Online Journal of Space Communication


Space-based Solar Power has failed to be competitive on cost in spite of decades of study. A new approach appears to resolve the cost issue, undercutting coal and opening huge markets for low cost solar power from space. There are two parts to the problem. First is the cost of lifting parts to Geosynchronous Earth Orbit (GEO; second is the mass of parts that make up a power satellite.

Our team is proposing a combination that makes use of Skylon to Low Earth Orbit (LEO), and a 15,000 ton payload ground powered electric propulsion from LEO to GEO. This strategy reduces the cost to under $200/kg, a 100-to-one reduction from the current cost for lifting communication satellites to GEO. Reaching these numbers requires a Skylon flight rate in excess of 10,000 per year. Even at $200/kg, the economics cannot tolerate more than 6.5 kg/kW for power satellites to undercut coal, e.g., 32,500 tons for a 5 GWe satellite.

Low (20%) efficient photovoltaic (PV) systems are very difficult to reduce below 10 kg/kW. A 60% efficient thermal design has one third of the light intercepting area of a 20% efficient PV power satellite. Carnot considerations require a high temperature ratio between boilers and radiators. The thermal cycles considered in our approach use concentrating mirrors to direct sunlight into high-temperature boilers.

The first working fluid proposed is potassium. After passing through a high temperature turbine, the condensing potassium heats a second working fluid (water or super critical CO2). Waste heat is channeled to low-temperature condensing radiators. Analysis found the radiators to be a relatively small part of the power satellite mass. Concentrators, boilers, turbines, generators, heat radiators and the transmitter massed close enough to 32,500 tons to merit further detailed investigation. The total, including rectenna, parts cost, labor and transportation, came to ~$2400/kW.

Levelized cost of electricity from $2400 capital expense came to 3 cents per kWh, comfortably undercutting coal at 4 cents. Displacing coal on financial merits bypasses debates about CO2 buildup and climatology. If designs and economics can be verified, and assuming rapid expansion beyond the first dozen power satellites, the human race could be off fossil fuels as early as the mid-2030s. To achieve this goal, power satellites must cost less than $2400/kW, installed. It all depends on keeping the power satellite reasonably low in mass and transportation costs extremely low.

Click here to see this team video: Team SunFlower - 2015 SunSat Design Competition



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