How much can DRL lights improve fuel consumption?

Lets say that DRL lights power consumption is about

P_DRL = 10[W].

Alternatively you can drive with “normal” lights on, that is: a front low beam + rear position lamps and registration plate lamps (in my case H7, R5W, W5W respectively)

P_NORM=2*55+2*5+2*5[W] = 130 [W],

we have omitted dashboard back-light but it shouldn't introduce too much error.

Volume of fuel V with energy density E_d needed to supply power P in time t is given by

where η_total is total efficiency.

Distance S is:

S = vt

where v is speed. We can also write:

lets insert t in the first fraction and we get:

Efficiency η_total is product of a engine efficiency η_engine, and a belt and alternator efficiency η_balt

If we want to calculate the volume fuel difference we should insert power difference into formula so:

Lets assume that belt and alternator efficiency is

η_balt = 50%.

In case of diesel engine

Ed = 37.3[MJ/ltr]

let also assume peek diesel engine efficiency

η_engine = 40%

The table shows fuel consumption at different speeds calculated according to presented assumptions calculated with formula (*)

In case of petroleum engine

Ed = 34.0[MJ/ltr]

and peek engine efficiency about

η_engine = 30%.

In real life we can expect much lower engine efficiency, depending on various conditions you can expect larger numbers, it is larger fuel savings. 

Profiling energy usage in a household

Energy consumption in my parents house is about 300 kWh per month. We have replaced incandescent light bulbs couple of years from now and we are systematically replacing fluorescent lamps with LED lamps because they consume even less power that fluorescent. We are moving toward energy-saving technologies. We are using solar water heater instead of electric boiler and whole house is equipped with improved thermal insulation. We live in central Europe so in winter it is nothing exceptional when you see -20 Celsius degrees (-4 Fahrenheit).

Yesterday I did a little experiment. When everybody was sleeping I switched off freezer, all computers and TVs, by switching off I mean pulling a plug from a socket. I was wondering how much current do consume devices which are switched on all the time, this devices are:
-microwave oven with nice shiny LED clock display
-conventional electric oven with another shiny LED clock display
-wi-fi router and power-over-ethernet power supply
-amplifier for a TV aerial
-electric stove (it was of course on idle)
-vent hood in a kitchen

We use an old plain electricity meter without digital display so to make total current consumption I had to use stopwatch to measure how much time does it take for a wheel inside the meter to make a whole turn. It was 312 seconds. Considering that 120 turns correspond to a 1kWh I calculated that a total idle power consumption of mentioned devices was around 96W. That is much energy. 96W 24/7 is around 70kWh per month. Idling devices are responsible for a 23% of power on a electricity bill.

Yeah, now I simply have to find out which devices are responsible for a most of this 23% and simply switch them off as often as possible. This devices:
-wi-fi router and power-over-ethernet power supply
-amplifier for a TV aerial
are on an attic and they are not_so_easy_accessible, so to ease my experiments I used a remote controller to switch them off without going to the attic. When I will repeat whole house idle consumption measurement with couple of devices switched off I will easily find power consumption of this two first suspects. I took a look inside the remote receiver, it has got transformerless power supply and it consumes about 1/2W so it will not introduce considerable errors to my measurements.