I have looked quite a bit into a heat to electricity machine, mainly to power an A/C unit off of solar hot water panels in the summer. As far as generating electricity from the sun (or heat), the most efficient way is through steam, this is why everything from a coal plant to a nuclear reactor use water and steam turbines to generate the electricity. Even some major solar plants (http://en.wikipedia.org/wiki/Solar_One) use methods to heat water into steam using the suns heat, PV panels are not very efficient and their efficiency falls off greatly when the angle or amount of sun is off from ideal, it is not a linear curve. As far as using a Fresnel lens to focus the sun, you have to have a special type of PV cell otherwise you will overheat and melt it. There are a few companies offering a focused PV system that follow the sun through the day. There is also one person using the Fresnel lens off of big screen TV's to focus the sun to generate steam for a steam turbine, he has a couple video's on YouTube (most are of this lense turning part of a brick into glass) A sterling engine works off of a temperature differential, the larger the difference the more power. There are a few people with boilers and a sterling engine but they are getting 4-5kw of power, not nearly enough to run a house. I did see this one device that appears to be a NG or LP tankless water heater about the size of a dishwasher, it has a sterling engine inside of it to reclaim some of the heat off of the exhaust and I think it generates 1kw or so. The best method I could find for generating electricity/running the house off of cheap or free fuel (sun or wood) was to minimize the amount you use. Here in Kansas City, the major uses of utilities is heating, cooling, the dryer, and cooking. I ran across something called a lithium bromide water chiller, they are used pretty widely in the industrial world to reclaim some waste industrial heat and chill water with it. The smallest I could find is a 5 ton unit and it operates on an intake water temperature of 150-180*F and has a output water temp of 40-45*f. Total power used is around 200w to run a cooling fan. One other site I ran across is a radiant heat installer that decided to do radiant cooling in his own house. With a ground water temp of around 60*f he was able to cool the house on all except the hottest days by simply circulating water through a heat pump ground loop (without the heat pump running of course). There are a lot of European companies that produce radiant cooling panels and it has been making some inroads in commercial USA, they operate on a water temp of around 60*, all you have to worry about is dehumidifying the air in humid climates.