I will take 10 just get them over to the US asap.

Wow this makes my day! I thought fresnel lenses would only be used on commercial utilities. It's great to see that they may decentralize this technology.Fresnal lenses get really hot--I hope that there method of dispersing the heat makes it usable for the rest of us. This is really important with that kind of increase in efficiency.

A heat diffuser? Why not use that energy to boil water and run a generator, producing even more electricity? Or use it to provide hot water or heat to a home?

And the only downside: It still doesn't solve the problem of LPG or propane for my cooktop. And, no, I will not voluntarily use an electric range.

I used to work as a grip for television and film lighting. A Fresnel lens is used to transform a point light source to a distant light source by spreading out the beam, more like the light from the sun where the beam is more or less divergent, depending on the focal length you choose. To foucs a beam, a lens more typical of an elipse light is used, similar to the kind found in magnifying glasses and field glasses which yield convergent beams. The source article you cite says "wide lense" and doesn't specify the type. Given their characteristics, the later type is probably in use.

Jerry Carter, is sorta right, there are Concave mimicking Fresnel lenses (like you see in the back windows of RV's and some trucks) and Convex mimicking lenses that work like a magnifying lens, i have a nice 3.5' one that i can melt stone with in the hot Southwest US Sun,

i do wonder about acrylic Fresnel's what with the propensity for UV breakdown, and sand pitting/scratching. id be surprised if it worked for more than 2 years here.

Icelander: if the solar cells get too hot, their efficiency will decrease. I don't know how cool they have to be kept, but I have a hunch they like to be kept below the temperature of boiling water. Also, adding a water cooling system to these machines would make them much more complex and at least a little more expensive.




I share Adric's concern about how well the material of the fresnel lens will stand up to UV exposure.

Looks interesting, but man do they have to de-clutter their website.

All I wanted to know: approximate wattage output per SunBall (yes, I know it will vary; just a ballpark).

Answer? Nowhere to be found after ten minutes of determined searching, which is far more than someone less, uh, determined would have given the task.

(By the way--treehugger webmaster person? I like ellipses, and the fact that your comment engine prohibits their use is annoying. Any idea why?)

From their Sunball calculator, they claim that in the south of spain you could get 545 kWh per year per ball, which averages out to about 60W (daily cloudy+sunny+night+day average). South of spain, of course, a good location.

Even if the fresnel lens lasts only 2 years (but i'm sure it will be longer), the point is plastic fresnel lenses are cheap PV cells are expensive. This ought to give more power with less solar cells.

From the technical breif:


1 solar ball = 370Wpeak


they have calculators too to find out how many you need depending on your azimuth. I'd need about 20 of them for my not so efficient house (~800kWh/mo). The nice thing is with local utlility rebates for solar (as long as a local installer carries these) i would only pay $200 a piece for these; $4k to power my house on solar? i'm sold!



Most of the good info is found by clicking on the "products" link on the left.

I'd be a lot more likely to buy one if the concentrated solar power was used to run a Stirling engine instead of a photoelectric cell. Why concentrate all that heat on a solar cell that loses efficiency as it gets hotte), when you could power a stirling engine and generate quite a bit more electricity?

I know, that would be more complicated, more moving parts and all, but a stirling engine is pretty simple, and could easily be made with tough, long-lasting, easy-to-change parts, especially the seals and bearings and other parts that will wear fastest.

It already has light sensors and a motor to keep it following the sun, replacing the solar cell with a stirling engine wouldn't add that much more complexity, and the parts would be far cheaper to replace than those 'high-efficiency' solar cells.

I suppose the biggest problem would be noise. Stirling engines would unavoidably make more noise than a silent solar cell.

It's too bad, really. I'd LOVE to be able to put a series of such devices on my roof. It's a nice flat roof, gets lots of sunlight all year, etc. For a solar-cell setup, I'd have to buy a huge slab of very expensive solar panel all at once. With something like this, I could buy and install them one at a time as I had funds, and I'd also have a lot more leeway in where I put them. I could make far better use of space than if I have to place big contiguous slabs.

In full sun you get approximately 1.4 kW/m2.

In the article it states a 1cm2 cell with a lense capturing 500 times as much light operating at 33% efficiency.

Thus it would look like
(1400 watts/m2) * 500 cm2 * 0.33 / (10000 cm2/m2) = 23.33 watts.

Which is a remarkable amount of power from such a small cell but not particularly attractive at $160 0 AUD

Just 0.16%? Thats 4 times new york state!

Why not the lens with a stirling engine?

similar track to these guys, check out the Sunflower solar concentrator.

http://www.energyinnovations.com/

whatever happened to the idea of super-heating a liquid (like maybe alcohol) with a system like this to drive a small steam turbine?

Regarding all of the stirling engine / turbine questions, there are people who do concentrated solar setups to run stirling engines and generate electricity: http://renewableenergyaccess.com/rea/news/story?id=38672


Note, however, that they do it with pretty huge dishes. My guess is that it's hard to scale the technology down to something that will easily go on a consumer's roof.

Also, existing solar modules don't need to be in a contiguous slab, each one just has to be somewhere that it gets good sunlight. As long as you've got an inverter that can handle different voltages, you can start with as little as one module and add more. A hypothetical solar-stirling device might be easier to integrate with a home's power system, but only if it output normal AC power right from the device.

Hi Guys,

Thanks for the kind comments about our SunBall. Here is a bit more info.

The cells we use are triple junction which means they convert ALL the solar spectrum (200nm thru 1,800nm) into electricity. That means they convert UV, light and IR into electricity.

The Fresnel lens material is optical acrylic, is 2mm thick and absorbs less than 1% of the solar energy, thus very little heating in the lens. The lenses passes almost all the UV, light and IR into the hungry triple junction cell below. The material will not discolour and or degrade. It is very stable and designed for this function.

There are 20 lens & cell combinations per 1m2. This means each lens & cell combo handles 50 watts of solar energy on the top side of the lens. About 49 watts passes through the lens and onto the triple junction cell which converts 35% (~17 watts) of the total solar spectrum into electricity. That leaves the cell with a heat load of 49 - 17 = 32 watts which is dissipated onto 900cm2 of 3 mm aluminium heat sink. The max cell temp rise above ambient is 10deg C. The SunBall heat load is 0.03W/cm2 as compared to a flat panel at 0.09W/cm2. Also the passive hemispherical aluminium heat radiator is in the shade as the SunBall is always pointing at the sun. It is also very easily cooled by passing breezes.

The Spectrolab triple junction cells have a heat derating on ONLY -0.04%/deg C. That 13.8 times less efficiency loss than silicon solar cells (-0.55%/deg C).

Combined with the dawn to dusk tracking the SunBall delivers very significant late hot summer afternoon energy whos timing overlaps peak network loads. The SunBall is a much more cost effective way to deal with electricity network peak loads and their very costly investment requirements.

Heating water is better done with a SunBall minus the lenses and triple junction cells and fitted with a 1m2 circular solar hot water heater. Our calcs suggest we will get over 200% increase in hot water generation due to the dawn to dusk tracking. More on that product later.

Please feel free to take this discussion and your questions further either here or on the SunBall discussion group (link on the web site).

The SunBall will change forever the way we generate electricity on the planet.

Regards,
Greg Watson
SunBall inventor

QUOTE: I suppose the biggest problem would be noise. Stirling engines would unavoidably make more noise than a silent solar cell.

Actually, Stirling engines are known for their extremely quiet operation - they're used on submarines, for example, where quiet is critical.

Not silent like PV, but not loud, either.

Great idea the sunball! How about those parabolic mirror solar cookers? wouldnt it be the same thing though if you put small solar cells facing the parabol mirrors with the back towards the sun? So the solar cells actually have the back to the sun and instead face the dish which faces the sun and reflect and concentrate the sunrays to the solar cells. A dish with a reflective surface might be cheaper that a fresnel lens.

A dish with a reflective surface might be cheaper that a fresnel lens.

Hi Bobby,

The biggest problem is that you can't use simple and low cost passive cooling and must pump cooling fluid to the cell.

Overall the Fresnel lens and passive cooling wins.

All the best,
Greg Watson
Green and Gold Energy
Adelaide, South Australia
+61 408 843 089
http://www.greenandgoldenergy.com.au
Online SunBall discussion group
http://groups.yahoo.com/group/sunball

Thanks Greg for expanding on our questions.

To be honest, I had been thinking of doing the same general idea but using high-grade aluminum to reflect light onto such a cell. The aluminum I was looking at costs a small fraction of what I'd imagine a fresnel lense costs, but is only 96% efficient.

If one mounts the cell upside down on a tower, and uses fishing line to suspend a dish, and feed the line through a linear actuator in order to angle the dish, they can achieve impressive tracking cost-effectiveness.

The frame I was thinking for the aluminum reflector was a PVC ring, which you seal with plastic and use another linear actuator and partial vacuum to achieve a near-parabola.

Come to think of it though, that's not much cheaper when it's all said and done, and it's alot more complicated...

Wait, I just did some reading and found out that while your cells are accepting UV and IR spectra, acrylic blocks a good percentage of the UV index and some of the IR. Also, your sunball uses an extremely heavy-weight (figuratively and literally) structure and tracking system, and according to your photos doesn't focus a very large area onto each cell.

Considering the costs involved, I believe a little more research may yield a light-weight and more modular design, and also that a more appropriate lense-cell combination could be used.

Fresnel + Superb PV = good idea.