New Type of Inverter Could Drive Down the Cost of Solar Power
ArrayPower says that it has invented a “sequenced inverter” design that could cut the cost of solar power by 10%.
For those that don’t know what an inverter is, don’t worry, it is easy to understand and I will explain it: a typical inverter for a solar-powered home converts the DC (direct current) power that solar panels generate into 120- and 240-volt AC (alternating current) power, the same as what your power outlet provides. Small solar setups often generate DC at 12 volts, and that 12 volts of DC power is converted into 120 volts of AC power, which is suitable for most household appliances, portable devices chargers, etc.
The new inverter setup mentioned above involves equipping each solar panel with a small inverter, instead of connecting all solar panels to one large inverter.
At a cost of one dollar per watt (of electricity generation capacity), commercial-scale solar panel purchases are less than one-third of the cost of the total cost of commercial solar power setups (including installation), which is $3.50 per watt, on average.
Typical solar setups suffer from lower efficiency because of the way the panels are connected, which is in series. A series connection means that electricity flows from one panel, through the other, and then the next, until it reaches the end of the circuit. When one panel is shaded, the power output of the rest of the panels is reduced because the electrical resistance of the shaded panel restricts the flow of electric current to the rest of the panels.
Each of the distributed inverters invented by ArrayPower attach to the back of each panel. They use rectifiers and transistors to boost the solar panels’ DC voltage from 60 volts to the 208 volts used on the grid. An inductor then briefly stores the current, allowing the device to emit discrete pulses of alternating current. The pulses are combined with those from a minimum of three other panels to provide three-phase AC current that is suitable for the electricity grid.
ArrayPower is a relatively young company that is headquartered in Sunnyvale, California.
h/t: Technology Review | Photo Credit: (adam) THEO
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Looks like micro inverters are finally coming to commercial installs. We use them on all of our residential installs and it make for a HUGE gain in power output and shade tolerance.
The crazy thing is that almost all modern electronics then re-convert that AC power back to DC for use internally. It seems to me that it’s past time to migrate to an entirely DC infrastructure, at least on the level of the individual home. Then the electricity from solar panels and whatnot could be used directly, and we would only have to deal with perhaps a single large inverter in the home for the connection to the grid.
As I understand it (and I don’t have any expertise on the matter), this all started back when electricity was first being rolled out across the planet. DC current doesn’t travel as well as AC current, so large distributed systems (like what we have in the U.S. and other countries) transmit power better in AC. So, that set us up for AC in our homes, and most electronics wanting AC input.
I agree with you.. if we’re going to be moving to more localized power generation, it makes sense to have devices that use DC power from the “grid”/outlet. I’m sure there are lots of pros and cons to discuss (beyond my knowledge), but at first glance, shifting our electric world to DC (at the appliance level) seems to make sense. … well, intellectually.. the problem will be that people won’t want to change over all their devices.. cost and convenience dictate the course. Even if it means killing the planet and our species.
Back in the early days of electricity, Edison promoted ac power and Westinghouse promoted dc power.
Westinghouse said that dec power was more efficient to distribute.
Edison claimed that ac would be safer and less expensive. Think about an on off switch, when the current alternates 60 times a second, the arcing is minimized. A dc switch required more sophisticated mechanics to eliminate arcing.
Also, imagine you grabbed a live electric wire with your hand. Your muscles would contract when electrified. Ac wire would be easier to let go of the wire because it changes polarity 60 times a second. Dc does not change polarity, so it would be harder to remove your hand from the wire.
Btw, Westinghouse invented the electric chair to propagandize ac power claiming it is just as dangerous.
Check out my company, http://www.nextekpower.com
Hello all, I am Kent Kernahan, inventor of the PAMCC technology discussed in this article.
As patented, the concept slices up the waveform in the time domain.
Pulse Amplitude Modulation Constant Current, its given name, describes it pretty well. The key to the invention is the conversion of Pulse Width Modulation to Pulse Amplitude Modulation by a psudo resonate filter we called a reconstruction filter.
This allowed the DCM output of the internal single stage differential boost to be converted into band limited PAM in one step.
As conceived, each PAMCC outputs a series of band limited pulses at a carrier frequency of about 30kHz modulated and synchronized with the baseband grid signal.
The individual PAMCC “Array Converters” are connected in parallel with their pulses offset in time to create a distributed multiphase inverter.
An important distinction from all other approaches that I know of is the carrier + modulation output which classifies each Array Converter as a modulator, a simpler thing than an inverter.
Since the reconstruction filters of each modulator were band limited to about 60kHz and had a bipolar half sine shape, The carrier was effectively canceled without a filter due to the out of phase current summation from multiple PAMCCs on the grid. The inspiration for this part came from multi path and beam forming techniques from my earlier background in RF.
So theoretically, no EMI for a large set because carriers of the same frequency summed out of phase cancel while the in-phase modulation builds. The grid itself actually demodulates a very clean ac waveform.
The idea behind three phase was to make the theoretical energy storage requirement close to zero because the power sum of three phase AC is constant.
So far, so good.
Now the mystery, I filed this patent in 2008 (it later issued with no prior art found), got the company funded in 2009 with a prototype.
Now it is 2012. I can find no evidence that it is listed with FCC, VDE, UL or any other agency. The TR article refers to 7 months of trials and I can find no data of performance ratios, third party verifications or reliability.
The photographs show a case that is maybe twice the size of enphase, however, the design should be a fraction of the part count.