Corporate Depreciation

Modified Accelerated Cost-Recovery System (MACRS) + Bonus Depreciation (2008-2012)
Under the federal Modified Accelerated Cost-Recovery System (MACRS), businesses may recover investments in certain property through depreciation deductions. A number of renewable energy technologies are classified as five-year property under the MACRS, often known as the energy investment tax credit or ITC to define eligible property.

More details on DSIRE.

Corporate Exemption

Residential Energy Conservation Subsidy Exclusion (Corporate)
According to Section 136 of the U.S. Code, energy conservation subsidies provided to customers by public utilities, either directly or indirectly, are non-taxable. This includes installations or modifications primarily designed to reduce consumption of electricity or natural gas, or to improve the management of energy demand. Eligible dwelling units include houses, apartments, condominiums, mobile homes, boats and similar properties.

More details on DSIRE.

Corporate Tax Credit

Business Energy Investment Tax Credit (ITC)
Concerning solar systems the credit is equal to 30% of expenditures, with no maximum credit. Eligible solar energy property includes equipment that uses solar energy to generate electricity, to heat or cool (or provide hot water for use in) a structure, or to provide solar process heat. Hybrid solar lighting systems, which use solar energy to illuminate the inside of a structure using fiber-optic distributed sunlight are eligible. Passive solar systems and solar pool-heating systems are not eligible.

More details on DSIRE.

Source: Database of State Incentives for Renewables and Efficiency (DSIRE)