mains - Power grids : AC vs DC

We know that we have now 50/60Hz in our walls due to mainly historical reasons - back 100 years ago there were no ways to up/down scale DC voltage.

These days we just have problems due to that - every single device sold have to have ~1uF cap per 1W of power before it's PSU to have enough power when we go through 0. (this problem does not exist in 3-phase power, but it available mainly in industrial applications only AFAIK) + caps have to have higher rated voltage to survive sine peaks + all this PFC mess.

Is that correct to say that if we were to design modern power grid, we would skip AC, and just have DC everywhere? As far as I see, it would significantly increase reliability & reduce cost of many devices out there.

Answer

Guy Allee at Intel Research wrote about this topic last year -- DC - An idea whose time has come and gone? -- in support of a 380VDC grid, with the following bullet points:

• 7% Energy Savings vs. High-Efficiency 415VAC; 28% vs Current Typical 208VAC


• 15% Less Capital Cost


• 15% fewer PSU components



• 33% Datacenter Space Savings


• 200% Reliability Improvement, which goes to 1000% if you directly connect the battery bus


• Elimination of harmonics and inherently immune to other AC power quality issues


• Natural affinity to alternate energy generation (Photovoltaic, and wind are ~400Vdc internally, and you actually lose energy & efficiency when you are forced to convert to AC)

He added in the comments:

We very deliberately picked 380Vdc because you want to get to as high a voltage as you can afford for efficiency. At the same time this standard is targeting Low Voltage applications only (<600V). We would have gone higher, but there are structural cost barriers at 400Vdc and 420Vdc. At 380Vdc we stay with the same volume parts ratings that AC is using and get the volume cost benefits of piggybacking on the bulk of current AC power supply component volumes. I’m sure you can also appreciate the significant cost adders that +/-340Vdc has on the personal safety equipment, which is why the standard allows for a cost-effective +/-190Vdc distribution. Thus we have the highest efficiency yet cost effective standard. And with the affinity among other industries, PV, wind, electric vehicles, and lighting, the volume economics seem compelling.

He also mentions the idea of a mixed distribution of both AC and DC within a building (e.g. data centers). For more on that initiative, see the EMerge Alliance website: http://www.emergealliance.org.