svetz
Works in theory! Practice? That's something else
A while back I was looking at bifacial panels on a string inverter, but discarded the idea as the power output was too variable and it messed up the economics.
That absolute max power is a only possible a couple of days out of the year on a fixed-tilt system (e.g., equinox after a hard rain at noon). But on average it'll be far far less. So if you size the system for 455W you spent a lot of money to handle power you'll almost never see.
This is basically the same dilemma about how much power to clip, but due to the variability of the magnitude is greater.
But if there was a current limiting device, you could size the system for the non bifacial wattage and clip the excess. Economically you'd come out way ahead because the bifacials would gather more light under the same conditions as their counterparts. At least that's what the SAM numbers looked like based on available string inverter sizes and costs.
It struck me that an inexpensive device that limited the PV output power would be useful, but didn't see anything appropriate. If you could find a fuse/breaker guaranteed to trip at X amps, but not at .95 X that would probably work, but AFAIK they're just not that sensitive.
Something like this could be done with some CTs and power relays to shut off one or more strings to reduce overall total, and on the old forums @PHoganDive posted this circuit which seems like it would do the job:
But DIY devices are not UL Listed devices. Any ideas on something out that that is approved that could do this at String level voltages and amps?
Example Depending on albedo, a bifacial panel's power output can be +30% the rated wattage; so a 350W panel can vary from 0 to to 455W at STC. |
That absolute max power is a only possible a couple of days out of the year on a fixed-tilt system (e.g., equinox after a hard rain at noon). But on average it'll be far far less. So if you size the system for 455W you spent a lot of money to handle power you'll almost never see.
This is basically the same dilemma about how much power to clip, but due to the variability of the magnitude is greater.
But if there was a current limiting device, you could size the system for the non bifacial wattage and clip the excess. Economically you'd come out way ahead because the bifacials would gather more light under the same conditions as their counterparts. At least that's what the SAM numbers looked like based on available string inverter sizes and costs.
It struck me that an inexpensive device that limited the PV output power would be useful, but didn't see anything appropriate. If you could find a fuse/breaker guaranteed to trip at X amps, but not at .95 X that would probably work, but AFAIK they're just not that sensitive.
Something like this could be done with some CTs and power relays to shut off one or more strings to reduce overall total, and on the old forums @PHoganDive posted this circuit which seems like it would do the job:
But DIY devices are not UL Listed devices. Any ideas on something out that that is approved that could do this at String level voltages and amps?