Solar-powered desalination system requires no extra batteries

This seems.. simple?

While it's an odd example for this place, I can bring up self-loading firearms (semi-automatic or automatic in today's terms) as a demonstration. Modern self-loading firearms are VASTLY simpler than the early attempts a century ago. They're an excellent example of engineering evolving under economic pressures.

Late 19th and early 20th century attempts at self-loading firearms were often ridiculous in their concepts; huge component counts, lots of tiny mechanisms, strange attempts at extracting recoil and gas energy, everything under the sun. The mechanisms engineers were crafting in literal garage workshops are stunning in their variety and staggering in their watch-like complexity. Some were genuine works of art.

Then the M1 Garand, the SVT-40, and afterwards the AK (under the economic pressures of WW2) demonstrated how much room there was to simplify and give various components double duties. Now, most modern automatic weapons derive from those designs, and the improvements since have been in the materials engineering: Stronger, lighter, thinner, and generally reducing the amount of steel to the minimum necessary.

The AK copied the STG-44 Sturmgewehr (literally "assault rifle, this is where the design and name comes from) which was revolutionary in design and abilities. Prior to the assault rifle solders weapons were either accurate long range rifles with high power cartridges or close range inaccurate sub-machine guns firing low power pistol cartridges. Military researchers realized that most solders were average people and could not make full use of the high power and accuracy. The solution was an intermediate cartridge that combines the longer range and accuracy of the rifle cartridge with the smaller profile and lower recoil of a sub machine gun. Now you have a weapon that can hit at a distance or go auto and fight close quarters. Huge advancement and advantage for the solders wielding such weapons. Kalashnikov was directly inspired by these abilities and developed the AK in response. Just about every modern "Assault rifle" is descended from the STG-44, not the AK.

The AK arguably took more influence from the M1 Garand, given its rotating bolt, locking lug arrangement, and long-stroke piston. The STG-44 definitely proved the effectiveness of an intermediate round to lay the groundwork for the form-factor.

Indeed. I should have mentioned that it was in fact inspired by both the M1 Garand and STG-44.