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INTRODUCTION

Using solar panels to generate electricity is fun and saves money. This guide walks you through buying panels, as well as making your own panels if you cannot afford pre-made ones.

The planet is a ball of rock travelling through a vacuum at 108,000 km an hour (in orbit around a nuclear furnace). Motivation for going solar need not involve wanting to save it. Your motives for wanting to learn, save energy and have fun doing so are not my concern, but if you are intelligent (if you can think for yourself) or reasonably well educated (if bright people have already done most of your thinking for you), then sooner or later you will go solar.

Solar panels are made of silicon solar cells. The panels can have any configuration of voltage output depending on the voltage characteristics of the solar cells they contain (their quality),  the number of solar cells used to make up the solar panel, and the intensity of the light they are exposed to. The best (most efficient) solar cells in widespread production are mono-crystalline cells. They have a higher energy density than poly-crystalline solar cells (you need less of them for the same power output, so they take up less space).

12 VOLT SOLAR PANELS

Usually they kick out well over 12 volts in a 9 x 4 solar cell configuration. In other words, 12 volt panels normally produce over 20 volts (22v in strong direct sunlight). 24 volt panels produce much higher voltage than this. But voltage is only half the picture. What really matters is power output in Watts, and for this we have to include the concept of current in amps.

Volts x Amps = (Power) Watts

For example, if a '12 volt' solar panel has an output of 120 watts, and really is generating precisely 12 volts (which would be unusually low voltage for a 12 volt solar panel)...this can mean only one thing.
12 volts x (mystery value) = 120 watts. The mystery value (in Amps) must be 10 amps. So that would be a powerful solar panel.

The only equation you need to know merits repetition.
Volts x Amps = Watts

More realistically, a 12v solar panel will churn out 17-18v in moderate sunshine, and over 21v in strong direct sunlight. The current (in amps) will be between 4 and 7 amps...e.g. 21.5v x 4.75amps = 102 watts.

So when you see a 12 volt solar panel advertised on Ebay as being a 100w panel, this means that maximum power output in Watts (in strong direct sunlight) will be about 100w. It will likely have the same or similar voltage/current characteristics as the panel in our example.

Think of volts as speed...the velocity of the electricity, and amps as the current or flow of electricity, like the flow of water in a river in cubic metres per second (current) versus the velocity of the water in metres per second (voltage).

Add a bunch of solar panels together (in parallel...which means joining all the red positive output leads from the solar panels together in one clump and joining all the black negative output leads together in another separate clump as well...causing current to stack) and you can approach or exceed your daily electricity consumption requirements.

After the capital costs of buying or making solar panels have been incurred (as well as further costs for ancillary items such as inverters which I will come to in detail), your solar system will generate free electrical energy for approximately 20 years before you need to replace the solar panels (they degrade very slowly over 20 years, with effect that electrical output will be 80% that of new solar panels after about 20 years).

Note also that electricity consumption is confusingly measured (by utility companies) in non-S.I. units of kW/h (kilowatt/hours). A kilo-watt hour is a pseudo unit equal to 1000 watts (1kW) per hour. So if your solar panel array generates 5kW (5000 watts) for 1 hour, that would mean you have generated 5kW/hours of electricity.

Look for the maximum power output in Watts of your solar panels, and try to stick with 12 volt panels because they are easy to work with and work with most add-ons, such as 12 volt batteries for example.

Three 80 watt solar panels should cost about £300 (\$600) including delivery. Mono-crystalline panels are more efficient than Poly-crystalline panels and should be slightly more expensive. Most of the poly-crystalline panels you see on ebay are blue and shiny looking. More efficient mono-crystalline panels are black or dark grey looking. Resin solar panels are inefficient and should be avoided. They are black and have few if any lines or wires on their surface. They are also very heavy.

If you cant afford pre-made solar panels, you can make your own (if you are intrepid enough), but beware of the practical implications. You will need to order solar cells (the components from which solar panels are made) bearing in mind that normally, you will be ordering them in multiples of 36 for reasons I shall return to. First of all, solar cells are really brittle. Open the package from your supplier with great care. Press them too hard when soldering and they will shatter. Look at them sideways and they will shatter. They are quite literally wafer thin, and brittle would be an understatement. You will need soldering tab wire to interconnect the solar cells (the tops of the solar cells...the surfaces facing the sun...are always negative) and some Rosin flux (in a rosin pen or in a jar). You apply the flux to the lines you want to solder on and then apply the pre-tinned tabbing wire with a 40w soldering iron, or higher.

Don't use a pointy soldering tip on your soldering iron. That may be fine when soldering the connections of your Op Amp onto a circuit board, but it's completely out of bounds for solar cell work.

Pressure = Force/area. This is why you can push a drawing pin into a wall but cannot push your thumb into the wall. Accordingly, use a flat ended soldering iron. If it gets ragged at the end (as it most certainly will), unplug it and gently file it flat with a suitable file. Keep it flat and you won't say drat.

Normally, two tab wires are soldered onto the top of the cells, and two more wires are soldered onto the back of the cells. But stay with me for a moment here because four bits of wire must seem confusing. It isn't.

A common misconception is that the two wires coming from the top of the solar cells are negative and positive respectively. No. The top two wires (sunny side up) are both negative and the bottom two wires (on the papery looking back side of the cells, the side not exposed to the sun) are both positive. In other words, in theory you solder 4 wires onto each solar cell. If you do so, the top two would be negative and the bottom two would be positive. But in practice, you only need two double length tabbing wires. The two double length wires are soldered to the dotted lines on the papery base of the first cell to the two continuous white lines on the top of the following cell. In this way, two longer tabbing wires interconnect two distinct solar cells (stretching from the bottom of cell X to top of cell Y). Two more entirely separate wires travel from the bottom of cell Y to the top of cell Z and so on. Think string of cells, like batteries in a torch. Added together in series (pos to neg to pos to neg etc).

Some solar cells even have 3 wire slots for top and bottom. Same principle applies. Top 3 (sunny side up) will be negative and bottom 3 (dark side) will be positive, but I have never used that type of solar cell.

In any event, the cells stack together like watch batteries in series. The wafer thin cells should be thought of as batteries. It helps to avoid confusion. The positive tab wires from the bottom of cell A (both of them) are twice the length they need to be so they can be connected with soldering lines on the top of the next solar cell. Then you get a new double length pair of tab wires and connect the bottom of cell B to the top of cell C etc. Like making a paper chain.

However, a long string of solar cells would be cumbersome (several metres high), so generally we make the chain of solar cells double back on itself. in a sort of zig zag. When the first 9 cells reach the top of the frame we made for them, they double back down the panel. Do this 4 times and you have a conventional 36 cell panel solar panel. 9 x 4.

Thicker flat wire called Bus wire is used to collect power from the ends of the cell strings. Remember, both tabs from the silicon negative (sunny side up) cells are joined to Bus wire. Equally, both tabs from the lower (positive) papery side of the cells (that do not face the sun) are joined together onto a different strip of thick Bus wire. In that way you end up with one negative and one positive terminal when you are finished. Thin tabbing wire would melt if you tried to use it as Bus wire, due to higher power output from a whole line of cells.

In any event, each solar cell churns out circa 0.5 to 0.62 volts. When you arrange then in a continuous string (+ve to -ve to +ve to -ve and so on...using distinct lengths of tabbing wire) this 'series connection' results in higher voltage. Voltage stacks in series. Current only stacks in parallel. Accordingly, when you join 36 solar cells together (in a 9 x 4 string configuration for example), you get for example 0.5v x 36 = 18 volts...which is the lower end of what you would expect from a 36 cell panel. In stronger sun, you might get 0.62v from each solar cell (0.62 x 36) = 22.3 volts. This is perhaps the highest figure you would reasonably expect for voltage, certainly in terms of what I have come to expect from my own panels, whether I have made them myself or bought them pre-made.

But this is the crux of the matter. Voltage on its own is irrelevant without knowing about current in amps. This is because voltage x current = watts (power). One is useless without the other. Fast flowing water with a low mass flow rate (high voltage/low current analogy) delivers low force per F = m*a (low power from a solar panel).

Equally, slow flowing water (low voltage/high current analogy) delivers low power as well. Both factors must be adequate for reasonable power output.

It all depends on the performance and quantity of the solar cells in terms of your current output, but in broad brush terms, you can expect upwards of 6 amps current from a 36 cell solar panel. At 21.5 volts x 6 amps = 129 watts. That would be a powerful panel.

Making your own panels is difficult (despite what some people who like to appear clever tend to say) because the hardest part (assuming you can solder the cells together without breaking them and assuming you get your bus wire right) is protecting what you have made. Solar panels are like Swiss watches. They need to have an excellent protective casings or they will fill up with condensation and stop working. Don't throw cracked or broken cells away. You are almost certain to break some of them, but they should still work in secondary little panels if you tab them together. And remember, the best electronic engineers are the ones who keep going through the errors and mistakes and get the job done. Persistence is the key to success in electrical engineering.

FRAMES AND CELL PROTECTION

You will need a wooden or (preferably) aluminium frame to protect the panels. You will need a tempered glass front panel for hailstone impact protection or alternatively some UV resistant perspex (perspex that does not go yellow when exposed to sunlight for long periods).

You will need special heat resistant silicon sealant to seal the edges of the panel so as to waterproof it. Worst of all, you will need special liquid resin (Dow make SYL resin that is excellent) that you pour over the back of the solar cells when they are face down (sunny side down) on the panel glass (on a level surface).

You pour this stuff directly onto your finished (completely connected) solar cells, right onto the back of the solar cells when the sunny sides are pressing against the front glass panel. The resin spreads out and seals the panels, aided by a very soft brush to ensure the back of the cells are evenly covered. This protects them from condensation and inhibits cell movement after the resin sets. Critically, it remains clear when exposed to sunlight. Most liquid resins go yellow or powder white in sunlight, and are useless for solar panels.

This specially made stuff DOW SYL stays clear. You can get similar products from other manufacturers as well but be careful what you pour onto the back of your solar cells. After spending that much time soldering and replacing broken cells you leant on to hard, there is nothing worse than getting the wrong resin or failing to make the protective frame for the panels properly.

There is not much of the right resin stuff about, and it costs about 50 sheets for 2 litres at the moment. Finding pre-made aluminium panels for your home made solar cell array is also difficult, short of importing them from China.

Incidentally, there is no duty on solar panels imported from China into the UK (so far as I am aware...at the time of writing). Importation fees seem to be relatively low, and logistics expenses should not be too bad either. Double check this before ordering, but it may be worth your while ordering a 'minimum order' direct from a manufacturer. This could be 100 panels or 50 panels or sometimes even 25 panels, for say \$6,000 US dollars.

A bunch of 25 high end panels from China (perhaps upwards of 300w from a single panel) could work out nicely... maybe keeping 15 for yourself and selling the rest on Ebay. Do the maths and see if it works. Alibaba is a good site for bulk purchases direct from Chinese manufacturers if you can handle the minimum order requirement and the shipping and other importation costs.

Getting back on point, the liquid silicon will set after a day or so, preferably without air bubbles (table must be dead level and you should use a stepper motor to vibrate the table to minimise bubbles when it is setting). In passing, broken laser printers are a good source for salvaging stepper motors. Printers pretty much all contain stepper motors, and if you strap one of these to the table you use to set your DOW SYL resin and power it up, that should really help reduce air bubbles.

Anyway, you should then seal the back of the panels with white liquid silicon (if you want to be a real pro), solder on a junction box to make connections easy and solder a diode into the positive output cable for reverse current protection (to stop your solar panel becoming a resistive load).

Hard work. But immensely satisfying. I recommend building at least one panel of your own from scratch. It is a useful thing to know how to do.

Getting back to pre-made panels, 24 volt panels can have efficiency improvements but they are not compatible with many widely available components so I stick with 12v panels to avoid frying anything.

If you have three 80 watt panels, each panel can generate up to 80 watts of power in strong direct sunlight. Three such panels will have a maximum electrical power output of 240 watts.

You can test the output of a solar panel with a multimeter. Measuring voltage is easy. But measuring current requires you to break the circuit by adding a small load...such as a solar voltage regulator. Check out videos on Youtube if you want to learn more about measuring voltage and current output from solar panels (remember that volts x amps = watts).

The more solar panels you buy, the higher the maximum power they deliver in combination. Check out the critical difference between connecting solar panels in parallel (to increase current...which is good) and connecting them in series to increase voltage (which is not recommended).

Power output depends on the amount of light falling on the panels...so in strong direct sunlight, you will invariably get maximum or close to maximum output from your panels. But in overcast conditions, you may only get 8 or 10 watts from an 80 watt solar panel (though you should get 20 or 30 watts if three 80 watt panels are joined together in slightly overcast conditions). Also, if you are in the UK, try to get MCS certified panels (approved by the government for grid tie systems). You may want the panels to be approved at some later point.

Ok. So you buy some solar panels...but what next?

GRID TIE INVERTERS

Get hold of a 'grid tie inverter'. A whichy whatty? Plenty of 350 watt grid tie inverters on Ebay only cost about £75 (\$150) or less, including delivery. I am not talking about proprietary inverters that cost a fortune and look like washing machines. These ingenious little devices that began appearing from about late 2010 onwards, take the electricity from your solar panels (any 12v solar panels) and pump it directly into your mains supply (any UK mains supply), slowing down your meter or even making the meter go backwards depending on the power your panel array generates. US versions are available, synched to 120v mains supply.

A Grid Tie Inverter has a typical electrical mains plug on it, but instead of consuming electricity when you plug it in, a Grid Tie Inverter...this is the clever bit... converts the direct current from your solar panels into mains Alternating Current, and pumps that converted solar electricity back INTO your electrical mains.

It converts the direct current (DC) power output of your solar panels into Alternating Current (AC) perfectly compatible with your mains electricity supply (so if you buy one in the UK, it will have 220 to 240 volt output and operate at about 60 Hertz).

In other words, the power coming from your solar panels (via a red (+ ve) positive cable and a black (- ve) negative cable) is connected to the back of the grid tie inverter (which also has two terminals, a black -ve one and a red +ve one).

When connecting solar panel leads to grid tie inverters, make sure you get the polarity right. Which is to say, connect red positive wires from the solar panels to the red positive terminal at the back of the grid tie inverter. Connect the black negative output cables from the solar panels to the black negative terminal at the back of the grid tie inverter.

Then, put your solar panels outside at a good angle to pick up as much sunlight as possible (south facing...about 45 degree inclination), and plug your grid tie inverter into your mains electricity...press the switch on the wall-socket  on and the switch on the grid tie inverter on and hey Presto. You are no longer an electrical moron. You are generating your own electricity. Congratulations.

The solar energy from your panels is now being converted into mains electricity...which is going back into your mains supply via the grid tie inverter...even though you have plugged it into the wall and even though this normally means an appliance is consuming electricity.

And this is the whole point. Instead of consuming electricity when you plug it into the wall, a grid tie inverter (connected to solar panels exposed to light) actually supplies electricity to your mains supply. It can even make your electricity meter run backwards...or at least slow the rate of your electricity consumption.

HIGH CONSUMPTION DEVICES - THE MORONIC INFERNO

Now you are generating your own electricity and putting it straight into the wall socket, you may want to begin thinking about reducing your electricity consumption.

A good place to start is by checking all your appliances' power consumption. They should be labelled with this information.

If you cannot find power consumption in Watts on the label, simply multiply your mains voltage (240v in the UK/120v in the US) by the current in amps marked on the device to calculate power consumption in Watts. Avoid using power hungry devices for prolonged periods.

Next, replace your halogen bulbs and so called 'low energy' mercury vapour bulbs with screw-in or bayonet type LED bulbs (which consume only about 10% of the power of conventional halogen bulbs for the same visible light output).

LED bulbs are more expensive, but they should last many more years (perhaps 25 years). Your energy savings will be considerable.

By way of example, a 6 watt LED bulb provides the same visible light (in lumens per square meter or lux) as a 60 watt halogen bulb.

Fancy reducing your lighting bill by 90%? Well just get on with it then. Try to overcome innate moronic impulses (which is to say, try to ignore the voice that says...'halogen bulbs are fine...these mercury vapour bulbs claim to be low energy...). Switch to LED bulbs now. Don't be a dunce.

Get rid of those crappy toxic mercury vapour bulbs. Bin the horrific halogens. Switch to mains powered LED bulbs as soon as you can.

A 6w LED bulb (60w halogen equivalent) will cost about £15 (\$30), but they should last for many years. A 60w LED bulb (600w halogen equivalent...6,000 lux...lu/m2) will cost about £100 (\$200). But long term, they will save you a lot of money.

In summary, a few solar panels added to a grid tie inverter should be capable of supplying most if not all of your domestic lighting power requirements...for 20 years or more.

FURTHER THOUGHTS

Keep your grid tie inverter below the solar panel maximum output. If you have three 80 watt solar panels (240 watt maximum output in strong direct sunlight), connect them to a 350 watt grid tie inverter. Do not be tempted to add another solar panel (making 320 watt max) as this may well overload a 350w grid tie inverter in really strong sunlight. They have a 300w continuous operating capability even if they claim they are 350w GT inverters.

So leave a good 20% margin so you don't overstretch your grid tie inverter.

Solar panels can sometimes exceed their stated maximum output in very strong direct sunlight. In other words, a 100w panel could churn out 110w in really strong direct sunlight. This is because solar panels are normally tested for output in a laboratory under light power input of 1000 watts per square metre. But real world conditions can sometimes exceed 1000 watts per square metre (such as for example when sunlight approaches maximum recorded levels of about 120,000 lumens per square metre (120k lux). If it is very sunny but temperatures are relatively low (e.g. if it is cool outside but the sunlight is very strong), panel specifications can be exceeded. Equally, if there are reflective sky conditions or light is somehow reflected onto the solar panels from mirrors, windows or other reflective surfaces, this can have the effect of amplifying or concentrating light falling on solar panels and boost their output in watts.

I have measured 86 watts of output from an 80 watt solar panel in strong direct sunlight, but why should I care about this? What is the problem if the panels operate better than expected?

The answer is that you want to avoid overloading your grid tie inverter. Don't have 4 x 80w panels connected to a 350w grid tie inverter. The notional 320w max output of the panels could well be exceeded. Leave a wide safety margin. A 350w GT inverter may well have continuous operational parameters of 300w (not 350w) so stay below the ceiling of your GT inverter unless you like them crispy.

Also, use thick 10 AWG wire or better to handle current you expect from your panels on very sunny days. These panels really work...producing dangerous levels of current, so take proper safety precautions (wear boots and gloves) or better still, get a friend who is an electrician to help if you are unsure about anything.

If you are careful with the appliances you use (60 watt laptops instead of 600 watt desktop computers), a micro-solar system is capable of supplying much essential power to your home and without doubt, your lighting requirements can easily be covered for the next 20 years or so even with low output panels.

High power consumption items such as kettles and vacuum cleaners consume a lot of power (1500 watts, sometimes 3000 watts) but...they are only on for short periods. They do not substantially increase your electricity bill. However, moderate consumption devices left on standby continuously do most of the damage (wide screen TVs seem to consume hundreds of watts even when on standby).

OFF GRID

If you want to charge 12 volt batteries on the other hand, you cannot use a Grid Tie Inverter. For off-grid applications (such as using a bank of batteries charged via solar panels), instead you must get hold of a solar charge regulator.

A 20 amp solar charge regulator will cost you about £20 (\$40). The purpose of a charge regulator is to prevent batteries being damaged through overcharging or over-discharging. For example, if you were to connect a 12 volt lead acid battery directly to your solar panels, it would start off fine as the panels charged the battery, but after an indeterminate period, the solar energy would overcharge and seriously damage your battery. A solar charge regulator prevents this from happening by turning off the charging power when the battery voltage hits a predetermined level (for example, 12.5 volts or 14 volts depending on the type of battery).

But it also prevents your battery being over discharged. If, for example, you were to connect a conventional (non-grid tie) inverter to your 12v battery (a device that converts 12v DC into 120 or 240v AC), and then connect a light or a TV to the battery, the battery will be damaged when too much power is drained from it. Solar charge regulators prevent these problems and your battery will last for up to 7 years or more, as opposed to failing within a few days.

If you really want an off grid system in which you store your solar energy in batteries, try to get good Gel (sealed ) batteries capable of deep cycle work. The expression 'deep cycle' means batteries that can be charged and discharged over and over again without losing much of their capability. Avoid discharging these batteries below 50% of their total charge capacity as a rule of thumb (e.g. get more batteries and join them together).

Sealed deep cycle gel batteries are excellent. They do not emit flammable hydrogen gas. But conventional lead acid auto batteries do and should be avoided in the home.

Whatever your preference, Conserve energy. Do this for your own sake, and for the sake of others...because there is no planet B.

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