TIM'S GUIDE TO OFF GRID POWER

A CLOSER LOOK AT THE ENERGY OF THE SUN.

When we think of energy we often think of oil gas and coal.

Yet the sunlight the earth receives in 20 days is as much energy as is believed to be stored in the earth’s entire reserves of fossil fuels.

95% of the suns energy released is as visible light, along with infra red and ultra violet light.

Light travels in small packets (photons) rather in the same way you could pass water in buckets along a chain of people.

The photons in the ultra violet region have more energy than the visible region; the photons in the infrared, which we feel as heat, have less energy than the visible region.

For solar panels it’s the visible light we are most interested in.

HOW TO USE CRYSTALLINE SILICON PHOTOVOLTAIC MODULES.

Ok, I promised an ABC guide, so solar panels.

Solar panels work by light hitting them, which dislodges electrons from atoms.

To make it very easy to understand just think about the more light that hits a panel the more electricity you get.

But even on a cloudy day panels will still produce some power.

It’s not impossible to make your own panels from scratch.

Solar cells are very simple they are made from materials that are neither insulators (like plastics) nor conductors of electricity (like copper wire) the materials needed are semi-conductors.

But as this would be beyond most people’s skills, and this is an ABC guide, we will assume that people will buy them.

Before you buy your panels, you have to decide what system you want e.g.

12/24/48 volts

I went for a 12 volt system as there are a lot more 12 volt items like TVs,

freezers, fridges etc on the market than 24 volt.

The first thing you need to work out is how much power you need.

Most people start with a back up system to the mains in case of power cuts, then add more panels as they go, a panel or two will produce plenty of back up power for lights, freezers etc.

So your panels have turned up, now your thinking what’s the best way to install them. You could put them on a south facing roof, but do you want to start drilling holes in your roof, if you don’t fix them properly the first gale might blow them off.

The way I did it was to attach them to a pole.

Cover the panels with something; you don’t want to have power trying to flow through them until everything is connected up.

You concrete a small section of metal tube into the ground, and then using a joining section add a large pole.

If you keep it under 4 mtrs high in total you should not be bothered by planning regs, (but best to check for your area) with a pole system you can turn the panels to track the sun giving you the best possible light all day. This can be done by hand or by a electric/clockwork motor.

Of course if you use a pole there’s an empty space on the top just great for a wind charger. A wind charger unlike solar panels could produce power 24/7 which is why I would recommend getting both.

Unless you live out in the country don’t get one bigger than a Mtr across,  that way you are not likely to get complaints about it.

A good 1000mm wide wind turbine will kick out about 90 watts at wind speeds of about 22mph. and will start kicking out power from wind speeds as low as 5 mph. I wont go into wind speeds too deep at this point.

But as a rough guide each time wind speed doubles, you get eight times as much power.

A wind turbine (from scrap) is very easy to make.

The turbine blades can be carved from wood, but this being an ABC guide again we will assume that you have bought one.

Please, please, don’t try holding it up into the wind with your hands to see it working.

The wind WILL twist it out of your hands and snapped blades and a trip to A+E are a hassle you don’t need right now.

PUTTING YOUR WIND CHARGER UP

For a wind charger to work at its best it must have free flowing air to pass through the blades. That means any trees or houses in the way will slow the wind. The best height for a wind charger is from 7 mtrs upwards, the wind moves a lot faster at this height.

The best and most safe way is to lower your pole to the ground, fix your wind charger to it with the power lead running down the inside of the pole if possible. (Tie a blade to the pole to stop it turning, you don’t want it working yet) an over speeding turbine without a load on it to slow it down will scare the cr*p out of you not to mention it wont do it any good. When ready, pull your pole slowly into the upright position. A pole must have guy wires to support it(at least 3 every 10 to 12 feet though I would recommend 4 for safety.)

A WORD OF CAUTION

For most people small turbine experimenting is stepping into the unknown.

If you were changing a bike inner tube for the first time or a car wheel you would probably know someone you could ask for advice about the best and most safe way, and to show you how to do it. Not many people know much about turbines, even a domestic installation electrician will probably be unfamiliar with variable voltage 3 phase turbines. So it’s down to you to make sure everything is connected properly and safe.

Ok we have our 12 or 24-volt wind charger and our panels.

You will need to fit a Schottky diode one must be fitted to each panel to stop the power flowing back from the wind charger back to the panels. (A one way valve for electricity)

(If you want a 24 volt system two 12 volt panels can be wired back to back to get 24 volts) now we turn to cable. The longer the cable the more power will be lost in transit from the turbine/panels. (Think of it as a hose pipe which leaks) so try and keep it as short as possible.

Minimum cable thickness must be 2.5 mm (each strand, i.e. brown 2.5mm blue 2.5mm) this in turn is connected to a charge regulator/controller. A charge regulator provides a battery management system for your charging source.

And should include the following,

Over voltage regulator, a shunt regulator which protects the batteries from over charging which will avoid the loss of electrolyte through gassing. It works by monitoring the charging source output at the critical cut involtage, which is 13.8 volts for a 12-volt system and 27.6 volts for a 24-volt system. It starts to dissipate the charging source energy as heat and reduces the current flow to the battery. A charge splitter if you want to charge two banks of batteries. An input for panels to be connected and one for your turbine. Battery bank inputs, and a voltage indicator so you can monitor the state of your batteries. And of course it must be fused.

BATTERIES.

The first battery thought to be invented is the Baghdad battery (250 years BC) the first continuous electric current batteries were invented over 200 years ago by Alessandro Volta (hence the name volts) his first battery was very crude by todays' standards.

It’s not impossible to make your own batteries for your off grid system from scratch, but with all the batteries to be found after teotwawki it’s not worth the trouble.

This is how the first battery was made. (For information only of course) a stack of paired copper zinc/silver disks separated from one another by cardboard disks moistened with damp salt. That’s enough on the history of batteries;

The most important rules for batteries are don’t let the voltage get too high or low.

Charging of batteries gives off hydrogen gas which is explosive, so make sure they are vented, (don’t smoke near them unless your tired of living.) Make sure you don’t short-circuit them because they will bite back.

Batteries for off the grid use.

Leisure/deep cycle batteries are specifically designed for good performance in terms of charge/discharge cycles. So these are the best types if you can get them. Batteries should be sized according to your load requirements. (If you use a lot of power get more batteries) Batteries may be linked in parallel to increase amp-hours, (+ to + - to - or in series to increase voltage. + to - - to + (if your not 100% sure how to do this. seek help)

Car batteries.

Car batteries can be used but they are designed for short bursts of energy.

Batteries like to charged steadily and gradually with whatever current holds their voltage at 14 volts (12 volt lead acid batteries) if you have too many batteries in a battery bank you may find that they don’t all fully charge. A way around this is an equalising charge; this done by bringing the voltage to 15 volts, if you take it above 15 volts the batteries may bubble violently and overheat which will cause damage to the batteries if prolonged. (Never do this to a gel type battery) please note overcharging of batteries may result in generation of sulphuric acid mist, which is a carcinogen.

The batteries I use have a window which if you look in you can see green for fully charged white for part charged or red for flat, this means I can look down my banks and see if any of the batteries have failed without having to take all the leads off (after shutting down the system first) and checking each battery with a volt meter. When joining batteries use as thick a cable as possible the cable I use is 25mm thick. If you can, use two banks of batteries, this way you will always have one bank in hand in case of problems with the system, giving you time to fix it without having to sit in the dark or all the food in your freezer going off, etc

So you now have your battery bank(s) charged, power just waiting to be used.

So how do you use it? You could just clip a 12v bulb (in a holder) to a couple of wires and hold them to the battery terminals with a couple of crocodile clips. That fine if you only want an emergency light. (You would normally use croc clips for higher wattage items like 12 volt TVs) for lower wattage 12v items the best way is to connect a 2-way cigarette lighter socket extension to the terminals that way you can connect two items at once.

INVERTERS

There is no reason why you can't run 240v items from a battery bank.

For this you need an inverter, this boosts 12v to 240v. They basically come in two sorts, pure sine wave and modified sine wave. They also come in a variety of sizes. There’s no point getting a pure sine wave in a small size because you will only end up having to get a bigger one as and when your system gets bigger, unless you only want it to run small sensitive items when your out and about.

So what is an inverter.

Its a device which takes power from your 12 volt dc source and boosts it to household ac electricity giving you the power to run items in your house which you now plug into the mains electricity. (Providing you have a big enough inverter) make sure for the UK your inverter your planning to buy is not 110 volt (if you plan to buy one on line.)

So how do they work?

The easiest way to explain it is, it boosts your power about 20 times by switching the power to create pulses of ac electricity.

So what is the difference between pure sine wave and modified sine wave? (Also called stepped wave, quasi sine wave, trapezoidal) pure sine wave power output is the same as you find in your home is also the most efficient.

(You always lose some power in the switching process) it also generates less heat in the switching process than modified sine wave ones.

Modified sine wave inverters.

The best thing about these types is the price. a small 150 watts inverter can be bought for about £29.99 however, if you want to run tv's or computers with this type you may well get interferance (with some sorts its really bad) also if you want to run any fluorescent lights on these sorts, forget it, all the types I have tried just won’t work with them.

Modified sine wave is an output, which tries to copy pure sine wave but does not quite make it.

These are ok for running non digital items lights etc, you can run TVs etc on these but the odds are you will get interference,

150 watts about 19.99

300 watts about £39.99

500 watts about £69.99

What size inverter should I get.

On the items you want to run there should be a plate saying what watts are needed to run it.

Add up all the items you need to run at the same time then that’s the size inverter you need.

E.g. video player 20 watts and TV (59cm) 115 watts energy saver light bulb

11 watts.

That’s 146 watts.

So you want a 150-watt inverter.

Will it run my batteries dead. Most inverters will sound an alarm when power is getting low then if you keep on taking power from the batteries it will switch itself off thus protecting your batteries from being drained to low. (Beware, on high energy item the alarm mode to switch off mode can be less than a minute on some inverters) with the smaller inverters you can plug them straight into a cigarette lighter socket, with the mid size ones they come with crocodile clips, the large ones are always hard wired to the batteries, fixed with battery terminals, all sizes should have a fuse of some sort between it and the batteries. (Some fuses are built into the inverters)