[00:47.30]Man:Hi Lin. How's your project coming along?
[00:50.26]Woman:Oh! Not very well. I've got all the information but I can't seem to organize it into a presentation.
[00:55.58]Man:Well, you'd better hurry. You only have one more week.
[00:57.70]Woman:Yes, that's okay. It's just that, oh.
[01:02.98]Man:Well, why don't you try your presentation on me? Maybe I can help.
[01:08.75]Woman:Oh really, great. Okay, well! I've chosen solar power for my subject and I'm going to talk specifically about domestic water heating. You know like the ones popular in America, I've got some facts here.
[01:22.48]Man:That's good. But just start your presentation from the beginning.
[01:26.38]Woman:Oh right, well. Here we go then. There are many reasons why we should be looking elsewhere for energy sources, as most people are aware fossil fuels and other such non-renewable sources are by definition finite, so something needs to be in operation soon.
[01:45.50]Currently, there are a number of alternative energy sources available which can with a little preparation be used to provide for a significant part of our domestic energy requirements.
[01:55.50]In this presentation I am focusing on solar power and its application as a domestic water heater. As a renewable energy source solar power is in many ways ideal. The amount of the sun's energy which reaches the earth every minute exceeds the energy that the global population consumes in a year.
[02:16.34]Although scientists argue that it is not finite, sunlight is certainly a long-lasting resource which is not depleted through use and solar power converters use this energy without needing any complex moving parts.
[02:31.98]Once collected and stored, solar energy can be used for many purposes but it is becoming increasingly popular as a domestic heating source. Generally a building that is heated by solar power will have its water heated by solar power as well and this has even worked in areas that are not exposed to long hours of direct sunlight, such as the United Kingdom, although not so well as in warmer climates.
[03:00.06]Man:Why have you stopped?
[03:01.75]Woman:Well, that's all I've got so far.
[03:04.59]Man:Well, let's start by talking about how effective it is.
[03:08.63]Woman:Oh, okay. Well, there are a number of factors that influence how efficient solar power can be. The first, obviously is the amount of sunlight and this is dependent on season, time of day and climate.
[03:22.53]Although the UK has something of a bad reputation for sunshine, it is actually quite productive during some parts of the year. Given a sufficient size of solar panel and water storage tank, solar power can provide all of our water heating requirements in June and July and even provide the majority until October.
[03:42.54]From October to the end of the year this figure falls dramatically. December is the least productive, being able to supply less than 5% of the average household's hot water requirement. It is at this point that solar power needs to be supplemented with a more traditional form of heating. From January solar power becomes more effective at a rate of about 20 percent per month, although this rise decelerates to around 18 percent by May.
[05:02.73]Man:Now say something about this water heater. Did you have any information about that?
[05:07.65]Woman:Oh yes. I've got an illustration of a water tank here.
[05:10.61]Man:That's good. But you'll have to describe it.
[05:13.45]Woman:Right well. The ideal water tank in the UK has a capacity of 45 to 50 litres, but must be at least 40 litres to be effective. The solar coil is put in the bottom of the tank to heat the water.
[05:26.73]Now remember that solar heated water will not get quite as hot as fossil fuel water heaters. The bottom half of the tank is normally 20 degrees and this is why it is important not to have a tank that is too large, as that would take too much energy to heat. In this illustration it rises to 40 degrees from halfway up. Don't forget that hot water rises, so the top third of the tank is the hottest and reaches an average temperature of 65 degrees.
[05:57.98]Man:And what's this second layer around the tank?
[06:00.98]Woman:Oh! That's insulation, because the tank is often either outside or just under the roof. Rigid foam is used as an insulation layer. It should be at least 80 millimetres thick all around.
[06:14.83]Man:That seems like a good presentation. All you need to do is to prepare some short notes and a larger illustration. So you can use it as a demonstration and you'll be fine.
[06:24.91]Woman:Oh! You think? So, well thanks very much for the help. Maybe I could do the same for you one day.
[06:29.99]Man:Maybe. Anyway, I have to go. Good luck!
[06:34.19]Woman:Thanks. Bye.
