[diarmuidie]

One of the big problems with PV and wind power is that they don't offer any inertial load on the grid. This means that once the percentage of these sources increase the grid frequency stability decreases.

When using renewables you must still generate a majority of your supply from a big rotating generator. The inertia of the spinning generator keeps the frequency from straying from 50/60hz.

In Ireland they broke a record a few years back for having 50% of the electric generation coming from wind power. This was at the upper limit set by the grid operator (eirgrid) because above this level the frequency of the grid becomes unstable. Even though more wind power was available they didn't add it to the grid.

[bavcyc]

I think the US uses 10% spinning reserve for generation (might be a NERC requirement?). Some plants (gas and certain hydro) have fast response times. Others (coal, nuke?) have a longer response time.

The biggest issue with wind is that the wind gusts so power output is variable.

As regards to frequency until your system has enough mass to influence the rest of the grid, the grid frequency is dominate. Even a 2,000 MW generation facility will not influence the grid frequency much, which is why it is important to sync to the grid as you connect.

[marshray]

Poor, poor, Ireland. That must be just awful for them. Thank God we in America aren't at risk of hitting that 50% figure of energy supplied by wind or solar.

[diarmuidie]

I should point out that it was only for a few hours in the early morning on a windy summers night (low base demand, no AC or heating demand).

On average though 2013 renewables provided ~17% of total demand [http://www.eirgrid.com/media/EirGridAnnualRenewableReport201...].

System Non-Synchronous penetration (SNSP) is a real-time measure of the percentage of generation that comes from non-synchronous sources, such as wind and HDVC interconnector imports relative to the system demand. In the Irish grid this is limited to 50% for stability.