The move to increase the percentage of wind and solar power into existing grids has become polarized, like many issues nowadays. Naysayers continue to perpetuate outdated assumptions, claiming that large amounts of solar and wind power operating in a grid is too expensive, risky to reliability and is wasteful of existing power plant resources. Many supporters, including those advocating a 100% renewable sourced power grid, downplay the technical challenges involved at very high levels.
As usual with such issues, the answer lies somewhere in between. And for those seeking guidance that isn’t excruciatingly technical, the International Energy Agency (IEA) has published “Getting Wind and Sun onto the Grid – A Manual for Policy Makers”. Twenty countries’ grids were used as references, from Mexico, with a low percentage of PV and wind in its grid, to high-percentage Denmark.
The manual lays out two theses to integrating PV and wind power into the grid. While there are technical challenges to achieving high levels of penetration of variable renewable electricity (VRE), such integration can be achieved manageably and cost effectively.
The IEA report explodes six “myths” about grid integration. In brief (1); weather factors are quite manageable (2); VRE does not impose high costs on conventional power plants (3); it does not require one-to-one back up (4); VRE is not very expensive compared to the alternatives; (5) it does not necessarily need storage, especially in early stages and (6) is not destabilizing.
The study then describes a number of stages or “phases” of VRE development. The first stage, or Phase One, is where VRE is in the low single digit percentages of penetration. At this point, to use highly technical language, it’s no big deal. Low daily variations are well within the operating capability of any decent grid.
At Phase Two, no strict penetration level is given, but it appears generally as VRE approaches or passes double digit percentage penetration. VRE becomes apparent to grid management, but not significant enough to impact the system as a whole. Local grid conditions may necessitate matching between demand and VRE output. Phase Three the presence of VRE becomes more apparent as its output can swing in large percentages of total capacity across the grid. Management of operating conventional power plants at different levels becomes important, as well as two-way flows of voltage levels. At this stage, the availability of flexible resources comes into play.
At Phase Four, variability can match 100% of power demand, and conventional power would need to respond in a variable fashion. This condition is where management practices such as using inertia of conventional power plants to act as short term energy storage can be deployed. Going beyond Phase Four, the use of the complementary VRE capabilities of solar and wind can be successfully used to a large percentage or completely in many locations. Where there is a lack of complementary resources, large scale storage, especially chemical or thermal, can be used to supplement.
Each phase in the manual is given a brief section with illustrative examples and tables. The summation gives a balanced appraisal, emphasizing implementation in stages, where changes can be made in accommodating fashion to conventional power plants and grid infrastructure, as the percentage of VRE increases. As such Getting Wind and Solar Onto the Grid can act as a bridge for policy makers between the public and power business and technical communities who may not be so enamored to change.
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