PV Gap

Marlene Said:

How could we exploit the solar resources of deserts in a way that would give enormous benifit?

We Answered:

Yes losses in traditional transmission might be too great however there are other possibilities:

HVDC is high voltage direct current transmission. "The longest HVDC link in the world is currently the Inga-Shaba 1,700 km (1,100 mi) 600 MW link connecting the Inga Dam to the Shaba copper mine, in the Democratic Republic of Congo."

Other potential transmission solutions may include: 2
Microwave transmission
Wireless transmission using the Yagi antenna
a superconducting line

Esther Said:

How can I ensure all my files are backed-up in preparation for the once in a generation solar storm?

We Answered:

optical media should be enough. this is the funnies question I read in a while - well done! NASA predicts some this or some that every year, they need to justify their funding in front of the Congress. please, use BIG GRAIN OF SALT with them :-)

Norman Said:

Why not build these for power generation?

We Answered:

have you looked at the stats??
Alot of different reason why not to build it.

1. the conversion rate is terrible. 1kW/m^2 is terrible. you can get between 5-20% out of different solar technologies. Wind gets much better energy conversation than solar does.
2. look at the land use. it uses 38 km^2. and also uses a 1000 meter tower. Land is expensive, it's the most expensive resource known to man. Also with 1000 meter tower, you would have all kinds of airspace (planes, etc) rules to figure out. Not very cost effective. Plus conditions need are very specific where they can be places. So there are very few places these can be put effectively.
3. Lastily, the performance of an updraft tower may be degraded by factors such as atmospheric winds, by drag induced by bracings used for supporting the chimney, and by reflection off the top of the greenhouse canopy.
4. How do you transfer the energy from very remote to very urban areas? they have to build all kinds of intrastructure to support that energy transfer, and no matter how hard you try you will lose some electricity over long runs.
So to sum it all up. It doesn't do a great job of converting sun to electricity, it uses way too much land for it's output. It needs very specific conditions for effective operations. Lastily, we do not have the technology/infrastructure to support moving that much power around.

Minnie Said:

In a world of distributed power generation does it make sense to move to DC?

We Answered:

There are two main important reasons AC is primarily used. They are transformation and switching.

Transformation is key with transmission and distribution. Transmission of electricity over long distances is done at high voltages in order to reduce losses. Every time you double the voltage, the power losses drop by a factor of 4. In order to achieve higher voltages, transformers are required. Transformers only work with AC only. Although there are DC-DC converters, they are essentially just DC -> AC -> DC and have low efficiency. Transformation of the high voltage down to a usable voltage is achieved by simple transformers also. Changing DC voltages is very involved, complicated and expensive for high power applications.

The other main reason AC is used is because it is easy to switch on and off. Believe it or not, most switches available on the market can not switch a DC voltage greater that 40-50V. When you try to break the current by opening a connection of high voltage DC (>50V) the point of contact will tend to arc. The DC resists being broken and will jump through the air as you open the switch. This causes a great deal of heat and sometimes smoke and fire. This is also the case for overcurrent devices such as fuses and breakers. Fuses can burst into flames if not properly rated for DC. In order to properly switch DC, you need capacitors and sometimes other specialty contacts such as gas filled. AC, on the other hand, is easily switched. Because it is constantly varying, current is easily broken. You can switch thousands of volts with the simple flick of a switch with no additional parts.

Another issue with low voltage DC is current. To carry any significant power in low voltage DC (ie. 12V) wire guages would get very large. For example, a standard 15A household circuit would use #14GA wire. If you needed to get the same power (ie. 1800 watts) from 12V you would need to pass 150A through the wire. That would require a #1GA wire! That is a lot of copper!

Using a computer as an example, the voltages that are required are mostly 12V and 5V. The motherboard uses a number of other voltages too. The easiest way to convert all these voltages from the standard 120V household circuit is to use a single transformer with multiple taps. That way, using a single transformer and set of windings, and voltage at all can be made. Even if you had 12V in your house, you would still have to use an inefficient DC-DC converter to get the 5V and other lower voltages. In the end, you end up converting to AC anyways to get other voltages.

There are many advantages of AC power. DC will probably never be main stream, but I do suspect that you will see various simple DC components. Things like simple 12V light bulbs could run directly off of solar collectors. Efficiency minded people with solar systems could implement various limited 12V circuits in their houses but it could never replace anything with any power, such as a toaster or hair dryer.

Hope that answered your question!


Additional EDIT:

DC for low power circuits in the home may not be a bad idea. Using the output of a solar collector directly would be an efficiency savings in the home. A fridge, though, would be a little too high power for DC. Lights and fans, on the other hand, could be DC. If I had a solar collector or similar DC source, I would not hesitate to run 12V or 24V DC circuits for lighting and misc. other things. The trouble is that the great majority of houses don't have a DC source readily available.

To say that most power ultimately ends up being DC isn't quite true when you look at society as a whole. The majority of the load in any grid is motors. This would include air conditioners, air handling units and machinery. DC motors are not near as efficient as AC, especially in high power. The DC loads in a grid would only make up a very small percentage of the total load.

Additional Additional EDIT:

I think that two wiring systems in a house would be a very good idea. The nice thing about the lower voltage DC is that it doesn't fall under the national electric code and can be wired any way the installer sees fit. The danger is low. Having it backed up by the grid is also the way to go as storage batteries are a constant maintenence item.

Like I said before, myself, I would not hesitate to run a number of 12V or 24V circuits in my house if there was a ready source of DC power.