Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1464
| Posted: 10:44am 07 Jan 2023 |
let's see the conversion efficiency:
assuming the volts and amps are calibrated to something close enough
for jazz..
IN: 91.5V x 26.9 Amps = 2460 Watts
OUT: 54.2V x 40.0 Amps = 2168 Watts
conversion efficiency = 2168 / 2460 = 88%
which is pretty good given the voltage difference.
When going from 91.5V to 54.1 V that is nearly a 1/2 drop and there
are some losses in this design that get big when the Vin:Vout ratio is large.
This is looking good.
I find with my two arrays, I run them at lower voltage ratios
when under large power loads. More like 75V to 50V and so the efficiency
is a bit better, more like 92%.
I designed the arrays to have max power voltages of about 75-80V.
Open circuit voltages are of the order of 95V.
Since there is a lot of conversion loss, I would be watching the heatsink temperature
and also the choke's temp. That is where all the losses go.
But anyway, it's greatly satisfying to see another mppt running.
here is today's data for the North facing array.
There is also an array that faces East and it contributes a good lot of energy
in the morning too.
There are two Volts scales. One is the battery. The other is the solar panel array's
voltage. That is why the scales are different.
Vout is battery voltage
Vin is array voltage or mppt input voltage
Iout is mppt controller's output current
9am to 11am it's in MPPT mode, getting as much as it can from the array.
The conversion voltage ratio is ranging from 54V (in) to 72V (in) into the battery that was from 51V to 54V.
Then the max battery voltage was achieved and so there is now no need
for lots of power. This means the panel voltage WILL RISE due to the conversion
needing only a fraction of maximum power. So the panel voltages rise to near open circuit from 11am to 12pm (when my other array kicks in and does the heavy lifting)
and after 12:30pm the North facing array takes over and keeps the battery
at it's bulk charge set point all day.
For the period from 12:30pm to stumps, this array provided all that was needed
and could do it using only a fraction of what was available.
So that is why the array voltage was mid point, around 85V, making about 20-25 Amps.
I know that this array is good for about 3000W but that is not needed in this case
with the battery's state of charge and the system's power load (the pool pump was on all day, pulling about 1kW)
I like these mppt controllers. They get most efficient when the battery needs the most energy (i.e. early in the day there will be low Vin:Vout ratio)
and then they look after the battery once it gets to absorb mode.
here is the data for the East facing array:
with these 2 arrays you can see I have more than enough power available
when the sun is out. I live in Melbourne and so that means the sun is not often
out and not much there when he is "out" during 1/2 of the year. Today was a good day.
The East facing array was simply not used at all from 1pm to 5:30pm
since the other array + controller already had the battery at absorb voltage by its self.
Once it got a bit closer to sunset, then both arrays started to work to keep the battery voltage up, as best they could. But soon there was not enough sun and they both signed off for the day.