Solar Energy in many countries is supported by various government and institutional incentives.
In the US, there are several Federal incentives. One of the most broadly applicable is an income tax credit. The program allows 30% of the cost of a solar system, including installation, to be deducted from tax debt. The credit can be carried forward year to year. There is a separate income tax form (5695) to apply for the credit.
The US income tax credit as well as other local and federal, institutional and governmental programs are well documented and discussed at:
Database of State Incentives for Renewables & Efficiency
Additionally, the USDA, through the National Resource Conservation Service, has incentives and reimbursements that might apply for solar water pumping systems in agricultural applications. These programs are administered county by county through the USDA. For information on available programs and to make application it is necessary to contact your local USDA county agent. The various programs and their requirements are set forward at:
NRCS Conservation Programs