# Values in a solar array

My dad had just bought a solar array of 4kW together with an inverter, a kaco powador 4400.

The array is now running and generating electricity. I am trying to understand how it all works, but several questions pop into my mind. Does the value of 'total yield' in the display reference the amount of kW generated during the day? is the solar array producing power or energy? how much power or energy is the array generating per second?

I asked these same questions to my dad, and he said that the value in the display is the total amount of kW produced during the day, but as far as I remember, you cannot produce power, for power is the rate at which energy is converted into actual work, right?

Could someone clarify the above?

• Power = Watts = instantaneous.| Energy = power x time = eg Watts x hours = Wh or kW.h |Display will most usefull sum Kw.h across small time segments to give total kWh = total energy fo day. – Russell McMahon Oct 12 '14 at 6:58

## 1 Answer

If they wrote the firmware right, a reading in kilowatts (kW) is the output of the solar array at that moment. The total "work", taken over time, will be in kilowatt-hours (kWh). The time period is arbitrary; it may be taken over the course of a day, or a month, or it may be a lifetime total.

If you want to work it out yourself, by recording the output each second, you still have to assume that the output over each second was constant. But that will normally be close enough. One second's worth of power, by the way, gives you watt-seconds, a unit not normally interesting unless you are looking at something like an impulse from a capacitor. 3600 consecutive 1-second readings will give you the output that was generated during that hour, and it will be in kWh. Remember, it's a cumulative total, just like filling a swimming pool.

• That means that the 'yield' is measured in kWh, right? The device has a datalogger which samples every second, if I sum up all the instant values taken at each second, can I calculate the yield in kWh? – Alan Cor Mar 22 '13 at 20:08