Solar/wind?

[Andy Hall]

Do you 'ave a leesonce for that minkey?

[MatSav]

No! I vas pissing by your door, ven I saw your general's outfart! ;-)

[Mary Fisher]

Says me and all the people I know who have invested in such devices.

Do you consider the payback time on everything you buy?

And power prices are more than double :-)

[Mary Fisher]

...

Oh come on!

[David Hansen]

On Mon, 28 Jul 2008 09:38:05 +0100 someone who may be "Mary Fisher" wrote this:-

Indeed. People who would probably never consider the simple payback period on other items, double glazing, car, kitchen and so on do claim to be interested in the simple payback period for renewable energy "generating" items. In my view many have an emotional opposition to renewables, or at least some forms of renewables, but try and disguise this by bringing in other arguments.

That is certainly the case on a large scale. For example when all the other arguments have been countered opponents of large scale wind farms generally resort to their real objection, an emotional argument about appearance.

[Bob Eager]

In my view many have emotional support for renewables, or at least some forms of renewables, but try and disguise this by bringing in other arguments.

[Huge]

Was that Bob or David?

Whatever ...

Hell, even I have emotional support for renewables, but they have to *work*. In the cruel hard light of economics and physics. If they don't, there's no point ot them, no matter how nice the idea might seem.

[dennis]

But they are green mugs who think they are helping and want to feel smug whatever the cost. The reality is that cost and environmental damage tend to be related.. if its expensive it probably damages the environment. So a long payback period means its probably not going to save any CO2 but may save money if fuel continues to go up.

Yes.

The cost to the environment hasn't doubled though.. you may save money at a cost to the environment.. this is the opposite of what you appear to think.

[John Rumm]

Other way round I would have thought? I would not have expected many compressors to run on 75W or less...

[Andy Hall]

That's because the industry around these uses payback period as a major selling point, so it's their own fault. One of the first rules of selling is to show the virtues of the product but not highlight the deficiencies. This doesn't mean lying about the product.

Generally this is the companies selling these things. If their arguments actually are weak on things like payback period, then they are rather stupid if they raise them.

If the argument for buying this stuff is not an economic one, but a feel good one, then the suppliers should emphasise that as the benefit. There are people around who will buy on that basis.

Well..... since the arguments for having these things are emotional rather than practical in the first place, it seems reasonable that the counter arguments can, in part be emotional as well.

[John Rumm]

That being one of the problems really. Lack of any hard numbers, but plenty of anecdotes and testimonials from people either selling the kit, or from those seeking to justify their investment in it.

No, but for something like hot water production, then yes - it is a significant factor. Probably secondary only to performance and suitability.

Hot water is hot water, so its difficult to have many other selling points.

And even then we are still looking at more than 10 years payback...

What did your Solartwin system cost including installation etc?

Once solar thermal becomes economically worthwhile, then would be the time to use it - volumes will have brought the prices of the hardware down as well. Meanwhile there is no harm in leaving the option open of using solar thermal if making other changes.

For something like pool heating, it is well worth doing already if you can DIY.

[Andy Dingley]

I'll be amazed if anyone here can get a 2kW turbine sited anywhere near their house (except The Natural Philosopher, who lives in a vast ivory tower that needs 10kW of continuous heating to be habitable).

The =A31500 turbines in the sheds won't produce anything like this much. You can self-build a maximally-sized turbine (for a generous domestic- sized plot) for a few hundred (Tim Piggott's books). You won't get this much power though, as you just won't have (unless you're lucky) space for a big enough blade disc.

Self-build turbines work because the generators don't have to be unusually efficient. It's not too difficult to make one that extracts nearly as much electrical energy from a given-sized set of blades as a "state of the art" generator. It's only a bit harder to contrive blade controls that let you use the blades effectively across a wide range of windspeeds, to at least as well as commercial small-turbine practice. With decent electronics you can certainly beat the CAT and the large turbine they have that's still using a load bank! The hard part, and what hurts the effective use of wind turbines on domestic plots, is the fundamental limit of what's extractable by a given blade diameter.

If anyone has a Welsh hillside, then go for it. But a backyard in downtown Milton Keynes isn't going to put much of a dent in your power bills, even if you can get permission for it.

[Andy Dingley]

Why not? They're only a very soft vacuum. If you're worried about the tiny pollution problem from the getters, then take a look at your TV long before your solar panels.

[Andy Dingley]

Yes they can! Getting that to work was the innovation that allowed the 3rd world vaccine fridges.

Do caravans (ie. cheap retail mass market) use compressors (yet)? My only experience with them even pre-dates the Peltiers.

[Andy Dingley]

Domestic-sized ones (and Rutlands) do. Given their replacement cost / access cost, thhe only practical option is a "sealed for life" approach. When it finally goes, then you're looking at _replacing_ the entire generator / hub / swivel package. As the blades will usually have a shorter life, they'd be replaced too - and probably had been beforehand.

The important factor here is to allow for blade replacement, and ideally blade replacement up-tower. Sealed-for-life design does at least mean an opportunity for decent weather sealing.

[Andy Dingley]

You should be able to do better than that, with decent blade design.

The _maximum_ power you can hope to extract varies with the cube of wind speed. Now the extractable power is a proportion of that, depending on the efficiency of your blades. This efficiency isn't constant. If you design the blades for best efficiency at lower speeds then you can reduce this falloff to much better than a cube law. They're less efficient at higher speeds, but then you have power to waste.

This only applies for small turbines, not for commercial generators. But for blade lengths under 1m (or 2m if you have an autoclave and can use composites) you can throw a "flimsy" low-speed blade up in a high wind and it will still survive it, just thanks to the scaling laws.

[Bruce]

My camper van's 12V fridge uses a compressor. It is a very low noise compressor and you cannot hear it start up, run or shut down. It cost me a fortune, well over twice the cost of a larger Electrolux conventional 3-way fridge. But it will run for many hours off a leisure battery when the engine isn't running and there's no 230V hook-up, which is why I thought it was worth it.

[Fran]

Marvellous place.

[Fran]

Why? What have Welsh hills done to you?

[Dave Liquorice]

I was thinking of the chemical used in the internal heat pipe. I don't know what it is though...