Energy efficiency of hybrid battery charge-discharge

it gets a little complicated. there is the mechanical and the electrical efficiencies. the electrical side is supposedly in the 90% range when it comes to efficiency.

supposedly the gas engine is somewhere around that 33% efficiency range. i don't recall the actual number at this time.

overall efficiency is based on what you are doing, temperatures, how you accelerate, etc, etc,...

i normally get 39 to 41mpg as an average for the past two years or so. very short trips and brisk accelerations.... earlier today i towed my trailer at a somewhat constant 55 mph. sometimes faster. i traveled 150 to 200 miles. added fuel 80 miles or so into the trip. average went up for that last bit of tank... low though. the rest of the trip i averaged 42mpg. i was pretty happy. i was on highway 14 i think. pretty steep. almost a grapevine.

 

No, it doesn't mean anything. the car is deciding whether it needs to send charge to/from the battery several times a second. it can also send/draw between 1 amp and 100 amps, so you may be seeing it charge at 10A for three seconds and discharge at 30A for one second, same amount of energy.

If it was only 33% there would be 66% lost as heat. as it is able to draw 21kw from the battery you would be dumping 42kw as heat. that is an insane amount of heat.

 

Don't put too much stock in that display. In the situation you describe, the battery really isn't getting used. A little goes in and out, but it's at trivial levels. Since the display is sampled and doesn't discriminate for small levels, you see that "in for awhile, out for awhile" display. In reality the current isn't doing that.

Tom

 

In and out of the battery is about a 15% surcharge

 

About half.

Going from shaft work (a turning wheel) to electricity, to DC, into the battery, out of the battery, inverted, then through the motor back to shaft work, you might get half back.

Better than nothing.

 

This post is key to understanding the efficiency of a gas/electric hybrid. There are serious losses associated with energy conversion, and the hybrid process suffers from these in spades. It's a horribly inefficient process. But here is where it gets interesting: as bad as it is, the losses with a conventional car are even bigger. It's not that hybrids are so great, it's just that they suck less than non-hybrids.

For example, take regenerative braking. Losses come from generating electricity with MG2, converting that electricity to the battery voltage, converting the electrical energy into chemical energy stored in the battery, converting the chemical energy back into electricity, converting the electricity to the motor voltage, and finally converting the electrical energy into mechanical energy in MG2. That is a lot of conversions, and a lot of energy gets dissipated as heat in the process. However, with friction braking *all* of the braking energy gets converted to heat: it is 100% inefficient. If we have a regenerative process that is 67% inefficient we still recover a "free" 33%, which is a lot better than zero.

The same is true with hybrid propulsion. The mechanical-electrical-mechanical path introduces losses, but in most cases the losses are less than those of a conventional transmission and engine forced to run at sub-optimal speeds. It's all about taking an inefficient system and making it a little less inefficient.

Tom

 

Using Torque app in my Gen2, the loss is about 22%. Details of the calculation are here.

 

Good data. I was close. Lose 22% going in, then 22% again going back out to the wheels later.

78% recovery, then 78% recovery again = 0.78*0.78 = 0.61. So you lose 39%. Of the original kinetic energy you had, 61% gets returned to you. Still better than none.

 

Hi everyone .

I have been recording the charge and discharge energy that the battery receives (and a lot more parameters) for more than one year and I can tell what is battery charge-discharge energy efficiency.

It is not possible to compute the efficiency in a single trip because the data is widely scattered. So I made a graphic of the battery energy "lost" Vs battery energy charged for trips and weeks. This "lost" energy is converted to heat.

In the following picture you see some 773 red dots for single trips and 47 blue dots for a week accumulated data. Each color has its own axes (blue values are 10 times red values)


As you can see the linear approach for the blue dots is good enough. The equation tells us that 10.5% of the energy charged into the battery is lost (converted to heat) and is never recovered as electricity from the battery. Also there is an overhead loss of 248 kilojoules per week in my usual utilization of the car (17trips per week of an average of 22.5 minutes) which represents some 0.4Watts "lost" energy with system off during the whole 7days x 24hours.

Big hugs from Frank

 

This is why when driving Not using the battery is more efficient..... eliminate that 30% loss as battery heat. Us experienced drivers always have a hard time explaining that to new drivers, because they think regen braking magically produces energy from the air (it really comes from the gasoline or diesel).

Driving the slow (60-65) helps because it means less braking needed to respond to changes in traffic flow & therefore less energy wasted.

In situations below 10mph, the engine is not very efficient and pure EV is better. (I think? Sometimes I wonder if an engine at 1500rpm actually is better than the EV mode with its inherent 70% inefficiency/conversion losses
.

 

Just remember, that rapid change in charge/discharge you see on the MFD is actually a "good thing (tm)". If the HSD didn't use the battery it would have to use the engine. Any time the engine in -any- car is asked to quickly add power the mixture must be "richened" (more fuel, less air). This contributes to lower fuel economy figures.

As far as the overall losses of running "from the battery", I have calculated it's around the 50% range. Many who calculate it forget that the initial losses are compounded by further losses in the chain. But my calculations are based on estimates not real world data so, as your EPA says, YMMV!

 

no. slow it down to 35 mph and see what the charge/discharge ratio is. should be higher.

your thoughts on efficiency maybe centered on the actions of the display and direction of the arrows but the car must deal with friction, climate, tire pressures, etc. all of which will ALWAYS lower the ratio of discharge to charge ratio. your car also has to deal with gravity which can help at times (downhill) but that is rare since even flat land driving still lowers efficiency.

imm; what you are probably seeing is imperceptible changes in altitudes. when I drove my Prius at highway speeds, the ratio was MUCH lower

 

According to Nissan their Leaf EV only recovers 40% of the car's kinetic energy. The rest is wasted as air resistance and rolling friction. I would not be surprised if the Prius' KE recovery is even lower, due to additional losses in the transmission, engine braking, etc.

 

The LEAF's ability to recover power from regen varies considerably according to batt temps, SOC, etc. But will say that the power of the motor can be as high as 80 KW while regen is only 30 KW so that is ummm, 30/80?? ya, I say 40% is pretty close...

FYI; the relationship between the max power of the motor and max regen has nothing to do with the efficiency and the key point to take away from this post is the variance in available levels of regen...

 

I think the key point is that most of a car's kinetic energy is Not recovered, but instead dissipated as heat by air resistance, rolling resistance, engine/transmission friction, etc. This is true of both hybrids and non-hybrids.

 

That's why teleporting is the real future.