Читать книгу Renewable Energy - David Elliott - Страница 21

The technical costs of balancing variable renewables have been extensively studied, and one widely accepted estimate in the UK context is that they might add 10–15% to power generation costs at medium levels of renewable capacity, depending on what balancing technology is used, although it would rise at higher levels (Heptonstall, Gross and Steiner 2017).

At present, most balancing is achieved by using gas-fired plants, their output being ramped up and down to compensate for the variations in supply and demand, sometimes coupled with pumped hydro storage, if available, and batteries for short-term storage. That may be fine, with some extensions, up to maybe a 40–50% renewable power contribution: by 2019 the United Kingdom had reached 38%, Germany was nearing 50% and Denmark had reached 55%.

However, at higher levels, more may be needed. For that purpose, although they may well be the main elements, gas-fired backup plants (usually the cheapest option) and energy storage facilities (usually more expensive) are not the only balancing technology options. As noted in the main text, demand can also be managed via smart grid/variable energy pricing to delay energy demand peaks when variable renewable inputs are low, and top-up power can be imported to meet the peaks via long-distance supergrids.

Both those options can be low cost in operational terms. Indeed, flexible-demand management and smart grids can save money by reducing/shifting demand peaks, while supergrid links allow not just for balancing inputs but also for exports of surplus for some countries, earning a net positive income and avoiding the need for (wasteful) curtailment (or dumping) of surpluses. For example, a study by the UK government’s National Infrastructure Commission claimed that an integrated flexible supply-and-demand management system, with smart grids, storage and also grid interconnector imports/exports, could save the United Kingdom £8 billion per annum by 2030 (NIC 2017). A study by Imperial College/OVO Energy claimed that just adding residential flexibility in domestic energy use (including for electric vehicle charging) could reduce whole-system costs by up to £6.9 billion per annum or 21% of total electricity-system costs. It was suggested that these savings could more than offset the cost of upgrading the power system. That does seem credible for some of the options. For example, introducing variable time-of-use energy tariff charges requires no capital outlay but would lead to reduced peak energy use and user costs and also lower system costs (Ovo/Imperial 2018). In all, it has been suggested that, if fully developed, system flexibility and integration could save the United Kingdom up to £40 billion by 2050 (Bairstow 2019a).

As noted above, as the renewable proportion goes up, so do the balancing costs, dramatically so in some modelling, for contributions of 70%, 80% and above. So savings like this would be welcome. However, there could be more savings to come if renewables expand even further. While balancing costs will rise until most power demand is met from renewables most of the time, after that any further expansion of renewable capacity, while requiring capital investment, will not incur extra power grid-balancing/backup costs. It will actually reduce the need for backup (more power would be available more often), while increasing the surplus that will be generated at times of low demand. The extra surplus would not be needed for balancing but would be available for heating, transport or export, or maybe conversion to hydrogen for these purposes, if that was the most lucrative option. In the latter case, more power-to-hydrogen conversion plants would be needed, but in either case the costs would be offset by the earnings from these end uses and the reduced system-balancing costs.

So a low-energy cost/high-renewables future may be possible, even given the need for balancing. That is certainly what a range of new scenarios propose, even those extending to supplying all energy, not just electricity. For example, the updated 2050 scenario produced by Professor Mark Jacobson and his team at Stanford University in California suggests that a system supplying 100% of global energy from renewables will not cost more than the current system and could actually be cheaper per kWh, even given the use of variable sources. Moreover, since it would avoid the increasing cost of fossil fuels and also the social and environmental costs of using them, it could be significantly cheaper overall (Jacobson et al. 2017).

Similar conclusions have emerged from studies by LUT University in Finland in conjunction with the Energy Watch Group (EWG) in Germany. They claim that 100% of energy, globally by 2050 or even earlier, is possible and would not cost more but in fact slightly less in direct cost terms: energy-generation costs would fall from €54/MWh for the system used in 2015 to €53/MWh with the new system, with balancing/storage, in 2050 (Ram et al. 2019). Note that neither the United States nor the European group saw nuclear as playing a role, not least because, as well as being expensive, it is inflexible and unable to balance variable renewables.

Making cost predictions so far ahead is obviously hard, and there have been queries about the use of projected average global capital costs for the calculations (Egli, Steffen and Schmidt 2019), given that there may be important local variations. However, that is difficult to predict, whereas the LUT researchers believe global-trend projections may be more reliable (Bogdanov, Child and Breyer 2019).