Well, Wikipedia claims

The Earth has an internal heat content of 10^31^ joules (3×10^15^ TWh), About 20% of this is residual heat from planetary accretion; the remainder is attributed to past and current radioactive decay of naturally occurring isotopes.

In that sense, it’s the only renewable energy source we have that’s not indirectly powered by the sun. It’s most similar to (proper) nuclear power, but the latter isn’t “renewable” because it requires digging up fuel from the crust.