Dial the clock forward a decade or so, and Japan will be getting a lot more of its electricity from renewable resources and a lot less from nuclear power and fossil fuels — that is, if you go by recent government announcements proclaiming 2011 an energy watershed.

But Yasuhiro Hayashi, one of Japan's top experts on power grids, says the current network can only handle a fraction of the solar- and wind-power that government goals call for.

Before the ongoing Fukushima nuclear disaster started in March, Japan's energy plan called for boosting solar-power generating capacity 10 times by 2020, to about 28,000 megawatts (MW), or 10 percent of the current total electricity-generating capacity.

Prime Minister Naoto Kan upped the goal at this May's G-8 summit by calling for solar panels on 10 million Japanese roofs, and for 20 percent of electricity to come from renewable sources by the early 2020s.

According to Hayashi, however, the grid can currently handle 10,000 MW of solar and wind power- a capacity roughly equivalent to the maximum output of 10 nuclear reactors.

"The existing goal was already quite challenging. To meet the new goal, we're really going to have to push hard," said Hayashi, a professor at Waseda University's Research Institute for Advanced Network Technology. "The current grid wasn't built for renewable energy."

A central technical problem stems from the fact that solar and wind power depend on the weather — and the weather changes a lot. The outputs of geothermal and biomass plants are more predictable.

"Electricity from solar and wind sources is wild. The amount generated fluctuates greatly," he said. When that unpredictable energy flows into the conventional grid in large amounts, controlling the quality of electricity becomes difficult.

That's because, in order to keep a stable voltage and frequency flowing from sockets and other home outlets, power companies must continuously adjust electricity supply to meet demand. If not enough electricity is supplied in relation to the quantity consumed, frequency falls below standard levels (for instance, from 50 hertz [Hz] to 48 Hz), which can cause electrical devices to stop working. In practice, a utility would opt for a blackout rather than allow this to happen.

In Japan, fluctuations on the demand side are extreme. "Everyone turns on their rice-cooker around the same time in the morning, goes to work and school around the same time, and watches television at night around the same time. That makes for big peaks and valleys in power use," Hayashi said.

Meanwhile, on the supply side, Japan's ability to adjust is limited. About a quarter of electricity comes from nuclear reactors, whose output level is fixed. And unlike European countries, which are connected in a mesh-like electricity grid that operates on a unified frequency, Japan's looks more like a fishbone: in each region a single power company controls both production and distribution, with limited links between regions and none to other countries.

In addition, when Japan first began to build its electric network, Osaka used a U.S.-made generator while Tokyo used a German-made model. The result — which remains unchanged — was that as power lines were extended out from Osaka, western Japan came to use its 60-hertz system, while eastern Japan followed Tokyo's 50-hertz lead. However, the two frequencies are incompatible without conversion — and only three converters exist.

Japanese power companies are thus less able than their European counterparts to adjust supply by sending or receiving electricity to or from other areas. Instead, they tweak it by burning more or less coal or oil. Add in large amounts of variable power from solar- and wind-farms, and matching supply to demand becomes difficult.

Within service areas, however, Japan already has an advanced "smart grid," an automated system that helps balance supply and demand and improve network efficiency. Even so, to handle lots of solar and wind power, Hayashi said the grid needs to be even smarter.

For instance, so-called smart meters can be installed in homes and businesses to show consumers how much electricity they are using compared to how much the network is generating, so they can adjust their usage in response. (Japan has yet to introduce this technology on a broad scale.)

Software added to wind turbines can allow them to change the angle of their blades to reduce or increase generation. Storage systems including batteries, electric cars and appliances that convert electricity into hot water can absorb excess electricity and release it when needed. Finally, improving connections within and between power regions will be key for improving flexibility.

All this takes money, time, and the political will to break up the power companies' strangleholds over regional networks — a move Prime Minister Kan has called for recently.

Hayashi said the government is helping to shoulder the financial burden. He is part of a three-year, ¥2.1 billion government-funded project to improve the ability of Japan's grid to handle power from new energy sources. The project brings together researchers from the University of Tokyo, Waseda University and the Tokyo Institute of Technology; manufacturers including Toshiba, Mitsubishi and Hitachi; and nine major power companies (all except Okinawa's). The Ministry of Economy, Trade, and Industry is also funding four regional grid-improvement pilot projects.

But whether that will be enough to create a grid that can meet Prime Minister Kan's ambitious new renewable energy goal remains to be seen.