Innovation is as much about redesign as new design. The following technologies, though rooted in ideas that are centuries old, are now seeing better days.

The steam engine

A technology that most people associate with the industrial revolution is finding a new life in the clean energy transition. Startup Terrajoule has raised $11.5 million to develop a unique brand of energystorage using steam generated by parabolic trough solar concentrators.

CEO Steve Bisset describes the design his company has resurrected as "a very-well refined thread of steam engine technology." Simple as this may sound, Terrajoule has attracted the attention of titans including Air Liquide.

The Stirling engine

Originally a competitor of the steam engine, the Stirling engine may soon work in tandem with its former rival to fuel the distributed energy revolution.

NRG Energy has called on the talents of inventor Dean Kamen to develop a device that turns the grid into a backup source of power for homes. The resulting Beacon 10 uses a Stirling engine to generate up to 15 kilowatts of power, and can integrate with a battery and rooftop solar. Numerous companies attempting to build solar Stirling engines have failed. But NRG believes its leasing strategy will make the technology attractive to consumers seeking independence from the grid.

The water heater

What would it take to turn that tank in your basement into a “breakthrough variable-capacity grid-interactive water heater?” About $20 in additional parts, says Sequentric Energy Systems.

The company has patented a technology that it claims will give utilities a simple and safe solution to using water heaters as part of demand response programs. The redesign of this common household appliance could soon provide load control and frequency regulation services. And with nearly 50 million water heaters already in place around the country, the potential opportunity is vast.

Securitization

Financial innovation isn’t a concept that we often associate with the past. But experiments with securitization began as early as the 18th century. This month, the practice was applied within the distributed solar industry for the first time: SolarCity offered over $54 million of Solar Asset Backed Notes in a private placement.

GTM Research’s Shayle Kann notes that a strong rating and reception for the package could “open the floodgates” for solar financing.

The clean energy industry is proving that everything old is new again.