It's too early to call it a rebound in cleantech VC. That might take a generation.

But, in the meantime, there's been a small surge of VC funding of cleantech companies in the last few weeks. Here's a quick roundup.

Aircuity banks $6.45 million for "airside efficiency"

Aircuity, an "airside efficiency" company, just banked $6.2 million in expansion capital. The round was led by Rivas Capital and included investment from existing investor Source Squared. Aircuity claims to provide "significant energy savings for commercial and institutional building owners while simultaneously improving the safety, comfort and productivity for occupants through continuous monitoring of the indoor environmental quality." Dan Diehl, Aircuity's CEO, said, “We are confident that our market opportunity is in excess of $5 billion. We know that in North America alone, there are approximately 10,000 laboratory facilities spending more than $7.5 billion a year on energy." The startup was founded in 2000 and is headquartered in Newton, Mass.     

ViZn adds a few million in funding for its flow battery technology

ViZn, a flow battery startup, added several more million dollars to its war chest, according to SEC filings spotted by GTM Research. As GTM's Jeff St. John has reported, ViZn recently launched its first commercial-scale product, an 80-kilowatt, 160-kilowatt-hour zinc redox flow battery housed in a 20-foot shipping container. It also announced its first deployment with Blue Sky Energy for an Austrian microgrid project, aimed at storing and balancing on-site solar generation.

ViZn’s systems are targeting a price point of $800 per kilowatt-hour for microgrid systems, Kirk Plautz, vice president of sales, said in a previous interview. The company’s longer-term goal is to put together five of these containers in a 1-megawatt, 3 megawatt-hour system. It has a “clear path” to reducing costs to about $450 per kilowatt-hour at scale, Plautz said.

ViZn has raised about $20 million to date.   

Yeloha, a "solar sharing network," raised $3.5 million

With a $3.5 million round led by Carmel Ventures, Yeloha has founded a peer-to-peer network that will let people participate in solar, whether or not they own their roof. As we reported earlier this week, Israeli entrepreneur Amit Rosner launched this new business to combine "the power of social networks and the appeal of the sharing economy." Its goal: to remove some of the constraints that make solar power inaccessible to so many. "We'd like to let anyone go solar," says Rosner. "No matter where they live, no matter what their income level is."

Solar wafer startup 1366 Technologies ups its Series C with $5 million

1366 Technologies boosted its Series C round to $22.5 million, adding another $5 million from new investor, Haiyin Capital, a China-based venture firm. The company's total financing is now $69.5 million and the new funds will be used for the commercial scale-up of its Direct Wafer Technology. 1366 Technologies’ Direct Wafer forms multi-crystalline wafers directly from molten silicon instead of the traditional multi-step energy- and capital-intensive process. The company aims to build a 250-megawatt factory in the U.S.

Solantro, advancing power electronics in renewables, scores $11 million in VC

In an extremely difficult fundraising environment for early-stage cleantech companies, Solantro Semiconductor, a renewables-focused power conversion chipset vendor, raised $11 million in venture capital. The funding came from existing investors Black Coral Capital, BDC, Presidio Ventures, Clean Energy Venture Group and EDC, as well as new investor Inerjys Ventures.

As we recently reported, Antoine Paquin, CEO of Ontario, Canada- and Silicon Valley-based Solantro, believes Moore's law can lower the cost of solar power electronics and that horizontal integration in inverters will yield more efficient designs that leverage the scalability of silicon and reduce cost in solar andstorageapplications.

Solantro designs and builds chipsets for use with solar module power electronics, which include microinverters from firms such as Enphase or SolarBridge (acquired by SunPower) and DC optimizers from firms such as SolarEdge or Tigo. The CEO suggests that the same chipset-based silicon integration of discrete electronic components that enabled cheap cellphones will enable lower-cost module-level solar panel electronics.

In 2012 Solantro raised a $10 million round A and also won $3.8 million from Sustainable Development Technology Canada.  

Smart buildings still an opportunity for venture capital

GTM's Stephen Lacey reported that building analytics company FirstFuel announced a Series C round worth $23 million to expand into Europe and build its offerings in deregulated U.S. markets. The recent addition of the Round C doubles FirstFuel’s total funding to $45 million. Next World Capital led the round and was joined by previous investors Battery Ventures, Rockport Capital, E.ON, Nth Power and new investor Electranova Capital, a fund sponsored by EDF Group in France.

Lucid, the maker of a universal operating system for buildings, added $5.9 million to its previous Series B round closed last June, according to SEC filings filed in late March. The Series B round was led by Formation 8 Partners with a follow-up investment from Zetta Venture Partners.

BuildingIQ, a startup with predictive analytics for HVAC systems, also closed a $2.7 million round in March as part of a $10.6 million offering, according to SEC documents. This follows BuildingIQ's $9 million venture raise in early 2013, which included Aster Capital, Paladin Capital Group and Siemens' venture arm. The company says it grew recurring revenue by 96 percent in 2014 and is now serving close to 20 million square feet of buildings with its analytics software.

Last October, startup Persistent Efficiency emerged with a stick-on submeter that reads magnetic fields from circuit breakers and reconstructs them into current, load and power factor. This week, the company said it had closed a $1.1 million seed round from angel investors, including Peter Rumsey, who previously backed Building Robotics. Persistent Efficiency CEO Jason Trager says the "Power Patch" can monitor power quality and energy consumption at a fraction of the cost of a traditional submeter. The company is looking to apply "assembly-line principles" to monitoring building energy use, and eventually build more analytics capabilities on top of its novel device. 

These investments follow a $14 million round closed by Blue Pillar in February to expand its monitoring capabilities for microgrids and critical backup systems in buildings. 

"Among the markets we're tracking, building energy management is second only to energy storage in terms of VC interest so far this year," said Andrew Mulherkar, a grid analyst with GTM Research.