| Every new technological development is bound to | | | | changes is too wide, then the inverters might |
| have some unforeseen consequences and the | | | | sense that the grid is lost momentarily and shut |
| move to install grid-tied home solar power (PV) | | | | down. The consequence of this would be to dump |
| systems is unlikely to be an exception. | | | | the whole generation load on to the power plant. |
| One such example came up recently in a | | | | Assuming it regulates the frequency quickly and |
| discussion group where one contributor posed the | | | | restores the normal grid operating parameters, |
| (as yet) hypothetical question in the following | | | | then the various grid-tied inverters would sense a |
| terms: | | | | restoration of grid power and resume sending |
| There is a community with 10,000 homes on an | | | | power to the grid. |
| island, which has one power plant to feed | | | | A pattern of shut down and restoration might |
| electricity to those homes. Along comes a solar | | | | occur, depending on the sensitivity of the |
| power sales agent, and soon over half the homes | | | | inverters, the responsiveness of the power plant |
| have installed grid- tied solar systems. Each one | | | | and the architecture of the distribution network. It |
| produces an excess of power during the day. | | | | might work satisfactorily, but it might not. |
| How would this work? | | | | A further unintended consequence would occur if |
| There are two answers. The first is that if the | | | | the total inverter output is greater than the total |
| grid-tied output is a small fraction of the total grid | | | | load, that is, if all the home solar power systems |
| generation (as it is in most countries now) there is | | | | generate more power than the grid requires in |
| not really a problem. However, and here is the | | | | terms of output, then the excess power will start |
| second answer, if the grid-tied inverter-supplied | | | | motoring the power plant and raising system |
| power were to grow to a significantly large | | | | frequency. The power plant will trip on reverse |
| proportion of the total generation, then there | | | | power and the frequency will become very |
| would be problems with stability and control. | | | | unstable. Once the power plant trips, the |
| Why would such problems emerge? | | | | frequency will swing around and the inverters will |
| Assuming the grid-tied inverters from all the | | | | shut down, thinking the grid is lost. This time, it |
| homes were pumping power back into the grid, | | | | really will be lost and the power plant will be |
| the power plant would be reducing output to try | | | | off-line, so everyone will be without power. |
| and maintain system frequency. If that single | | | | For these and other reasons, utilities will set an |
| power plant can regulate fast enough when the | | | | upper limit on the amount of grid-tied energy |
| clouds pass overhead and then clear, system | | | | production, solar or wind, they are willing to |
| frequency could be maintained. | | | | connect. This whole area will require further study |
| However, if the variation caused by these sudden | | | | if home solar power systems become popular. |