The relevant bit is in the
Internal Revenue Code Section 30, which applies to low-speed electric vehicles (so-called "neighborhood electric vehicles" or NEVs) and to two- and three-wheeled electric vehicles. This section called for a 10% rebate up to $2500, and expired on Dec 31 2011. This section was originally introduced back in 1991 (!) as part of the
Energy Policy Act of 1992, and appears to have evolved from its original intent (mainstream 4-wheeled vehicles) to apply instead to NEVs and 2- and 3-wheeled vehicles.
(f) Termination
This section shall not apply to any vehicle acquired after December 31, 2011.
There is also the newer
IRC Section 30D credit which applies to highway-capable 4-wheeled electric vehicles such as the Chevrolet Volt and Nissan Leaf. This credit was introduced by
H.R. 1424 on 3/9/2007.
(a) Allowance of credit
There shall be allowed as a credit against the tax imposed by this chapter for the taxable year an amount equal to the sum of the credit amounts determined under subsection (b) with respect to each new qualified plug-in electric drive motor vehicle placed in service by the taxpayer during the taxable year.
...
(d) New qualified plug-in electric drive motor vehicle
For purposes of this section—
(1) In general
The term “new qualified plug-in electric drive motor vehicle†means a motor vehicle—
(A) the original use of which commences with the taxpayer,
(B) which is acquired for use or lease by the taxpayer and not for resale,
(C) which is made by a manufacturer,
(D) which is treated as a motor vehicle for purposes of title II of the Clean Air Act,
(E) which has a gross vehicle weight rating of less than 14,000 pounds, and
(F) which is propelled to a significant extent by an electric motor which draws electricity from a battery which—
(i) has a capacity of not less than 4 kilowatt hours, and
(ii) is capable of being recharged from an external source of electricity.
(2) Motor vehicle
The term “motor vehicle†means any vehicle which is manufactured primarily for use on public streets, roads, and highways (not including a vehicle operated exclusively on a rail or rails) and which has at least 4 wheels.
Emphasis added. 30D does not have a fixed sunset date, but instead will phase out for each manufacturer once they have individually sold 200k units in the United States.
(e) Limitation on number of new qualified plug-in electric drive motor vehicles eligible for credit
(1) In general
In the case of a new qualified plug-in electric drive motor vehicle sold during the phaseout period, only the applicable percentage of the credit otherwise allowable under subsection (a) shall be allowed.
(2) Phaseout period
For purposes of this subsection, the phaseout period is the period beginning with the second calendar quarter following the calendar quarter which includes the first date on which the number of new qualified plug-in electric drive motor vehicles manufactured by the manufacturer of the vehicle referred to in paragraph (1) sold for use in the United States after December 31, 2009, is at least 200,000.
(3) Applicable percentage
For purposes of paragraph (1), the applicable percentage is—
(A) 50 percent for the first 2 calendar quarters of the phaseout period,
(B) 25 percent for the 3d and 4th calendar quarters of the phaseout period, and
(C) 0 percent for each calendar quarter thereafter.