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6 June 2007

This time, a few thoughts about how to expand your solar power system. Hope you find them interesting.

1) System Expansion
2) Solar Garden Lights

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1. System Expansion
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So, you've installed a solar power system, or you've inherited one with a house you've bought. But it doesn't provide sufficient power. How can you expand it? There are a number of possibilities:

- Add more modules and / or batteries. That's the obvious way, but there are limitations. What if the controller can't handle the extra current? Well, you can change it for a larger one, so that's not a great problem. But it's best if the modules and batteries you add are of the same type as the existing ones. This may pose a problem if they are no longer available. And there is a limit to the number of batteries you can put in parallel. And, if the existing batteries are nearing the end of their life, then it would be more sensible to replace them altogether.

Practically, it depends on the nature of the system. If you have a system with two 70 Watt modules and one 100 Ah vented battery, then adding one more module and one more battery of the same type, if not the same exact model, will work fine. If the system already has four batteries in parallel, then you might add one, but certainly not another four. You have to use your judgement and common sense.

- Double the voltage. If the system is a 12 Volt one, you can double the voltage to 24 Volts. If the controller is a self-selecting one, such as the Morningstar Prostar, then you only have to rewire the system, and you can double the number of modules and batteries without increasing the current. The downside? It won't work if you've got 12 Volt lamps and you'll have to change the inverter. But you'd probably want to do that anyway.

- Add another autonomous system. This may be a good solution if you have a completely separate power requirement, for example a new building on the same site. I wouldn't recommend having two or more separate systems in the same place though, apart from special applications such as medical refrigeration which require complete autonomy.

- Add new modules and controller, but use the same battery. This may be an option if you have two different sized arrays. But, check with the controller maufacturer first - there may be an interaction between the controllers.

- Throw it all away (or sell it on ebay ;o)) and start again. If it's a big increase in capacity you need, this may turn out to be cheaper. Anyway, it's best to cost it out and check.

The lesson here is; if at all possible, avoid the situation arising in the first place. Make sure you've taken all the loads into account whan you design the system, allow some reserve capacity and leave room for expansion if you might need it.

To do the calculations you'll need a guide, and I know the very thing:
The Solar Power Design Manual.

And if you subscribe to the list on the download page, you'll get updated versions for no extra charge, as soon as they're uploaded.

2. Solar Garden Lights
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I really like the little cheap solar garden lights which can be bought in supermarkets. In fact, our garden is rapidly filling up with them. When I look out of the window in the evening there are loads of little white and orange pools of light, and it's really pretty.

But there's another reason I like them, apart from the way they look. When people come to see us, they remark on them, and ask how they work. I think they're a great advertisement for solar power - they perform a function, and they are silent and completely reliable. I think they really help in persuading people that solar power is a genuine alternative, and not just in hot countries.

So I thoroughly recommend them if you're lucky enough, like me, to live in a country where the cost of little gadgets is inconsequential. If you don't then I hope that the advances in technology and decrease in cost represented by these lamps soon bring you greater comfort and prosperity.

25 March 2007

Sorry about the time between this newsletter and the last one. It hasn't really been the sort of weather that makes me think about solar power, more like wood-cutting weather, but summer time started here today and it got me thinking again...

1) Price goes down again
2) A few thoughts about earthing
3) Heat that water

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1. Lower Price
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This really isn't anything to do with solar power, but it is to do with my Solar Power Design Manual. A couple of months ago I increased the price. The theory is this - price goes up, sales go down, total income remains the same. True, but that's not what I want. I want more people to know about solar power. So I put the price down again and that's where it will stay for the forseeable future.

So, get it now, at the new, old, lower price:

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And if you subscribe to the list on the download page, you'll get updated versions for no extra charge.

2. Earthing low voltage systems
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The other day I got an email from one of my customers asking why my wiring diagrams show only the batery neative terminal earthed, and suggesting that the solar array should be earthed as well. A good question.

The correct answer to the question is that your wiring should be in accordance with the wiring regulations of the country you're in. That may well require the earthing of the module frames, in which case you should do that. Most manufacturers provide an earth terminal; if your modules don't have one then you can use one of the mounting bolts. Remember to remove the anodising first though.

So why don't I show that in the diagrams? Two reasons really:

a) It avoids confusion. It's very important not to earth either output terminal - I've seen the negative earthed and that can short-circuit the controller, causing it to overcharge the battery. The less complex the diagram, the less likely confusion is to arise.

b) It's not necessary. Electrically I mean. It works like this: If you earth the battery negative terminal, and everything is connected to the battery, then the highest voltage that can exist in the system is the open-circuit voltage of the array. In a 12 Volt system that's 20 Volts or so, which isn't considered dangerous. Of course, if there's an inverter in the system then its output is 110 Volts or 230 Volts AC, but the input and the output are electrically isolated and the AC side will be earthed just as if it were a grid-connected circuit.

All the same, earth the module frames if you want, or if the wiring regulations tell you to. And of course, these are only my opinions and you should always gain the opinion or assistance of a qualified person if you're at all unsure.

3. Water heating
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Any of you who are familiar with solar technology will know that photovoltaics is no way to supply heat. And also that water heating panels are the most cost-effective and easiest way of displacing fossil fuel usage.

So, now our house is essentially finished, I'm going to install some solar water heating. Of course I want to do it all myself, so I looked around for a decent DIY design. And there isn't one, at least not one I'm happy with. So I've done one myself, which has got nothing to do with putting radiators in boxes and painting them black. If you're wondering, that works OK actually, but I'm looking for something a bit better.

Don't hold your breath; I've got to build it, install it and test it yet, but if it works as well as I hope it will I'll publish the design. It should all be standard parts which you can get at any hardware or DIY shop, and I've got an idea for a heat exchanger to work with mains pressure systems. I've done the calculations so I know that bit will work. And I've bought most of the bits already.

31 January 2007

Today, a short note to give you advance notice of a price rise, plus a look at lighting.

1) Buy Now!
2) What sort of lighting?

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1. Buy now!
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I've been told that my Solar Power Design Manual is too cheap. So I'm going to increase the price, but I thought I'd tell you first. The price increase is scheduled for 6 February - next Tuesday. if you're interested I'd advise you have a look now:

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My apologies if you've already got it.

2. What sort of lighting?
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It used to be straightforward - use a fluorescent lamp for general lighting and a halogen lamp for directed light. Perhaps it's not so straightforward now that LED lighting has become common.

How good are LED lights? Well very good actually - highly efficient and cool running. But that's not their main advantage really, it's the ability to direct a very small amount of light exactly where you want it.

In fact, an LED light is not quite as efficient as a compact fluorescent lamp - it doesn't convert as much of the electrical power to light. But, where can you get a fluorescent lamp that only consumes a couple of Watts? If you've got an application that needs highly focussed light, or a very small amount of light, then LED lamps may well be the best choice. They make very good torches for instance. But if you want to light a room then a fluorescent lamp with an electronic ballast is still the best bet. For now.

11 January 2007

Here's wishing you a belated happy new year.

The winter solstice is behind us now here in the northern hemisphere, but it's still a long time until the sun is high in the sky.

Today, how to make money from my book, plus a look at the effect of shadows on your solar array.

1) Become an affiliate
2) Why shading has a big effect on performance

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1. Become an affiliate
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Have you got a web site about solar power? If so, why not promote my book, the Solar Power Design Manual? All you have to do is put a link on your site - if anyone buys the book through it, you get half of the money. It's that simple.
Sign up for free here:

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You can even put the link in an email or blog; you don't have to have a site of your own!

2. Why shading has a big effect on performance
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Is it really worth worrying about a bit of shade on your solar array? I mean, a few square centimetres of a whole panel can't make that much difference can it?

Well yes it can actually, and the reason is to be found in the law that states that the current in a series circuit is the same at all points.

Stay with me here: A standard 12 Volt module is not a single cell but (usually) 36 cells connected in series. Therefore, if the current in one cell is reduced then the current in the entire module is reduced by the same amount.

As an example, let's assume you have a module with cells 10 cm square. Now let's say that a shadow 5 cm square falls on the module - a pretty small shadow? Yes, but if it falls on one cell it will mask 25% of the area. That will have the effect of reducing the current in all cells by 25%, and therefore reducing the power output of the module by 25%. Not such an insignificant shadow after all then...

The conclusion to be drawn from this is that it's very important ot avoid shading the modules, even slightly. That becomes all the more important in the winter, when the sun is low in the sky and the insolation is significantly lower.

If I were you, I'd pop outside and check that no tree branches have grown across the array since last year!

15 November 2006

Today, no need to design your own solar power system. Why? I've done it for you!

1) Complete Solar Power Systems
2) Insolation - how sunny is it here?
3) Phantom Loads - Update

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Teach yourself all about Solar Power

http://www.solar-power-answers.co.uk/solardesign.html
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1. Complete Solar Power Systems
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Are you confused about how to design a solar power system to suit your needs? I've produced instructions for three systems to cover most eventualities. Download them here:

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http://www.solar-power-answers.co.uk/publications.html
http://www.solar-power-answers.co.uk/products.html
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Do exactly what they say or modify them to suit your needs - it's up to you.

2. Insolation - how sunny is it here?
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The sun shines all day here, so there must be loads of power available, mustn't there? What about days when it's overcast, will solar power work?

The answers to these questions require an understanding of the concept of insolation. Insolation is the measure of the amount of solar energy falling on the Earth's surface - for solar power applications it is usual to use the daily average insolation by month, falling on a tilted surface of 1 square metre.

The insolation is measured in kilo-Watt hours, so the daily average is measured in kilo-Watt hours per metre squared per day (kWh/m2/day). Conveniently for us, when the sun is high in the sky on a cloudless day, the solar radiation at ground level is almost exactly 1 kW/m2, that is, every square metre has a kilowatt of visible radiation incident upon it. This is the power level that the output of a solar photovoltaic cell or panel is rated at.

All this means that, for practical purposes, the insolation can be taken as equivalent to the number of hours of full sunshine per day. So if you say that the insolation for a particular place is 4 kWh/m2/day, then you can assume that that is the same as 4 hours of sunshine, so a panel rated at 50 Watts will deliver 50 x 4 = 200 Watt-hours of energy per day before losses in the charging system. That means that you don't have to worry about whether it's sunny or not; as long as the battery is big enough to overcome the peaks and troughs you know how much power you can use.

Practically, insolation may vary between 1 kWh/m2/day in northern Europe in winter, to 7 kWh/m2/day in Sub-Saharan Africa or the Australian Outback.

Find out more about insolation here:

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http://www.solar-power-answers.co.uk/solardesign.html
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3. Phantom Loads - Update
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The last issue had an article in it about phantom loads. One of my readers very helpfully sent me a link to a company which makes a product which helps to deal with the problem. It's a device which you plug all your computer peripherals into which switches off the mains to them when you power the computer down. It would work equally well for hi-fi equipment, and no doubt there are many other applications which I haven't thought of yet.

The URL is:

http://www.oneclickpower.co.uk/

13 October 2006

Today, how to avoid using more power than you think you should.

1) Phantom Loads - where's all that power going?
2) Solar Power Design Manual
3) Economics of Solar Power

1. Phantom Loads - where's all that power going?
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If this is an unfamiliar term then read on. A phantom load is any device that uses electricity even when it's switched off. They fall into two basic categories - appliances that have a standby setting such as televisions, and appliances with an external power supply.

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But why do we care? Surely they use hardly any power? Well that's not always the case, and in fact phantom loads can add up to a very significant proportion of the total load, simply because they're off for a large proportion of the day!

Here's an extreme example: The satellite television receiver in my house consumes 70 Watts when switched on. A lot, but not too bad. But it consumes 63 Watts when it's switched off! If you assume that it's on for 4 hours per day (a lot), then its energy consumption is 70 x 4, or 280 Watt-hours. But its consumption for the 20 hours when it's off is 20 x 63, or 1260 Watt-hours. So it uses 4.5 times more energy when it's not in use than when it is. That can't be right.

So what's to be done? Well, with the example above, not much. The receiver supplies power to the heater in the LNB (the bit sticking out of the dish) to stop it getting damp, plus it needs to be on overnight to receive software updates. Until the manufacturers are encouraged into reducing the power consumption it's no Sky TV for solar users.

But the good news is, most things you can either unplug or switch off. Television sets for example, usually have a button on the front that switches them off properly. Use it. The same with most Hi-Fi equipment. If you buy a multi-way extension lead and plug all your little power supplies into it, then you can switch them off when you're not using them.

The most important thing is, if you're buying new appliances for solar power systems, don't just look at the power consumption when on, try to minimise consumption when off.

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Modules, controllers and other system components

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Buy securely on line for shipping Europe-wide
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2. Solar Power Design Manual
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The solar power design manual teaches everything you need to know about stand-alone solar power systems. Equally applicable to enthusiasts, engineers and development workers, it covers the design and installation of solar photovoltaic systems from first principles to final commissioning.

Find out more here:

http://www.solar-power-answers.co.uk/solardesign.html

3. Economics of Solar Power
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I'm often asked "how much will it cost for a three bedroom house?" Well, there's no straight answer to that, because you need to work out the energy requirement of the house and its occupiers, and relate that to the insolation. One thing's for certain though - if you're connected to mains electricty then a stand-alone solar power system will never compete on a cost per kilowatt basis.

Now, that's not to say that solar power is always more expensive - not at all. Let me explain. The cost of electricity delivered by a solar power system is not determined by the fuel costs. That is because there are no fuel costs. But it's not free. The system components, particularly the batteries, have a finite lifespan. If you include the cost of replacing them when they're worn out, then the cost of the electricity produced is usually about the same as the cost of mains electricity.

But that assumes that you're competing with an existing grid connection. In fact, that's very rarely the case. What you're more likely to be competing with is either a very expensive new connection or another form of generation. In these cases solar power can be very competitive indeed. The cost of bringing a mains connection even a few kilometers can, in many cases, be tens or even hundreds of thousands of pounds, dollars or euros. You can buy a lot of modules and batteries for that kind of money.

And when you compare solar generated electricity with electricity generated by a diesel genset, then the advantages become even clearer. Even if it's close to the fuel supply, then the cost per kilowatt is much higher, more like three times as much. And that's before you start to look at servicing costs (every 75 hours) or the cost of transporting fuel.

There are other potential reasons that also make good economic sense. For instance, consider the case of roadside monitoring equipment. It may be close to the grid, but if it only consumes milliwatts, then the standing charge is going to far outweigh the cost of the photovoltaic system.

So all in all, it's not just environmentalists that need to consider solar power. And for everybody living in an ordinary house, on the grid, then a grid-connected system may be the way forward. There are no batteries involved and therefore the economics are far more clear-cut. Once the rest of the European Union follows the lead of the Netherlands in making it very easy to connect such a system to the mains, then the way will be paved for the necessary expansion in renewable energy generation capacity. I live in hope.

6 September 2006

After a rather longer delay than I was expecting, I'm back at my desk. We had a sudden overwhelming urge to convert the attic. Oh well, I've got a nice new office now.

1) Absorption Fridges - why they're a bad idea
2) New product range
3) 24 Volt Wiring

1. Absorption Fridges - why they're a bad idea
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I was going through my emails just now and found a couple that I had forgotten to answer - sorry - and which raised important points. The first was from a guy wanting to run a fridge freezer which consumes 3.2 kWh per day. I guess this is a caravan type absorption fridge, but it might just be an enormous compression fridge. Anyway, let's assume it's the former.

If you're not familiar with the terminology an absorption fridge, rather than push the refigerant around with a mechanical compressor, uses a second fluid which absorbs the refrigerant at key points in the cycle. This is then circulated by applying heat at the right point.

This is an old, but excellent technology. I remember my family having an Electrolux fridge when I was a child, which was silent and amazingly effective at freezing the milk. I've also seen them operating in developing countries keeping vaccines cool on a dribble of kerosene. Most people will know them, however, from the tiny caravan fridges that run on gas or the car battery. I've got one in my barn at the moment in fact. But they're inefficient.

I've just had a look at some numbers. From the Dometic website, the electricity consumption of a 142 litre absorption fridge with a small freezer compartment is 3.2 kWh / 24 h. Roughly the same sized 12 Volt compressor fridge from Shoreline Refrigeration (143 litres) consumes 345 Wh in the same period. That's over 9 times less! So you can see that it would pay for itself in no time. Dometic fridges are very good, but run them on gas!

Shoreline Refrigeration: http://www.boatfridge.com
Dometic: http://www.dometic.com/

Or you can use an inverter to run a mains fridge. The only small inverter that I know that will do that is the Steca Solarix Sinus range. Find out more here:

http://www.solar-power-answers.co.uk/products.html

2. New product range
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You might have guessed from the link above - I've introduced a range of solar power products. There is everything you'll need to build a solar power system; panels, controllers, batteries, lights and inverters. Plus you've got an expert (me) on hand if you need advice.

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Buy securely on line for shipping Europe-wide

http://www.solar-power-answers.co.uk/products.html
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I'm particularly pleased with the solar LED torch - it's much nicer than the others I've seen - £19.95 or 29.95 Euros. I must like it; I've got two myself. They're great for putting the bins out - it's pitch black here in the winter. Have a look, I think you'll like it.

3. 24 Volt Wiring
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I've been asked a few times what the yellow wire is for in the wiring diagram at http://www.solar-power-answers.co.uk/inverter_system.html so here's the reply I gave to the last person who asked:

"The reason it's like that is that it's a 24 Volt system diagram. Panels are 12V nominal output, so they need to be wired in series/parallel, but it can't be done like the batteries, because it's necessary to keep the junction boxes sealed.

So, the way it's usually done is to split the array in half, and wire each half in parallel. Then the positive of one half is connected to the negative of the other, hence the yellow wire, giving a 24 Volt nominal output on the other positive and negative connections.

In fact, it's normal to use a two core cble where the yellow wire is, so that the output cable can be connected in just one junction box. Some panels have an extra unconnected terminal to facilitate this."

I think I'd better put that on the page so that everybody understands.

A quick word on 24 Volt systems might be appropriate. It used to be that 24 Volt was the only option for inverter based systems. That was because there were no decent inverters available in 12 Volt versions, and those that were were expensive. That's not true any more, and in fact, for systems of 1 kW peak or less, you may well be better sticking to 12 Volts.

You'll still need shorter or fatter cables mind you, so if it's a long way from the array to the battery then 24 Volts will still be better. It's just not essential any longer.

6 July 2004

1) I've moved
2) Development expert

1. I've moved
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I'm sorry there hasn't been a newsletter for a while now. That's because I've been moving house. The place we've moved to needs a fair bit of work so there won't be much for the next few months either. When I get round to it I'll be puttig some solar water heating in. I'll document that as it happens on the website.

2. Development expert
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My friend Ian is a true expert in solar power for developing countries. I worked with him for years, and these days he's got his own company designing, supplying and installing solar power systems all over the world. If you've got any interest in development I strongly suggest that you investigate his new website. It's at:

http://www.brightlightsolar.com

And of course there's a link at:

http://www.solar-power-answers.co.uk

That's all for now.

28 March 2004

1) Products page
2) What size modules?
3) Design manual

1. Products page
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Thanks to an affiliate agreement there is now a full range of solar power products available from my website. Take a look at the new 'products' page at:

http://www.solar-power-answers.co.uk/products.html

There are all sorts of useful things like solar mobile phone chargers and garden lighting, and more serious stuff with panels of up to 100 Watts.

2. What size modules
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The other week, somebody asked me: "If the calculated array size is 100 Wp, is it best to use two 50 Wp modules, five 20 Wp modules or one 100 Wp module?".

On the face of it of course it doesn't matter, but it's worthy of further discussion.

Let's start with the case of a 12 Volt system. All the modules will be connected in parallel, so the peak wattage is all that's important. So, does it matter if you use lots of little modules or one big one? Electrically no, but you should consider these points:

- Each extra module requires interconnecting cables.
- The cost of smaller modules is likely to be higher.
- Because of the framing, smaller modules take up more space per watt.

However:

- A large number of small modules may be more flexible.

So, generally, the bigger the better except where the particular installation requires greater flexibility. It will take up less space, be easier to install and more reliable and probably cheaper.
However, if you're offered a job lot of small modules, don't turn them down out of hand. Cost in the extra cabling and they may still turn out cheaper.

What about 24 Volts? Because the nominal voltage of your average solar panel is 12 Volts, they have to be in series / parallel. That means that there have to be an even number. In this case, five 20 Wp modules or one 100 Wp module won't work. The only viable option is two 50 Wp modules wired in series.

So it's not always as simple as it seems. The Centre for Alternative Technology used to have a 1 kW solar roof made from 10 Watt thin-film modules. They wouldn't be my (or their) first choice, but they were donated, so suddenly it makes sense. Last time I went there they were dismantling it though, so perhaps it wasn't such a good idea after all...

3) Design manual
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My new book has got a title. It's called the "Solar Power Design Manual". Probably. I haven't finished it yet though. Soon, honestly...

26 February 2004

1) Wiring diagrams
2) Book update

1. Wiring Diagrams
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One of the things that a lot of people search for on my website is wiring diagrams. With this in mind I've produced a couple of example schematics. One is for the type of simple lighting system which is commonly used in the developing world and the other is for a more complicated system which incorporates an inverter. You can find them at:

http://www.solar-power-answers.co.uk/wiring.html

Hopefully these will help you out with where all the wires go if you're in any doubt.

2. Book Update
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Once I'd uploaded the wiring diagrams I thought that they could usefully be incorporated into my "Solar Power Questions Answered" book. While I was there I made all the links work properly as well. If you want a new copy you can get it from:

http://www.solar-power-answers.co.uk/subscribe.html

While you're there feel free to give a copy to your friends or colleagues, or better still ask them to subscribe.

26 January 2004

1) New inverter
2) Battery care
3) Any links?
4) What no book?

1. New inverter
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MDS Battery have launched a new small inverter which offers good value for money at a special offer price.

Check it out at link obsolete

2. Battery Care
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The promised cold weather reminded me that this is the time of year when it's important to make sure that any batteries you have are in tip-top condition. It doesn't just apply to solar power systems, but any lead acid batteries like your car battery. Batteries that are not in use are especially vulnerable to cold weather.

Here's how to keep your batteries in the best of health:

- Give the tops a good clean. In damp weather the grime that collects on top of the battery case can become conductive and increase the rate of discharge.

- Look after the terminals. Clean the terminals well, use a wire brush if necessary but make sure that any metal dust is cleaned away afterwards. Check that the terminal bolts are nice and tight and then apply a covering of petroleum jelly (Vaseline). Do not use ordinary grease.

- Top up the electrolyte. If your batteries are the type that can be topped up, make sure that the electrolyte level is correct. If there are no marks, then it should be covering the plates but no higher than the separator bars that should be visible in the top. Use only distilled or de-ionised water, and do it before they are charged if possible.

- Give them a good charge. If your system has a way of delivering an 'equalising charge' then use this. The intention is to make sure that every cell is fully charged. A good charge from the mains or a generator through a battery charger will also do. It is particularly important that batteries that are not in use get a good cahrge at this time of year as it is possible that the electrolyte will freeze if they are allowed to discharge. If this happens then the plates will buckle and the battery will be scrap.

- Don't ask too much of them. Remember that a battery can't supply more energy than it has received. In the winter the demand from lights is greater, but the amount of power available is less. Plus, the effective capacity of a battery is reduced by low temperatures. The battery should be spending most of its time nearly fully charged, not nearly discharged. Now is the time to see if your system can cope with the demands placed upon it.

If you follow these steps you should have a battery which will survive this and future winters intact. The lead-acid battery has plenty of faults, but it's still the best thing we've got so look after it and it will pay you back.

3. Any links?
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I've added a link submission script to the links page. If you have a solar-related website or know of a good one please submit it at:

http://www.solar-power-answers.co.uk/solar_power_links.php

Two new ones have been added already. Have a look:

http://www.solar-power-answers.co.uk/solar_power_links.php

4. What no book?
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I know, I haven't started yet.

If you have any ideas about what should go into it, questions you'd like to see answered and that sort of thing then I'd still like to know.

mailto:book@solar-power-answers.co.uk

All suggestions gratefully received.

24 October 2003

1) Website changes
2) Using an inverter
3) Portable solar panel
4) Ideas please

1. Website Changes
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Now the autumn has really started here in mid-Wales it's given me an opportunity to do some much needed site maintenance. There are no great changes, but I've updated the links page to get rid of any broken links and added an exciting new mail order equipment supplier.

The equipment page has also changed. I was never really happy with it so I've taken the pictures away and made it easier to understand.

Check it out at http://www.solar-power-answers.co.uk/

2. Using an Inverter
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I had an e-mail a while ago from someone asking how much power an inverter uses. It's a question I get asked a lot, and there's no simple answer.

Of course there is an answer to the question, but it's another question: 'How much power are you going to use?'

Here's how you work out how much power an inverter uses, and ultimately what its energy requirement is:

- List all the things you are going to power from the inverter.
- List the power consumption of each item.
- Go through the list and add up the maximum likely power consumption at any one time by deciding what things will be on at the same time. Multiply by 1.2 to give a 20% safety factor and that's the continuous power rating of your inverter.

- Find out the inverter efficiency. Ask the manufacturer or, if you can't find out, assume it's 80%
- Divide the power consumption of each item by the efficiency of the inverter, e.g. if it's 80% then divide by 0.8 to give a bigger number. Use these numbers to size the system in the normal way.
- If the inverter will be on for extended periods without a load, consider the no-load power consumption of the inverter as another DC load.

Simple really.

3. Portable Solar Panel
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I've been sent details of a lovely little portable solar panel. It has a peak output of 13 Watts and a nominal voltage of 12 Volts. It folds up into a briefcase shape with a carrying handle and I reckon it would be ideal for people who need to charge batteries in the middle of nowhere. Check it out at link obsolete

4. Ideas Please
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I'll be starting work on a new e-book soon. It will be a comprehensive guide to designing a solar power system which follows on from the introduction given by the free book.

If you have any ideas about what should go into it, questions you'd like to see answered and that sort of thing then please let me know at:

mailto:book@solar-power-answers.co.uk

All suggestions gratefully received.

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