Houses with solar panels have become commonplace. Residential wind turbines have lagged behind. In part, that’s because the technology of building a rooftop turbine is more complicated.

Commercially available home turbines have been modeled on the same technology used for utility-scale wind farms. But hey have not been satisfactory.

Wind power accounts for about 7% of the electricity produced in the US, but that’s 40% of the electricity from renewables. Utility-scale wind farms chew up so much land that they can’t be built near urban areas. But it’s urban areas that use the most electricity.

If some new technology makes rooftop wind turbines feasible, it can increase the amount of distributed energy available to the grid and reduce the need for long and expensive transmission lines.

This post will examine why the familiar rotors don’t work well for home use and describe two innovations that might work better.

Current state of the art wind turbines

Probably everyone has seen tall towers with three rotating blades. These are called horizontal-axis wind turbines (HAWT). Their history dates back to ancient windmills, their current form to airplane propellers.

Larger wind turbines work more efficiently than smaller ones. Today’s rotor blades have become so gigantic that the distance from tip to tip is longer than the wingspan of a Boeing 747 jet.

That brings up the first problem with that design for home use. A single small rotor doesn’t produce enough electricity to be cost-effective. The blades spin much faster than utility-scale turbines. They’re more dangerous to birds. What’s more, the number of moving parts make breakage and expensive maintenance more likely compared to passive solar panels.

A review of residential wind turbines describes six with output from 500 watts to 2000 watts. Those at the low end can reduce electric bills some, but they can’t provide enough electricity to power the entire house during an outage.

One of them is a vertical-axis turbine. That design hasn’t worked well at utility scale but is quite practical for residential use. It has low output, but because it doesn’t need as much air space, the review suggests installing two or three of them.

The ones with higher output cost the most. Some are too heavy to mount on the roof and require towers.

A new, more compact rotor design

A Dutch company called Archimedes, founded by Marinus Mieremet, has devised a new concept for rooftop residential wind energy.

Instead of the propeller-inspired three-blade rotor, its inspiration comes from the Archimedes screw.  This ancient technology can lift water either to irrigate fields or pump water from ships. It has recently been adapted as a water turbine.

Archimedes’ wind turbine, called the Liam F1, is a cone-shaped spiral. Like traditional rotors, it pivots to face into the wind. But its shape allows wind to enter from as much as 60 degrees from the axis.

Theoretically, wind turbines can use just under 60% of wind’s kinetic energy. This figure is known as the Betz limit. Most existing turbines operate at about 50% of the Betz limit.

Mieremet claims 80% efficiency for the Liam F1. He also claims it is “quieter than the sound of people talking.” Traditional HAWTs can be very noisy, although the makers of residential wind turbines also claim theirs are virtually silent.

What’s more, Mieremet claims that his turbines are much less expensive. It can take as much as 28 years to earn back the investment on an ordinary household HAWT. He estimates that the Liam F1 can earn back its cost in less than half that.

To be sure, it costs more than the most expensive of the more traditional residential wind turbines use mentioned earlier. But they are do-it-yourself kits that don’t include installation cost.

The technology has been available commercially since 2014. Supposedly its 1,500 kilowatt-hours per year supply half the consumption of an average home. That’s an average home in the Netherlands. American homes use as much as 11,000 kilowatt-hours. Still, the Liam F1 can supply more than a third of it. Coupled with solar panels, it enables off-grid living even for energy-sucking homes.

Look ma! No moving parts!

Sandia National Laboratory has worked with Texas Tech University and the University of California at Davis.

The team tested a completely different technology. Like the traditional HAWT, it takes inspiration from aircraft, but the wings instead of the engines.

Called the Aero-MINE (for Motionless INtegrated Energy), it has no visible moving parts.

The project proposal envisioned these benefits:

As customer-scale storage and grid-tied electrical systems become more widely available, distributed wind energy has the potential to supply, alone or in concert with distributed solar, a large fraction of business and residential power needs, both day and night. Aero-MINEs overcome existing limitations of distributed micro-wind energy in that they can safely and quietly extract more wind energy by having a larger equivalent swept area. In rooftop and building-integrated settings, Aero-MINEs provide a viable complimentary power source for climate control of commercial and public buildings, manufacturing facilities, and data- centers and server-centers. They are scalable, safe, and passive, making them attractive for apartments and communities.

Airfoils provide enough lift to raise very heavy aircraft miles off the ground. The Aero-MINE combines two partly hollow airfoils and mounts them on a roof, perpendicular to the ground. As wind flows between them, it builds low pressure there.

Slits in the airfoils suck air in and drive it downward to a generator in ductwork under the roof. Except for the generator, there are no moving parts. The system is as passive and modular as solar panels and less toxic to manufacture. In fact, the airfoils come from large-scale 3D printing.

Like the Liam F1, the Aero-MINE works well as a residential wind turbine along with solar panels. Unlike the Liam F1, however, it is not yet commercially available. With the Sandia project finished, it remains to be seen if it can be scaled cost-effectively.

Note:

Sustaining Our World has been named one of the Top 100 Eco Friendly blogs for 2020.

Sources:

Aero-MINE (Motionless, INtegrated, Energy) for distributed, scalable wind power / Sandia National Laboratory, April 2017
Best home wind turbines / Mariah Grimwood, Renewable Resources Coalition. February 27, 2019
Is this odd-looking wind turbine the most efficient you can buy? / Tuan C. Nguyen, Washington Post. June 20, 2014
Rooftop wind power might take off by using key principle of flight / Andrea Thompson, Scientific American. April 21, 2020
Silent rooftop wind turbines could generate half of a household’s energy needs / Chris Agnos, Sustainable Human. March 21, 2019
Why rooftop wind power hasn’t really worked—until now / Caroline Delbert. Popular Mechanics. April 29, 2020