Telkes joined the MIT Solar Energy Conversion Project, marking a shift in her career toward focusing exclusively on solar energy research and development. This was a critical point in her career, and she began to focus on innovations using heat storage.

During the early years at MIT, Telkes dedicated her time to the development of solar heating systems. This was a pioneering effort to create an environmentally-friendly alternative to traditional heating methods.

During World War II, she invented a small solar still for military use. This device was capable of distilling seawater into potable drinking water, proving invaluable for soldiers stationed in arid or marine environments. The solar still was an important step towards more widespread adoption of solar technology.

Telkes designed and built the Dover Sun House in Dover, Massachusetts, with architect Eleanor Raymond. This was one of the first houses to be heated entirely by solar energy. It used a unique thermal storage system using Glauber's salt to store solar energy, a pivotal advancement in the field.

While the Dover Sun House was initially successful, issues with the Glauber's salt system arose. The salt tended to stratify, losing its heat-storing capacity over time. This led to performance issues and ultimately, disappointment with the project's long-term viability. Telkes resigned from the project and felt her work was unfairly criticised, leading to her leaving MIT.

Despite her innovative contributions, Telkes left MIT, reportedly due to disagreements over the direction and viability of the solar energy research program. The problems with the Dover Sun House significantly impacted her standing within the institution.