diff --git a/src/barotropicqg.jl b/src/barotropicqg.jl
index 33652276..26ca824e 100644
--- a/src/barotropicqg.jl
+++ b/src/barotropicqg.jl
@@ -331,9 +331,9 @@ set_U!(prob, U::Float64) = set_U!(prob.sol, prob.vars, prob.params, prob.grid, U
     energy(prob)
     energy(sol, grid)
 
-Returns the domain-averaged kinetic energy of solution `sol`.
+Returns the domain-averaged kinetic energy of solution `sol`: ∫ ½ (u²+v²) dxdy / (Lx Ly) = ∑ ½ k² |ψ̂|² / (Lx Ly).
 """
-energy(sol, grid::AbstractGrid) = 0.5 * ( parsevalsum2(grid.kr .* grid.invKrsq .* sol, grid) + parsevalsum2(grid.l .* grid.invKrsq .* sol, grid) ) / (grid.Lx * grid.Ly)
+energy(sol, grid) = parsevalsum2(sqrt.(grid.Krsq) .* grid.invKrsq .* sol, grid) / (2 * grid.Lx * grid.Ly)
 energy(prob) = energy(prob.sol, prob.grid)
 
 """