Solar Production in Relation to Amps

[Chamuit]

I am not active in the solar field, so bear with me.

If a home had an hourly outflow of 120 kW, does that mean that the array produced an excess of 2kW/minute (~8A)?

I know production is not linear.

 

[jaggedben]

Solar production is not different from consumption elsewhere.

I don't follow your numbers, and you didn't mention volts or phases. 120kW at 240V single phase would be roughly 500A, for example. That corresponds to 2 kilowatt -hours per minute, but that isn't a number you use to get amps.

I don't know what you mean by production not being linear. Power to amps is a linear equation if voltage is constant.

 

[ggunn]

I am not active in the solar field, so bear with me.

If a home had an hourly outflow of 120 kW, does that mean that the array produced an excess of 2kW/minute (~8A)?

I know production is not linear.

An hourly outflow of 120kW doesn't make any sense; kW is a measurement of power, not energy. If a system produced 120kilowatt-hours in an hour and its output were constant, that would mean that it had a steady state output of 120,000 Watts, which is an awful lot of power for a residence. A typical large-ish residential inverter might be on the order of 8kW; that would be 15 of them running full out.

Typically we load inverters up to a DC:AC ratio of about 1.2; a 120kW AC PV system might be loaded with 144kW of DC modules. A typical residential PV module (commonly called a "panel") might be rated at 300 Watts and measure something like five feet by four feet. 144 kW would be 480 of them; how big is this house?

To close the loop on your question in the subject line, an 8kW inverter would have a maximum output of about 33.3A, so 15 of them would produce about 500A.

 

[Carultch]

Power is to energy as speed is to distance.

The kW are your units of power, which is a rate. The kW-hrs are your units of energy, which means kilowatts multiplied by hours, which is cumulative. It's a little inconvenient that we have the hour unit "upstairs" in the unit of energy, instead of "downstairs" in the unit of power, like we are accustomed to seeing (e.g. miles vs miles/hour), which commonly leads to misunderstandings.

The kW is what can be calculated from Volts and Amps. To get kW-hrs, you need to multiply kW by time given a constant rate. Or if the power isn't constant, multiplication becomes integration.

Assuming the rate is constant, 120 kW of power would be 120 kW continuously throughout the hour(s) in question. But 120kW-hrs, would mean every minute adds 2kW-hrs to the total. This is an unrealistic amount of power for most residences. We'd be talking about the amount of power you might expect for a mansion, instead of a run-of-the-mill middle class home.

I don't know what you mean by production not being linear. Power to amps is a linear equation if voltage is constant.

I think the OP means is constant, instead of linear.

 

[Chamuit]

@jaggedben ben Sorry about the kW instead of kWh.

I received this picture of a report from a colleague. The question asked was, "what is the amperage out?" This is a residence, so 120/240.





I interpret this as the total produced and not the rate. So, the residence produced 2kW per minute to achieve the ~120kWh?
120 kWh ÷ 60 minutes = 2 kWm
2kWm ÷ 240V = 8.3 Am (using Pf = 1)

Am I thinking of this correctly?

@Carultch - correct. Constant.

 

[Carultch]

I interpret this as the total produced and not the rate. So, the residence produced 2kW per minute to achieve the ~120kWh?
120 kWh ÷ 60 minutes = 2 kWm
2kWm ÷ 240V = 8.3 Am (using Pf = 1)

Am I thinking of this correctly?

Thinking about minutes is distracting you from the meaning of these terms.

There is already a time unit in the denominator of kilowatts, since Watts means Joules/second. Inserting another time unit downstairs (e.g. kW/hour, kW/minute, kW/sec) would mean the ramp rate of power, a term that is related to power in the same way as acceleration is related to speed.

Kilowatt-hours means kilowatts multiplied by hours. Given 120 kW-hrs in 1 hour, this means 120 kW-hr / (1 hour) = 120 kW for the average power associated with this time interval. Assuming it is constant, this means we want 240V * Unknown Amps to equal 120,000 Watts. Solve for the unknown amps, and get 500A.

Since this is unrealistic for an individual residence, I suspect that there is more to the spreadsheet that might give some context. Maybe the column refers to kW-hrs on each hourly meter reading, and you'd have to subtract the previous reading to get the kW-hrs you care about.

Another possible explanation is that the current transformer ratio is incorrectly configured inside the meter, assuming it is the type of meter that uses CT's.

 

[jaggedben]

@jaggedben ben Sorry about the kW instead of kWh.

I received this picture of a report from a colleague. The question asked was, "what is the amperage out?" This is a residence, so 120/240.


View attachment 2558983


I interpret this as the total produced and not the rate. So, the residence produced 2kW per minute to achieve the ~120kWh?
120 kWh ÷ 60 minutes = 2 kWm
2kWm ÷ 240V = 8.3 Am (using Pf = 1)

Am I thinking of this correctly?

@Carultch - correct. Constant.

Yeah I'm gonna agree with Carultch that that max hourly output is likely either mislabeled or some kind of error. As I said above, for 120kWh in one hour, that's an average of just under 500 amps. The only 'residential' service I've seen over 500A was for a multiacre compound with multiple buildings, and it was three phase! So either it wasn't really 120kWh, or it wasn't for one hour the way 'max hourly' sounds like.

Do not try to covert to minutes. Just divide kWh by hours to get kW. 120kWh in one hour is 120KW, on average. Since 60mins = 1hour, 120Kwh divided by 60mins is still 120kW. If it were 120kWh in 2 hours, that would be 60kW.

 

[Chamuit]

I wonder if he's got C&I customers mixed in... I'll ask.