Wednesday, February 20, 2013

The physics of Musk Part 1

This post was originally going to start out as a brief expose regarding electric vehicles/solar technology. One topic led to the next, and now I've compiled a significant amount of data, some of it being quite interesting. It will probably become several posts, discussing several topics.

This started with a youtube of Tesla Motors/ Space-X CEO Elon Musk. The South African entrepreneur who's talent for physics and business gives Tom Perkins a run for his money on being the closest individual akin to Tony Stark. The competence Elon convey's is quite remarkable, and seems quite logical.

In the video, Elon elaborates that one day he'd like to see all domestic transportation being conducted by EV. Well, that shouldn't be a surprise, he does run an electric car company; but is it possible, and does it make sense?

There are a dizzying amount of ways to generate electricity, we are going to start with solar, as his involvement in Solarcity tends to make me believe that he sees that as the most immediately beneficial

The sun produces around 1330 watts per hour of energy delivered to earths atmosphere. Of that, approximately 30% is reflected back away from earth. The net is approximately 1000W/hr at the surface of earth, without cloudcover, based on the sun at zenith. The energy will follow a gradient up and down to it's maximum values, but we will use all maximum values for the purpose of this article.

So, if we absorb 1000W/hr of direct sunlight, how much does that translate to?

Quite a lot actually. If we took every single family household in the US, somewhere around 114,761,359 homes, and outfitted them with the as yet un-invented 100% efficiency solar collector array with average roof of 1500sq ft; we would collect 1.6x1013Watts/hr, Or 16,062.57GW/hr sunlight.

Current daily average electricity production in the USA is approximately 11,234.67GW.

So, the sun can provide more energy in 1 hr, than we consume in an average day? That's what the data says. It also merits this as an energy source worth investigating.

In order to get that energy you would need 100% roof coverage, 100% panel efficiency, 100% inverter efficiency, no cloud cover and have all systems up an operational. You would also need zenith light production for the the entire day to maintain that production rate.

But it all can't be that good. Solar panels on the north side of a standard pitched roof anywhere north of Mexico are do not have full exposure, they'll never collect the maximum value. The eastern and western faces will only have partial exposure, one in the morning, one in the afternoon--let's assume 60% total exposure. Most cities in the US fall between 25 and 75% sunlight exposure due to cloud cover, further reducing yield. These values cannot be altered, we cannot change our orientation to the sun, we can construct new homes to cater to it, but correction of existing is not immediately possible. This yields values between 2,400 and 7,200GW/hr. Still an astounding amount of energy.

So why hasn't this been invented? One of the inherent difficulties with sunlight is the spectrum. The light we absorb is approximately 52% IR, 44% Visible, and 3%UV. Current technology has been reasonably successful at collecting different parts of the spectrum, but doesn't yield much in comparison of the whole spectrum. An average panel can collect around 13.9W/sqft/hr, or approximately 14% efficiency. They also lose their ability geometrically with any shading or cloud cover. Inverters, friction loss of the wire, storage of the energy all present inefficiencies in the system.

The most detrimental issue they face though is the installed expense. At $2-3,000 per installed KW they are cost prohibitive, and do no serve any other function. If at some point in the future they can be engineered to collect a greater margin of power, and provide a secondary function, say that of the actual roofing material. They then may become economically feasible.

Stay tuned, more to come. Especially covering EV efficiency, drawbacks, the grid, other production and storage methods.

No comments:

Post a Comment