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Q: Do you foresee a time when when buildings and homes will be run on DC and the utility will provide a converter at the customer interface? Seems like this would be a better, more efficient solution than having each electronic device having it's own converter. This would also provide a better interface with distributed generation, particularly PV solar. Going further - do you foresee a time when the entire system will be composed of dc microgrids connected by HVAC transmission?
Paul Johnson, Colorado, U.S.
A: It is very possible that out in time buildings and homes could run on dc, especially if there is an effort to develop and provide more devices such as appliances that run on dc. More extensive deployment of solar pv systems would also contribute to a move towards dc with the incentive to reduce losses from the conversion to ac. If this happens to any great extent it may very well encourage utilities to provide conversion services as the grid will still be required as back up if nothing else.
On the other hand, the possibility of the widespread connection of microgrids by high voltage sources, although conceivable, is remote. The practicality of this along with the economics would make it very challenging at least in the foreseeable future..
Matthew C. Cordaro, PhD
Trustee at Long Island Power Authority, Former Utility CEO, University Dean
A: Yes, but..... The various industries are moving to DC but it is not a one overnight switch nor is there the same trend in all industries. For example, in terms of electric power distribution, direct current would make sense if the power electronic-based transformer to transform voltages from the medium voltage level (few to several kV) to low voltage (the utilization level inside an office building or a home) would be cost-competitive to the conventional ac winding-to-winding transformer. It is not there yet, but it is coming with the cost of power electronic devices and systems falling. For the building industry the concept of direct current makes a business sense already now. If you take, say, 380 V DC and have a one, centralized PE converter from 220 V AC to 380 V DC and distribute the DC within the building you can optimize the system, reduce the losses and number of conversion steps. Industry organizations such as EMerge Alliance (emergealliance.org) promote direct current in those kinds of environments, office buildings, campuses, data centers, telecom, etc.
Data center industry is perhaps even a better example how DC can benefit the owners, operators, and users of the ever growing industry. Since all the critical electrical load is IT load and almost all of it use power supply units (PSUs) to convert 240 V AC or even 400 V AC into 380 V DC and then covert it again to 12 V DC and even again to 1 V DC at the microprocessor level, it makes just a logical sense to centralize and optimize at least the first step of this conversion, i.e. 240 V AC to 380 V DC rather than having it done 20,000 times in 20,000 almost identical PSUs.
On the other end of the spectrum, wind energy turbines operate as variable rpm devices, i.e. the power they generate at the rotating machine level is not 50 or 60 Hz. Therefore what is typically done is that all the turbines need the Power Electronic based converter that transforms this power to fully synchronous 50 Hz or 60 Hz of the collector grid. This PE converter actually has a DC link inside it as an intermediate step. So, it makes a perfect sense to "collect" the power from all the turbine within a wind farm as direct current, utilize only half of the existing PE based converters (variable frequency to DC part) and then, after aggregating, convert the direct current to synchronous AC only once at the substation level.
If one adds to it the photovoltaic (PV) renewable energy the situation is even simpler. PV is inherently DC so one can aggregate the DC first and then either convert it to the synchronous AC in one shot or distribute the low voltage DC (say 380 V DC as above) within the building or the data center if these facilities are physically close by (like PV on the roof or parking lot).
At the HVDC transmission level direct current is already established as an important part of the transmission backbone for most systems in the world. The primary advantages are clear and well documented.
So, the short answer is yes, it is coming, but it is not an overnight process and it will not displace AC any time soon.
Director of Technology, Power Products
A: Yes, it is perfectly conceivable that DC will play a major role in powering our homes, industry and our community. If we want to take this discussion to the extreme view you could see a DC backbone in the USA going from HVDC to MVDC to LVDC. As you know we already have HVDC in common use today and you may also know we have DC in data centers but it is not commonly known that we (ABB) have MVDC in use on shipboard applications. So conceptually these could all come together to make a DC grid in the USA.
I cannot say if these technologies will ever truly come together to create a whole DC grid however, from a more practical sense you will see DC being applied in certain areas like Data Centers where the heavy use of power and multiple power conversions create inefficiencies. I can see a future home having a DC buss as well as AC. Why not? As we add more and more electronic devices into the home there could be cost and energy savings through the reduction of converters in the units. A DC buss would save the home owner and manufacturer money. There are a lot of companies looking at the possibilities and some applications already exist, so I think it is safe to say “yes” someday in the not so distant future DC will be used in a broader sense in homes and industry.
One last comment, Microgrids are becoming a big topic around the globe. Adding distributed energy resources (DER’s) which in many cases generate power and go through an AC-DC-AC conversion, it will make sense to reduce this to AC-DC conversion, create a MVDC buss and provide power to the community on a local basis. We have already “pitched” the concept to some audiences with good feedback.
Vice President/GM Microgrids NAM
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