Parabolic solar dish help

[Lacelotte]

Hi guys, I've recently converted my old sky dish into a solar dish using 1cm by 1cm square mirrored tiles. Now the dish itself works perfect for concentrating the heat and light on the focus point. However, I am finding it a little hard to find an efficent concentrator to tap into both the heat and light.

I'd really like to use this to heat and power the lights in my green house. Has anybody got any ideas on how to utilise both the heat and the light for the desired result?

Thanks in advance for any help you may be able to give.

Shane

[Martin]

lights in a greenhouse? - pretty doubtful.......about all I can think of is to put a matt black painted coke can full of water at the point of focus of the mirror, and bung it in the sun - it should give you enough hot water to make a mug of tea to sustain you in further endeavours!

[Lacelotte]

I've managed to get the dish to power a multiple LED light which gave off enough light to light up the cupboard under my stairs.

I know that a sterling engine can be used on the larger more commercial dish's but I dont have the know how to build a crude one or the money to buy one.

That's why I was wondering if anyone had suggestions as to at least use the heat produced to help heat my greenhouse?

[Martin]

have a gander at Dick Strawbridge's "It's not easy being green" website, and have a butcher's at his"greenhouse heat sink idea" - you basically dig a hole in the greenhouse, bung some piping in it, fill with broken glass (smashed by some special machine that gives "safe" bits), then he's got a simple fan blowing hot air from the apex of the greenhouse through the piping in the glass - it stores the heat, and releases it overnight. You may be able to perhaps "supercharge" the system by putting some black metal pipe at the point of focus, and blowing air through it fairly slowly, and then into a heat store like that............... 8)
I reckon the main practical difficulty would be "tracking" the mirror to keep up with the sun. There are some very crafty solar cookers/ovens out there, if the weather keeps fine I am tempted to have a go (mostly cardboard with aluminium foil glued to it!) 8)

[Lacelotte]

Thanks Martin. I've found a few websites with designs for making a basic solar tracking devices. One guy actually sells them on Ebay. Only problem is that they dont come with servo's to actually turn the thing around. May have to enlist the help of my sparky mate to manage this one

[Muddypause]

Hello Shane, and welcome. I always did like Andy Capp.

I'm glad to think that someone has actually thought of something useful to do with a satelite dish. Nev may have some comments, too, because I know he has been playing around with solar ovens and parabolic heating things.

I'd just like to make the following comments:

First of all, although it is easy to think of light and heat as two different things, in fact they are just different expressions of the same thing - energy. What you have built is something that concentrates the radiant energy of the sun that shines on it. You cannot, in literal terms, store the 'light' from the sun, for later use when it gets dark. But you can store it's 'energy'. This usually involves heating water, or stimulating a photovoltaic cell.

In order to make best use of the parabolic reflector over a period of time, you are going to have to find some way of making it track the sun. When it was a satelite reciever, it only needed a fixed mounting because the satelite it was aimed at was in a geostationary orbit - that is to say, always in the same place relative to the surface of the earth. The sun, obviously, is not like that. It may be OK for short periods to aim it at approximately where the sun is, but in a short while it will need realighing.

Another thing to consider, is just how much energy you are actually collecting. If your dish is, say 500 mm in diameter, it will have a sectional area (ie, the flat area of that diameter) of, roughly, 2,000 cm². If this is focused onto an area of 10 cm², then the energy will be concentrated (multiplied) 200 times. That should be pretty impressive in terms of those ten square cm, but don't forget that you are not increasing the overall amount of energy that falls on the dish - you are still only collecting 2,000 cm² worth of the sun's energy. This means that the amount of energy that falls on that focal 10 cm² will be the same as the energy that falls on, say, a solar heating panel of about 45 cm x 45 cm. Because of what it does, your parabolic reflector may be able to make a small amount of water boil quickly (which the panel would struggle to do), but if used to heat a larger volume, the theoretical input will be the same.

Anyway, to the point. You've obviously put some effort into this project, and I really like the thinking that went into it. But I'm not sure it is the best application for achieving the results you want.

[Lacelotte]

Thanks for your advise.

To be honest, the ideal of converting the old satelite dish was one I came up with whilst I was working on another project (totally unrelated). I've since moved onto a larger model for that experiment, leaving me with my smaller dish to try and put to good use elsewhere.

As I said earlier, I have found a guy who sells a basic tracking devices on ebay. May be worth me looking into.

I'm open to ideas as to the best way of using this dish, though I was hoping to use it to come up with a way of trying to heat my greenhouse.

It's good to hear that one of Hartlepool's most famous son's is still well liked They are hoping to build a statue of Andy Capp quite soon, like that of desperate dan in... Glasgow/Dundee? Providing, that is, the PC crew don't get their way

[Cheezy]

All I can think of is using it to focus the light on a small solar panel.

You can buy small ones quiet cheaply, but these suffer in the winter due to our lower light levels, at least with the dish following the sun it would boost this.
You can buy solar panels that charge batteries and have light sensors in them which then power outside lights.

These are usually LED for low volts and wattage, however if you could come up with enough power you could always power an old fashoned light bulb which are inefficient and give out heat and light, thus prolonging your growing season and giving a bit of heat into the greenhouse.

I thought there would be a statue of the monkey hanging!.

No offence everyone, just a bit of local NE banter

[Wombat]

G'Day All,

Yep, Stew, I made a parabolic reflecting solar concentrator but mainly for cooking and boiling water. Mine is much smaller and if I could get hold of a satellite dish I would have a go at the same thing.

Perhaps you could use the heat to generate electicity with a peltier effect device.

I think that using the dish to concentrate light onto a solar (PV) panel may not be such a good idea unless you had a way of concentrating the light without concentrating the heat! The hotter the panel gets the less efficient and I think the temperature acheived by the dish would do unpleasant things to the panel.

Another way would be to run a loop or spiral of copper pipe in the focus of the dish and use it to heat the water and then pump it through pipes in the greenhouse. But then you still have the problem of tracking......

Thats my two bob's worth anyway.......

Nev

[Muddypause]

Another way would be to run a loop or spiral of copper pipe in the focus of the dish and use it to heat the water and then pump it through pipes in the greenhouse. But then you still have the problem of tracking......

That might not be such a bad idea. With a tracking device, you would need to make the pipework flexible, but a coil of microbore copper (maybe 6 or 8mm bore) fixed in the focus may be able to transfere the heat to a larger storage tank. I would contend that there would be greater heat losses compared to a solar panel, but the overall efficiency might not be compromised too badly because it will be tracking the sun in a way that a panel doesn't.