Bringing about structural change in a country’s power system requires an energy policy supported by the long-term commitment of the political elite to tackle entrenched interests. Renewables are at the center of efforts to diversify and help countries wean themselves off carbon-heavy energy supplies. IEA scenarios indicate that generation from solar photovoltaic’s (PV) and wind are likely to contribute the highest shares of renewable energy in the future power mix. While large-scale integration of variable renewables is already a reality in many countries, the IEA points to the fact that “not all systems are in an equal position to deal with variable renewables.” Even though there is no technical limit on how much variable generation a power system can absorb, the IEA says, problems may occur if all renewable energy generation is concentrated in a single place, “where the grid is weak and load centres far away.” This currently applies for less than 5% of installed wind and solar PV capacity.
IEA chief executive Maria van der Hoeven went even further in a February 22 interview with the Christian Science Monitor stating: “You have to choose your renewable energy sources based on the indigenous sources you have. [In Europe] wind is more available in the north than it is in the south. (…) It’s important to choose your technologies based on resources you have because otherwise your feed-in tariffs will be quite high.” Fundamentally, this raises two related questions: First, should wind turbines be only built where it’s windy, and solar panels where it’s sunny? Second, how important is a timely transmission grid expansion for the integration of renewables into an existing power system?
A 2013 study by Ecofys energy consultants analyzing “Impacts of restricted transmission grid expansion in a 2030 perspective in Germany,” provided for SEFEP (Smart Energy for Europe Platform), offers insight into how to increase shares of renewable electricity in the power generation system and also discusses the impact of rapid or slow transmission grid expansion related to the integration of renewables. Inter alia, three findings stand out for the purpose of this article. First, the analysis refutes the idea that “wind should be built where it’s windy, and solar where it’s sunny” elaborating that “a scenario with more wind where it is less windy [- the same applies for solar installations -] can help hedge the risk of delayed transmission network expansion.
Second, not enough flexibility in the power system to accommodate all renewable power generation is costly on various levels. Third, this study provides solid rationale for pursuing timely and robust transmission grid expansion: It is the cheapest way to integrate greater shares of renewables; it increases the stability and the resilience of the power system and reduces the costs of providing important ancillary services such as frequency regulation between various regional grids needed to maintain system stability.
Another important consideration is that a robust grid – one with ample interconnections – facilitates future expansion of renewables and creates a more flexible grid. As in-feed from intermittent renewable sources increases, the need for flexibility rises too because output needs to vary directly with consumption.
The following chart shows the regulation regions of the four German transmission system operators (TSO). Transmission grid restrictions exist within the regions, but grid reliability remains strong because Germany has built out considerable electricity generating capacity oversupply, as evidenced by electricity exports to neighboring countries.
German Transmission System Operators (TSO)
German Transmission Lines by Voltage Category
Wind Power Capacity in Germany
Notes: Wind Power Capacity in megawatts (MW) increases along color spectrum from white to blue
It is apparent that ‘power-sharing’ across regions could save money. New expensive infrastructure is required, such as interconnections across the grid to increase interoperability, which is achieved by aligning technical standards and grid codes. In Germany, for example, so-called “power autobahns” could move excess supplies of renewable energy across the country, primarily to the south. The following chart shows the US power grid, which is a similarly stable power system to Germany’s, defined by the IEA.
US Power Grid
The US grid generally consists of three separate sections, the Eastern, Western and the Electric Reliability Council of Texas (ERCOT). The Eastern and Western are separated by geography, while Texas opted to remain separate from the others. This illustrates again that not much power is exchanged between the sections. To date the US has lower penetrations of distributed renewables vis-à-vis Germany. In order to benefit from the predicted future boom in renewables, current wind energy in the Midwest and solar PV in the Southwest of the US will either have to be connected via power-lines to the urban population centers on the East and West Coasts – an extremely expensive and largely discredited endeavor – or renewable energy capacity needs to be distributed more widely throughout the nation.
A future strengthening and expansion of US grid infrastructure would help smooth out the variability of wind and solar PV by aggregating their electricity production over large stretches of land. Terry Boston, CEO of grid operator PJM Interconnection, shared his thoughts on the US electric grid: “High voltage, direct current [- the most efficient means of transmission -] is probably the way to go if we’re starting our grid anew, instead of the alternating current that dominates the American grid. Beyond that, standardization is a crucial component that is sorely lacking from today’s grid.”
In sum, the Ecofys study shows that possible uncertainties about the speed of grid expansion – due to budget constraints or lack of political will – are no reason to slow down the expansion of renewable generation. An anticipatory power grid design strategy favoring a balanced distribution of renewable generation, while taking into account predictable transmission grid bottlenecks is required. Keep in mind, however, that adding renewable power generation to a utility’s supply mix will require that the utility also acquire more ‘predictable’ conventional supplies, as the utility then needs to respond to uncertainty at both ends – supply as well as demand.