And the profits grow

[kandrathe]

The reason photosynthesis isn't efficient is because 90% of the energy being stored is in turn used to maintain the survivability of the organism doing the storing. Non biological photosynthesis, as technologies advance, will circumvent this limitation. The "huge breakthroughs" you speak of still assumes a linear technology advancement path when technologies advance on exponential curves (or more accurately multiple exponential curves). The question isn't "even if we can increase the efficiency *this much*" it's a question of how accurately we can predict where we are on the technology curve for solar power (or hydrogen fuel cells, etc. etc. etc.). The efficiency is going to get better, I'm confident in making that prediction. Thinking about technology in a linear fashion tends to lead to two falacies: we overestimate tech advancements in the short term, and we vastly underestimate tech advances in the long term.

The dilute nature of solar power is not due to limitations in technology. It is due to the amount of solar power hitting the Earth at a given area over a measure of time. I believe we are well beyond the point of being able to replace our current consumption of petrol fuel with the amount of energy hitting the earth from the sun. I believe the current optimum of solar capture on Earth is around 1000 watts per square meter. At space with 100% capture the ratio is 1340 watts per square meter. The amount of loss is due to atmosphere, dust, distance, etc. Usually, at most points on Earth the solar capture capability is far, far less. For comparison, a gallon of gasoline contains about 1,300,000,000 joules of energy. For electric power comparison, 1 joule = 1 watt second.

1000 watts is 1.34 Horsepower. The curb weight of a Volkswagen is 1,090kg. Add four slim passengers at 55kg each, and we have 1310Kg to move. Assuming we are just accelerating on a flat plane, we can use the formula KE (joules) = 1/2 Mass * Velocity ^2, or 1/2 * 1310 Kg * 24.5872 Meters/Sec ^2. So, to accelerate our VW with passengers to 55 mph (or 24.5872 M/s) it will take 395967.41 joules. Remember that 1 joule = 1 watt second, so we can calculate the watts or seconds required to move our vehicle. I'm guessing that our vehicle has around 2.5 meters width x 4 meters length. Also assuming it is directly pointed at full sun gives us 10 meters^2 * 1000 watts, or 10,000 watts per second. Solving 395967.41 joules / 10,000 watt seconds potential gives a theoretical minimum time to achieve zero to 55 mph on a flat surface, or 39.6 seconds. Now add some hills, some additional resistance from snow, loss of energy from stopping and starting, and you'll need much more than the 10Kw potential. But, if we can reduce the weight, or store some energy in compact batteries then it has a chance. The issue is still energy density, and solar (including bio-fuels) will not do it alone.