2. The cost per kilowatt-hour and payback time for wind generated power.

There are various ways of calculating the total costs of installing, running and decommisioning a turbine and no attempt has made in the program to provide sophisticated means of doing this. Rather this is left to the user because there are too many scenarios to take into account. At the most basic level, a user can obtain a quotation from a manufacturer for the cost of installing a turbine and use this as the basis for obtaining the costs per kilowatt-hour. On the other hand, other users may want to include interest payments, inflationary effects, grants received and so on.

The expression for the costs of the electricity per kilowatt-hour is

where P_m is the turbine mean power already calculated from the previous form and L_t is the turbine lifetime in hours.

When the option to calculate the cost per kilowatt-hour is selected from the menu bar, a form similar to the one shown below opens up. All that is necessary is to enter an estimate of the installation costs (however calculated) and, if they are significant, decommissioning and annual maintenance costs. These are usually small compared to the installation costs for small turbines and so generally can be ignored. For larger turbines, they may be more significant and annual maintenance costs primarily concerned with the infra-structure associated with the wind generated power can amount to around 20% of the fixed costs.

Once the installations costs are entered, the 'Calculate costs per kilowatt-hour' button can be clicked and this results in a display similar to the one below for the cost per kilowatt-watt hour as a function of the mean wind speed and the expected turbine lifetime. The turbine lifetime can be adjusted with scroll bars and its influence on the costs instantly displayed. The monetary units of the costs per kilowatt-hour are one hundredth of the units used for the installation costs so that, for example, if the installations costs are in US dollars, the costs per kilowatt-hour will be in cents. For installation costs in British Pounds, the unit costs will be in pence.

Some users will also be interested in the time it takes to recover the cost of a wind turbine installation.

P_m is again the mean power from the turbine and C_r is the cost per kilowatt-hour of the electricity against which the payback period is being assessed. This might either be the cost of the electricity that the turbine is seeking to displace or, say, the cost of any payments that you receive from government incentive schemes for producing 'green' power - like the US Renewable Energy Credits or the UK's Renewable Obligations Certificates.

The payback period option is also available from the menu bar and, in this case, a form like the one below opens up. Once again, only installation costs have to be entered and then the 'Calculate payback period' button can be clicked.

The calculation of the payback period depends on the cost per kilowatt-hour of the electricity that the wind turbine is seeking to displace or, alternatively, the cost of the electricity that the user will receive through some government incentive scheme such as the US Renewable Energy Credits or the UK's Renewables Obligation Certificates. This reference cost can be adjusted by scroll bars and the impact of this on the payback period instantly displayed.

Both the cost per kilowatt hour results and the payback period results can be printed and/or saved in comma-separated-variable files so that they may be imported into spreadsheet programs like Excel.

Next, the power-output profile menu option.