Designing Cheaper Solar Energy

Storage, engines, installation and actuation can be changed to make solar energy cost less than natural gas.

In this Solve for X talk Bill Gross tackles the problem of making solar energy cheaper. Not just cheaper, but less than natural gas and with no subsidies. Solar energy, even when subsidized, currently costs around $0.20 per kilowatt hour.

The price of photovoltaic modules is coming down but total installed system cost is still very high. Photovoltaic cells costs $224 per square meter while Concentrated Solar Power costs $18 per square meter. Bill tells us that installation costs are what make solar expensive.

Metal racks, frames, gearboxes and gears are all heavy and bulky. Their massive strength is required to keep stability when under heavy wind pressure. The power plant and cooling towers need to be built with a large-scale construction project.

All of these factors add up to a cost of $100-200 per square meter installation costs. Solar projects require 95% of the capital expense to be paid up front. In contrast a fossil fuel plant only requires 5-10% at the start of a project.

Bill has a rich history of energy innovation, starting with stirling engine builds in high school. He sold parabolic solar plans through Popular Mechanics, and has invested more than two hundred million dollars trying to lower the cost of solar.

Bill outlines four major areas that require improvement to make solar more economical:

Storage. The plan is to use rocks in the tower to store heat and allow the plant to be run at night.

Engines. A modular engine can be put at the base of each tower and produces electricity. The only thing that needs to be moved will be electrons.  

Actuation. Concentrating sunlight is really moving photons. The concept here is a retractable pool cover solar field. When the wind blows above 25 mph the field is covered.

Everything below the cover is lightweight so actuation can be wire drive with thin steel cables. The idea is to hide from the elements instead of fighting the elements.

Installation.  Gross’ concept is to use robotic field installation, with a few robots in the back of a truck driving across the solar field. As the truck drives at one mile per hour the field can be formed and installed in place. Throughout history only 100 gigawatts of solar have been installed, but this slow moving truck could do 100 gigawatts in a month.

These factors could drive the cost of solar installation down to $47 per square meter instead of $150. A field needs to be four times bigger to run twenty four hours instead of six per day but if the field is cheap enough then the size will not be an issue.

Gross closes his talk with the suggestion that the only way to get widespread solar is to win on price. Using these four radical ideas the estimate is that solar energy can be $0.049 per kilowatt hour.