My town has started its second heat wave already. Someone at GPUGrid showed me a way to save about 30% on electricity without sacrificing any noticeable performance by reducing default 250 Watt upper limit to 160 Watt and increasing the clock speeds to compensate. Here's how for Linux Mint. Create an executable script and put it in Startup Applications so it'll run on boot up.
BOINC_PL.sh:

#!/bin/bash
/usr/bin/nvidia-smi -pm 1
/usr/bin/nvidia-smi -acp UNRESTRICTED
/usr/bin/nvidia-smi -i 0 -pl 160
/usr/bin/nvidia-settings -a "[gpu:0]/GPUPowerMizerMode=1"
/usr/bin/nvidia-settings -a "[gpu:0]/GPUMemoryTransferRateOffset[3]=400" -a "[gpu:0]/GPUGraphicsClockOffset[3]=100"
/usr/bin/nvidia-settings -a "[gpu:0]/GPUFanControlState=1" -a "[fan:0]/GPUTargetFanSpeed=75" -a "[fan:1]/GPUTargetFanSpeed=75"

That's for a single GPU. If more than one GPU expand it like so:

#!/bin/bash
/usr/bin/nvidia-smi -pm 1
/usr/bin/nvidia-smi -acp UNRESTRICTED
/usr/bin/nvidia-smi -i 0 -pl 160
/usr/bin/nvidia-settings -a "[gpu:0]/GPUPowerMizerMode=1"
/usr/bin/nvidia-settings -a "[gpu:1]/GPUPowerMizerMode=1"
/usr/bin/nvidia-settings -a "[gpu:0]/GPUMemoryTransferRateOffset[3]=400" -a "[gpu:0]/GPUGraphicsClockOffset[3]=100"
/usr/bin/nvidia-settings -a "[gpu:1]/GPUMemoryTransferRateOffset[3]=400" -a "[gpu:1]/GPUGraphicsClockOffset[3]=100"
/usr/bin/nvidia-settings -a "[gpu:0]/GPUFanControlState=1" -a "[fan:0]/GPUTargetFanSpeed=85" -a "[fan:1]/GPUTargetFanSpeed=75"
/usr/bin/nvidia-settings -a "[gpu:1]/GPUFanControlState=1" -a "[fan:2]/GPUTargetFanSpeed=75" -a "[fan:3]/GPUTargetFanSpeed=85"

Use [3] for Pascal (e.g. GTX 1080) and [4] for Turing (e.g. RTX 2080).
Then make the script executable:

sudo chmod +x BOINC_PL.sh

Then run coolbits once the first time to enable it:

sudo nvidia-xconfig -a --cool-bits=28 --allow-empty-initial-configuration

You can look in the config and scroll down to make sure it took:

sudo xed /etc/X11/xorg.conf

There should be a Section that looks like this:

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "AllowEmptyInitialConfiguration" "True"
    Option         "Coolbits" "28"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

If you find a more energy efficient set of parameters please share.