Tuesday, July 22, 2014
Think shrink! Min it to win it! Smaller is baller! That's what the Little Box Challenge is all about: developing a high power density inverter. It’s a competition presented by Google and the Institute of Electrical and Electronics Engineers Power Electronics Society (IEEE PELS) -- not only a grand engineering challenge, but your chance to make a big impact on the future of renewables and electricity.
With the rise of solar photovoltaic panels, electric vehicles (EV) and large format batteries, we’ve seen a resurgence in the over-a-century-long feud between Thomas Edison’s direct current (DC) and Nikola Tesla’s alternating current (AC). The electric grid and most higher power household and commercial devices use AC; batteries, photovoltaics, and electric vehicles work in DC. So the power electronics that convert between the two -- rectifiers (AC->DC), and inverters (DC->AC) -- are also gaining increased prominence, as well as the DC/DC and AC/AC converters that switch between different voltages or frequencies.
While different flavors of these devices have been around for well over a century, some of them are starting to show their age and limitations versus newer technologies. For example, conventional string inverters have power densities around 0.5-3 Watts/Inch3, and microinverters around 5 Watts/Inch3 -- but lithium ion batteries can now get 4-10 Watt Hours/Inch3. So for a 1-2 hour battery pack, your inverter could end up being bigger than your battery -- a lot to carry around.
Some recent advances may change what’s possible in power electronics. For example, Wide-bandgap (WBG) semiconductors -- such as gallium-nitride (GaN) and silicon-carbide (SiC) -- not only enable higher power densities than conventional silicon-based devices do, but can also convert between DC and AC at higher temperatures, using higher switching frequencies, and with greater efficiency.
But even WBG materials and other new technologies for power electronics run into limits on the power density of inverters. Photovoltaic power and batteries suffer when they see oscillations on their power output and thus require some form of energy storage -- electrolytic capacitors store that energy and bridge the power differential between the DC input and the AC output, but that makes the devices much larger. Household and consumer devices also need to add filters to prevent electromagnetic interference, so that’s even more bulk.
When it comes to shrinking these devices, inverters may have the most potential. And because inverters are so common in household applications, we hope The Little Box Challenge may lead to improvements not only in power density, but also in reliability, efficiency, safety, and cost. Furthermore, it is our hope that some of these advances can also improve the other types of power electronics listed above. If these devices can be made very small, reliable and inexpensive, we could see all kinds of useful applications to the electric grid, consumer devices and beyond, maybe including some we have yet to imagine.
To recognize the role academics have played in pushing the forefront of new technologies, Google has taken a couple of special steps to help them participate:
- Research at Google will provide unrestricted gifts to to academics pursuing the prize. This funding can be used for research equipment and to support students. Visit the Little Box Challenge awards for academics page for more info -- proposals are due September 30, 2014.
- Academics often have trouble getting the latest technology from device manufacturers to tinker on. So Google has reached out to a number of WBG manufacturers who’ve put up dedicated pages detailing their devices. Check out the Little Box Challenge site to get started.
We hope you’ll consider entering, and please tell your colleagues, professors, students and dreamers -- you can print and post these posters on your campus to spread the word.