East Japan entered its fifth day of power rationing on Friday, with no end to the planned blackouts in sight. The power shortages began last week when a massive earthquake and tsunami knocked nuclear power stations offline. The local electrical utility can't make up the shortfall by importing power from another region, though, because Japan lacks a national power grid, a consequence of a decision taken in the late 1800s.
Japan's electricity system started in 1883 with the founding of Tokyo Electric Light Co. Demand quickly grew and in 1895 the company bought electricity generation equipment from Germany's AEG. In west Japan the same evolution was taking place, and Osaka Electric Lamp imported equipment from General Electric.
The AEG equipment produced electricity at Europe's 50Hz (hertz, or cycles per second) standard while the General Electric gear matched the US 60Hz standard. That probably didn't seem important at the time - after all, lightbulbs are happy on either frequency - but the impact of those decisions is being seen today.
All of eastern Japan, including Tokyo and the disaster-struck region to the north, is standardised on 50Hz supply while the rest of the country uses 60Hz.
Connecting the two grids is possible, but it requires frequency changing stations. Three such facilities exist, but they have a total capacity of 1 gigawatt.
When the quake hit, it shut down 11 reactors including three that were in operation at the Fukushima Daiichi plant that is now at the centre of Japan's nuclear problems. With the 11 reactors offline, 9.7GW was gone from eastern Japan's electricity production capacity.
And that's the root of Tokyo's current electricity problems: utility companies in west Japan are unable to make up for all of the lost power.
On Monday the government appealed to east Japan to cut consumption and the region responded. Lighting has been reduced in offices, neon signs are dark and passengers in some stations are being asked to take the stairs instead of the escalator.
A series of daily rolling blackouts was also introduced to keep total demand below supply. By switching off power to 10 million homes around Tokyo, the utility company is able to keep the lights burning in the capital.
Or, at least that's the theory.
Tokyo Electric Power Co. (TEPCO) warned on Thursday that an unpredictable and massive blackout faced Tokyo that evening. The cold weather had led many to switch on heaters and demand was getting dangerously close to TEPCO's remaining 33.5GW capacity.
Tokyo responded. Almost immediately offices let people out early, railway operators cut services and unneeded lights and appliances were switched off in homes. The city escaped the predicted power cuts, but for how long that can continue is unclear.
TEPCO has warned the power cuts will last until at least April and even after that the need to conserve energy will continue.
Several of the Fukushima Daiichi reactors will likely never come back online. Tokyo's energy worries are largely dependant on when or if the other power stations can be restarted.