Additionally, their stocks are difficult to define accurately, except for biomass. Even so, it would make sense to measure only those resources with slow replenishment rates (such as wood). Thus, stocks of renewable energy resources are not included in the FDES. However, the consumption of renewable energy resources can be measured in terms of energy produced (e.g., hydroelectric power, solar energy generation and wind energy production) and is included in the FDES under Topic 2.2.2: Production, trade and consumption of energy.