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Old 12-07-2011, 06:12 PM   #1
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Solar at the cottage?

I,m interested in solar lingo things I should ,how to,s etc? For example,amps and watts,what it takes to run anything from a fridge to stereo to a water pump,etc. is there charts for example?


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Old 01-18-2012, 02:16 PM   #2
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All these must be considered. Most solar panels put out DC (direct current) power, just like batteries do. Small solar systems use 12 volts DC, just like your automobiles do, while larger installations may use 24, 48 volts, and sometimes even more. A device called an inverter is needed to convert that power to the 120 volts alternating current (AC) that is needed to power appliances. AC power pulses back and forth 60 times a second. Grid-tied inverters synchronize these pulses with the grid's pulses and will put excess power back into the power grid that you are not using, and your meter will spin backwards Voltage is like water pressure, and appliances are very specific on how much voltage they need. Amerage is another way of measuring electrical power. This is sort of like a gallons-per-minute measurement. In other words, the volume of the power flow. Wattage comes from multiplying both the voltage and the amperage together. For example if I look at a television that uses 3 amps at 120 volts, the TV consumes 360 watts of power. You can look at the back of most appliances and devices and they should have a label on them as to how much power they use either in ampers or watts, and always the voltage. If you are getting serious about a solar system, or at least knowing exactly what your appliances are doing get a watt meter, like a "watts up?" or a "Kill a watt" and plug them into it.

There are also off-grid inverters. These inverters store the power your solar panels make into a battery bank as DC power, and then convert it to AC power as you use it. These are mostly used in secluded areas where it would be too expensive to run electrical lines. They are also frequently used in RV's and boats that are used where there are no power connections. Sometimes though, users of these systems will run DC appliances too. Many new lighting solutions today run off of 12 volts. One can simply attach these low voltage DC lights up to a battery, and run it directly without needing an inverter. This is also a good solution if you are in an area that experiences frequent power outages.

It is important to make sure you have enough wattage on your inverter to power what you want to operate, and the size of your solar panels. Installing 5000 watts of solar panels and a 3000 watt inverter means that you cannot use 2000 of the watts your solar panels will produce. Also, you will not be able to run high wattage appliances off of the inverter. Most grid-tied inverters send power directly to the grid, and this isn't a factor, but in an off-grid system this is extremely important. One of the biggest problems is having enough "surge" power. Appliances with motors, like refrigerators and such require high amounts of startup power for a short time. I purchased a small 15 cubic foot refrigerator that was energy star compliant hoping I could run it off of battery when the power went out. My power meter said it used a paultry 80 watts while running, but upon startup, pulled 1200 watts for a split moment to get the compressor started! I was intending to use it with a little 500 watt inverter I bought at a truck stop, but had to fork over some dough for a 2000 watt inverter! You may run into surge issues attempting to start your water pump. It may pull only a few hundred watts while running, but probably pulls up to 2000 watts or more to get started.

With this being said to, sizing your loads is very important. Using energy efficient lighting and appliances, and also TURNING THEM OFF WHEN FINISHED USING THEM goes a long ways when running off grid. There's lots of nice lighting technology out there to reduce lighting loads to a minimum like LED's and CFL's. Entertainment devices are also fairly efficient as long as your TV is not too terribly big and you are not trying to cause seismic disturbances with the subwoofer. Climate control however can be a big challenge, and it's not recommended to solar power for climate control.


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Old 01-18-2012, 02:30 PM   #3
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If you are choosing to go off-grid, you will need a charge controller for your batteries too. Many off-grid inverters have these built in, but if you go the low voltage lighting route, with no inverter, you will still need one. Using a solar setup on my camping trailer, I have found that a pair of golf-car batteries work great for my wife and I for a weekend's worth of power. The camping trailer has 12 volt flourescent and LED lights in it. It also has a 12 volt propane fired furnace in it too. We usually don't use but about 30 to 50 amperes in a weekend's time.

You will need to access your load based on useage. If you are there only on the weekends, you can probably get by with relatively few solar panels, but lots of batteries. That way, they have all week to charge up. If you plan to be there for weeks at a time, you will need more solar panels to keep your batteries topped off, but can surprisingly, get by with fewer batteries (unless the area gets several days of cloudy weather). One important thing to keep in mind is that you don't want to run the batteries slam down. The batteries will last for several years if you do not let them discharge below 50% or so, so double the battery capacity for what you think you will need.

There's some math involved in your calculations to get you in the ball park. First, determine how much power you will be getting off the solar panels. if you have a 100 watt panel that puts out 12 volts, you are getting about 8.3 amps an hour (100 / 12 = 8.3) This is optimum conditions however. You will need to determine how long the sun is shining on your solar panel, and it will also have reduced capacity when the sun is not directly shining on it...for the sake of this demo, let's say your solar panel gets sun on it 6 hours of the day. I am going to reduce the amperage to 6 amperes that it puts out because it's only going to have sun shining on it directly unless you go out and move it every few minutes. This means that you are now going to put 36 ampere -hours into your batteries (6 amps X 6 hours = 36 amp-hours)

If you are gone monday thru-friday, it means you can have a maximum of 180 amperes of charge built up throughout the week...about the maximum capacity for a set of golf-car batteries. Any excess power is just shed off in the charge controller, so you you only use say 50 amp-hours of power on the weekend, you need more batteries, and then you can use electricity more recklessly

I recommend one of these meters once you get a system together:

I have a tri-metric in my camping trailer, and it works great giving accurate power measurements
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