The short answer is no.
PWM controllers are just fast switches.
When the conditions are such that the power is in excess of what can be used, the switch opens up. It does it in pulses as it attempts to regulate the voltage. Hence the name pulse-width modulation. It is never fully off - just the duty cycle changes to adjust. So yes, power is not used but it is power that couldn't have been used. Like when the battery is full and there is no other load, like an inverter..
But when the battery is not full, or you are pulling other loads from it, the pulse-width gets to be nearly at a 100% duty cycle - meaning that all the energy the panels can produce is transferred.
PWM pulse-widths are continually changing depending on the load and type of battery. You don't want sealed lead-acid batteries bursting, nor do you want open flooded batteries boiling dry. So it quenches the power to keep things regulated. In the end you get all the power you can be used but any reduction is not due to inefficiency. It is under program control.
Wikipedia definition of PWM with diagrams
Here is today's plot of my secondary PWM charger with a 50 Watt panel on a 12 Volt marine battery - it powers the motors which aim my soar panel pairs. (The downward spikes are when the motors (3 of them) activate to reposition the panel pairs)
You can really see how the pulses work, on a cloudy day :
This is very bad for my ham radios. It generates a lot of radio noise.
The PWM charge controller is just one piece in the overall system. Every single device or connection in the system is going to lose some power.
My MPPT charge controller is about 90% efficient. My oversize inverter is about 92% efficient. If you plug in anything with a power converter in it (like a laptop charger), then you lose another 10% or so.
The BIG ONE is that solar panels are tested at 68 degrees. But mine get up to about 120 while operating here in the desert so there goes another 20-25%. Doesn't matter what kind of controller you use. That's just physics. Batteries get more efficient as they get warmer, but solar panels get less efficient as they get hot.
Check out the kind of temperatures I have to deal with:
Using higher voltages is why the MPPT controller is a much better choice than a PWM controller for any non-trivial system. Cable is expensive. Just like the power company - their long-haul lines can be up in the 100KV range, and they still use wires that are about 3 inches thick. That is many dollars per foot.
With PWM you do not have the option of running such high voltages. Your input voltage can't be very much higher than the highest charging voltage or the controller will dissipate the difference as heat. (There are losses in everything, remember - thermodynamics - even the transistors that do the switching) Hence the cooling fins on them. My original 12V system took a lot more amps because the volts were so low.
$$ P = V \times A $$
So now with the MPPT Tracer Commander I run 120V at just a few amps, running through 8 Gauge cables.
The size of the cables is determined by the square of the amps. So if you cut the voltage in half you need to double the amps and have have 4x less resistance in the cable to run the amps you need to get the same amount of power transfer.
Cable is sized by using this rule:
$$ P = A^2 \times R $$
If you want the same power at one third the voltage then you need 9 times less resistance because of all the extra Amps required to carry the same amount of power. That translates to needing much thicker cables for low-voltage systems.
That's what killed off the Edison power stations when Tesla came along with AC that could be stepped up in voltage. Edison had to deliver it at the voltage at which it was being used. He had to have power stations every few miles because of resistance losses in his DC cables. We all know the rest of that story.
I have 6 panels wired in series, (that's up to 120 volts), so the MPPT Tracer controller converts that to the optimum voltage for my 24V 500Ah battery bank (Near 30V for Boost phase, less for Float phase) plus all the gadgets I run both from the inverter and straight from DC.
Wikipedia Definition of Maximum Power Point Tracking
Here is a plot showing the action of the Renogy Tracer Commander MPPT controller. Not at all the same as the PWM unit. This one is running 6 100W panels in series (up to 20 volts each for a total of 120VDC) into 4x 122 Ah deep-cycle Marine batteries wired in series/parallel (24 V bank) and the yellow section shows when the inverter is on, running all the lights and computers. Again, this was a cloudy day but look at how the MPPT controller maintains the voltages because it has so much to work with:
If you want to learn about how the various kinds of controllers work, please allow me to recommend that you watch this video:
** -----> https://youtu.be/g-hqt6pvGxo <-----**
In it, KE0OG, the Original Genius, explains it all for you.
One thing he stresses does not affect me - the partial shadowing. It used to be true that just a tiny shadow on the corner of a panel could cause them to entirely quit working. But my panels have bypass diodes at each cell so the power just goes around the shadowed cells.
Also, I use flooded lead-acid deep cycle Marine batteries. Yes, I have to check them periodically, but the MPPT charger keeps the voltage under control so they do not boil the water away. The fastest way to kill a battery of this type is to let it expose any of the plates to the air. I keep them in Marine battery boxes so there is no acid gasses inside the home.
Since mine follow the sun I can fit 6 panels in the space I have available and get enough power for 24 hour operation.
Towards the end there is a cameo of my system shown. He thinks I have gone a bit overboard. My panels swivel to follow the sun, for instance. If they didn't, I would need twice as many to get the same total power in a day.
Think of it like this: You have a spigot for water outside your house (or in your kitchen). Even when it is shut off there is pressure - that is volts. Then when you hook up a hose to run a sprinkler and turn on the spigot you have water flowing - that is amps. And if you are using it to fill a bucket then that is Watts. The amount the bucket gets full per hour is Watt-hours. In a day, you want as many Watt-hours as you can get. The batteries are the bucket. But it also has a spigot that runs my gadgets.
The trick is to keep the bucket full enough that you have water all night when the sun isn't shining. In my case, I have automatic lights for the kitchen and bathroom, etc., that turn on when someone is there, so I am using the sun's power at night because I stored it up during the day.
This video explains the fundamentals and decisions to make in building out a solar power plant. Choice of a charge controller is front and center in the explanation.
In the end you will see why the Tracer is worth the cost.