Please activate JavaScript!
Please install Adobe Flash Player, click here for download

Global Futures Report 2013

24 n Gas turbines (peaking and non-peaking). Many scenarios call natural gas a “bridging” or “transitional” fuel toward high-renew- ables futures. Experts envisioned growing use of combined-cycle and simple-cycle gas turbines for balancing grids, particularly for complementing wind power. However, experts pointed out that most combined-cycle plants that exist today were not planned nor designed to operate on a variable regime. Constant ramping up and down creates excessive wear and tear, lowering lifetimes and increasing maintenance costs. Simple-cycle turbines make better peaking plants but are significantly less efficient. Spanish experts noted that Spain had planned to add simple-cycle turbines on to the grid for balancing high shares of wind power; however, these plans were shelved due to underutilization of already-existing combined- cycle gas plants.12 n Strengthened transmission capacity and interconnection. Utility experts pointed to stronger transmission capacity as an important means to balance power flows and variable sources within a region, as well as to deliver renewable generation from remote locations. The extreme end-point cited by some experts is a theoretical “copper plate” in which unlimited interconnection exists. However, experts questioned the degree to which networks can be expanded given environmental and social issues, as well as levels of investment required (particularly in developing countries). Many emphasized the difficulties in terms of transmission planning and social acceptance of new overhead transmission. Some countries may turn to buried underground transmission to achieve a stronger balancing capability while mitigating social issues, although under- ground transmission is more costly. Denmark has already mandated that all new transmission be buried underground.13 Experts also pointed to stronger cross-border interconnections to transfer renewable power generated in one country to neighbor- ing countries. They envisioned future possibilities like Bhutan hydro and Sri Lanka wind power flowing to India; Mozambique hydro and Namibia wind power flowing to South Africa; and renewable power transferred among China, Mongolia, Japan, South Korea, and other Asian countries through an “Asian super grid.” European experts envisioned “Desertec” transfers of renewable power from northern Africa to Europe, as well as a Europe-wide “super grid.”14 n Energy storage. Hydropower has been a traditional form of large-scale energy storage on power grids, in the form of both conventional and pumped hydro. (See hydropower in Chapter 6.) In recent years, grid-tied battery storage has made inroads and shows much promise for the future, according to storage experts. Until more recently, grid-tied battery storage has been perceived as expensive and the province mainly of demonstration projects. However, an increasing number of commercial battery storage projects today are dispelling that perception, particularly in “niche” applications that are profitable under current conditions. Some of these are for centralized grid support and others are much more decentralized. Storage experts cited many examples of present-day commercial storage projects using batteries, as well as an increas- ing proliferation of distributed batteries at points of customer end-use.15 Beyond hydro and batteries, solar thermal power (CSP) plants also offer storage capabilities using embedded thermal storage. Many currently operating CSP plants typically have 4–8 hours of ther- mal storage that allows evening operation and can provide firm dispatchable power for spinning reserve, balancing, and ancillary services. CSP experts envisioned thermal storage capacity increas- ing to 24 hours in the longer term. Storage experts also cited other possible technologies for the future. From a grid stability perspec- tive, different storage technologies are suited for different balanc- ing time frames, ranging from minutes to hours, and even to days or weeks.16 n Ramping and cycling of conventional plants. Conventional hydropower plants (even without pumped storage) are routinely used to ramp and cycle. For other types of conventional power plants, however, ramping and cycling on a daily or hourly basis can be controversial, said experts, who noted that a major paradigm shift is implied. In particular, existing coal plants can be modified to allow ramping and cycling beyond original design parameters, and operated to provide more flexibility, although not without additional costs in terms of reduced equipment lifetime, higher maintenance costs, and stability of emissions equipment. Although ramping and cycling costs are not well known, and utilities resist such operation, some utilities have indeed converted coal plants to ramp and cycle.17 Nuclear plants can also ramp and cycle, and in some countries today, nuclear plant output is routinely cycled on a daily or weekly basis to handle grid conditions. A 2011 OECD study concluded that, “modern nuclear plants with light water reactors have strong maneuvering capabilities [to operate in load following mode].” The report notes that, “in Germany, load-following became important in recent years when a large share of intermittent sources of electricity genera- tion (e.g. wind) was introduced to the national mix.” The report also notes that ramping and cycling costs for most existing nuclear plants—beyond lost revenue from lower output—are confined to minor increases in maintenance costs.18 Beyond the six measures just described, other balancing options that are less commonly cited but still considered important by some experts include: (1) using biomass combined heat and power (CHP) plants with heat storage embedded in the CHP plants or locally with end-users, to allow variable operation of the power generation side of the CHP plant; (2) generating synthetic gas or hydrogen from surplus renewable electricity for injection into the natural gas grid as a means of absorbing excess generation on-demand; and (3) aggregating the charging/discharging of large numbers of electric vehicles through centralized “smart grid” mechanisms (see also the following section on transport integration).19 Over the past decade, there has been much debate and contro- versy about the level of variability from renewables that power grids will be able to cost-effectively support and integrate. Much of this discussion has revolved around what percentage (share) is a technical “upper limit” to integration, with conservative numbers such as 10% or 20% often cited. A number of studies show dif- ficulties above these levels without aggressive balancing measures. But other studies show the potential to reach higher shares with sufficient use of the balancing measures discussed earlier.20 For example, GEA (2012) concluded that up to 50% shares of vari- able renewables can be accommodated in most existing systems with investments in grid flexibility, gas turbines, energy storage, and demand management. NREL’s (2012) Electricity Futures Study analyzes a range of U.S. cases from 30% to 90% shares by 2050, and concludes that it would be possible to attain a high share (80%) from technologies that are commercially available today, RENEWABLES GLOBAL FUTURES REPORT 02 INTEGRATED FUTURES: CHALLENGES AND POSSIBILITIES

Pages Overview