3 ms·

Why not just include a cheap resistance heating element mounted somewhere safe so worst case your solar system has some load to take the power?

by api 8y ago

sathackr 8y ago
You would have to constantly adjust the resistance of the element to sink the proper amount of power. Some inverters allow you to over-size the DC(solar) size of the system and indeed dissipate power in excess of its capability as heat. There are inverter systems that can do nearly anything you want, but they are not typically installed.
- dbuder 8y ago
  You could have a motor with a weight on the shaft spin one way and then another. You would have some idea of the maximum size of the load that needs to be dumped. A couple of washing machine motors should do it, or an air conditioner that faces outside.
amluto 8y ago
That’s a pure waste of equipment. A maximum power point tracker can simply move away from the maximum power point to reduce production. Essentially every solar installation has an MPPT. The only insteresting bit is figuring out when and how much power to avoid producing, and it’s exactly the same problem as figuring out when to dump power into a dump load. A case where a dump load is important is small scale hydroelectric power. If you try to draw less than full power from the turbine, the turbine will start spinning faster and faster. So you can use (slow and complicated) valves or mechanical brakes, or you can use a dump load. An interesting case I don’t fully understand is how an off-grid (islanded) SolarEdge system handles a full battery. If I understand correctly, the SolarEdge modules independently track the maximum power point and produce an output voltage of P/I where I is the current drawn by the inverter. So, if the inverter draws less current, the string voltage will increase and the same power will be produced. I think SolarEdge targets 450V for the string, so, even if the modules have a maximum output voltage, there’s not a lot of head room before the string hits 600V and risks exceeding the wire insulation rating. My guess is that the inverter will turn the array off entirely when the battery is too full. Or perhaps the modules have a smallish current limit, and the inverter can reduce its effective input impedance if it needs to curtail production.
- sathackr 8y ago
  The SolarEdge system I have targets 380v. At power up, it runs the string voltage up to 500v to test for isolation(short-to-ground) issues. It has a mode that can temporarily run the string voltage up to 1000v to meet testing requirements in some jurisdictions. Each panel has a "Power optimizer" installed -- basically just a DC-DC converter that has active communication with the inverter. It should be able to control the power production of the entire system by limiting the current supplied by each module, though I don't know for sure that this is how it does it.

Why not just include a cheap resistance heating element mounted somewhere safe so worst case your solar system has some load to take the power?

by api 8y ago

Why not just include a cheap resistance heating element mounted somewhere safe so worst case your solar system has some load to take the power?

sathackr 8y ago

You would have to constantly adjust the resistance of the element to sink the proper amount of power. Some inverters allow you to over-size the DC(solar) size of the system and indeed dissipate power in excess of its capability as heat. There are inverter systems that can do nearly anything you want, but they are not typically installed.

dbuder 8y ago
You could have a motor with a weight on the shaft spin one way and then another. You would have some idea of the maximum size of the load that needs to be dumped. A couple of washing machine motors should do it, or an air conditioner that faces outside.

amluto 8y ago

That’s a pure waste of equipment. A maximum power point tracker can simply move away from the maximum power point to reduce production. Essentially every solar installation has an MPPT. The only insteresting bit is figuring out when and how much power to avoid producing, and it’s exactly the same problem as figuring out when to dump power into a dump load. A case where a dump load is important is small scale hydroelectric power. If you try to draw less than full power from the turbine, the turbine will start spinning faster and faster. So you can use (slow and complicated) valves or mechanical brakes, or you can use a dump load. An interesting case I don’t fully understand is how an off-grid (islanded) SolarEdge system handles a full battery. If I understand correctly, the SolarEdge modules independently track the maximum power point and produce an output voltage of P/I where I is the current drawn by the inverter. So, if the inverter draws less current, the string voltage will increase and the same power will be produced. I think SolarEdge targets 450V for the string, so, even if the modules have a maximum output voltage, there’s not a lot of head room before the string hits 600V and risks exceeding the wire insulation rating. My guess is that the inverter will turn the array off entirely when the battery is too full. Or perhaps the modules have a smallish current limit, and the inverter can reduce its effective input impedance if it needs to curtail production.

sathackr 8y ago
The SolarEdge system I have targets 380v. At power up, it runs the string voltage up to 500v to test for isolation(short-to-ground) issues. It has a mode that can temporarily run the string voltage up to 1000v to meet testing requirements in some jurisdictions. Each panel has a "Power optimizer" installed -- basically just a DC-DC converter that has active communication with the inverter. It should be able to control the power production of the entire system by limiting the current supplied by each module, though I don't know for sure that this is how it does it.