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>We can never be sure that every building’s solar is properly isolated from the grid. I believe it's part of requirement for solar installation to stop feeding

by tguvot 5y ago

>We can never be sure that every building’s solar is properly isolated from the grid. I believe it's part of requirement for solar installation to stop feeding power to the grid in case there is no power from the grid.

nostrademons 5y ago
Yes, and this is why grid-tied solar installations go out when the power goes out. You need a battery backup for energy independence. This catches a lot of first-time solar owners by surprise if they don't do their research; they think that solar will mean they don't lose power if there's a daytime power outage, but unless they also get a battery they lose it anyway.
- tfigment 5y ago
  You may also be restricted from exporting back to grid at all if there is battery involved by some utilities.
- franga2000 5y ago
  Would a battery really sove that though? If regulations say that anything feeding the grid should shut down if it detects an outage of incoming power (I'm still perplexed as to how you'd measure that on the same conductor, but it's not really my field), wouldn't a battery feeding the grid have to do the same. And if you have the cut-off "upstream" of your house (so your house can still get power from the battery, but the grid doesn't), then why couldn't you do that just with the panels and no battery? Obviously a battery would be better, but in terms of cutting power in an outage, I can't see a difference.
  - andreareina 5y ago
    I imagine it's two separate inverters, a solar inverter that cannot function without grid power and a separate battery inverter. The two feeding the house circuit via a break-before-make transfer switch reduces the chances of accidentally back-feeding the grid because the isolation switch didn't work.
  - nostrademons 5y ago
    When the grid goes down the panels power the house if there's electricity demand, or the battery if there's not. The reason this doesn't work without the battery is that in any closed circuit, electricity production must equal electricity demand at all times. The grid can aggregate millions of households and then has peaking power plants to adjust electricity production to meet electricity consumption. Residential solar panels have no such mechanism - if it's the middle of a summer day and the only appliance you have plugged in is your computer, then that computer is getting your ~4kW of power and is gonna fry. Add a battery and any excess power instead goes to charge the battery. When the battery is full, the grid is off, the house isn't drawing anything, and the panels are still producing, then the circuitry does some trickery to just disable the panels. (I think the inverters actually feed the power back 180 degrees out-of-phase so it cancels out the other power coming from the panels, but the details are beyond me.) Note that the panels are actually disabled at this point, though - they're effectively producing nothing, not just producing less. That's why this doesn't work without the battery - you can break a circuit entirely to stop power from flowing, but as long as the circuit exists without energy storage, power in must equal power out.
m4x 5y ago
It's part of the requirements, but that doesn't guarantee it will happen. Equipment can fail to operate correctly (or be misconfigured) and you still need to verify that the power is correctly isolated before doing work on potentially live conductors.
dreamcompiler 5y ago
That's IEEE 1547.
- sneak 5y ago
  There's a firewire/IEEE1394 joke in here somewhere.

by tguvot 5y ago

nostrademons 5y ago

Yes, and this is why grid-tied solar installations go out when the power goes out. You need a battery backup for energy independence. This catches a lot of first-time solar owners by surprise if they don't do their research; they think that solar will mean they don't lose power if there's a daytime power outage, but unless they also get a battery they lose it anyway.

tfigment 5y ago
You may also be restricted from exporting back to grid at all if there is battery involved by some utilities.
franga2000 5y ago
Would a battery really sove that though? If regulations say that anything feeding the grid should shut down if it detects an outage of incoming power (I'm still perplexed as to how you'd measure that on the same conductor, but it's not really my field), wouldn't a battery feeding the grid have to do the same. And if you have the cut-off "upstream" of your house (so your house can still get power from the battery, but the grid doesn't), then why couldn't you do that just with the panels and no battery? Obviously a battery would be better, but in terms of cutting power in an outage, I can't see a difference.
- andreareina 5y ago
  I imagine it's two separate inverters, a solar inverter that cannot function without grid power and a separate battery inverter. The two feeding the house circuit via a break-before-make transfer switch reduces the chances of accidentally back-feeding the grid because the isolation switch didn't work.
- nostrademons 5y ago
  When the grid goes down the panels power the house if there's electricity demand, or the battery if there's not. The reason this doesn't work without the battery is that in any closed circuit, electricity production must equal electricity demand at all times. The grid can aggregate millions of households and then has peaking power plants to adjust electricity production to meet electricity consumption. Residential solar panels have no such mechanism - if it's the middle of a summer day and the only appliance you have plugged in is your computer, then that computer is getting your ~4kW of power and is gonna fry. Add a battery and any excess power instead goes to charge the battery. When the battery is full, the grid is off, the house isn't drawing anything, and the panels are still producing, then the circuitry does some trickery to just disable the panels. (I think the inverters actually feed the power back 180 degrees out-of-phase so it cancels out the other power coming from the panels, but the details are beyond me.) Note that the panels are actually disabled at this point, though - they're effectively producing nothing, not just producing less. That's why this doesn't work without the battery - you can break a circuit entirely to stop power from flowing, but as long as the circuit exists without energy storage, power in must equal power out.

m4x 5y ago

It's part of the requirements, but that doesn't guarantee it will happen. Equipment can fail to operate correctly (or be misconfigured) and you still need to verify that the power is correctly isolated before doing work on potentially live conductors.

dreamcompiler 5y ago

That's IEEE 1547.

sneak 5y ago
There's a firewire/IEEE1394 joke in here somewhere.