If I were building my own house, I would make it small and efficient and on a rehabilitated brownfield, but until then, I’ll maintain among other things the cloth napkins and occasional batch of solar-powered (mostly) yogurt.
First, if you need more details, look up a basic yogurt recipe. If you’re set, press on.
On a reasonably sunny, temperate day, bring 8 cups (or desired amount) of milk to 180-200 degrees Fahrenheit in a pot. (I measure temperature with a meat thermometer.) As the milk begins to cool, fill a large mixing bowl with cool water. Place the pot with the milk into the water, like a double boiler, but don’t submerge it. The water will heat up, the milk cool, faster if you stir it. Once the milk is between 100 and 120 degrees Fahrenheit, pour a little of it into one (or several, as needed) containers with some yogurt already in it. (I use about ½ C yogurt total for 8 C milk). Swish around to mix the milk and yogurt thoroughly. Fill the container the rest of the way with milk. Seal the container.
I then pour the warm water from the mixing bowl into a cooler without a top. This step recycles the heat. I set the containers of brewing yogurt into the water, put it all outside under a sheet of plate glass (vented slightly as needed) to let the sun keep everything around 100 degrees Fahrenheit. Let stand 4-10 hours, depending on taste, and at least until the milk has thickened into—voila—yogurt.
Taste-test to make sure nothing went wrong in the process. Hot yogurt doesn’t taste great, but it tastes like yogurt. So far, I’ve never had a batch go wrong.
Maybe more fun than practical, but the solar option saves you those hard-to-recycle plastic tubs and helps you appreciate microbes and nuclear fusion more.