In earlier blogs I’ve commented on Solar PV and Concentrating Solar Power. Here I will comment on Solar Satellite Power Systems (SSPS). As proposed, such systems would use electricity generated by a collection of solar PV panels in geosynchronous orbit (i.e., an orbit above a fixed point on earth) to power a microwave generator. The generated microwaves would be beamed through the atmosphere to a ground-mounted receiver (‘rectenna’) that would convert the microwaves to electricity that would be distributed to consumers via the terrestrial grid.
This concept first received NASA attention and review in the 1970’s which raised a number of issues which still remain problematic. A small group of SSPS enthusiasts still promote the technology but broad support is lacking.
The obvious advantage of SSPS is its access to unimpeded radiation from the sun without the interference of clouds or atmospheric absorption and scattering. This is partially offset by the need for the microwaves to pass through the atmosphere to the rectenna but presumably a microwave frequency would be chosen with minimal atmospheric absorption. It should also be noted that every step of SSPS is technically feasible and well established – solar conversion to electricity, microwave generation, microwave transmission through air, microwave collection and conversion to electricity, and grid transmission.
Personally, I am not a supporter of federal investment in the technology for the following reasons:
– putting anything into orbit is expensive, very expensive, and until these costs are reduced significantly SSPS will not be cost competitive.
– economics dictate that large SSPS concentrations (100’s to 1,000’s of MWe’s) be placed in orbit. One suggestion I recall is to place a 10 GWe unit in geosynchronous orbit to supply the electrical needs of New York City. In my opinion this is crazy – putting all your eggs in one highly vulnerable basket.
These vulnerabilities include exposure to higher-than-usual radiation levels in space which will shorten expected equipment lifetimes, possibility of collisions with space debris and micrometeorites, ordinary technical failures (with a lot of electricity potentially at risk), and vulnerability to sabotage/attack in the event of international tensions.
– aircraft will need to avoid the beams passing through the atmosphere to avoid any possible impacts to humans from exposure to relatively high strength microwave signals. Birds will be another potentially impacted species.
– the large land areas required for rectennas which would ideally be located in close proximity to cities with large electricity demand.
So, is SSPS a viable option for future electricity supply? Not in the near- to mid-term in my opinion. Long-term may be a more optimistic story. Solar PV costs are now much lower than they were just a few years ago and going down, radiation resistance of solar cells and microwave generating equipment may be improved, the cost of insertion into geosynchronous orbit will hopefully come way down, and small SSPS units (100-300 MWe) may become practical to be considered. The other problems would remain, and terrestrial competition from other renewable electric technologies will increase.
In a time of limited federal budgets R&D investment in SSPS does not strike me as a prudent use of government funds. Nevertheless, I recognize that SSPS has its core of ardent supporters (several came to my office while I worked at DOE) and I hope some of them will comment on this blog with their own views.