Sunday, May 1, 2016

Green energy balancing: impacts and reactions

Renewable energy sources are variable, and ways have to be found to compensate for that. Fortunately there are many, as my new book ‘Balancing Green Power: how to deal with variable energy,’ tries to show. While no single grid balancing option will be sufficient on its own, it suggests that, taken together, in an integrated and widely interconnected approach, using a range of renewable sources, including the non-variable options, effective balancing should be possible. Certainly the range of approaches is quite large, including energy storage, flexible backup plants, smart grid demand response and supergrid imports and exports.

However, some may have problems. For example, in relation to balancing of local surpluses and shortfalls across wide areas by interconnectors, it remains unclear how much excess output will be available when needed for trade. Much will depend on prices and market structures, as well on which renewables are developed and where they are located. Perversely, if supergrids spread, countries may be tempted to reduce their renewable over-capacity, and so have less to trade. It is also likely that there will be large surpluses in the summer, when demand is less and solar at a maximum, during which time few trades will be viable or needed, with some of the renewable capacity being left idle.  Storage capacity will also be unused then, unless it is inter-seasonal storage, and not much of that may exist. 

Given that renewable capacity may have to be set higher than would otherwise be needed to meet demand, there will also be surplus production at other times, for example when wind output is high and demand low. As critics have pointed out, in some scenarios, assuming extensive renewable expansion, the surplus can be quite large and would be very wasteful.  However, this misses the point that, not only can some curtailment be avoided by supergrid exports, some of the excess can be stored directly, or converted into valuable storable fuels, for later use, possibly in other sectors e.g. heating and transport. 

In addition to technical and economic issues like these, which I look at in detail, there is also the question of social and environmental impacts. Given that the aim of balancing is to aid the development and use of clean, green energy systems, it is fortunate that most of the balancing systems looked at in the book seem to be environmentally unproblematic, with perhaps the exception of pumped hydro storage. Some environmentalists have opposed large hydro projects, though that has mainly concerned major new projects in remote areas that might not be suited to pumped storage. Much of the current development work concerns modifying and perhaps linking up existing, often smaller, hydro projects, so that they can operate in pumped storage mode, although some new medium-scale systems are also being developed. 

Some energy storage systems involve the use of toxic materials (e.g. in batteries), but non-toxic versions are being developed. Hydrogen storage and transmission also has risks, but so does the storage and transmission of most fuels, with hydrogen arguably being one of the less risky options: it is lighter than air and so disperses easily. Supergrid links may be invasive, but there are options for overlaying them with existing grids, or putting some sections underground. That is easier with HVDC than with conventional DC grids since, as the energy losses in transmission are lower, there is less heat to dissipate, although going underground would still add to the cost. 

The use of biomass, as a firm source of energy, and for production of biogas as a possible energy storage medium, opens up some environmental issues. Some environmentalist oppose the use of biomass for energy production on the basis of land-use and ecological impacts: it depletes a crucial carbon sink, reduces the area available for food production and can undermine local biodiversity. However, biogas produced from farm and food wastes should not face these problems, and avoids the release of methane into the atmosphere, in which case it should be able to play a role in balancing variable renewables on a sustainable basis. Some other forms of biomass may also be less of a problem, short rotation coppicing of fast growing non-food crops for example, although clearly careful regulation is needed, as with all types of renewable system. 

Although the environmental and safety issues of the balancing options do not seem insurmountable, in some cases, there might be negative public reactions to deployment, as there have been in the case of renewable deployment generally. On the supply side, some of the changes will be essentially invisible to the public. Most utility-run storage facilities, pumped hydro apart, will look much like any other plants. Similarly for most back-up plants and associated biogas/syngas stores and Power to Gas conversion plants. As indicated above, supergrid links may however be much less invisible, although, like hydro, they would be remote from most people, and, with supergrids, there are options for going underground in sensitive areas.

On the demand side, there would be more intimate and widespread interactions. It is not clear how consumers will react to smart grid demand management and time-of-use pricing system and how much that will help limit peaks and avoid energy waste. Most consumers are likely not to want to have to be bothered with energy management, so automated systems may prove acceptable, as long as they see some benefits. These benefits however may be longer term and not just economic and there are data protection and privacy issues.

However, if the new system can be seen to deliver energy reliably, without undue costs or impacts, and without too much need for behavioural change, then it may be widely supported. Then again, some consumers seem willing to voluntarily adopt new energy systems, perhaps wishing to make personal contributions to energy sustainability on behalf of future generations. The growth of the ‘prosumer’ self generation movement in many way challenges the technological and market status quo, making old certainties redundant: a new system may be emerging. And that will have to include new balancing systems.

‘Balancing Green Power’, Institute of Physics Publications:


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