Economic payback is defined as the number of years it takes to recoup the money that the system cost to install (and maintain) originally.
PV SOLAR SYSTEMS: The initial installation cost does not vary much from site to site (unless the roof is difficult or very high) and this is also true for the income earned - unlike the wind, the sun's irradience is quite similar over the year, within the same region (e.g. south UK, Midlands, North, Scotland etc).
Typical payback time tends to be 7-9 years (with existing Feed In tariff's.)
WIND SYSTEMS: Again, the initial system installation cost is very similar from site to site, however the income earned (directly related to electricity generated) varies considerably. For example a very windy site with a mean wind speed of 7 m/s will 'earn' twice that of an average wind site with a mean wind speed of 5 m/s. This obviously means that the economic payback time will be half...
Typical payback time can vary from 4-8 years (with existing Feed In tariff's)
Of-course the income generated (tax-free) by any renewable generator includes such things as:Savings on bills; Exported power; Increased revenue (for businesses)FIT's - the government has set up a scheme whereby all green electricity generators (i.e. wind and PV) earn 22-28p per KWh of electricity GENERATED - even if it is then used on-site and not exported!