Steady state represents the equilibrium of the economy in the long term. Equilibrium occurs exactly when the investment equals the break-even investment. As a result, capital stock does not change.
The overall change in the capital stock is equal to new investment minus depreciation: change in capital stock = new investment − depreciation rate × capital stock.
For the change in the capital stock per worker, as opposed to the rate of change, multiply each side by k, or K/L, as convenient: ∆k = (I/K - δK/K)K/L – nk = I/L - δK/L – nk, this simplifies to: ∆k = i – (δ + n)k.
To be more specific, the steady state level of capital solves the following equation: k = k(1 − δ) + sAf(k). At the steady state, the amount of capital lost by depreciation is exactly offset by saving.
The Solow growth model focuses on long-run economic growth. A key component of economic growth is saving and investment. An increase in saving and investment raises the capital stock and thus raises the full-employment national income and product.
The key assumption of the Solow–Swan growth model is that capital is subject to diminishing returns in a closed economy. Given a fixed stock of labor, the impact on output of the last unit of capital accumulated will always be less than the one before.
This parameter can be calculated based on the steady state definition where the rate of input is equal to the rate of elimination. Thus, the average concentration at steady state is simply the total exposure over 1 dosing interval divided by the time of the dosing interval.