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I am looking for a solution to replace a broken electricity generator.

I am considering using solar panels or a wind turbine. Or even both.

I need it for an animal shed and the targeted consumption units would be a couple of light-bulbs (5-10) initially and in the future maybe something more.

Unfortunately my know-how related to such things is close to zero but I would like to improve this. I don't mind a little bit of own research and some DIY job. The animal shelter would be used in winter too.

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    Welcome to Sustainable Living! What are your considerations? Most sustainable, most cost-effective, easiest to install? – THelper May 6 '13 at 17:23
  • I think the topmost concern is cost-effective for now. Thank you! – user503413 May 6 '13 at 18:22
  • Do you have a grid connection? Do you plan to heat the shelter in winter too? – Peter Ivan May 13 '13 at 6:57
  • The grid connection is to expensive, this is one of the main reasons I consider alternative sources. Heating is not of concern for now - it has a wood fired stove. – user503413 May 13 '13 at 7:26
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A specific answer to your very narrow question wouldn't be much use to anyone else; and you haven't given us enough information to give you a specific answer anyway.

But what we can do, is give you the types of information you'd need to make a decision.

And I'll restrict it just to PV and wind, as that's what you've asked about; others reading this might want to ask another question, if they were interested in other types of renewables: solar thermal, hydro, geothermal, and so on.

1. Understand your demand profile.

First you need to know the profile of your electricity use. Ideally hour-by-hour for a whole year; but at least an understanding of what's likely to be the two underlying cycles:

  1. annual variations - how the load varies by month in a typical year.
  2. daily variations - how the load varies by hour in a typical day.

One of the most effective things you can do, is to max out the efficiency of the equipment you want to power: so LED lighting that's over 100 lumens per watt, that sort of thing. That minimises both the generation capacity, and any storage capacity, you might need.

2. Understand the potential supply profile

2a. Solar

The nature of the solar resource, for photovoltaics, will be influenced by local shading patterns: the exact geometric configuration of buildings; and by the climate of the region you are in. If you can find a big-enough surface area that you can mount PV panels that would slope towards the equator, and almost never be shaded, that removes the local shading from the calculation, and that makes thing a lot simpler. To get typical PV yield for your region, and to find out the best slope, then use a tool such as PVGIS or PVWatts

2b. wind

The wind profile is much much more susceptible to local geometry than solar is. But you should be able to get a decent broadbrush indication from your national meteorological service, or one of the various global wind-resource maps, to get a first estimate. You can pretty much ignore most roof-mounted turbines: they've such a low yield that many won't generate equivalent energy to that used to make them. Pole-mounted turbines are a better bet, but if you're in an urban area, then it's fairly unlikely that wind will be a contributor.

3. Understand correlations between supply and demand

Some demands are positively correlated with wind or solar; some are negatively correlated. It's important to understand those correlations, otherwise you risk generating power at all the wrong times, and not at the right times.

For example, lighting may be predominantly a night-time demand, so it would be strongly negatively correlated with solar, and that's a bad thing.

To take some counter examples: solar for air-conditioning would be a good match, because air-conditioning demand is higher when it's very sunny. Wind in the UK is higher in winter than summer, so a demand that is higher in winter than summer would be a positive correlation and a good match: for example, heating.

4. Storage

Generally, when many people think about renewables, they usually assume local storage is essential. And in most circumstances, they're wrong. The exception is when the site in question is not grid-connected.

In such a case, then you'll have two choices: storage, or load disconnection. Storage is usually expensive, so make sure that you know the value of load disconnection, to price the storage correctly.

There will then be a trade-off between the amount of storage you need, and the over-supply of generation capacity that you get.

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Combining wind turbine and solar panel is my favorite (that has not come to reality by now...). Both of them are weather dependent but in an almost anti-correlated way. It means they complement each other very well most of the time of the year.
Here in continental Europe, usually when it's a sunny day it's rarely windy. And when the weather is changing or in winter, it's cloudy and windy. So you'd profit from solar panels during sunny and summer days and profit from wind turbine on bad weather and winter/late autumn days.

The points made by EnergyNumbers are all valid but I'd stress an importance of a storage because you mention an old generator. It probably means you're not grid-connected. You'll have to balance:

  • You'd still need some (back-up) generator - much smaller and much less used than the previous one. The main sources would be PV panels and wind turbine(s).
  • Adding some kind of batteries to the system. Storing energy increases the build costs which you want to minimize. But the more you store the smaller and less used generator would be.

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