I want to calculate how much heat (from solar energy) is stored in Birch wood (1 cubic meter)Is my?

(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)