If two dissimilarly charged conductive bodies come in contact, the electrons from the body of higher electron concentration will move to the body of lower electron concentration to balance the electron concentration of both bodies. The calculation is based on the total energy output during the year divided by the maximum wind energy output. Actually, hydroelectric and coal-fired power plants produce electricity in a similar way. In many cases, amortization is also considered with electricity pricing because in the next 40 years close to 80% of the power stations will need to be replaced. There are also inherent problems with the hydroelectric power system that uses a pump storage plant system to deliver water to the top reservoir which was discussed in the preceding paragraphs.