Thank you for your suggestion. We agree that solar cookers have a useful role to play, as your work has shown.
We also believe that gas and electricity have an important role to play. As Professor Kirk Smith wrote in an editorial in Energy for Sustainable Development in 2011 (http://ehs.sph.berkeley.edu/krsmith/publications/2011/cooking_gas_esd_2011.pdf), for "convenience, controllability, [and] time savings," half the world cooks with just two types of cookstoves: electricity and gas. Solar energy can of course produce electricity, with which to cook. But it is also the case that, for better control over heat, many cooks prefer gas to electricity.
For those wishing to cook with gas, natural gas would be the fuel of choice. But many parts of the developing world do not have natural gas distributed to households. And natural gas is not available to rural households even in the richest of countries. As such, LPG will continue to be the cooking fuel of choice for millions of households.
Given the price of LPG today, we agree with you that LPG would not be a fuel for the poorest of the poor. Our approach is certainly not to promote a universal price subsidy for LPG with the objective of enabling the poor to cook with it, because the fiscal burden would be unsustainably large. But there are also many households who are capable of switching to LPG for cooking but continue to cook with solid fuels for a variety of reasons -- lack of familiarity with LPG, fears about safety, lack of enforcement of sound rules and regulations, lack of adequate competition resulting in high prices, or lack of reliable cylinder delivery. In such circumstances, addressing these problems can enable households to shift away from solid fuels to a gaseous fuel.
It is also important to bear in mind that the contribution of LPG for cooking to global oil consumption is very small. Even if one third of those currently cooking with solid fuels were to switch to LPG between now and 2030, and each household (of 5) consumes 10 kg of LPG a month for cooking, that would amount to an annual increase of less than 40,000 b/d, or 5% of the increase in global oil consumption this year.
In our quest to achieve universal access to clean cooking and heating solutions, we believe we need to look at all options that can eliminate the harmful indoor air pollution -- and all too often the drudgery associated with fuel collection -- caused by cooking. Solar cooking is certainly one of the solutions, together with other options.
Thank you again for your comments.