The Revenge of DC...

[edatoakrun]

First I'd heard of this project:

Statnett and National Grid NSN Link Limited are working together on proposals to construct an electricity link between Norway and the UK.

NSN Link will connect the electricity systems of the two countries via high voltage subsea cables from Kvilldal in Norway to Blyth in the UK.

Linking Nordic and British energy markets will bring a number of benefits, including:
•Increasing the security of electricity supplies for both countries.
•Providing opportunities for shared use of renewable energy – helping both countries to meet domestic and international renewable and climate change targets.

•Providing additional transmission capacity for electricity to be traded between both countries, supporting economic growth in Norway and the UK.

Passing through Norwegian and British waters, NSN Link aims to be operational in 2020 and will be the longest subsea interconnector in the world.


Facts
Owners: Statnett and National Grid NSN Link Limited
Locations: The cables will link Kvilldal in Norway and Blyth in the UK
Planned capacity: 1400 MW
Voltage: 515 kV
Length: Over 700 km
Completion: 2020

http://nsninterconnector.com/about/what-is-nsn-link/" onclick="window.open(this.href);return false;

The NSN Link,[1] [2] is a subsea high-voltage direct current electricity cable under construction between Norway and the United Kingdom...

The cable will run from Kvilldal, Suldal, in Norway, to Blyth in the United Kingdom.[2] The route survey was conducted by MMT in 2012.[9][10]

The interconnection may also connect the North Sea wind farms as well as offshore oil and gas platforms, becoming the backbone of the proposed North Sea Offshore Grid...

http://en.wikipedia.org/wiki/HVDC_Norway%E2%80%93Great_Britain" onclick="window.open(this.href);return false;

 

[Moof]

Electrical Engineer here.

The terms AC and DC get tossed around as if all AC is the same, and all DC is the same.

The brilliance of of the AC 3 phase power grid is in the ease of pushing power over huge distances with low loss, while still being able to deliver a low 120/240 V to to the end customers, all with just a few percent along the way, and all done with wire and iron cores.

Oscillating voltages allow a simple transformer (iron core plus some copper wire) to reliably go from many kV down to your household 120/240 V system (or the inverse). The higher the voltage for a given power, the lower the current, so less I^2*R losses. So 10x the voltage results in 0.01x the power loss in the transmission lines.

DC cannot easily be changed in voltage. Your PC has to take in 120V AC, which it converts to a ~350V DC voltage using 2 half wave rectifiers (or a full wave rectifier if you flip that 12/240 select switch). It then chops that (converts to AC square waves) to drive a transformer to step down the voltage to the usual 5, 12, -5, -12, and 3.3 V supplies.

Guess what? You are still not done. The processor runs off of ~1-1.5V DC at many amps (like 20-50 amps). This cannot be done directly by the power supply, as the losses in the wiring from the supply to the processor would be terribly inefficient. So yet another DC-DC converter steps the 3.3V down. In reality all DC-DC converters are a DC to AC to DC converter.

So why did Edison fail? Without an easy and efficient way to got from modest 100-200V DC up to kV's for transmission he had devised a system that put generators every few blocks to keep the wires short enough to make the whole thing sort of work. Westinghouse/Tesla could generate power over at Niagra falls (or wherever) and push it hundreds and hundreds of miles to where it was needed.

Similarly, if you tried to have a household 5V supply, anything that pulled lots of current would require super fat wires to keep the voltage losses acceptable (usually 10% drop at most).

How about solar? Solar panels vary in output voltage somewhat depending on the sun's intensity and the panel's ambient temperature, and you can't draw too much current or the output voltage collapses. A good inverter adjust the load the panel "sees" to optimize the output power for the current conditions to optimize the system efficiency. So you lose ~5% in the inverter, but you would lose MUCH more if you plugged the panels directly into a DC power bus of any fixed voltage. In fact some solar inverters these days can handle partial shading and maintain near full efficiency despite the weakest link issue if the panels had been strung in series before connecting to the inverter.

 

[edatoakrun]

Report on a pilot project taking an entire factory complex off the (AC) grid:

Bosch Building DC Microgrid At California Honda Plant

April 13th, 2015 by Aisha Abdelhamid

With a proposed award from the California Energy Commission, Robert Bosch LLC plans to demonstrate the effectiveness of its renewable-based microgrid platform. The project aims to highlight the benefits and viability of a commercial-scale direct-current (DC) building grid, in comparison with conventional alternating-current (AC) grids. The DC building grid will consist of rooftop solar PV arrays connected to energy-efficient DC lighting, ventilation, and energy storage systems on a 380-volt DC bus.

The California Energy Commission funds will provide an opportunity for Bosch to demonstrate a low-cost, highly energy-efficient microgrid solution. Designed to demonstrate a cost-effective approach to transforming commercial buildings to zero-net-energy users, this innovative Bosch DC microgrid will be installed at an American Honda Motor Co., Inc., (NYSE: HMC) parts distribution plant in California...

http://cleantechnica.com/2015/04/13/bosch-building-dc-microgrid-california-honda-plant/" onclick="window.open(this.href);return false;

I hope they also plan to add DC charge stations/Vehicle to Grid capability to the microgrid and that Honda decides to sell vehicles capable of charging and Discharging there...

Imagine the plant workers commuting in BEVs, powering the microgrid in early morning hours from their excess battery capacity, then recharging in the afternoon when the microgrid's solar generation exceeds demand.

Electrical Engineer here.

The terms AC and DC get tossed around as if all AC is the same, and all DC is the same.

The brilliance of of the AC 3 phase power grid is in the ease of pushing power over huge distances with low loss, while still being able to deliver a low 120/240 V to to the end customers, all with just a few percent along the way, and all done with wire and iron cores...

Want to try to explain to non-EEs what the recent developments have been that now make DC superior to AC for long range transmission?

 

[muus]

DC is used for long range power transmission. The main benefits are lower losses (can use higher voltages) and you don't need to synchronize the frequency of the source/load.

AC is easier (much cheaper) to step-up step down.

http://en.wikipedia.org/wiki/High-voltage_direct_current" onclick="window.open(this.href);return false;

 

[JeremyW]

DC is used for long range power transmission. The main benefits are lower losses (can use higher voltages) and you don't need to synchronize the frequency of the source/load.

Actually, the main advantages to HVDC for very long range power transmission are that they use less conductor and therefore very light and cheap towers. They only need two conductors (or even just 1! but this is rarely done outside of emergency operations) and the ability to use the entire conductor for current transfer (AC power only flows on the skin of the conductor) save quite a bit of cash on the conductors and towers and in essence pay for the converter stations at either end.

AC also has some disadvantages that over very long spans there are issues with charging currents caused by capacitive loading of the transmission line to the earth itself. There's also phase angle, voltage, and stability issues when looking at single lines going very long distance, but it gets complicated to explain without dipping into some theory.

The ability to work independent of frequency (and phase angle) is a pretty big deal, too, for connecting different interconnections (like East-West in the US and North-South of Japan) HVDC is really nice in the ability to adjust power flow; often generators are moved up and down not for power needs but to move around power flow on AC lines.