What Does an Inverter Do?

     An inverter changes one kind of power [usually DC (direct current) from batteries, solar panels or windmill] to AC (alternating current) power that matches your utility grid.

Choose an Inverter to Meet Your Peak Power Needs

     You may have already calculated what power output is necessary to live your life style. If you choose an inverter that won't support your life style then you must at the very least choose a size that will sustain your food safety and emergency lighting during a power outage. Otherwise, when the electric utility fails, you're dead in the water as far as a renewable energy system is concerned.

      If you choose an inverter to just transfer power as it is being generated by solar panels, and/or windmill max power output, there's no backup for a utility power outage. In southwestern Virginia when hurricane Hugo hit, we were out of power for 5 days and couldn't even pump gasoline to run a generator. Talk to the people from New Orleans (Katrina) or from the floods of Fargo, ND. Not to mention the north east electric grid power failure. Hey,  "Never design a dwarf!" Here's some more info on power grid failures.

Max Emergency Output Power Needs

    I live in the country. Here's the game I play when the utility power goes out. First thing I do is turn off all the 220 circuits in my two circuit breaker boxes. These include base board heat,  bathroom heaters, water heaters, water pump, clothes dryer, and electric stove. My 110 circuits include refrigerator, freezer, coffee maker, micro wave oven, hot plate, floor fans, computers with UPS, TV, toaster, wash machine, space heaters, bath room exhaust fans, Monitor Heaters (computer controlled fuel oil heater with fan) and lights. All the 110 circuits are switched except the refrigerator and freezer.

     I need inverter capacity to run the refrigerator, freezer and water pump. Because I never know when they will kick in and they're not synchronized. I need additional power for lights and what ever else to sustain an emergency life style like hot water for bathing, heat for cooking etc. Most can be rationed and rotated to minimize peak power. Refer to Current Power Usage to review how to make these calculations.         

     Your whole family needs to be intimately involved with the conservation of power usage in order to prevent overtaxing your system. Should you overtax your inverter too frequently or to much, your inverter will fail and you'd be  "out of luck" for any usable renewable energy.

     "Never design a dwarf!" Remember Murphy's Law, "Your inverter won't fail at a convenient time".
    If your inverter is wired into the grid system through a circuit breaker, it can be protected from damage when the electric utility fails. It will require a manual reset in the dark unless you have a separate emergency light that comes directly from the inverter and located at the circuit breaker box.

Match Battery Bank Input

     Your battery bank may be a 12 volt system or 24 or something else. Make sure you select an inverter that accepts the output of your battery bank voltage. Remember the higher the voltage the lower the current for the same power transfer. And the lower the current the lower the power loss in the wiring. Conserving power loss in your system raises the efficiency of your system and gives you more power for your life style. First you design the system that works for you. Then you tweak the design to make it more cost efficient.
Trade - Offs

     1. If you want less weight, run higher voltages in your system. After all:

 power = voltage x current (V*I)

Lower current can use lighter weight wires for the same power loss during power transmission.

     2.  If your inverter is used only to deliver power for net metering, you may be power neutral but you may not have enough capacity to sustain yourself during a power outage without a supplementary source like a gasoline powered electric generator to make up the difference. Even then, you will need a switch to isolating yourself from the electric power grid.

     3.  In most cases, the greater the capacity of an inverter the higher the cost. Consider the differences between a 2.5 kw and a 5 kw inverter.  They're  $249 for the 2.5 kw and $449 for the 5kw inverter. You'll need to shop around to get one to match your system and also meet you need. Up front money may be your biggest trade off against probability of grid failure consequences. Just remember, "Murphy was an optimist."

Load Balancing

All-in-one [Charge Controller - Inverter]

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Karl Kinkel, President & Founder
Longsgap Services LLC
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