♪ (music) ♪ You know, it's hard keeping up with all the new clean and green technologies for generating renewable energy. Tell me about it. There are so many awesome innovations with great potential. Wave and tidal energy, bird proof wind power, paint that gathers solar energy, What will we think of next? And some of these renewables aren't so new. Take wind power, it's been around for centuries. And some form of the hydropower has been around since late 1800s. In California, we currently receive around 15% of our energy from this source each year. Unless there's a drought. Renewables count on the fact there will always be water, wind and waves to gather energy. Or sunshine. Take solar energy. The Sun powers the Earth's system and more than meets our energy needs. And there're so many ways to harness energy from the Sun. Large-scale concentrated solar power uses mirrors to direct huge amount of sunlight to a smaller area.
Electricity is generated when the light is converted into heat, which drives a turbine connected to a generator. Photovoltaics, the solar energy that's most familiar, can be small or big scale. Take San Francisco's Sunset Reservoir here. The Sunset Reservoir solar array generates about 5 megawatts of renewable energy for San Francisco. That's the equivalent to about 500 homes a year that it powers. Photovoltaic cells actually absorb the energy of the sun. This energy hits the solar cells, exciting electrons in a semiconductor. These electrons can be captured and converted into clean electricity. That's so cool, I never knew what was going on here. Why aren't solar cells on every roof? Especially if it's good for environment? Well, I heard that solar energy can be expensive to install. How can we provide this source to every home? Grid Alternatives is a nonprofit organization that has a mission of bringing renewable energy technologies to under served populations.
For the last 10 years we've done a total of more than 6,300 installations across the country. So the 6,300 systems that we've installed will save the families that we've installed them for more than $165 million, over the course of their lifetime. It will also offset greenhouse gas emissions, to the equivalent of almost to half a million tons. And that is also the equivalent of taking 91,000 cars off the road, or planting 11 million trees. I am in. Solar can save the world! I don't mean to literally rain on your parade, but solar can't always be our energy source. What happens if it's night time or if it's cloudy? There are ways of extending solar's reach beyond sunny days, but don't take my word for it, let's hear from an expert. You can store solar energy either as electricity or as heat.
The most obvious place you think of storing that electricity is in a battery, but that's still pretty expensive. There are actually less expensive ways to store solar electricity. One is called pumped hydroelectric storage, where you have two reservoirs– one higher reservoir, one lower reservoir, and when you produce electricity often, when you don't need it for something else, then you can use that electricity to pump the water up to a hill to the second reservoir, and then, when you need the electricity, you can allow the water in the upper reservoir to drain down, run through a turbine to generate electricity. So that's a method of storage that's less expensive and actually pretty common throughout the world today.
It seems like we're going to need many sources for our power in the future. Speaking of other sources– Wait, where the heck are you? I'm at the Geysers geothermal power plant. Geothermal is energy way from way deep in the earth. (John Avery) The Geysers is the largest geothermal power plant in the world. We produce approximately 725 megawatts. We have approximately 350 steam wells that collect the steam from below ground in the geothermal reservoir, and then those wells feed pipelines and eventually gather to our main lines, for example, this pipeline here which goes into our turbine building there and enters the steam turbine generator and that turbine is coupled to the generator which is rotating at 3,600 RPM, or 60 hertz, supplying the electricity to you.
Wow, there are a lot of renewable options. Yeah, we didn't even tell you guys about this dance floor that generates the electricity by,… well, dancing. But remember, in addition to all these new technologies, we have to consume less energy and use it more efficiently. So that there's enough to go around. ♪ (music) ♪ So if we cut down our energy use, does that mean we can stop dancing?.