My first step was to do a calculation to figure out if my idea was crazy. I started with my goal: Make the solar equivalent of the hot-water tap on a coffee machine.
How much power do I need?
Lets say I want to fill up my mug with hot water in about 15 seconds. That means I'll need to do about 1 liter per minute starting at room temperature (~20°C) and ending at tea temperature (~80°C). That's a 60°C temperature change, and water has a heat capacity of 4.18 kilojoules per kilogram °C. So, for 1 liter (one kg.) we need 250.8 kilojoules. To do that in 60 seconds, we need about 4.2 kilowatts of power. That's a lot!
How big of a mirror is that?
In most places, on a clear sunny day, there's about .8 kilowatts of sunlight per square meter. That means that we would need 5.25 square-meters of mirror, which would be a dish 2.6 meters (8.5 feet) across!
That was a lot bigger than I could make, but it gave me an idea of scale. For example, if I could wait 1 minute instead of 15 seconds for my cup of water, I only needed a 4-foot dish. In the end, I decided to make a 36" dish because that was the biggest I could make on my laser cutter without slicing up my support rings into smaller pieces (which is certainly an option.)