(Genuinely curious since I’ve spent the day doing math adjacent to this one)
The sun releases 3.846×10²⁶ watts. The sun has a volume of 1.4×10²⁷ cubic meters.
Therefore the sun releases less than one watt per cubic meter.
Scanning a 2010 article: Energy from Waste: Reuse of Compost Heat as a Source of Renewable Energy it looks like composting facilities make about 1 to 10 megajoules/kilogram over a fortnight. At 10⁶ seconds per fortnight gets us 1 to 10 watts per kilogram of compost. At a minimum of 100kg/heap (anything less is a pile, a mess, or a spill) it is a trivial exercise to show that compost is orders of magnitude more energetic than the sun.
Now if Hacker News would just allow stick figure cartoons maybe we could lure Randall Munroe into answering these questions for us.
On the other hand, the sun is a cosmic compost heap. ;-)
So, compared to any Earth-bound compost heap, each bit of the sun's surface (wherever you draw the boundary) has more heat-generating interior backing it up.