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The crisis at Japan's Fukushima power plant has sparked a national review of energy policy and turned public opinion largely against nuclear power, but Shinji Fujino of the argues this is just a small part of the serious electricity supply challenge the country now faces.

The earthquake on 11 March triggered the automatic shutdown of reactors at 11 of Japan's 54 nuclear reactors, with a total capacity of 9.7GW.

At the moment, only 18 nuclear reactors are producing power. The rest have either been shut down because of safety concerns or for routine maintenance.

In addition to the nuclear reactors, thermal power plants with a total capacity of 9.4 GW were also shut down following the natural disasters.

In total, Japan's power supply capacity in the affected area has been reduced by about 40%, which is almost equivalent to the national capacity of Switzerland or Austria.

In terms of its energy supply, Japan is isolated, having no interconnections with neighbouring countries. The national transmission system is divided into two separate frequency areas - the 60 hertz (Hz) western system and the 50 Hz eastern system. Although the two areas are interconnected using three frequency converters, the total shared capacity is comparatively small (roughly 1 GW). Thus the east of Japan, which includes Tokyo and the tsunami-hit areas, has faced serious power shortages.

In the first weeks after the disaster, the government and electricity companies asked all electricity consumers to voluntarily reduce their energy usage. In addition, rolling blackouts were implemented to try to balance supply and demand.

Electricity companies have taken many measures to restore power supply, including repairing damaged thermal capacity (fossil fuel power plants damaged by the earthquake and tsunami), bringing back thermal plants which were closed for inspections, and also thermal power plants that were previously decommissioned. Thanks to these actions, the supply-demand balance has improved and large-scale blackouts have been avoided.

However, the real challenge is in the summer months - the peak period of power demand in Japan, when temperatures in Tokyo routinely exceed 30C and air conditioning accounts for about 50% of total electricity consumption during peak hours.

In response to this challenge, the government has announced a plan it calls Electricity Supply-Demand Measures in Summer Time which demands a 15% reduction in usage for all electricity consumers. The plan aims to minimise the impact of power shortages on people's everyday lives and on industry, while ensuring that any power reduction will not impair Japan's economic recovery.

How can it be achieved? Big businesses could install more energy-efficient machines and equipment, and shift or shorten the working times of staff. In offices and households, people could turn off lights and IT equipment and no longer leave electrical devices in stand-by mode. The government can take mandatory action to regulate the big energy consumers under the current regulatory framework. For others, including households, action is voluntary.

In parallel with these short-term measures, the government has started to reconsider its mid- to long-term energy policy. At the moment, Japan relies on nuclear for about 30% of its power supply. The last national energy plan, published in June 2010, proposed nine additional nuclear units by 2020 and 14 or more by 2030. These large increases in nuclear capacity were expected to contribute to achieving Japan's ambitious CO2 emissions-reduction target (25% below 1990 levels by 2020).

Planning new nuclear reactors will now be much harder. Agreement from local residents will be necessary before restarting shutdown nuclear reactors - making it very difficult to bring them back online even after stress tests or upgrading.

For the time being, electricity companies will have to bridge the gap between supply and demand by increasing capacity in thermal power plants, in particular plants fired by Liquefied Natural Gas (LNG). Given the available facilities and supply risks of each fossil fuel, LNG will be expected to play a major role. However, greater use of LNG could result in higher electricity prices as well as higher CO2 emissions, which will make it more challenging to meet the Kyoto Protocol target (6% below 1990 levels for the first commitment period 2008-2012).

Japan has a relatively small share of renewables, which account for approximately 5% of its total primary energy supply. The current National Energy Plan has set a target of 10% by 2020. At the G8 summit in France this May, Mr Kan announced a plan to increase renewables to more than 20% of total electricity supply by the early 2020s. The government also plans to install 10 million rooftop photo-voltaic units (solar cells) by 2030. Owing to geographic and climatic conditions, the resource potential for renewable energy in Japan is relatively low when compared with other developed countries.

But necessity is the mother of invention. Tackling these challenges head-on could help Japan's economy to recover, and become more competitive in the long-term.

Shinji Fujino is head of the country studies division of the International Energy Agency and is currently in charge of reviewing energy policies of the IEA member countries.