(1 cubic meter of Birch) Is my calculation correct?

Before calculating the heat I need to find out how much energy hit the Birch wood (1 cubic meter) by the sunrays and the weight of 1 cubic meter Birch (670kg)

cp - specific heat of the Birch
q - solar radiation in 1 square meter - 1 Langley (41840 J/m²= 41840 J/m3)
T - 20C
m - mass of Birch wood 670kg

cp = q/m x T

cp = 41840 / 670 x 20
cp = 41840 / 13400
cp = 3.122 J/kgC

...then the heat stored in Birch-

q = V ρ cp dt
= m cp dt
q = sensible heat stored in the Birch (J)
V =volume of Birch (1m3)
p =density of Birch (670 kg/m3)
m =mass of Birch (670 kg)
cp = specific heat of Birch by solar radiation (3.122J/kgC)
dt = temperature change (T-20C)

q = 1m3 x 670kg/m3 x 3.122J/kgC x 20C
q = 41834.8kj
qkWh = 41834.8kj / 3600
= 11.62 kWh
The heat stored in 1 cubic meter Birch is 11.62 kWh
(Note: 1 kWh = 3600kj)