Grouch1980
Senior Member
- Location
- New York, NY
Hi all!
So I'm starting to delve into the field of Photovoltaics. I do have a few questions, some basic, any help would be great!:
1. I read that the purpose of the OCPD fuses on each string (where required) is to prevent fault current from the other strings from flowing into the faulted string. The fuse on the faulted string will then blow, and the currents from the other strings will continue to flow normally, to the load. Wouldn't the blocking diode located on each string accomplish that though?... doesn't that prevent fault current from flowing into the faulted string? Why need the fuse then?
2. The bypass diodes on the solar modules...when they bypass a certain segment of series connected solar cells, the solar module is still producing current from the other segments, minus the current from the segment that is shaded / damaged and bypassed by its diode. is this correct?
3. When you size a PV installation for a townhouse for example, what's the usual starting point? do you go by the maximum sized breaker you can place on the panel, not exceeding 120% of the panel bus between all sources (PV and utility)? I would assume that if you use that as a starting point, that's the max sized system KW wise that you can use. and then a further limit would be the size and shape of the roof, possibly shrinking the system even more. and then of course is what can the owner afford.
4. I've seen designs where the positive and negative wires from the strings each go into its own MPPT on the inverter. Is that typical for an MPPT, where you have one MPPT for the + wires and one MPPT for the - wires?
As always, thanks!
So I'm starting to delve into the field of Photovoltaics. I do have a few questions, some basic, any help would be great!:
1. I read that the purpose of the OCPD fuses on each string (where required) is to prevent fault current from the other strings from flowing into the faulted string. The fuse on the faulted string will then blow, and the currents from the other strings will continue to flow normally, to the load. Wouldn't the blocking diode located on each string accomplish that though?... doesn't that prevent fault current from flowing into the faulted string? Why need the fuse then?
2. The bypass diodes on the solar modules...when they bypass a certain segment of series connected solar cells, the solar module is still producing current from the other segments, minus the current from the segment that is shaded / damaged and bypassed by its diode. is this correct?
3. When you size a PV installation for a townhouse for example, what's the usual starting point? do you go by the maximum sized breaker you can place on the panel, not exceeding 120% of the panel bus between all sources (PV and utility)? I would assume that if you use that as a starting point, that's the max sized system KW wise that you can use. and then a further limit would be the size and shape of the roof, possibly shrinking the system even more. and then of course is what can the owner afford.
4. I've seen designs where the positive and negative wires from the strings each go into its own MPPT on the inverter. Is that typical for an MPPT, where you have one MPPT for the + wires and one MPPT for the - wires?
As always, thanks!