Solar Electricity Handbook 2011: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems - Michael Boxwell (2011)
Congratulations on getting this far. If you are doing this for real, you will now have a garage or garden shed full of solar panels, batteries, cables, controllers, isolation switches, RCDs and whatnots. The planning stage is over and the fun is about to begin.
Before you get your screwdriver and drill out, there are just a few housekeeping items to get out of the way first…
Have you read the instructions?
No, of course you haven’t. Who reads instructions anyway? Well, on this occasion, it is worth reading through the instructions that come with your new toys so that you know what you are playing with.
Pay particular attention to the solar controller and the inverter: there are many settings on most controllers and you need to make sure you get them right.
There are a few safety notices we ought to go through. Some of these may not be relevant to you, but read them all first, just to make sure.
Remember, you are working with electricity, dangerous chemicals and heavy but fragile objects. It is better to be safe than sorry.
Your First Aid kit
You will need a good First Aid kit on hand, including some items that you will not normally have in a regular First Aid kit. Most specifically, you will need an eye-wash and a wash kit or gel that can be applied to skin in case of contact with battery acid.
Chemical clean-up kit
You will be working with lead acid batteries that contain chemicals that are hazardous to health. You will require the following:
· A chemical clean-up kit suitable for cleaning up battery acids in the case of a spill
· A supply of strong polythene bags
· A good supply of rags/ disposable wipes to mop up any battery spillages
Chemical clean-up kits and chemical First Aid kits are available from most battery wholesalers and industrial tool suppliers. They only cost a few pounds. You probably will not need them but, if nothing else, they buy you peace of mind.
Considering the general public
If you are working in an area where the general public has access, you should use barriers or fencing, and signage to cordon off the area. Clear diversion signage should explain an alternative route.
In this scenario, I would recommend employing a professional team of builders to carry out the installation work on your behalf. They will already understand the implications of working in a public area and the relevant Health and Safety regulations.
Even if you do not have to consider the general public, you should still consider the people around you. Children love to get involved with these sorts of projects and there really can be some safety issues involved. Keep children out of the way, and let anyone in the vicinity know that you are working with high voltages and to keep away.
Working at height
You are very likely to be working at height and quite possibly crawling around on slanted rooftops.
Make sure you are using suitable climbing equipment (ladders, crawler boards, safety harnesses, scaffolding). You can hire anything that you do not have at reasonable prices.
If you have any concerns about working at heights, or if you are working beyond your area of competence at any time, remember there is no shame in hiring a professional. A professional builder can fit a solar array to a roof in 2–3 hours. This is typically less than half the time it takes an amateur DIY enthusiast.
Batteries, large inverters and solar arrays can be heavy. Solar panels themselves may not be heavy in their own right, but when several of them are mounted on a frame and then lifted they are heavy, bulky and fragile.
Moving and installing much of this equipment is a two-person job as a minimum. More people can be useful when lifting a solar array into position.
Working with batteries
Lead acid batteries are extremely heavy, in some cases weighing as much as an adult. Use proper lifting gear to move them, and look after your back.
Heavier batteries quite often have hoops in the top case. To lift a battery, I tend to use a piece of rope threaded through these hoops to create a carrying handle. This means I can carry a battery close to the ground and reduce the need to bend over to lift it.
Lead acid batteries contain acid. Unless they are gel batteries, the acid is in liquid form. It is extremely corrosive and extremely dangerous to health. Splashes of liquid from the batteries can cause severe chemical burns and must be dealt with immediately.
When working with lead acid batteries, stay safe:
· ALWAYS wear protective clothing, including overalls, eye protection (either protective glasses or a full-face shield) and protective gloves. I would also advise you to wear steel toe-capped shoes
· Keep batteries upright at all times
· Do not drop a battery. If you do, the likelihood is that the battery has been damaged. In the worst-case scenario, the casing could be cracked or broken
· If you drop a battery, place it immediately in a spill tray (a heavy-duty deep greenhouse watering tray can be used if necessary) and check for damage and leaks
· If you have a damaged battery, both the battery and the spill tray must be double-bagged in sealed polythene bags and marked as hazardous waste
· If you have a spillage from a battery, mop up the spillage immediately using rags or disposable wipes. Place these rags in a polythene bag, seal it and mark it as hazardous waste
· If any spillage from a battery comes into contact with clothing, remove clothing immediately and dispose of it in polythene bags
· If any spillage from a battery comes into contact with the eyes, wash repeatedly with eye-wash and seek urgent medical help
· If any spillage from a battery comes into contact with the skin, wash off immediately with water, apply an anti-acid wash, cream or gel to stop burning and then seek urgent medical help
· If you end up with battery acid in your mouth, wash your mouth out with milk. DO NOT swallow the milk. Spit it out. Then seek urgent medical help
· Do not smoke near batteries, and ensure that the area where you are storing the batteries is ventilated
· Prevent arcing or short circuits on battery terminals. Batteries can provide a huge current very quickly. Should you short-circuit a battery with a spanner, the spanner is likely to be red hot within a few seconds and could easily lead to fire or explosion. Remove any rings, bracelets or watches you may be wearing and keep tools a safe distance away from batteries
You need two different sets of gloves for installing your solar array: a set of chemical gloves for moving batteries and a set of electrical protection gloves for wiring up your solar system.
When choosing suitable chemical gloves for working with batteries, consider the following:
· The gloves need to be quite strong, as lifting and moving batteries is hard on gloves
· A good grip is important
· Buy a glove with a medium or long cuff length, in order to protect both the hands and forearms
· The gloves should be made of a suitable material to protect against battery acid
The Health and Safety Executive website suggest that 0.4mm-thick neoprene gloves will give suitable protection through a full shift. If you do splash your gloves while working with batteries, make sure you wash them or replace them immediately, in order to avoid transferring acid to other parts of your body.
Electrically-insulated protection gloves give protection when working with high voltages. These are vitally important when working with high-voltage solar arrays and are recommended for all installations.
Electrically-insulated gloves come with different ratings to provide protection at different voltages:
· Class 00 gloves provide protection for up to 500 volts
· Class 0 gloves provide protection for up to 1,000 volts
· Class 1 gloves provide protection for up to 7,500 volts
· Class 2 gloves provide protection for up to 17,000 volts
· Class 3 gloves provide protection for up to 26,500 volts
For most solar installations, Class 00 or Class 0 gloves are the most appropriate. Remember that the open circuit voltage of a solar array can be more than double the nominal voltage of the solar array: twenty solar panels connected in series may only have a nominal voltage of 240 volts, but the open circuit voltage could be over 500 volts.
Like chemical gloves, choose gloves with a medium or long cuff length to protect both your hands and forearms.
If your electrically-insulated gloves are splashed with battery acid, remove and replace the gloves immediately.
All electrically-insulated gloves should be visually inspected and checked for tears and holes before use. Class 1–3 gloves require full electrical testing every six months.
I make no apologies for repeating my mantra about electrical safety. Electrical safety is extremely important when installing a solar electric system.
Solar panels generate electricity whenever they are exposed to sunlight. The voltage of a solar panel on an ‘open’ circuit is significantly higher than the system voltage. A 12-volt solar panel can generate a 22–26 volt current when not connected.
Connect several solar panels in series and the voltage can get to dangerous levels very quickly: a 24-volt solar array can generate 45–55 volts, which can provide a nasty shock in the wrong circumstances, whilst a 48-volt solar array can easily generate voltages of 90–110 volts when not connected. These voltages can be lethal to anyone with a heart condition, or to children, the elderly or pets.
Solar systems produce DC voltage. Unlike AC voltage, if you are electrocuted from a direct current, you will not be able to let go.
Batteries can produce currents measuring thousands of amps. A short circuit will generate huge amounts of heat very quickly and could result in fire or explosion. Remove any rings, bracelets or watches you may be wearing and keep tools away from batteries.
The output from an inverter is AC grid-level voltage and can be lethal. Treat it with the same respect as you would any other grid-level electricity supply.
In many countries, it is law that if you are connecting an inverter into a household electrical system, you must use a qualified electrician to certify your installation.
Assembling your toolkit
As well as your trusty set of DIY tools, you will need an electrical multi-meter or volt meter in order to test your installation at different stages. You should use electrically-insulated screwdrivers whilst wiring up the solar array, and a test light circuit tester can be useful.
There are a few sundries that you ought to have as well:
· Cable ties are very useful for holding cables in place. They can keep cable runs tidy and are often good for temporary as well as permanent use
· A water- and dirt-repellent glass polish or wax, for cleaning solar panels
· Petroleum jelly is used on electrical connections on solar panels and batteries in order to seal them from moisture and to ensure a good connection
Preparing your site
As mentioned in the previous chapter, you may need to consider foundations for ground- or pole-mounting a solar array, or strengthening an existing roof structure if you are installing your solar array on a roof.
If you are installing your batteries in an area where there is no suitable earth (ground), you should install an earthing rod (grounding rod) as close to the batteries as is practical.
Testing your solar panels
Now the fun begins. Start by unpacking your solar PV panels and carry out a visual inspection to make sure they are not damaged in any way.
Chipped or cracked glass can significantly reduce the performance of the solar panels, so they should be replaced if there is any visible damage to the panel. Damage to the frame is not such a problem, so long as the damage will not allow water ingress to the panel and does not stop the solar panel from being securely mounted in position.
Next, check the voltage on the panel using your multi-meter, set to an appropriate DC voltage range.
Solar PV panels generate a much higher voltage on an ‘open’ circuit (i.e. when the panel is not connected to anything) than they do when connected to a ‘closed’ circuit. So do not be surprised if your multi-meter records an open voltage of 20–26 volts for a single panel.
Installing the solar array
Cleaning the panels
It is a good idea to clean the glass on the front of the panels first, using a water- and dirt-repellent glass polish or wax. These glass polishes ensure that rain and dirt do not stick to the glass, thereby reducing the performance of your solar array. They are available from any DIY store and many supermarkets and car accessories stores.
Assembly and connections
Some roof-mounted solar mounting kits are designed to be fitted to your roof before fitting the solar panels. Others are designed to have the solar panels mounted to the fixing kits before being mounted to the roof.
With a pole-mounted system, you typically erect your pole first and then fit the solar panels once the pole is in position.
A ground-based mounting system is the easiest to install, as there is no heavy lifting.
Typically, you mount and wire the solar panels at the same time. If you are stepping up the voltage of your system by wiring the panels in series, wire up the required number of panels in series first (i.e. sets of two panels for 24 volts, sets of four for 48 volts).
Once you have wired up a set of panels in series, test them using your multi-meter, set to a voltage setting to check that you have the expected voltage (20 volts plus for a 12-volt system, 40 volts plus for a 24-volt system and 80 volts plus for a 48-volt system).
Take care when taking these measurements, as 40 volts and above can give a nasty shock in the wrong circumstances.
Once you have wired each series correctly, make up the parallel connections and then test the entire array using your multi-meter, set to the appropriate voltage setting.
If you have panels of different capacities, treat the different sets of panels as separate arrays. Do not wire panels of different capacities together, either in series or parallel. Instead, connect the arrays together at the controller.
Once you have completed testing, make the array safe so that no one can get an electric shock by accident from the system. To do this, connect the positive and negative cables from the solar array together to short-circuit the array. This will not damage the array and could prevent a nasty shock.
Roof-mounting a solar array
If you are roof-mounting a solar array, you will normally have to fit a rail or mounting to the roof before attaching the solar array.
Once this is in place, it is time to fit the array itself. Make sure you have enough people on hand to be able to lift the array onto the roof without twisting or bending it. Personally, I would always leave this job to professional builders, but the best way seems to be to have two ladders and two people lifting the array up between them, one on each ladder, or using scaffolding.
Once your solar array is in position, route the cable down to where the solar controller is to be installed. For safety purposes, ensure that the cables to the solar array remain shorted whilst you do this.
If you are installing a DC isolation switch and a residual current device (known as a ground fault interrupter in North America), install them between the solar array and the controller.
Once you have the cables in position, un-short the positive and negative cables and check with a meter to ensure you have the expected voltage readings. Then short the cables again until you are ready to install the solar controller.
Installing the batteries
Before installing the batteries, you may need to give them a refresher charge before using them for the first time.
You can do this in one of two ways. You can use a battery charger to charge up the batteries, or you can install the system and then leave the solar panels to fully charge up the batteries for a day or so before commissioning the rest of the system.
Put a sticker on each battery with an installation date. This will be useful in years to come for maintenance and troubleshooting.
Positioning the batteries
The batteries need to be positioned so they are upright, cannot fall over and are away from members of the public, children and any sources of ignition.
For insulation and heating purposes, batteries should not be stood directly on a concrete floor: during the winter months, a slab of concrete can get extremely cold and its cooling effects can have detrimental effects on batteries. I prefer to mount batteries on a wooden floor or shelf.
If there is little or no ventilation in the area where the batteries are situated, this must be implemented before the batteries are sited.
As batteries vent hydrogen, which is lighter than air, the gas will rise up. The ventilation should be designed so that the hydrogen is vented out of the battery area as it rises.
It is important that the battery area is easily accessible, not just for installing the batteries (remembering that the batteries themselves are heavy), but also for routinely checking the batteries.
As mentioned earlier, if you are installing your batteries in an area that can get very cold or very hot, you should insulate your batteries.
Polystyrene (Styrofoam) sheets or foil-backed bubble-wrap can be used underneath and around the sides of the batteries to keep them insulated. DO NOT INSULATE THE TOP OF THE BATTERIES as this will stop them from venting properly and may cause shorts in the batteries if the insulating material you use is conductive.
Once the batteries are in place, wire up the interconnection leads between the batteries to form a complete battery bank.
Always use the correct terminals for the batteries you are using and make sure the cables provide a good connection. You should use battery interconnection cables professionally manufactured for the batteries you are using.
Use petroleum jelly around the mountings to seal it from moisture and ensure a good connection.
Next, add an earth (ground) to the negative terminal. If there is no earth already available, install an earthing rod (grounding rod) as close as possible to the batteries.
Now check the outputs at either end of the batteries using a multi-meter to ensure you are getting the correct voltage. A fully-charged battery should be showing a charge of around 13–14 volts per battery.
Installing the control equipment
The next step is to install the solar controller and the power inverter if you are using one.
Mount these close to the batteries. Ideally they should be mounted within a metre (3 feet), in order to keep cable runs as short as possible.
Most solar controllers include a small LCD display and a number of buttons to configure the controller. Make sure the solar controller is easily accessible and that you can read the display.
Some solar controllers that work at multiple voltages have a switch to set the voltage you are working at. Others are auto-sensing. Either way, check your documentation to make sure you install the solar controller in accordance with the manufacturer’s instructions. If you have to set the voltage manually, make sure you do this now, rather than when you have wired up your system.
Inverters can get very hot in use and adequate ventilation should be provided. They are normally mounted vertically on a wall, in order to provide natural ventilation. The installation guide that comes with your particular make of inverter will tell you what is required.
Some inverters require an earth (ground) in addition to the earth on the negative terminal on the battery. If this is the case, connect a 2.5mm² green-yellow earth cable from the inverter to your earth rod (ground rod).
If you are installing a DC isolation switch between the solar panels and your control equipment, connect that up first and make sure it is switched off.
Once you have mounted the controller and inverter, connect the negative cables to the battery, taking care that you are connecting the cables to the correct polarity. Then un-short the positive and negative cables from the solar array and connect the negative cable from the solar array to the solar controller, again taking care to ensure the cable is connected to the correct polarity.
Now double-check the wiring. Make sure you have connected the cables to the right places. Double-check that you have connected your negative cable from your solar array to the negative solar input connection on your solar controller. Then double-check that you have connected your negative cable from your battery to the negative battery input on your solar controller and your inverter. Only then should you start wiring up your positive connections.
Start with the battery connection. If you are planning to install a fuse and DC isolation switch into this cable, make sure that your fuse and switch work for both the solar controller and the inverter (if you are using one). Connect the inverter and the solar controller ends first and double-check that you have got your wiring correct, both visually and by checking voltages with a volt meter, before you connect up the battery bank.
Finally, connect up the positive connection from your solar array to the solar controller. At this point, your solar controller should power up and you should start reading charging information from the screen.
Congratulations. You have a working solar power station!
Installing a grid-tie system
Before starting to install your grid-tie system, you must have already made arrangements with your electricity provider for them to set you up as a renewable energy generator.
Regulations and agreements vary from region to region and from electricity provider to electricity provider, but at the very least they will need to install an export meter to your building in order to accurately meter how much energy you are providing. They will also ask for an inspection certificate from a qualified electrician, to confirm that the work has been done to an acceptable standard.
Physically, installing a grid-tie system is very similar to installing any other solar energy system, except, of course, you do not have any batteries to work with.
However, you do have to be careful while wiring up the high-voltage solar array. When the solar array is being connected up you can have a voltage build-up of several hundred volts, which can quite easily prove fatal. If building a high-voltage array, cover the solar panels while you are working on them and wear electrically-insulated gloves at all times.
Commissioning the system
Once you have stopped dancing around the garden in excitement, it is time to test what you have done so far and configure your solar controller.
Programming your solar controller
The type of solar controller you have will determine exactly what you need to configure. It may be that you do not need to configure anything at all, but either way you should check the documentation that came with the solar controller to see what you need to do.
Typically, you will need to tell your solar controller what type of batteries you are using. You may also need to tell your solar controller the maximum and minimum voltage levels to show when the batteries are fully charged or fully discharged. You should have this information from your battery supplier, or you can normally download full battery specification sheets from the internet.
Testing your system
You can test your solar controller by checking the positive and negative terminals on the output connectors on the controller using your multi-meter. Switch the multi-meter to DC voltage and ensure you are getting the correct voltage out of the solar controller.
If you have an inverter, plug a simple device such as a table lamp into the AC socket and check that it works.
If your inverter does not work, switch it off and check your connections to the battery. If they are all in order, check again with a different device.
Charging up your batteries
If you have not carried out a refresher charge on your batteries before installing them, switch off your inverter and leave your system for at least 24 hours in order to give the batteries a good charge.
Connecting your devices
Once you have your solar power station up and running and your batteries are fully charged, it is time to connect your devices.
If you are wiring a house using low-voltage equipment, it is worth following the same guidelines as you would for installing grid-voltage circuits.
For low-voltage applications, you do not need to have your installation tested by a qualified electrician, but many people choose to do so in order to make sure there are no mishaps.
The biggest difference between AC wiring and DC wiring is that you do not need to have a separate earth (ground) with DC electrics, as the negative connection is earthed both at the battery and, if you are using one, at the distribution panel.
If you are using 12-volt or 24-volt low-voltage circuits, you can use the same distribution panels, switches and light fittings as you would in a grid-powered home. As already suggested, do not use the same power sockets for low-voltage appliances as you use for grid-powered appliances. If you do, you run the risk that low-voltage appliances could be plugged directly into a high-voltage socket, with disastrous consequences.
· Once you have done all your preparation, the installation should be straightforward
· Heed the safety warnings and make sure you are prepared with the correct safety clothing and access to chemical clean-up and suitable First Aid in case of acid spills
· Solar arrays are both fragile and expensive. Look after them
· The most likely thing that can go wrong is wiring up something wrongly. Double-check each connection
· Check each stage by measuring the voltage with a multi-meter to make sure you are getting the voltage you expect. If you are not, inspect the wiring and check each connection in turn