Is one method better than the other, or merely a matter of preference? On one hand, kinetic energy generation requires movement, whereas, a light-powered watch, such as a Citizen Eco-Drive model, is obviously more unassertive, and therefore requires less moving parts.
Fewer parts is frequently better re long term trustworthiness, however in the case of a watch it's likely more of a moot point since analogue watches are already made of a zillion parts, so what real difference will a few more make.
Some background on how both these power systems function is likely in order before drilling down to deciding which is best. Glaringly, this discussion has nada to do with watches requiring daily winding either.
Seiko pioneered the self-winding watch back in 1980. They created a way to interpret the motion of the wearers arm movements into the mechanical energy critical to wind the watches mainspring. The fancy word kinetic simply means motion-generated mechanical energy.
The way they do it is by letting arm motion swing this rather odd-shaped rotor, weighted heavily on one side, around a winding mechanism that, with the usage of specialised reversed gearing, will only move in one particular direction. The result is a wound mainspring.
This actually will keep the watch wound as long as it’s worn and so receiving kinetic energy input. However , when left off the arm for a couple of days, it might stop. This is especially germane since I am focusing on dive watches, which might or might not be worn as a regular everyday watch.
To unravel this problem, Seiko added a battery to store the surplus kinetic energy. Now, assuming the battery is completely charged, the watch can lie still for years and still not require winding.
Instead of kinetic energy, Citizen developed a technique to utilize light as a energy source. And it doesn’t have to be daylight – any source of light will do fine.
On the faces of their Eco-Drive watches, Citizen places little solar cells that transform light into electrical energy. This energy is then picked up and stored in energy cells, like a battery, that may supply power for extended periods, even without light.
Again, since were talking about dive watches, this is particularly useful for someone that only uses the watch for diving, vs wearing it each day. By storing up energy for use later, these watches may be left idle for extended periods, and still show the correct time.
In reality many new models, both kinetic and solar, have a hibernation mode where after sensing no movement for a lengthy period, the hands and dial functions stop moving to save energy. But the quartz movement continues to keep the right time, so that once the watch is moved again, they sense that and reset to current.
Battery technology has come quite a ways as well , so it’s gotten to the point at which this storage cell or battery, would last past the lifetime of the wearer. That suggests the battery would never need replacing, making these watches super environmentally friendly.
So which is best? Well, if the watch is worn with any amount of regularity, it appears to not particularly matter. Either power source will work fine. You may also see that either type watch can get left idle for various times starting from months to years, and continue to keep correct time.
I suppose if one left the Citizen solar watch in a drawer long enough, it would ultimately stop from absence of light, but then so would a Seiko kinetic watch from lack of movement. At the day's close, it’s kind of illogical to buy any watch and leave scattered around for ages so the answer needs to be that both energy generation methodologies work fine, and it simply becomes a matter of personal taste.