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CWR: What are the implications for energy consumption of these targets?
PZJ: There are two different implications – one to save energy, other to use energy. With the target to control discharge of pollution we need energy to build and operate waste treatment – these are both energy consuming. So to reach water targets, we need to consume energy and this increases energy demand.
On the other hand, if we can use recycled water, this can imply saving energy. If you bring water from far sources this requires energy, but using recycled water from nearby sources clearly is a better solution in terms of energy use. For now, we do not know the net implications. Assumptions are, though, that for cleaner water we will use more energy.
CWT: So to meet the water quality targets, treatment rates for both industrial wastewater and municipal sewage will increase, which could increase energy consumption in this sector.
Water use efficiency targets, on the other hand, could be achieved through improved water management and water conservation technologies. Management measures do not necessarily increase energy consumption. However, some of the low-water technologies, such as dry-cooling and hybrid cooling used in the power sector, have a relatively high “energy penalty,” increasing overall energy demand.
CWR: What do you see as the trade-offs between water usage and the need for energy?
CWT: The power sector is among the most water-intensive industries. Some power-generating technologies such as hydroelectric, geothermal, and concentrating solar power (CSP) have low greenhouse gas emissions but high levels of water consumption, while conventional coal-fired technologies have modest water usage but very high greenhouse gas impacts. For example CSP consumes 3-3.5 m3/MWh of water while a subcritical coal plant with a closed-loop cooling system only consumes around 1.6m3/MWh. Some alternatives, such as solar PV and wind power, can reduce onsite GHG emissions and water consumption to zero but are less economically competitive in the near term.
However, “negawatt” measures, those that reduce the need for electricity generation in the first place (such as energy-efficient buildings and appliances) not only save money and reduce GHG emissions, but also eliminate the corresponding water use.
PJZ: There is a trade off but recent technology progress also shows how to break the link between the two. In Northern China, many power plants have started employing air cooling technology that substitutes water for cooling. The other possibility is to use more efficient power generators, grids and pumps for water transport in cities. In the short term, the linkage between water and energy will remain but in the longer term it depends on technological change. This will involve looking at what we can do to fund better technology, introduce incentives and encourage new policies.
CWR: While aware of the need to diversify its energy sources and reduce greenhouse gas emissions, it seems China is starting to realize that alternatives to coal are running up against water limits as well. What are some of the issues here?
PJZ: There are several issues here related to the water-energy nexus. Let’s start from Concentrating Solar Power (CSP), which also needs water to produce, to store and, transform the energy into vapor. So for some specific solar technologies you need a lot of water. Nuclear power needs a lot of water for cooling. China has an ambitious target to expand total energy use and this needs complimentary water supply regardless of the energy source. So it doesn’t necessarily mean that when you diversify energy sources that you eliminate the water problem.
The partial answer to this is to introduce incentives – for example, correct water pricing or allocation of water quotas, which are measures we have already been using for a long time. The other is to develop water-saving technology. But this is all complicated. There are many factors to consider. If the price can reflect the real cost of energy generation that is fine but for some end users, the real c