is it possible to show us the power supply and could you write a short installation stepp info? What raspi image do you use, and what for software package you have installed and what have you changed in the configuration... ans so one...
For the power supply, I'm using a +10 year old Corsair TX650 (650w, 80Plus Bronze). It won't be the most efficient power supply, because of it's age. Also power supplies are the most efficient when you use 50% of their total rated output power. But hard to find (impossible?) a 200w 80Plus Platinum computer power supply. And I didn't want to buy a new one, to only save ~1$ per month of electricity.
It is kept on, with a "jump start" adapter, like these : https://i.imgur.com/ERai2HX.jpg
And I use the 6-pin PCIe connector on the R909. In theory that plug is rated for 75watts (link). But I don't worry about that. Just check it's well plugged in.
For the configuration and installation of the Raspberry Pi, I've got an old model, so I went with the command line OS, no fancy interface or desktop.
To "flash" the SD card, I used Raspberry Pi Imager (link), selected Raspberry Pi OS Lite, and in the advance options activated "Enable SSH" giving a username and password. I'm using a SSH connection to connect to the Raspberry Pi.
Once everything is copied, put the SD card in the Raspberry, and turn it on.
Connect the Raspberry to the network. You'll need it's IP address to connect to it. You can find it on the router, or with a program like Advance IP Scanner (link).
Once you found the IP address, you can connect to it with the program Putty (link).
It will ask for the username and password you entered earlier.
For the installation of CGMiner, I used Kano's website : https://kano.is/gekko.php
sudo apt-get update
sudo apt-get upgrade -y
sudo apt-get install -y build-essential autoconf automake libtool pkg-config libcurl4-openssl-dev libudev-dev libusb-1.0-0-dev libncurses5-dev zlib1g-dev git
cd
git clone https://github.com/kanoi/cgminer.git
cd cgminer
CFLAGS="-O2 -march=native -fcommon" ./autogen.sh --enable-gekko --enable-icarus
make
sudo apt-get install -y openjdk-8-jre-headless
To run CGminer, and start mining, I go in the CGminer folder (cd CGMiner), and enter this command :
sudo ./cgminer -o mining pool -u btc address -p x --gekko-start-freq 400 --gekko-r909-freq 525
I saw somewhere that you should be able to enter that command without "sudo". But if I don't enter "sudo", it can't access the USB peripherals. I'm too lazy to find the fix.
I use "Screen" to be able to run multiple programs in the terminal (CGMiner and HTop) : https://raspi.tv/2012/using-screen-with-raspberry-pi-to-avoid-leaving-ssh-sessions-open
I use "HTop" to see the CPU and RAM usage : https://linuxhint.com/raspberry-pi-cpu-usage-monitoring/
Nice, 99W all in. 2.055TH is about 97% of ideal for that speed, which is pretty solid considering 525MHz is an overclock. I'm pretty proud of the R909.
I'm happy with it also. I ordered six Compac F, before the announcement of the R909. I ended up not using the Compac F, as the R909 is much easier to power, is compact, and needs only one fan to cool down (compared to the Compac F that needs one fan each, plus the USB Hub that has a fan also).For my question what numbers should I look at for the "rejected shares" and "hardware errors", if I looked up correctly, these are the calculation to get the "rejected shares" and "hardware errors" percentage :
Number taken from my earlier screen capture. You need to take the values that are at the top
rejected shares percentage = R * 100 / (R+A+HW) = 6944 * 100 / (6944+14955024+7616) = 0.046%
hardware errors percentage = HW * 100 / (R+A+HW) = 7616 * 100 / (6944+14955024+7616) = 0.051%
If these calculation are correct, I think I have some headroom to lower the voltage, and watt usage. 2Th/s was my goal, I don't want to push it more.
On graphic cards, I'm happy when these values are bellow 1%.
Aber mal im ernst, wer Spaß dran hat, hat bei überschaubaren kosten ein Hobby bei dem noch als Bonus ein ziemlich fetter Gewinn in Form eines Blocks winkt. 
