index Expo Renew Nonrenew 2source Slowren Factors Recycle Daypr

Growth on Two Sources


A system of this type uses two energy sources, one renewable, the other nonrenewable. When the nonrenewable source is used up, the growth declines back to a steady state based on the renewable source.


  • A population of microbes which decompose a pile of leaves and the leaves falling from the trees.
  • The world economy growing up on both fossil fuels and renewable sources.
  • Diagram


    N = nonrenewable energy source
    J = steady inflow of energy
    Q = stored biomass
    K*JR*Q = part of J that goes into the system
    K3 = increasing factor of Q
    K7 = increasing factor of Q
    K8 = decreasing factor of Q


    DN = -K4*N*Q
    JR = J/(1 + K*Q)
    DQ = K7*N*Q + K3*JR*Q - K8*Q


    The graph shows the changes of N (red) and Q (green) over a time period.
    Source code:

    "What if" Experiments:

    Think about the renewable and nonrenewable sources of our economy:

  • If we find more fuels (N), will our industrial society peak higher or last longer?
  • If pollution increases giving us less available clear sun and rain (J), how will this affect the growth and future of the economy?