Derate question

[DTP]

I am installing a solar system that is 54 panels at 410w, it will be 22,140 kw. The fuses or breaker would be sized at 90A. The exterior electrical panel is a meter main combination that is 200A max with a 200A main breaker. It is impossible to perform a load side connection in this style meter main combo. There is currently a generator breaker in the panel and there is a generator interlock kit installed already. I am currently looking at a plan set that would have me performing a load side tap but I feel that is incorrect as we would need to ensure the system is not on when the generator is in use. The only way to do that would be for the homeowner to remember to shut the disconnect off prior to running their generator or installing the solar as a back fed breaker. I know I would need a different style interlock kit but my issue is the derate. In order to install it properly we would need to derate to 150A. My question is would I be able to derate from 200A to 150A? Also I forgot to mention yes there is a 200A sub panel inside their home.

 

[don_resqcapt19]

I am installing a solar system that is 54 panels at 410w, it will be 22,140 kw. The fuses or breaker would be sized at 90A. The exterior electrical panel is a meter main combination that is 200A max with a 200A main breaker. It is impossible to perform a load side connection in this style meter main combo. There is currently a generator breaker in the panel and there is a generator interlock kit installed already. I am currently looking at a plan set that would have me performing a load side tap but I feel that is incorrect as we would need to ensure the system is not on when the generator is in use. The only way to do that would be for the homeowner to remember to shut the disconnect off prior to running their generator or installing the solar as a back fed breaker. I know I would need a different style interlock kit but my issue is the derate. In order to install it properly we would need to derate to 150A. My question is would I be able to derate from 200A to 150A? Also I forgot to mention yes there is a 200A sub panel inside their home.

Do you mean replace the 200 amp main breaker with a 150 amp main breaker? If so, you would have to prove that the load does not exceed 150 amps. Either do a full Article 220 load calculation or use the provisions of 220.87.

 

[solarken]

I am installing a solar system that is 54 panels at 410w, it will be 22,140 kw. The fuses or breaker would be sized at 90A. The exterior electrical panel is a meter main combination that is 200A max with a 200A main breaker. It is impossible to perform a load side connection in this style meter main combo. There is currently a generator breaker in the panel and there is a generator interlock kit installed already. I am currently looking at a plan set that would have me performing a load side tap but I feel that is incorrect as we would need to ensure the system is not on when the generator is in use. The only way to do that would be for the homeowner to remember to shut the disconnect off prior to running their generator or installing the solar as a back fed breaker. I know I would need a different style interlock kit but my issue is the derate. In order to install it properly we would need to derate to 150A. My question is would I be able to derate from 200A to 150A? Also I forgot to mention yes there is a 200A sub panel inside their home.

Did you mean it is impossible to perform a "supply side connection" in the existing meter main combo?

Is the Generator breaker and interlock in the exterior meter-main panel or the interior sub-panel? If it is in the exterior, and there are not a lot of loads needing backup in that panel, can you move the generator breaker and interlock to the interior panel, add a 150A or 200A main breaker to the interior panel (if MLO), downsize the main breaker in the exterior panel to 150A, and land the 90A solar connection there, and leave the outside as un-protected by the generator, and the inside as your critical loads panel backed up by the generator? You would still need to do the load calculation per 220 as suggested. Of course any critical loads that exist in the exterior panel would also need to be relocated to the interior subpanel.