But the sun doesn't black out!
March 12, 2011 3:15 PM Subscribe
Why do my solar cells have to shut down in the event of a blackout?
I picked up an informational brochure from Home Depot (in Pennsylvania) regarding solar cells. The FAQ includes the following:
Q: What happens if the utility power goes out?
A: During any type of blackout, the system will automatically shut down and restart once the utility power is restored. This shutdown is required by law.
What is the specific law that mandates this? Is it state or federal? More importantly, what is the rationale for such a law? Is it based in electrical engineering necessity or political compromise?
I picked up an informational brochure from Home Depot (in Pennsylvania) regarding solar cells. The FAQ includes the following:
Q: What happens if the utility power goes out?
A: During any type of blackout, the system will automatically shut down and restart once the utility power is restored. This shutdown is required by law.
What is the specific law that mandates this? Is it state or federal? More importantly, what is the rationale for such a law? Is it based in electrical engineering necessity or political compromise?
Best answer: It's (more or less) based in electrical engineering necessity. The issue is that technicians from the power company will be out working on lines to restore electrical service during the blackout. If your solar panels are connected to the electrical grid, you are feeding energy into those lines, which could put linemen at risk during a blackout or at a minimum, complicate their work. See backfeeding for more information.
Similarly, if you have a generator connected to your electrical system, you are usually required to use a transfer switch to isolate your home from the grid to ensure that your generator doesn't backfeed power into the system. It might be possible to engineer a system like this for solar, but I can see how PA law or utility company regulations would have a blanket prohibition in the interest of safety.
posted by zachlipton at 3:25 PM on March 12, 2011 [1 favorite]
Similarly, if you have a generator connected to your electrical system, you are usually required to use a transfer switch to isolate your home from the grid to ensure that your generator doesn't backfeed power into the system. It might be possible to engineer a system like this for solar, but I can see how PA law or utility company regulations would have a blanket prohibition in the interest of safety.
posted by zachlipton at 3:25 PM on March 12, 2011 [1 favorite]
To be worthwhile, most solar cell systems pump energy back into the grid as an additional savings to the owner. If the power company (the controller) shut the line down for maintenance (like during a blackout)it is because they do not want the lines energized while they are being worked on.
Your cell will be powering the grid is a safety hazard if that happens.
posted by Drasher at 3:27 PM on March 12, 2011
Your cell will be powering the grid is a safety hazard if that happens.
posted by Drasher at 3:27 PM on March 12, 2011
Your grid-tied inverter has to be prevented from back-feeding the grid for at least 2 reasons.
One is that workers would like to avoid being electrocuted while working on power lines that have been shut down either by local protection or by generation failure.
The other reason is the need for synchronization between the 60 cycle rhythm of the power provided by the power company and the same 60 cycle power provided by your inverter. If your inverter is feeding the grid when the grid is down, and the grid comes back up and it's not exactly in sync with your inverter, your inverter will be overwhelmed and possibly damaged.
posted by the Real Dan at 3:30 PM on March 12, 2011 [1 favorite]
One is that workers would like to avoid being electrocuted while working on power lines that have been shut down either by local protection or by generation failure.
The other reason is the need for synchronization between the 60 cycle rhythm of the power provided by the power company and the same 60 cycle power provided by your inverter. If your inverter is feeding the grid when the grid is down, and the grid comes back up and it's not exactly in sync with your inverter, your inverter will be overwhelmed and possibly damaged.
posted by the Real Dan at 3:30 PM on March 12, 2011 [1 favorite]
Actually, you want it tied into the main grid in most areas as batteries are very sub-optimal for energy storage and an expense many solar cell owners would like to avoid.
Typically, you're going to be generating more power during the day while you're at work and not using that much power. At that time, many utility companies will buy that energy from you, and you're simply using the normal power grid when the sun's down. So you reduce your bill and strain on nonrenewable energy, but you will not need to lose energy due to conversion to battery storage.
posted by mikeh at 4:08 PM on March 12, 2011
Typically, you're going to be generating more power during the day while you're at work and not using that much power. At that time, many utility companies will buy that energy from you, and you're simply using the normal power grid when the sun's down. So you reduce your bill and strain on nonrenewable energy, but you will not need to lose energy due to conversion to battery storage.
posted by mikeh at 4:08 PM on March 12, 2011
Because the solar cells aren't meant to be the only power for the house.
Ignore all the other stuff. It is correct, but confusing. The panels are like buying a small electricity generation company. Even though they connect together through the electric meter, logically the meter is two separate pieces: one that measures energy sent out to the grid by the panels, and the other measures energy pulled off the grid by your house.
At the end of the month, your bill reflects the amount of power your house used the amount of power your panels generated.
Note: almost all electricity generation facilities need to be connected to an already running power grid to work properly. If everything goes dead (this happened in the Northeast Power failure a few years ago), someone has to fire up a gas or diesel generator to get everything going again.
posted by gjc at 1:24 PM on March 13, 2011
Ignore all the other stuff. It is correct, but confusing. The panels are like buying a small electricity generation company. Even though they connect together through the electric meter, logically the meter is two separate pieces: one that measures energy sent out to the grid by the panels, and the other measures energy pulled off the grid by your house.
At the end of the month, your bill reflects the amount of power your house used the amount of power your panels generated.
Note: almost all electricity generation facilities need to be connected to an already running power grid to work properly. If everything goes dead (this happened in the Northeast Power failure a few years ago), someone has to fire up a gas or diesel generator to get everything going again.
posted by gjc at 1:24 PM on March 13, 2011
This thread is closed to new comments.
posted by dantodd at 3:22 PM on March 12, 2011