"I don’t think in a survival situation it comes close to burnable fuels for generating heat."

Large array solar can generate temperatures into the thousand of degrees Farenheit [ see for example http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar_plants.html#Parabolic%20Troughs], though typical small cooker designs get into the 250 - 450 degree Farenheit range by design [ see for example . http://home.att.net/~cleardomesolar/parabolic.html].

Improvised solar can be as simple as a board, a tire, a black pot , and a pane of glass:
http://www.solarcooking.org/plans/tire_eng.htm
Making a solar still and cooker from improvised materials should be on the list of survival skills. Check out this parabolic solar cooker basket made of found materials, including in part of of blackberry branches and tin can lids!
http://www.appropedia.org/Parabolic_Basket_Solar_Cooker

“The next time we tested the cooker, we used a quart-sized jar that was painted black and created dead air space by placing a transparent pickle jar over it. That day, we set up the jar at 11:20 am on a warm sunny day without wind. After an hour, the water inside the jar was starting to bubble, meaning that we surpassed pasteurization temperature. After about two and a half hours the water in the quart jar was at a rolling boil.”

Like all survival gear, solar needs to fit the situation. For your fixed site survival retreat or large bug out vehicle, a large solar device is possible and smaller types easily incorporated. For man-portable solo survival situations, you are probably looking at a small, folding system which will cook and pasteurize water, but may not boil water except in near ideal solar conditions.

BobS and I have explored some of the virtues and vices of solar versus Thermette in earlier parts of this thread. I think going with a Thermette makes sense much of the time; I intend to buy one in the future. I think going solar has tremendous potential and am exploring its use now; many others around the world have been using solar on expeditions for more than a century.

My main point: consider taking a hard new look at solar.