| Quad | One quadrillion Btu (1,000,000,000,000,000 Btu). |
| Qualification Test | A procedure applied to a selected set of photovoltaic modules involving the application of defined electrical, mechanical, or thermal stress in a prescribed manner and amount. Test results are subject to a list of defined requirements. |
| Qualification Test (PV) | A testing procedure for PV modules relating to electrical, mechanical, or thermal stress. |
| Qualifying Facility | A cogenerator or small power producer which under federal law, has the right to sell its excess power output to the public utility. |
| Qualifying Facility (Qf) | Under PURPA, QFs were allowed to sell their electric output to the local utility at avoided cost rates. To become a QF, the independent power supplier had to produce electricity with a specified fuel type (cogeneration or renewables), and meet certain ownership, size, and efficiency criteria established by the Federal Energy Regulatory Commission. |
| Quartz-Halogen Light | An incandescent lamp filled with halogen gas. Somewhat more efficient than standard incandescents. |
| Quasi Sine-Wave | A description of the type of waveform produced by some inverters. |
