is they don't need a charge controller and can be over charged or let go completely dead and will still work like normal when you recharge them. They are currently pretty pricey and there is probably no good reason for the high price.

Brian

Foofire,

You may want to place a high power zener (or a few in parallel with a low values resistors at each zener for power sharing) to prevent overcharge. This way, the overcapacity of your panels will not turn your batteries into an HHO generator .

Overcharging a battery is not desirable and reduces its life drastically. (Almost as bad as deep discharging) The zener diode power should be almost what your panel can take.

One could also use a controlled load to absorb the surplus energy. This could be done using a resettable timer relay on your freezer (cold storage load). The freezer is powered when you have full batteries using a voltage sensor or if the max off time is exceeded. Most freezer can be a day or two without running before they thaw if not open . With this, when your batteries are fully charged, you divert your surplus power into the freezer and "store" the energy. You might want to set its thermostat a bit colder than normal to maximize the "storage" capacity and lengthen the off time possible.

The hot water heater is another loads that you can use in a similar fashion.

This should maximize your efficiency by doing "peak shaving".

Good luck,

GA, only because there's no EA (Excellent Answer) rating!

Thank you fro the good comment and GA.

When one can manage the load, electrical storage needs becomes smaller. This is the basis of the intelligent grid that some day will be wide spread.

In Quebec, we have a popular program with the electric utility company called bi-energy. At my previous house, I had an oil/electric heating system. Using a simple exterior temperature sensor and a relay, the furnace (major load in winter) would use oil when below -13C and electricity above. Simultaneously, the meter would switch to a higher rate when it was very cold. To encourage us, the warm rate was better than what other people were paying. This reduced my energy bills (oil + electricity) by ~20% per year. We also avoided to do the laundry or baking on very cold days etc... We had an indicator telling us when the electricity was more expensive and we shifted the activities that could be delayed by a few hours or a day. This helped the utility company to minimize the demand during peak periods when it was very cold.

The intelligent grid tries to reproduce that in a more automatic form. These same principles are even more rewarding for off grid applications to meet the instantaneous energy production that vary wildly through the day.

BRILLIANT! BOTH IDEAS BRILLIANT!