We built an electric cube heater, powered by a 100-watt solar PV panel. During the day, the solar panel slowly heats the cube, which radiates heat to its surroundings. Due to its high thermal mass, the object continues to radiate heat for hours after sunset.
The heat cube can serve multiple purposes. You can use it as a modern variant of a preindustrial foot stove. Put your feet on the cube and throw a blanket over your lap to trap the heat.
Historically, foot stoves contained glowing sintels from the fireplace, but an electric version is safer and healthier. There is no risk for carbon monoxide poisoning or fire. The heat cube contains no flammable materials.
I suspect the added cost/environmental cost of adding a slightly more complicated setup than panel <-> fixed resistor, such as an mppt would be a worthy tradeoff.
I understand the point of the blog is to reduce the inputs to simplify, especially in eschewing batteries, but I suspect the loss in efficiency of not tracking the max power point would be significant.
I do like the concept though, in terms of shifting heat from daytime to later in the day, and localizing it into a box, rather than heating your whole house. It feels like the kind of thing you would put in your bedroom to help keep it warm into the evening.