Many of the cottages build up to the 1950’s used solar water heaters for their showers. It was simply a metal tank painted black. The sun’s rays heated the water.  For some cottages this was the only hot.. or lukewarm water available. 

The concept worked pretty well if the sun was shining and you were the first person to use the shower. If it was cloudy or others had used up the warm water, then you got an icy shower. 

Outdoor showers are still popular but of course, they are connected to a real hot water heater. 

The image below shows the concept in action. It was simple enough and worked for the most part. 

And you thought your Grandparents didn’t know anything about conservation and renewable energy.