Tidal power: What's holding it back?

Three startups in Houston are using a technique similar to fracking, a practice used in the oil and gas industry, to store renewable energy without batteries. They use excess renewable energy to pump pressurized water into manmade caverns underground. When energy is needed, they open the caverns, sending the water back to the surface to turn a turbine and generate power.

The California-based startup Magrathea Metals is producing magnesium with renewable energy to make the process less expensive and material-intensive. The company aims to make the more environment-friendly metal competitive with steel and aluminum.

The renewable energy technology company Minesto developed tidal kites that generate electricity from ocean tides. The machines are attached to the seabed and pushed through the water in a figure 8 pattern. The movement spins a turbine that generates electricity.

Eversource Energy, a utility company in Massachusetts, installed a networked geothermal system that provides heat for residential and commercial buildings across the city of Framingham. The connected system allows excess heat from one building to be redirected to another that needs it. It’s the first of its kind in the United States.

A utility company in Framingham, Massachusetts, worked with climate advocates to build a unique geothermal heating and cooling project that spans a whole neighborhood. A group of residential and commercial buildings share the infrastructure necessary to harness stable underground temperatures for heating and cooling, which reduces their greenhouse gas emissions and energy bills.

Public schools in St. Paul, Minnesota, are installing geothermal systems to heat and cool buildings with energy harnessed from underground temperatures. The efficient, affordable energy source allows them to keep school buildings at a comfortable temperature during the increasingly warmer summer months.

California and Texas are among the states in the U.S. installing giant lithium-ion batteries to store renewable energy to use when the sun isn’t shining and the wind isn’t blowing. These batteries are reducing the use of fossil fuels as a backup energy source when demand is high.

Thermal storage technologies are lowering businesses’ energy costs and carbon emissions while reducing strain on the grid during peak times. Two hotels in California implemented a system that makes ice when energy demand is low and uses the ice during peak demand times to cool the building.

After adding electric school buses to its fleet with the help of grant funding, Morris Area Schools saw its fuel costs drop from about $3 per gallon to the equivalent of about $1 a gallon. Each bus is estimated to help cut roughly 140 tons of carbon emissions over its lifetime.

To mitigate the carbon dioxide emissions generated by tourism, the community in Juneau, Alaska, created the Alaska Carbon Reduction Fund as a type of carbon offset program. Tourists pay an emissions fee to the fund when doing certain excursions, and that money is used to install heat pumps for residents who earn less than 80 percent of the median income.