IEEE PES Atlanta: Space Solar Power

This week at the IEEE PES Atlanta lunch event, the topic was on space solar power (SSP) . The presenter was Space Solar Power Institute President Derel Preble. Here are my notes from his presentation.

NASA started research on SSP in the 1980s. The principle is relatively simple: harvest photovoltaic (PV) energy from solar rays in the space before they get attenuated by the Earth's atmosphere, then transmit that energy to the ground using a low density microwave beam. Such beam would not be attenuated by the atmosphere. The energy from the beam would be collected using antennas rectifiers ("rectennas"). Each geo-orbit satellite could provide 1 GW of power. Northrop Grumman has committed $17 million for SSP research at Caltech to further advance the field.

There are big advantages to this concept, shown in the photo above:

• Maximized PV energy collection,
• Reduced transmission losses to the ground,
• 24-hour availability without weather sensitivity,
• Dispatchability (can modulate output anytime),
• Reduced land use, with dual-use of land for farming.

The major drawbacks are the high financial and engineering risks:

• Prohibitive cost to build/launch satellites (sweet spot at $150/lb with reusable rockets),
• Challenges harvesting/capturing the energy transmitted from the satellites,
• Maintenance of the equipment in space (by robots),
• Effective, large scale storage (compressed air seems most cost effective).

Space solar power should be transmitted on a reserved microwave frequency, such as 5.8 GHz, to avoid interference with other equipment. Microwave ovens operate at 2.5 GHz. The Georgia Tech students in Prof. Durgin's lab presented their work on building a cost-effective rectenna to harvest 5.8 GHz microwaves using off-the-shelf products (e.g. a regular printer). They are able to use the energy from an emitter one meter away to power a diode!

Derel Preble noted important aspects of offsetting fossil fuels and carbon emissions:

• There are no actions in place to mitigate rising CO2 levels (EPA hearing Atlanta Nov. 2015).
• High CO2 levels decreases the nitrogen nutrients absorbed by plants, negatively affecting cattle quality in turn.
• While high fuel prices tend to lead to recessions, the economy doesn't improve with low fuel prices after a recession as consumers struggle to recover.
• Energy ROI (EROI) must be considered when designing renewable energy production and storage. "Buffered" EROI is half when including storage (energy buffers) because of the energy involved to build the storage technology. Derel Preble mentions that it is not worth the EROI trying to store PV and wind output.

In conclusion, I am excited to learn about space solar power because it is an opportunity to make the most of our Sun. What is still unknown is whether launching costs will be favorable, and whether the technology to harvest energy beams is feasible.