Off Grid Electric closed its Series D funding Friday with $55 million from Helios Investment Partners and General Electric’s venture capital arm.

The round adds to a growing roster of home solar providers operating in developing countries that are pulling in large sums. In 2017, M-Kopa raised $80 million, Greenlight Planet raised $60 million and Developing World Markets financed 11 companies with a $60.8 million social impact note.

According to GTM Research solar analyst Benjamin Attia, Off Grid's $55 million is likely the biggest pure venture equity investment for a home solar provider on record.

The announcement comes days after Husk set a record for the largest investment to date in a single minigrid company.

The growing size and number of investments in off-grid companies indicates the sector is maturing. A recent analysis from the International Energy Agency found that through 2030, off-grid energy systems are the cheapest option for 70 percent of rural users who will gain electricity access. 

Off Grid Electric -- known as Zola in its service areas -- serves over 150,000 homes with its off-grid solar home systems. The latest investment round will fund an expansion into Ghana, where the startup will continue a partnership it recently started with French utility EDF in the Ivory Coast region. CH Group, a company based in Ghana with subsidiaries in energy, telecommunications and other industries, rounds out the deal with a 20 percent stake. 

"The subsequent investment into expanding this partnership with EDF is an important signpost for more market activity beyond the grid from global energy majors," said Attia. "As the off-grid energy access space matures and the pay-as-you-go solar business model is increasingly proven, energy giants and other strategic investors from the technology, infrastructure and information sectors are taking notice."

EDF said off-grid power represents "a strong contributor" to the expansion of its business.

“For us, the sale of 10,000 off-grid kits in Côte d’Ivoire within the space of just a few months is living proof of the appeal and efficiency offered by off-grid solutions,” said Marianne Laigneau, senior executive vice president of EDF’s international division. 

The new investment brings Off Grid’s offerings into four countries throughout Africa, including the Ivory Coast, Tanzania and Rwanda. 

According to the company’s CEO, Xavier Helgesen, the improving economics of solar make growth possible. “The fundamental economics drive this all,” Helgesen told Bloomberg.

GTM Research’s latest global PV system pricing report puts most major markets at or below $1 per watt, with a capacity weighted average of $0.84 per watt. By the end of 2022, that is projected to fall to $0.75 per watt.   

The investment in Off Grid, which is also funded by companies such as Tesla and Total, shows the blossoming viability of the pay-as-you-go business model. Both Off Grid and Husk sell energy on a pay-as-you-go basis. That payment method is becoming an increasingly important tool for expanding electricity access in underserved areas. According to Attia, it has "grown by impressive leaps and bounds in recent years."

A report out this week from the World Bank Group’s Lighting Global Program and the Global Off-Grid Lighting Association (GOGLA) found that between 2012 and 2017, companies using the pay-as-you-go model accounted for about 85 percent of growth in off-grid solar investments.

Bloomberg New Energy Finance data shows that pay-as-you-go home solar systems in areas without grid power grew from 300,000 systems sold by December 2014 to 1.1 million in December 2016. The World Bank and GOGLA predict that pay-as-you-go will continue fueling growth of solar home systems through 2022. 

Attia said Engie's 2017 acquisition of Fenix International helped validate the pay-as-you-go model, adding that a flurry of strategic acquisition is likely on the horizon. He also expects consolidation, partnerships and mergers among companies with similar supply chains or software. But he added, "The sector will face headwinds from unclear or restrictive import policies, a lack of minigrid regulatory frameworks, and component quality issues" going forward, even as energy majors look to the sector "in a big way in 2018."

According to the World Bank and GOGLA report, off-grid solar devices could reach 740 million people in 150 million un- or under-electrified houses by 2022. Off-grid solar investments doubled between 2012 and 2016.

With its latest funding, Off Grid Electric aims to claim 20 to 25 percent of the country's residential off-grid market share by 2022.