# Fresnel Lens and boiling water **URL:** \ **Category:** Factual Questions\ **Created:** [November 8, 2012, 3:35am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326 "2012-11-08T03:35:42Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![EnerCarto](https://avatars.discourse-cdn.com/v4/letter/e/bc8723/32.png) [@EnerCarto](https://boards.straightdope.com/u/EnerCarto)\ **Post date:** [November 8, 2012, 3:35am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/1 "2012-11-08T03:35:42Z")
Would it be feasible to rig up a Fresnel Lens to boil water in a closed system to turn a steam turbine to power a house? ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [November 8, 2012, 3:42am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/2 "2012-11-08T03:42:30Z")
[It sounds possible.](http://bclee.net/lens.html) ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [November 8, 2012, 3:53am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/3 "2012-11-08T03:53:46Z")
> [@EnerCarto](#): > > Would it be feasible to rig up a Fresnel Lens to boil water in a closed system to turn a steam turbine to power a house? > **[Solar thermal energy](https://en.wikipedia.org/wiki/Solar_thermal_energy)** > > Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors. Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are generally unglazed and used to heat swimming pools or to heat ventilation air. Medium-temperature collectors are also usually flat plates ... Current efficiencies of small-scale solar thermal installations are around 25%. Peak solar thermal radiation on a cloudless day is about 1 kW / square meter. So, you could realistically generate 250 W of electricity for each 1 square meter of lens, when the sun is high in the sky on a cloudless day. The output rate would be smaller in the mornings and afternoons, on cloudy or hazy days, etc. So, yes, it is “feasible”. Not quite practical, but feasible. EDIT: I think that actually boiling water and turning a steam turbine would decrease the efficiency - small steam turbine are not very efficient. The 25% efficiency number is apparently from a Stirling engine. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 8, 2012, 3:59am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/4 "2012-11-08T03:59:03Z")
If you want to generate electricity, you would be much better off just using Photovoltaic panels. The combined efficiency of a boiler/generator is going to be worse than a PV/inverter system, plus there isn’t the maintenance nightmare of dealing with boiling water… ---
**Author:** ![EnerCarto](https://avatars.discourse-cdn.com/v4/letter/e/bc8723/32.png) [@EnerCarto](https://boards.straightdope.com/u/EnerCarto)\ **Post date:** [November 8, 2012, 4:03am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/5 "2012-11-08T04:03:13Z")
Thats a lot of lens. I’m from sunny Lake Havasu City, AZ where we get clouds for maybe 2 weeks out of the year total. Didn’t even think about the Stirling Engine. I was thinking about charging up a bank of batteries to store the power. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 8, 2012, 7:03am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/6 "2012-11-08T07:03:19Z")
A parabolic mirror is probably easier and more scalable than a Fresnel lens. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [November 8, 2012, 8:48am UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/7 "2012-11-08T08:48:40Z")
> [@beowulff](#): > > If you want to generate electricity, you would be much better off just using Photovoltaic panels. The combined efficiency of a boiler/generator is going to be worse than a PV/inverter system, plus there isn’t the maintenance nightmare of dealing with boiling water… Not sure if they’re talking about useful energy captured, or electricity generated, but the Wikipedia page says “STE is different from and much more efficient than photovoltaics, which converts solar energy directly into electricity.” ---
**Author:** ![sidecar\_jon](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@sidecar\_jon](https://boards.straightdope.com/u/sidecar_jon)\ **Post date:** [November 8, 2012, 5:01pm UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/8 "2012-11-08T17:01:40Z")
A historic aside of interest is “…A Solar engine was demonstrated at the Universal Exhibition, Paris in 1878 …” it was used to print the newspaper apparently. [http://lunaticoutpost.com/Topic-A-Solar-engine-was-demonstrated-at-the-Universal-Exhibition-Paris-in-1878](http://lunaticoutpost.com/Topic-A-Solar-engine-was-demonstrated-at-the-Universal-Exhibition-Paris-in-1878) so it can produce useable work! ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [November 8, 2012, 6:07pm UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/9 "2012-11-08T18:07:03Z")
> [@AaronX](#): > > Not sure if they’re talking about useful energy captured, or electricity generated, but the Wikipedia page says “STE is different from and much more efficient than photovoltaics, which converts solar energy directly into electricity.” Yeah, on a 100 Megawatt scale. Try that on a Kilowatt generator and see what you get… ---
**Author:** ![Learjeff](https://avatars.discourse-cdn.com/v4/letter/l/94ad74/32.png) [@Learjeff](https://boards.straightdope.com/u/Learjeff)\ **Post date:** [November 8, 2012, 6:33pm UTC](https://boards.straightdope.com/t/fresnel-lens-and-boiling-water/640326/10 "2012-11-08T18:33:22Z")
Concentrating the light increases the temperature, so makes thermal engines more efficient. But why concentrate the light and use a thermal engine? Keep it distributed and either warm water (to heat the house in winter) or for photovoltaic. In general, photovoltaics cells aren’t more efficient with more concentrated light. There are some industrial solar generator designs that focus the light, but that’s to allow the use of smaller PV cells, not to increase efficiency overall. So, I don’t see a big lens improving things much.