Solar might be useful in the tropics, but will always be a marginal player in northern latitudes, which is why Europe is actually a better example. Europe will need nuclear fission, nuclear fusion, or space solar power.
Quote from: RonM on 05/01/2018 08:33 pmQuote from: LM13 on 05/01/2018 02:31 pmI'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna? How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna? The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.Not quite. You can make the Earth receiver smaller (for a given transmission frequency) only by making the space transmitter bigger. That would then concentrate the microwaves to a higher density. I would suggest a legal maximum size of transmitter and power, which would physically limit the beam intensity. (Probably to 1KW/m2).That way, the only way a SF writer can conjure up death rays, would be by taking over multiple Solar Power Sats and pointing them all at the White House at the same time. (In which case, the President would need to shelter under some aluminium foil).
Quote from: LM13 on 05/01/2018 02:31 pmI'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna? How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna? The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.
I'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna? How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna?
That's an awful lot of expense to get surface power equal to what the sun delivers for free.
The question for efficiency and cost effectiveness is one thing. But there are other questions..Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam?
Quote from: Semmel on 05/02/2018 07:51 pmThe question for efficiency and cost effectiveness is one thing. But there are other questions..Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam? Some of these can be mitigated by design choices.If your space power sat is at GEO, and has its antenna and solar panels the same size, if it is under xGW, for a given frequency, the power onto earth can't exceed 1kW/m^2 or whatever limit you think appropriate.More involved schemes are possible.
Al‐Asad (Iraq) includes 20,000 people living on 18 square miles, with an internal bus system, 48 1megawatt (MW) generators, 32 MW of continuous power demand, 1.1m gallons of water/day demand,1.2m gallons of water/day supply, 9 water wells, Reverse Osmosis Water Purification Unit (ROWPU),water treatment facilities treating 60 gallons/person/day, 6,771 facilities, and 193 spot generators...A 600 soldier FOB requires a convoy of 22 trucks per day to supply the base with fuel or waterand to truck away wastewater and solid waste...As of November 2007, 80 convoys were continuouslytraveling between Kuwait and Iraq (with 70% transporting fuel or water), exposing a critical vulnerabilityto Improvised Explosive Devices (IEDs) as they transported supplies from surrounding nations....FOB Planning Factors:500 man base camp -- 182 kW1,500 man " " -- 486 KW3,000 man " " -- 988 KW10,000 man " " -- 3,293 KW...The USMC Energy Assessment team calculated the contractor delivered fuel to CampLeatherneck in Afghanistan at $6.39 per gallon, and $11.70 per gallon to deliver the fuel to the tacticaledge (FOB Dwyer, 50 kilometers from Camp Leatherneck).148 An earlier estimate puts FY 02 standardDESC fuel price at $1.34 per gallon, a “true cost” of USAF tanker‐delivered fuel at $17.50 per gallon, and“hundreds of dollars per gallon for Army forces deep in the battlespace.”
You can sell power on a constant basis greatly reducing the need to ship a lot of mass of batteries too.You can plan independently of settlement details. A power sat can sell power to most locations on Mars surface. You just have to bet there will be a market for your power to start designing and building power sats.If there are unexpected finds and people want to set up new outposts to exploit them, you’re ready to sell them power.On the surface, PV would require more upkeep because of sand and dust than rectennas. PV is easier to deploy and fully automate in space.
Originally I wanted to address Musk's erroneous statements and ask whether BFR could enable Space Solar Power, rather than discuss the merits of Space Solar Power.
Quote from: AncientU on 05/02/2018 01:19 pmThat's an awful lot of expense to get surface power equal to what the sun delivers for free.It's a lot more than the sun delivers for free. In northern Europe...
Attached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.
The main effect of the D region is to attenuate signals that pass through it, although the level of attenuation decreases with increasing frequency.
Northern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.
Quote from: RonM on 05/02/2018 09:16 pmAttached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.Good study. It shows the system was feasible, with problems, with 1980s technology. It would be nice to update it to current tech.Regarding the atmosphere:http://www.radio-electronics.com/info/propagation/common/atmosphere.phpIt seems that a high density of radiation will ionise particles, which then block radio waves. However, this can't be the whole story because most radiation is coming from the sun (1.3KW/m2), so why would a weaker microwave signal make this worse?It does say:QuoteThe main effect of the D region is to attenuate signals that pass through it, although the level of attenuation decreases with increasing frequency.So it might be better to go to >5GHz signal. That reduces the transmitter size, which increases the heat problems.The efficiency chain was interestinghttp://prntscr.com/jd69buand they reckoned 30,000 tons: http://prntscr.com/jd69zlEven with BFR prices, that mass would need to come down a lot.
Quote from: alexterrell on 05/03/2018 10:55 amNorthern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.The world is growing, by the end of this century demand for energy is likely to be roughly proportional to population, making northern Europe niche. And the US has cleaner energy than much of Europe, such as Germany, but much lower prices (because Germany has particularly non-optimal clean energy policy combined with low sun).Again, Northern Europe is not an appropriate benchmark for global clean energy. And is a bad target for space solar power as well due to the high latitude.
Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case.
At some point, the whole world should aim for European levels of power consumption.