powerpanel: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/sbin/powerpanel - from package: nut

You may install the required package with command yum install {package}

Error in other languages:
powerpanel: bevel nie gevind nie
powerpanel: comandă negăsită
powerpanel: comando não encontrado
powerpanel: commande introuvable
powerpanel: command not found
powerpanel: käsku ei ole
powerpanel: không tìm thấy lệnh
powerpanel: komanda nerasta
powerpanel: Kommando nicht gefunden.
powerpanel: kommandot finns inte
powerpanel: komut yok
powerpanel: nie znaleziono polecenia
powerpanel: níor aimsíodh an t-ordú
powerpanel: no se encontró la orden
powerpanel: no s'ha trobat l'ordre
powerpanel: opdracht niet gevonden
powerpanel: parancs nem található
powerpanel: perintah tidak ditemukan
powerpanel: príkaz nenájdený
powerpanel: příkaz nenalezen
powerpanel: команда не найдена
powerpanel: командата не е открита
powerpanel: 命令找不到
powerpanel: コマンドが見つかりません