A team of researchers at Purdue University are retrofitting a 1920s home to run completely on DC current.
A 1920s-era home in West Lafayette, Indiana, has been converted to run entirely on direct current (DC) power. Graduate students live in the house full time, while Purdue researchers (from left) Eckhard Groll, Jonathan Ore and Alex Boanta monitor the energy efficiency of its self-contained DC nano-grid.
Image: Purdue University photo/Jared Pike
While most homes run on alternating current (AC) power because that’s what comes from the utility lines from the grid, researchers at Purdue University decided to switch a home over to all direct current (DC) power.
Why? Back in the late 1800s Thomas Edison had a dream of a DC-based electrical infrastructure, but that dream lost to George Westinghouse’s AC system. In recent years, however, with renewable energy sources generating DC power, it would make a home more efficient if the electricity did not have to be converted to AC.
“We wanted to take a normal house and completely retrofit it with DC appliances and DC architecture,” said Eckhard Groll, the William E. and Florence E. Perry Head of Mechanical Engineering, and member of Purdue’s Center for High Performance Buildings. “To my knowledge, no other existing project has pursued an experimental demonstration of energy consumption improvements using DC power in a residential setting as extensively as we have.”
The project to transform a 1920s-era West Lafayette, Indiana home into the DC Nanogrid House began in 2017 under Groll’s direction. The first years were spent renovating and upgrading the infrastructure, and they added insulation and new windows to increase the home’s energy efficiency.
Rectify Solar provided a full installation of solar panels on the roof, while industry partners supplied new appliances and HVAC systems. The rooftop solar system brings the all-electric home to net zero. Rectify installed Panasonic 330 panels rated for 14.3 MWh annual production, inverters from CE+T America, and a lithium iron phosphate POM Cube 20 kwh battery system, rated at 12.5 kW continuous power.
“Large-scale distribution of DC power through a house in the 21st century is really uncharted territory,” said Jonathan Ore, a 2020 Purdue Ph.D. graduate who served as the lead researcher on the project. “You can’t just go to the hardware store and buy DC circuit breakers or other critical distribution systems. We had to create this infrastructure from scratch.”
Purdue researchers, in collaboration with Rectify Solar, developed and jointly own a patented distribution system that enables the house to integrate both DC power from solar panels, wind turbines or battery storage with AC power from the local utility.
“The creation of the 380-volt DC load center was definitely a challenging and rewarding experience,” said Phil Teague, co-founder and CEO of Rectify LLC. “We used biomimicry and the neural connections of the brain as our inspiration, and added smart technologies and control mechanisms. Transitioning to DC can simplify homes, buildings and the grid as a whole. This project helped me realize that DC is not only the future, it always was.”
“A DC-house can potentially sustain itself for short periods of time by generating its own renewable energy and detaching from the grid through the help of on-site stored energy,” said Ore. This ultimately minimizes the strain on the outside grid in emergency situations. Events like the Texas storm are perfect illustrations of how a DC-house can benefit individuals and the community.”
To monitor the DC home for its comfort and usability, graduate students are living in the home full time. They’ve installed sensors in every room to detect whether people are present so that the HVAC system only heats or cools the areas of the home that are in use.
“This gives us the opportunity to perform both cutting-edge research on energy-saving opportunities and observe its potential benefits in a truly real-world setting, rather than just relying on simulations,” Groll said.
“It’s been really amazing to see the interest in this,” Ore said. “We started this project as just a proof of concept. But as our country experiences more and more issues with the grid, companies are actively seeking to integrate our work. People are interested in it from every aspect: from the electrical side, from the thermal side, from the automation and management side. This is a perfect testbed to experiment with those technologies.”
Purdue innovators have worked with the Purdue Research Foundation Office of Technology Commercialization to patent this technology. The researchers are seeking OEM partners to continue developing their technology and to take it to market.
As a result of this project, Phil Teague will be speaking at RE+ in Anaheim next month about this project on the topics of “DC is the Future, It Always Was”, and “DC Microgrid Design-Build Lessons Learned”.
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Let me see if I understand this. These folks have completely retrofitted a house to run on dc that required replacing all the electrical appliances and breakers for achieving some level of added efficiency. This seems to be a perfect example of just because you can do something, it doesn’t mean that it’s a good idea.
That is your opinion. I’ve lived in a DC home 25 yrs and this is the future as lower cost, more efficient. Another great thing is it is EV pack voltage nom so EVs can connect at low cost to charge, use as storage to run the home. Solar, small wind, etc can charge the battery directly. Many A/Cs as variable speed as they should be, many work on DC as they have a universal input or specifically designed for DC normally. Others work on 48vdc for homes running that. You’d likely have to add to the wiring or replace it but in old homes this is easy normally and many x needed anyway. 380vdc nom is a good voltage to make small microgrids too without costly inverters and their idling current wastes.
It makes complete sense! Most of our lighting (LED) can be run easily on DC – most of our electronics are purely DC, and we have to plug in transformers to reduce the AC voltage to the 5-24v most of these devices use, or to charge the batteries. Motors are more and more commonly DC, and any appliance or tool that uses one can be retrofitted easily. Panels generate DC, batteries store DC. What doesn’t make sense is letting someone patent any of this, or adding any barriers to developing this further. We should be developing standards that encourage the adoption of DC in all new construction, or remodeling.
Exactly. It can all be done. What doesn’t make economic sense is retrofitting an entire existing electrical residential and commercial infrastructure.
You must have no experience with 100 year old homes – to make them efficient, they generally require a substantial amount of work – insulation in walls and ceilings that never had any, replacing heavily corroded old plumbing, and even removing old knob-and-tube wiring ( and the occasional gas lighting fixture) and replacing it all with safe/modern systems. It makes far more sense to do these retrofits with an eye towards the future – and that includes solar, batteries, and even DC wiring.
@Tad Laird “It makes complete sense! Most of our lighting (LED) can be run easily on DC”
Absolutely, I have put my kitchen lighting on battery fed 12V DC a few years ago. This way I have lighting even when there is an outage. I can charge the battery from solar or cheap off-peak energy. But the most effect has brought some moderate under-volting. Using a buck converter, I can run the lighting off 9V. Which brings down the power needed to under 1W. This way I can stretch the amount of light available in an outage. Although it has turned out, I now use it on 9V pretty much all the time. I have integrated a switch, so that I can pick if I want to run of stabilised 11.5V or 9V.
One issue though, is to find switches for the wall, that are permitted for DC.
As a child in the 1940/50’s… there was only 240V DC in Calcutta (Kolkata now) as well as several other Towns and Cities in India and assume elsewhere too…. ALL APPLIANCES WERE DC… I remember we used to have a DC Fridge which used a small electric heater.. instead of a Compressor (Kelvinator..??).) …. the rest was all DC.. Light Bulbs, Electric Stoves/Heaters Pumps, Radio (no TV then) .. NOTHING NEW AGAIN…
Perhaps the Egyptians (during those Pyrmaid Building Times) used DC too .. as they have found vessels there that look like Batteries…
NOTHING NEW HERE… Just Bringing the Old Back Again … and “guarded” by a Patent too..???
Just one word of caution… if you touch a DC live wire… either it will Throw you Off (negative wire..??) or “Not Let Go”.. (postive wire..??).. so BEWARE…
Yes, many devices today are in fact DC. However, lighting, electronics, variable speed DC motors, PV modules/strings, batteries all use, generate or store energy at different voltages. A TV or computer monitor may require 400 VDC, while lighting may be 24 VDC, and small devices 5 VDC. A PV string might be anywhere from 50-450+ VDC. You’ll still need DC/DC conversion everywhere, which if I understand correctly is part of the reason AC distribution won in the first place: ease of voltage conversion using transformers (along with the inherent safety of AC). Is DC/DC conversion that much more efficient than a AC/DC inverter? I’m not saying it’s a bad idea, but there’s not enough information here to understand how these nuances will be addressed or what the net benefit will be.
If DC becomes economically feasible by its own accord, fine. Don’t be stupid and make some dumb declaration like “we will be all DC by 2050”. Let the market decide. Don’t use my tax dollars to make your dream dictate come true!
DC electric was/is economically feasible on its own accord (for me at least) since 1995. Even paying outrageous prices for the panels at the time, it was a bargain as the alternative was to run a gasoline generator for the cottage. DC is niche market, but a large one worldwide as most of the developing world is not connected to any kind of the grid except in large centres. I think the market and industry supporting DC does not need any external support. The university students did it as an exercise not as a proof of concept as there is no real world application for the project. (I’m pretty sure)
As a proof of concept — these are university researchers after all — this is a great idea. (Now, trying to convince builders to do this on new construction, that’s a much, much harder problem!) One thing not mentioned is what DC voltage they are running. Seems to me they are replacing all the old AC/DC converters with new DC/DC converters to get the right voltage. Is that still a win?
@Nick Mitchell “Seems to me they are replacing all the old AC/DC converters with new DC/DC converters to get the right voltage. Is that still a win?”
Your switching power supply is pretty much a rectifier with a DC-DC converter, it would be a miracle if it were not more efficient. Albeit the efficiency of the circuitry depends on the design and chosen parts. And if you happen to have/use an old transformer (non-switching) AC power supply, those are terribly inefficient. Everything is more efficient than those.
No need for the high voltage battery plant. There are hundreds ( perhaps thousands) of off grid cottages and homes that are running with only 12V DC wiring. Most of what we need in the way of electric powered devices have useful DC varients. Refrigerators and freezers are available in 12 or 24 Volt DC. LED lighting of course is available in 12 volt DC as are various fans and water pumps to run the other mechanical systems. Basically, anything that can be powered off of a “cigarette lighter” outlet is applicable. No exotic battery plant is needed either. 12 Volt deep cycle, either old fashioned lead acid or the pricier ( but cost effective Lithium Iron) batteries can be scaled to you needs. One important detail is to wire the house with #10 wiring for most circuits and #6 for the higher amperage devices like refrigerators.
Precisely! Just like we have standards for 110v or 220v wiring, with different plug shapes for different amp ratings, we could come up with a simple standard for 12v and 24v DC, with a couple different plug types (not so many!) for those. We could even have built in transformers that fit existing wiring boxes that install standard USB A or C outlets. I’ll admit we’ll still have need for cooking and heating, but maybe heatpumps will work, and maybe induction will work – I don’t claim to be an EE, but 12v DC systems are all around us, and applying that to our homes just seems incredibly logical to me, and we don’t need to start by completely re-inventing the wheel
I do believe that there IS a manufacturer of 24 and 12 Volt DC heat pumps! Not really ethical to paste links, sorry.
I am excited to try to follow this, (no experience in engineering/electrical), because I hope for more (!) than already amazing and fast evolution of photovoltaics:: I would also want to be in a culture change about – usage – to complement the new science. Parameters we are offered by utilities’ developers and financiering corporations regarding what we should want and what is available in the real world, are often mostly about how the real world can conform and perform for a preferred business model producing a preferred profit margin. Please continue this story.
I ran all my 12-volt DC to the battery compartments of APC or Belkin UPS units with the appropriate fuses so that AC table lamps, computers and monitors and other low wattage devices could all be run off the 12-volt battery DC power converted to AC at the UPS. Plugging the UPS into a remote-controlled wall outlet switch gives the ability to transition back to AC when the batteries are low. The air conditioners take a 3,000-watt pure sine wave inverter for each with parallel #2 copper conductors to cover inrush at cycling. 8,000 watts of solar panels and 8,000 amps hours of Deep cycle marine RV batteries covers all but the 220-volt 5,200-watt electric clothes dryer that is still on the utility power and the 220 volts cook top four burner range. Since most inexpensive appliances such as toaster, blenders, microwave ovens are made to use with AC power and any appliances that are made for DC power are sold at a premium of up to 800% more, converting DC to AC will need to be the norm for the foreseeable future.
What if this retrofit was just one, of say 30 similar one on a city/town block, a block with its own DC microgrid that could eliminate all the inverters in each home, except for the microgrids point of contact with the macro grid,, aggregate the communities energy resources and provide these resources for microgrid ancillary service, resources for the regional wholesale market (FERC 2222) and scheduled DC fast charging for the block’s EV’s. Might this be a step towards energy democracy, an item mentioned in DOE’s “energyshed” concept?
When I built my home in 1990, I used 12 volt lighting throughout – from a 12v lead acid battery and a couple of solar panels. Initially we used 10watt halogen lamps, then later some 12v compact fluorescents. Now we entirely use 12v LED fixtures supplied from a 200 Ah Lithium Iron Phosphate battery (and still using the same panels). As mentioned by someone above, this is wonderful if there is ever a utility outage because all of the lighting remains usable. We have a separate small 12v distribution board to maintain segregation from the mains power. I think that it would make sense to always install LED lighting systems in this way. It seems a bit pointless to wire lighting circuits at mains voltage, only to then install little transformers at all the (LED) light fixtures!
If you take the time and expense to wire your own DC, you can leverage you DC even further. Most people are unaware that you can buy straight 12 ->24 DC refrigerators (not to be confused with the 2 way and 3 way units for motor homes). They aren’t fancy and the biggest I’ve seen are 16 cubic feet but you can always by multiple units and they also make DC chest freezers. There are at least 2 manufactures who’s products are distributed in North America. The only catch is they draw 5 amps DC whereas your lights drawing current in the milliamp range. Therefore your wiring for the larger appliance may have to be 8 AWG, 6 AWG or even 4AWG if the runs are more than 55 feet. Bathroom fans? Yup, 12 Volts units are available. Ceiling fans ? Yup, 23 Volt units are available. Water pumps for irrigation or water features are available in 12 and 24 volt DC.
“inverters from CE+T America” what are the inverters for if it’s an all DC house?
What type of heating/cooling does this home have? If it has a geothermal heat pump, I’m surprised it isn’t a completely or nearly complete autonomous installation.
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