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Going Off The Grid Is A Great Option These Days
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Here are some simple steps to make your off the grid dream a reality: .JPG)
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Many folks in Hawaii and all over the world would like to be off the grid with their electric and hot water. Just imagine for a moment that you have no more electric bill. You will have no more dependence on an uncaring corporation that cares more about profits than you. You will have the luxury of standalone power and will still have power for refrigeration, communications, water pumping etc, when the rest are in the black and at the mercy of a for profit utility. I have been off the grid for 12 years now and have watched all the gear get better and better by leaps and bounds. It’s been an exciting adventure, and it’s time to go off the grid if you can afford it even in a small way. Micro off the grid systems are very useful for communications and small low power applications. A micro off the grid set up also costs a micro amount of dough too. So let’s start with a small set up explanation so you can see what you’ll want for a large system.
Here are some simple parts you’ll need for micro off the grid:
1. PV modules
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PV stands for photovoltaic it’s just an easy way of saying photovoltaic. If you’re hip say PV instead of fumbling on the pronunciation of photovoltaic. Then you are cool and up to date. Please refer to my article on how does a photovoltaic cell work.. PV modules come in a wide variety of flavors. It’s virtual Baskin Robins out there on the PV module market today. There is no such thing as a traditional and conventional PV module contrary to popular belief. They all, however, come in standard nominal voltages of 12 and 24 volts DC. Now, with the advent of maximum power point tracking (MPPT) you have the option of wiring your PV modules to higher voltages than your battery. The new MPPT charge controllers will take high voltage from say 6 -12 volt modules in a series string. The MPPT charge controller down converts the high voltage say 135 volts DC and finds the maximum power point for a given battery say, 12.8 volts for a 12 volt battery. The volts are dropped down and the amperage is increased at the MPPT. The MPPT is the sweet spot and increases power using it. This saves on wire and makes your off the grid system perform up to 25% better. I always spec out MPPT charge controllers these days for maximum performance. Any DC voltage over 50 volts can be dangerous but are relatively safe compared to the high voltage grid tied systems are installed at all over without batteries. Grid tied PV voltages are commonly at 500 volts and pose a danger of deadly shock and arcing in the event of a solar storm. Because it’s DC, the very high voltage electricity will bore a hole right through your finger: ouch! Grid tied PV systems die along with the grid during a blackout or brownout. This is a distinct advantage of off the grid and grid tied battery systems. They never shut off. Plus, off the grid PV voltages are at a much safer voltage of 150 volts DC or less. This will prevent accidents and arcing. Always buy a good digital meter and find the volts DC setting for measurements and polarity checks.
Test your PV module and check the open circuit voltage if it’s a 12 volt nominal module the O. C. voltage should be 18-22 volts DC depending on the module. If it’s a 24 volt nominal module then the O. C. voltage should be double like 36-44 volts DC.
2. Charge Controller
Let’s take the MPPT BZ 250 HV charge controller as an example for micro PV.
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You will take up to four 12 volt nominal PV modules and wire them in a daisy chain series string. The BZ 250 HV will handle up to 250 rated watts total of PV modules. I set one up with 272 total rated watts and it works fine. It has four Uni-Solar laminates rated at 68 watts each. Then the voltage open circuit will be around 82. The BZ MPPT 250 HV can handle the high voltage up to 100 volts O. C. (open circuit). This makes it simple to run one pair of positive and negative wires down to the charge controller through a breaker or fuse on the positive leg at 8-10 amps. They are made in St. Louis Mo. And cost a micro $160 or so. They have an adjustable float voltage on the circuit board on the back. It’s the yellow trim pot. Turn it counter clock wise until the float voltage is about 13.5. Batteries like to be charged to a high voltage first for a couple hours then floated out at a lower voltage. The voltage for bulk/absorb is pre-programmed to 14.1 which is good for all 12 volt batteries with sealed or flooded electrolyte. They come with no enclosure so you can make one out of wood or pay the $40 extra for the metal enclosure. Take care hooking it up because the terminals are small. With #10 stranded wire divide the bunch in two to fit around the small screws on the terminal block on the back in a fork shape, it will fit. The BZ 250 HV gives battery voltage or amperage in, on a decent sized LCD display with a selector switch.3.Combiner/breakers
It’s smart to place a current protection device on the positive leg of every circuit into and out of the charge controller. If you have multiple circuits or strings then you can buy a combiner box with breakers rated to 150 volts DC. This is a good place to put in lightning arrestors for DC to protect your new charge controller from damage by high voltage surges from lightning or solar storms.
4:.Batteries
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Use a good battery, new is best. Check to make sure there is enough distilled water and top them off if they need it. Do not over fill your battery though, it will allow the acid to leak out so watch to make sure the level does not go above the indicator in each cell. Tractor batteries in the large 8D size are heavy duty and a good value. We have found them for $180 each. You can use 12 volt car batteries but they are not designed for deep cycle use. Another choice is a marine deep cycle battery at 12 volts. They have a wing nut on the terminals that will help with installation. Never short out a battery with a wrench or whatever, it will explode so use eye protection and have baking soda or laundry detergent on hand to counter act an acid spill. I do not use baking soda any more to clean off batteries. Just use some good distilled/RO water to rinse them off with. A dielectric grease is good to prevent corrosion and you can paint red and black silicone on the terminals for corrosion prevention and short out prevention. Always take care when wiring batteries. I have a couple of open end wrenches with electric tape all over them to prevent short outs. If you get sealed AGM or Gel cells then you never need to add water. They cannot be charged to over 14.1 volts though with a 12 volt battery. There are options these days for batteries. I like the NiMH ones which have no acid or lead in them, they are known as green batteries. They are in use in the Prius hybrids but are not really available yet in industrial versions which you’ll need. You could create a large pack by combining many D cells together. I shy away from Li-Ion batteries because of explosion hazards. I do like my new Makita drill with the light weight 18 Volt lithium cells in it though. You can place a ground rod in and bond the negative terminal to it for addition lightning protection.
5.Inverters
When it comes to inverters you get what you pay for. There are many low cost high powered inverters on the market that take you DC from the battery and invert it to AC. They call them inverters because they do the opposite of a rectifier. An inverter makes AC from DC and a rectifier makes DC from AC. Because of Tesla, most electronics must have a rectifier circuit to change the AC to DC. If you can get a 12 volt electronic device they work more efficiently because they use the DC power directly from the battery with no inverter needed. .jpg)
The low cost inverters give a squared off version of what a sine wave form should look like. They are known as modified sine wave or more appropriately called modified square wave inverters. The wave form has voltage spikes that will damage sensitive rectifier power supplies. If you try to use a UPS to protect your gear it will not accept the output from a cheap modified sine wave inverter. With a sine wave inverter your electronics will last longer and perform better. For small inverters I like the Exeltech sine wave models from the Texas manufacturer. Mine is for 12 volt batteries and works great. It will work with a UPS for a computer backup.
The low cost inverters give a squared off version of what a sine wave form should look like. They are known as modified sine wave or more appropriately called modified square wave inverters. The wave form has voltage spikes that will damage sensitive rectifier power supplies. If you try to use a UPS to protect your gear it will not accept the output from a cheap modified sine wave inverter. With a sine wave inverter your electronics will last longer and perform better. For small inverters I like the Exeltech sine wave models from the Texas manufacturer. Mine is for 12 volt batteries and works great. It will work with a UPS for a computer backup..JPG)
Add a surge capacitor to a modified sine wave inverter and it will clean up the wave form so it more closely matches a sine wave. This is a cheap way to clean up the crumby power from a cheap inverter. When it comes to inverters you get what you pay for really.
Inverter chargers are the standard these days for off the grid homes. They work as an inverter and battery charger in one. When a generator is started they sync up to it if they can and a relay flips inside so your home is running off the generator and your batteries are charged at the same time. They cost $1500-$2000 and are a must for off the grid homes. They are all sine wave type for high quality power.
At the top is a shot of two Outback Power inverters in a dual configuration for 220 volt power. The system is integrated so all the components talk to each other. The bottom inverter sleeps away and a transformer makes 220 VAC from a single master inverter until the load gets to over 12 amps then the second inverter wakes up and surpluses the power. This way the system saves 20 watts extra power. They are made in Washington and represent the state of the art in off the grid inverter design. They are available in a Grid Tied version that will pump power to the grid after the batteries are charged and make the meter spin in reverse for net metering.
This is a very brief discussion of off the grid basics, if you want to know more send me an e-mail:
Mahalo this is part of my off the grid series for the Honolulu Examiner.
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