WindSail Capital Group is a Boston-based investment firm providing growth capital to companies advancing energy innovation, climate tech, and sustainability. The firm specializes in flexible financing solutions—primarily senior secured loans—that facilitate growth while minimizing dilution.
36% of their portfolio is in Climate & Energy. Deal activity decreased year-over-year (1 deal in the last 12 months vs 2 prior). Their most common stage is growth (45% of deals). Average disclosed round size is $14.4M (across 10 rounds with reported amounts).
Portfolio
9
Fund Size
—
Top Stage
Growth
Last 12 Mo
1
Team
MR
Michael Rand
Co-Founder & Managing Director
IB
Ian Bowles
Managing Director
MT
Matthew T. O'Rourke
Managing Director
Portfolio Breakdown
Stage Distribution
Sector Distribution
Investment Activity
DealsAvg Round Size
Portfolio
11 investments
| Company | Round | Amount | Date |
|---|---|---|---|
 Nanoramic Laboratories | Unknown | $54M | Nov 2025 |
| Nanoramic Laboratories | Unknown | $44M | Dec 2024 |
 WeatherFlow-Tempest | Growth | $3M | Dec 2024 |
| WWeatherflow | Growth | $3M | Apr 2023 |
 Velocia | Growth | $2.5M | Aug 2022 |
 Ubees | Growth | $8M | Aug 2021 |
 Varentec | Series A | $7.7M | Nov 2019 |
| VVarentec | Unknown | $5M | Nov 2019 |
| Varentec | Series C | $13M | Sep 2013 |
| EEccentex, Inc. | Strategic | — | — |
| DDC Systems | Growth | $4M | — |
Top Co-Investors
Bill Gates2 shared
Khosla Ventures2 shared
3M Ventures2 shared
GM Ventures2 shared
Top Material Co., Ltd.2 shared
Techstars1 shared
Station F1 shared
ITOCHU Corporation1 shared
Last updated: 20 October 2026