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Towards Smaller Solar Inverters

Inverters are getting smaller.

We’re talking here about the inverters used in solar cells to convert the DC that they generate into AC for the grid. But there seem to be a couple of different motivations for this reduction in inverter size; I was made aware of them by a two different product releases.

First came an SoC from Semitech. Semitech has primarily been focused on power-line communications (PLC) on the so-called Smart Grid. Their focus hasn’t so much been on residential settings, where broadband connections dominate, but rather longer-distance machine-to-machine narrowband connections. We’re talking hundreds of (electric) meters communicating over a few kilometers.

That said, they noticed an opportunity. Traditionally, a single inverter will serve multiple panels; this helps keep cost down (always an issue as solar struggles to compete with other forms of energy). But Semitech notes that there are some weaknesses with this arrangement. In particular, the one inverter becomes a single point of failure that can take all of its panels out of action. Efficiency also gets tuned to the needs of the worst (e.g., most shaded) panel – meaning that energy is wasted from the other panels.

The ideal would be a micro-inverter for each panel – something that’s generally been a cost challenge. So Semitech is trying to reduce that added cost by integrating the inverter electronics (not the transformers) into the PLC chip. So any inverter that was intended to communicate could get the inverter control circuitry almost for free (it’s a small add-on to the PLC circuitry, which dominates the chip).

Semitech_image_ret_copy.png

(Click to enlarge)

Image courtesy Semitech.

By the way, apparently the same chip can be used for LED control if loaded with different software.

Meanwhile, ST Microelectronics announced a rather simpler product: an SiC diode. It replaces larger devices that have been needed in order to provide sufficient overcurrent margin. The new SiC diode can handle higher current spikes, contributing to a smaller inverter.

In this case, the small-inverter drive comes from a project driven by Google and IEEE called The Little Box Challenge. Here the idea is that smaller inverters will reduce the size of the cooler-sized box that’s currently needed for a residential solar installation. That makes it less of an eyesore, reduces the footprint, and – critically – reduces cost.

If you’re not part of the Challenge yet, it’s too late; registration is closed. The final prize will be announced next January.

That said, ST also seems heavily focused on the automotive market, saying that the new diode meets the requirements for such applications as on-board battery chargers for plug-in hybrids. It has a reverse breakdown of 650 V, and they boast zero recovery time.

ST_screenshot.png
 

Image courtesy ST Microelectronics

You can find out more about these two products in the releases (Semitech and ST); you can find out more about the Little Box Challenge here.

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