Who Can Sell Power to the Grid?

It is not really a question of whether you ‘may’ connect your inverters to the grid. It is a question of whether it will actually work for you. And there is a distinct possibility that if you purchase the right equipment and get the right permits that it will still not work and you will have your dreams of getting paid by the power company more than it costs you to purchase from them dashed into pieces and leave you wondering why. Why doesn’t this work? The circumstances are not common, but they do exist and you should know before you start whether your grid tie system will or will not work.

Allow me to explain how a voltage drop applies here. You see, the wire that connects your electric meter to the power company’s step down transformer has a resistance. You can find out exactly how much by measureing it or approximately how much by consulting the CRC Manual of chemistry and physics.

You will find that the voltage delivered to the wire at the power company’s step down transformer is one value while the voltage measured at the top of your main circuit breaker panel is lower. How much lower? That depends upon how far away from the transformer you are and also how much current you are consuming when you make the measurement. It could be several volts. If the wire is a half mile long, as it may be in a rural area, then the voltage drop is larger yet.

“So what!” you say. Well, here is the problem. Let’s say that the voltage drop from the transformer to you is 5.0 volts and the voltage at the transformer is 130 volts. The power at your main circuit breaker panel is then 125 volts, which is well within the specifications. But now you have a grid-tie inverter and a $40,000 solar array and battery system feeding it. How much voltage do you have to produce at your breaker panel in order to actually push power back on to the grid? Well, as I see it you need to overcome the voltage drop from the transformer to your main panel and then add some. At a minimum, you need to produce 135 volts.

What is your refrigerator going to do when you apply 135 volts to it? What are those little CFL lights going to do with 135 volts applied? What if it takes 137 volts to actually push power back to the grid? You should understand that your new plasma TV has its limits. Maybe that was a bad example because many new electronic devices such as computers are able to accept up to 240 volts AC and still work properly. But the refrigerator has a limit, and your well pump, and the whole house air conditioner, and several other expensive appliances in your home or business have upper voltage limits. Apply 137 volts to these devices on a continuous basis and you will shorten the life of those products.

The conclusion is this. Not everyone can sell power back to the grid. It is not a matter of permission or the right grid-tie inverter. It is a matter of physics and you will not disobey the laws of physics.

Questions or comments? Please add yours below.

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