Your battery bank is all charged up and now you need a way to run your 115v appliances. Power invertes turn your batteries DC voltage into AC. Your two main options are true sine wave or modified sine wave. The version you pick depends on the application. True sine wive most accurately reproduces what you get out of a wall socket white flowing alternating waves. A modified sine wave is a cheaper easier to produce version that has a more on and off state rather. After reading this why would anyone not go with the full sine wave? True sine wave inverts can be fairly costly but worth it for your sensitive electronics like TV’s, Computers, printers, fax machines, and general entertainment products. If you are running tools, lights or other general purpose utilities you should be safe with a modified sine inverter.
Batteries are a reliable way to store all your newly harvest energy. But what type of battery should you use in your solar/wind/hydro system? Well there are 4 main type of batteries each with their own advantages and disadvantages. When sourcing out your first battery bank look for deep cycle batteries. Deep cycle batteries are designed to have many continuous deep discharges where a standard car battery is only intended for short bursts of power. Car batteries can be use however their life span will be diminished if discharged to low.
Golf Cart Batteries
Golf cart batteries are popular due to their low price and are great for a budgeted system. Golf cart batteries come in 6/8/12v. Your system could use either a single 12v or 2x 6V batteries wired in series.
Lead Acid Flooded cells.
Lead acid like common car batteries will have caps on the top to top up with purified water. If you are using a non sealed ac battery you will want to store them in a well vented area as hydrogen is produced when the batteries charge
Gel Cell Battery
Gel batteries are sealed and alleviate the need to worry about a vented storage location. These batteries are great for using inside your house.
AGM or Absorbed Glass Mat batteries are one of the best batteries for off grid applications, this how ever come with a higher acquisition cost. AGM batteries do not give off a gas, and are sealed so there is no worry of acid spilling over. They come with a higher price tag but should make up in the added system performance.
Battery Amp Hours Ah
Every Battery will have a rating of its capacity or Amp Hours (Ah). This rating will tell you how many amp hours the battery will put out and for how long. Most electronic will state their power usage in watts. If you have a radio that is 12v 20watts you would divide 20Watts/12Volts = 1.667. If you want to run the radio for 5 hours a day we take 5×1.667 = 8.333 amp hours. If you want your batteries to last you should never drain it below 50% capacity, so in the case we would want a battery with at least 16.6 Amp hours or multiple batteries wired in parallel to make up the Ah capacity.
Batteries can be wired in either parallel, series or both depending on your application requirements.
Another thing to keep in mind is the voltage of you power source. Most panels come in 12/24/36 volts.
If using a 36V solar panel you will need to wire 3x 12v batteries in series to to get 36 volts.
If you are wanting to add extra capacity to your system you will wire your batteries in parallel.
For example if you have a 50amp hour battery you could run light bulb that drew 5 amps for 10 hours. If you added 2 batteries in parallel you battery bank would be able to run the same bulb for 20 hours.
Heating hot water can be one of your home biggest expense. Building a solar hot water heater could save you thousands of dollars worth of electricity or be last link in building your off grid home. In many rual areas central hot water isnt always an option, instant water heaters can be effective but also consume a lot of energy, which is a no no when running your off-grid home of batteries.
Building the Heater
The Solar Hot Water heater has two main components, a hot water tank and a solar collector. Solar collectors work by extracting energy from the suns rays. In this case the solar consists of black pipes contained in a glass covered housing.The black coating absorb the suns rays and heat up, the water is then pumped into the hot water tank for storage.
The solar collector is made up of 1/2 inch and 3/4 inch PVC pipe and florescent light bulbs. The collector is encased in an insulated box with glass on one side.
The solar collector is made up of 1/2 inch and 3/4 inch PVC pipe and florescent light bulbs. The collector is encased in an insulated box with glass on one side.
The solar collector is approximately 2.5 m2 (27 ft2), the pipes that are exposed to the sun have a total volume of about 18.5 liters (5 gallons), which is equivalent to 6% of the volume of the hot water tank. (Meaning that if the water circulates 16-17 times all the water in the tank will have been heated once, in theory).
To make the plumbing part of the heater I bought 64 T fittings and with them made 2 pipes, 32 T’s each with the T’s butt up against each other. Then between the two I put a pipe that was just a bit longer than a florescent bulb.
To prepare the bulbs remove the metal end caps on each end, then poked a large hole in both ends so that a 1/2 inch pipe could fit through. (See below for more on how to complete this step) Then push a piece of a sponge through a couple of times to clean out the powder. While working with florescent bulbs be sure to wear a mas and glove inorder to avoid contact with the dangerous chemicals inside.
bulbs were painted black on the back side, and the pipes were completely painted black. Then I closed off the ends of the bulbs with tin foil and a bit of spray foam, since they are just used as a basic insulator its not that important that they be air tight. The solar collector was lined with black plastic, underneath were some Styrofoam sheets to help insulate the heater.
The panel was installed at a 35 degree angle and about 1 foot below the bottom of the water tank. It is below the tank so that it does not act as a water cooler at night. Basically, the cold water is already at the bottom, so it should not circulate with the water in the hot water tank.
On sunny days when the outside temperature is in the mid 80′s the water heats up to about 135 or more. Even on cloudy days the water heats up to the 90′s. We installed it a month ago and since then we have only turned our electric shower head on full blast once. On cloudy days we turned it on only half way (2500 watts vs. 5000 watts).
Connecting it to the water tank – I put 5 holes into the tank. They are listed here from highest to lowest. # Over flow – just a pipe that carries water out of the tank if the float were to malfunction and it were to over fill.
# Water Intake Valve. Just a pipe and float that fills up the tank with more water as we use it, similar to what is used in a toilet tank.
# Hot water pipe. This feeds the house with hot water. It is above the two pipes that feed the solar heater so that there is always water in the solar heater. This protects it from over heating if our water pump shuts off and no water comes into the tank to replace the water we have used.
# Return from Solar Heater. This pipe connects to the top of the solar heater, and to the top of the tank, just below the pipes above. As the water is heated it becomes less dense and rises. As it rises cold water takes its place. So the hot water flows slowly through the return to the top of the tank.
# Supply to the Solar Heater. This pipe connects to the bottom of the solar heater, it also connects to the bottom of the tank. It supplies the solar heater with the cooler water that settles to the bottom of the water tank.
Cheap $30 Backup System for Cloudy Days:
On mostly cloudy days the heater reaches about 90 degrees, on very cloudy and windy days it wont get above 80 and may only reach 70. So I came up with a backup. (Note: while I have this tested and installed, I actually have it unplugged to save electricity). I bought a ‘Bucket Heater’ that automatically turns on at 80 degrees and turns off at 110.
Why I built the solar water heater this way
After doing a lot of research on the internet, and a couple experiments I came to a few conclusions.
# While glass does block/reflect some of the light, it also creates an insulating buffer. The benefits of the insulating buffer out ways the lost light. This is essentially the same insulating concept used in double glazed windows.
# Since the temperature loss increases when the difference between the outside temperature and the temperate inside the water heater increases, it is better to heat a lot of water to 110-115 degrees, than to heat a little water to 150 degrees. For example, if the hot water tank is at 150 and the outside temperature is 80, there is a 70 degree difference and more heat will be lost through the insulation than if the temperature difference was 30 degrees, and the hot water was at 110.
# Passive solar heating requires (as the name implies) no moving parts. As water warms up it becomes less dense and moves upward, pulling cold water into the collector. This requires no pump, making it very simple and energy efficient, as well as there being less to go wrong.
# A solar heater would heat the water using two forms of heat transfer, radiation and convection. Radiation would reach at best 180 degrees of the pipe, convection would reach 360 degrees of the pipe, doubling the surface area. In other words, as well as trying to expose the pipes to as much sun as possible, I needed to also trap hot air produced by the radiation around the pipe to help heat it even more.
With this in mind I set out to design a solar collector. I priced copper but found it to be very expensive. PVC was much cheaper, but it does not withstand more that 135 degrees. This I found out not to be entirely true.
After some tests I found that the PVC pipe itself will withstand higher temperatures without losing rigidity, however I assume that the fittings would begin to fail at lower, but still hot, temperatures. I should also note that the water pressure in the collector is very low, just as much pressure as is created by about 2-4 feet of fall, others who had failures in their PVC fittings had put their heater inline before their water heater, as a primer. Unlike houses in the USA where the water enters the house already pressurized, houses in rural Brazil have water tanks in their attics to create pressure. So I figured that the max temp for my PVC would be higher than the standard since I have sub standard pressure and will subject the pipes to much less stress.
So decided to go with PVC and to insulate the fittings from the temperature inside the collector and protect them from sunlight. That way only the pipe itself would be exposed to the sun light and the highest temperatures.
Since I wanted to try to keep the heat close to the pipes I decided to use old florescent bulbs to act as a second glazing. The wind will cool the glass panels that cover the solar collector, which in turn cools the air inside the collector. The florescent bulbs act as another barrier. The trap in the hotter air around the pipes and keep it from circulating with the cooler air outside of the bulbs. In tests the pipes with bulbs heated up faster and to a higher temperature than those without.
Sun Trackers are a great way to get maximum performance out of your solar panels. Positioning your solar panels in a fixed location will do the job, but you will be robing your self of free power and maximum efficiency! The only downfall of a solar tracker is it takes energy to move the motor to reposition the panels so they are always facing the sun. Overall an efficient Solar Trackers can produce 30-50% more amp hour making it a very worth while project.
A simple solar tracker can be built using some common radio shack parts, to upgrade this project to full size, you would simply use a heavier duty motor and relays which would be dependent on the size of your panels and how much energy is needed to rotate them.
3 x LDR
1 x 33 R Resistor
1 x 75 R Resistor
1 x 100 R Resistor
1 x 10K Resistor
1 x 20K Resistor
1 x 2N4401 Transistor
1 x TIP120 Darlington pair
1 x 9v Relay
1 x 5v Motor
With the schematic laid out, you can see it is a very simple design. The position of the sensors is what allows this system to track the sun.
Sensor #3 is located in an inverted enclosure so that the light will only hit it when its facing directly at the sun. When the sun leaves photoresistor #3, its resistance increases switching on the Darlington pair which interns switches on the relay that drives the motor. When sun hits the photoresistor it’s resistance decreases disabling the Darlington pair and in turn stopping the motor.
Now you may ask what happens when the sun goes down or is hidden behind a cloudy sky? Does this tracker aimlessly scan the sky? well this is where photoresistor #2 comes in, Flush mounted this little guy can see the entire sky. When photoresistor #2 senses the sun is out it drives the NPN transistor low. If the sun should disappear for the evening, the lack of sun will raise the resistance which brings the NPN transistor base high turning the darlington pair to low and disabling the tracker. Sensor #1 is mounted to the east, which will sense the sun rising in the morning.
I hope this tutorial on building a solar tracker has inspired you to build your own! If you build your own large scale tracker be sure to post what you used for a motor and any upgrades to this system.
The 1000 Watt flux wind turbine was created as part of an off grid power project. This wind turbine uses a permanent magnet alternator to generate 3 phases to charge the battery bank. This wind turbine works spinning 2 magnet discs on both sides of the coils to generate electricity. The act of moving magnets of opposite pols past a copper coil will generate an electrical current. The first step will be to build the magnet disk. Using a piece of wood and a jig saw cut out slots equally spaced around the circle for your magnets, it is important to note when laying out the magnets be sure to adjust the polarity (N S N S N .. ect) For this turbine we used 24 magnets in total, 12 for each disc.
Once you have your template the next step is to lay the magnets in place on top of a smooth surface, use plastic or carboard to build jacket around the circle of magnets. Note: you will want to build two of these disk, one for each side of the coil. For magnets you need to use either neodymium or rate earth magnets.
Once this frame is in place remove the wood template place a small cylindrical object the center magnets (a paper cup worked in this case!). Pour fiberglass resin into the mold and let dry. This will create a very solid disk to house our rotating magnets.
Now that we have our magnet disks hardening its time to build the coils! When building the coils, its a good idea to use 2 strands of wire per coil. A single strand would produce approximately half the out put giving you a 500W wind turbine, so fro maximum output double it up! Now you need to create 9 coils using 14 gauge coper wire. The coils are wired in a rectifying diode pattern in order♠ to let the electrons flow one way. The number of turns of wire will depend on your desire output voltage.
Voltage to turn ratio is as follows 12v – 35 turns, 24v – 75 turns, 48v – 144 turns ect.
Using a sheet of wood out a circle the approximate size of your magnet disc, affix the cutout onto another board to giver your self a “mold” to resin in your copper strands. Be sure to place a smaller circle in the center of the mold for your future shaft to go through. Since we have 9 coils we are creating a 3 phase pattern, every third coil (the corresponding matching tape) is wired together in series. Lay the wires in a 2 phase wye pattern, lay on some fiberglass matting and apply fiberglass resin.
Next we need to build the hub for all this to to be mounted to, The hub is created by using two pipes and some Harley Davidson wheel bearings. The smaller pipe is placed inside of the larger pipe secured by the wheel bearings.
The video below is an overview of the wind turbine in this tutorial by Steve Spence. So be sure to check it out, you also get a sneak peak of his recycled off grid home.
The blades were built out of 2 x 6 pine boards cut at a 10 degree angle and sanded to a smooth air foils finish. This design was created by Steve Spence, for more information on this project be sure to check out http://www.green-trust.org