The promise of clean, hybrid energy systems

There is a general misunderstanding that renewables, solar, wind and nuclear energy are in conflict with each other. However, this perception is not correct.

Both nuclear and renewable energy sources are important to reduce the import of fossil fuels. Both sources are important to reduce greenhouse gas emissions, carbon dioxide and methane, as well as a number of air pollutants that are harmful to both the environment and public health resulting from burning fossil fuels such as NOx, SOx and particulate matter.

However, the intermittent nature of solar and wind has a significant impact on grid stability and overall societal costs, reflecting negatively on the overall economics of renewables. Either storage or backup power is needed for the significant fraction of time when power is not produced from renewables. Typically, natural gas must be kept ready to cycle on to replace renewables when it is not available which will offset the overall benefits from renewables. 

Storage ranges from fairly simple systems involving pumped water, extensively used in Switzerland and used at a few locations in the United States, but hardly viable for Jordan, to batteries. Batteries have their own challenges, and will be expensive for the foreseeable future, for several decades to come. The figure quoted recently for the new Tesla battery system was $350/kWh, not a low cost for maintaining the stability of a grid. To keep the storage cost in such a system at 5 US cents/kWh, 7000 cycles would be needed to cover the production costs, not considering losses from loading and draining the batteries.

Thermal storage systems appear far more promising, with a cost projected at $5/kWh for systems using firebrick, but no commercial firebrick system has yet been deployed by a utility, and only nuclear and solar thermal are well matched to such heat storage.

A more promising approach to energy generation under study in many countries involves hybrid energy systems that combine the best features of clean renewables and nuclear power. System designers are demonstrating how intermittent renewables and base-load nuclear power generation can be coupled together to supply all the electricity needs of a grid plus other important products, like desalinated water, heat generation or hydrogen production, by running both the renewable and nuclear facilities at maximum output and efficiency, and switching excess power into the secondary product whenever grid needs are fulfilled for solar powered systems in the morning. Stored energy at a nuclear power plant (NPP), thermal energy or hydrogen production in the future, accumulated when renewables are working can be used to generate electricity at night for the solar case when intermittent renewables are idle.

In this context, integration of hybrid systems encompassing renewable and nuclear systems needs to be factored into Jordan’s future energy strategy.

Hybrid operation of an NPP can be utilised to tackle intermittency of renewables by switching production between electricity and other products such as district heating, process heat for the industry, water desalination and, in the future, hydrogen production. For example, when the sun is shining, an NPP can produce those products other than electricity because solar photovoltaic (PV) cells are supplying electricity, and when the sun is down or in cloudy winter conditions, the NPP starts to produce electricity, since PV power is not available.

Jordan is considering several small modular reactor (SMR) designs, among which are high temperature gas cooled reactors (HTGRs). Besides their inherent safety features, HTGRs have unique characteristics of high temperature operation, which can use rejected heat for desalination, provide processed heat for industry, and high efficiency hydrogen production in the future. HTGR design is a good candidate for hybrid production of electricity, desalinated water, process heat and hydrogen with good efficiency. The Japan Atomic Energy Agency has an experimental HTGR with operational experience with Helium (He) gas, at temperatures as high as 950°C. Hydrogen production using the Sulphur-Iodine process and control methods for hybrid production have also been investigated.

While high temperature reactors will offer advantages when they are in commercial operation, other hybrid options are under study using current light water reactors (LWRs).  In the US, National Renewable Energy Laboratory and Idaho National Laboratory teams have studied the use of LWRs with high temperature steam electrolysis for hydrogen production, as well as many other applications of hybrid systems, including desalination.

Recently, a number of storage options, besides expensive batteries, are being developed, such as storage by compressed air or production of hot water, heat, or hydrogen, among others, which are used in a later stage for electricity production or can be used in  the industrial or transport sectors.

Given the promising benefits of hybrid energy systems, the Ministry of Energy and Mineral Resources should join international efforts and include it in their upcoming national energy strategy.

The writer is commissioner of nuclear power reactors at the Jordan Atomic Energy Commission.. He contributed the article to the Jordan Times.