[Fish]

Originally Posted by Baby Lee

Are you seriously in the dark, or trolling, because the explanation exists, but is cumbersome to assemble for lay persons.

In the shortest possible snippet, power companies put a great deal of effort into transmitting a clean sine wave at a reliable magnitude and frequency. Solar and Wind collects DC power and ancillary devices rectify that power into an AC sine wave of, ideally, identical magnitude, frequency, and phase angle. To the extent their devices fall short, they are wasting their power and destroying a portion of the power the generation plant created.

Think double dutch coupled with Frogger, with the solar power being the rope jumper/frog.

They've done plenty of testing and modeling to determine what the electrical grid can handle with regards to input from solar/wind/etc. And there aren't really any problems until you get to over 30% penetration. Wind power is what causes the most invariability. Solar is fairly consistent. Here's a study done on WestConnect Energy:

http://www.nrel.gov/docs/fy11osti/50057.pdf

Operations with 35% Wind and Solar Energy

The power system is designed to handle variability in load. With wind and solar, the power system is called on to handle variability in the net load (load minus wind minus solar), which can be considerable during certain periods of the year. Figure 2 shows the load (purple line along top edge), wind (green), solar (PV in orange and CSP in yellow), and net load profiles for the 30% case during two selected weeks in July and April. In the July week, (left plot), the net load (blue line along bottom edge) is not significantly impacted by wind and solar variation. However, in the April week (right plot), the high, variable wind output dominates the net load, especially during low load hours, leading to several hours of negative net load during the week. This week in April was the worst week in terms of operational challenges of the three years modeled.



How much wind and solar generation can the system handle? No significant adverse impacts were observed up to the 20% case in WestConnect, given balancing area cooperation. Increased wind/solar generation in the rest of WECC (20/20% case) led to increased stress on system operations within WestConnect, with some instances of insufficient reserves due to wind and solar forecast error. These can be addressed, but the system has to work harder to absorb the wind/solar. Operations become more challenging for the 30% case in which load and contingency reserves are met only if the wind/solar forecasts are perfect.

Infrastructure balancing would be necessary, but feasible. Their results show some decent cost savings.

Benefits of 35% Wind and Solar

Wind and solar generation primarily displace gas resources nearly all hours of the year, given the fuel prices and carbon tax assumed for this study. Across WECC, operating costs drop by $20 billion/yr ($17 billion/yr in 2009$) from approximately $50 billion/yr ($43 billion/yr in 2009$), resulting in a 40% savings due to offset fuel and emissions. Figure 4 (left plot) shows the overall impact on the operating costs of WECC for the various penetration levels under the In-Area Scenario with a state-of-the-art (SOA) forecast. The 30% case shows WECC operating cost savings of $20 billion/yr ($17 billion/yr in 2009$) due to the wind and solar generation resources.

Figure 4 (right plot) divides these values by the corresponding amount of renewable energy provided. In the 30% case, this equates to $80/MWh ($60/MWh in 2009$) of wind and solar energy produced. These operating cost savings would be applied toward the costs of wind and solar energy, and depending on the magnitude of these costs, may or may not be sufficient to cover them. At a $3.50/MBTU gas price, wind and solar primarily displace coal generation. With lower gas price assumptions, operating cost savings are about 40% or $46/MWh ($39/MWh in 2009$).

Key Conclusion:

No need to commit additional reserves to cover increased variability – In addition to contingency reserves, utilities are required to hold variability or load following reserves to cover 10-minute load variability 95% of the time. With wind and solar, the net load variability increases and in the 30% case, the average variability reserve requirement doubles. However, when wind and solar are added to the system, thermal units are backed down because it is sometimes more economical to back down a unit rather than to decommit it. This results in more up- reserves available than in the case when there is no wind and solar. Regulating reserves are a subset of the fast variability requirement, but are held separately from the 10-minute variability reserves. While WWSIS did not evaluate which units were on AGC, the minute-to-minute analysis showed that sufficient regulating reserve capability was available. Down reserves can be handled through wind curtailment when other resources are depleted. A wind plant can reduce its output very quickly in response to a command signal. Simulations in this study show that down reserves can be implemented through command signals (ACE signals) from system operators.