5. Installation and Commissioning
Before commencing the installation it is important to familiarise yourself with the manufacturer’s instructions supplied with each of the components. The site visit will have allowed you to identify a mounting position for each item. It will be helpful to draw a wiring diagram before starting the installation. Every system will be different, but see appendix 4 for example wiring diagrams.
There is no correct order for the installation of the various system components, only their eventual connection and commissioning.
5.1 Safety
At all times during the installation, the safety of the installers and public must be paramount. Keep the public away from the installation site at all times, using barriers or fencing where necessary. Pay particular attention to the safety of children.
5.1.1 Electrical
Although solar power systems are generally low voltage, always observe the wiring regulations for the country of installation. Bear in mind the following:
- Inverter output is mains voltage AC and can be lethal. Treat as for any other mains supply.
- Solar arrays generate electricity when exposed to the sun, whether connected to control equipment or not. Treat solar array output cables as live and cover solar array when making connections.
- The open circuit voltage of a solar array is significantly greater than the system voltage. For example a 48 Volt array can have an open circuit voltage of nearly 90 Volts, which can be lethal to children, the elderly or anyone with a heart condition.
- Batteries can produce currents of hundreds or even thousands of amps giving rise to the risk of fire. Take great care to protect the battery terminals from shorting by tools and remove all jewellery.
If in any doubt about your abilities, or if required by local regulations, then a qualified electrician must be employed.
5.1.2 Chemical
Lead acid batteries contain dilute sulphuric acid and liberate hydrogen when charging. Observe the following precautions:
- Take great care when filling batteries with electrolyte; wear suitable protective clothing including eye protection and carry out in a well ventilated area, preferably outdoors.
- Do not smoke near batteries and ensure room is well ventilated.
- Take care to prevent arcing near battery terminals as explosion may result.
- Keep first aid and eyewash equipment close at hand when working on batteries.
5.1.3 Handling
Batteries and solar arrays present certain hazards in handling as follows:
- Lead acid batteries are extremely heavy. Use appropriate lifting gear and ensure adequate help is available.
- Most solar panels are made from glass. Treat as fragile.
- Installing solar arrays may involve working at height. Observe all necessary precautions and employ the services of a qualified rigger or roofer if necessary.
5.2 Array
The installation of the solar array is determined by the type of support structure, but is normally completed in three stages. The photographs accompanying this section were taken during a solar power course in Angola, and illustrate some of the difficulties faced when certain tools and equipment are unavailable.
5.2.1 Assembly
Before fixing to the roof or ground the solar panels must be mounted to the support rails to create a single unit. In larger systems the solar array may be split into sub-arrays. Each of these is treated as a separate solar array.
If a proprietary support structure is used then the correct nuts and bolts will be supplied. Otherwise use high-tensile nuts and bolts the correct size for the mounting holes in the solar panels, and ensure that either locking washers or self-locking nuts are used to prevent loosening as a result of vibration due to the wind.
Lay the solar panels face down in the correct alignment. Ensure that the ground is flat; a grassed area is ideal. Place a blanket or similar on the ground to avoid any damage to the glass. Bolt the mounting rails to the solar panels, taking care to ensure that no strain is placed upon the solar panels. Do not put any weight on the solar panels themselves.
5.2.2 Connection
It is usually easiest to connect the individual solar panels together and connect the long output cable to them before putting them into position, especially if they are to be roof mounted. Connect all the solar panels together first; either in one, two or four groups depending on the system voltage and then connect the output cable. Check that all connections are sound before replacing the terminal box covers as this is hopefully the last time you will see them.
5.2.3 Testing
It is best to test the solar array before mounting to avoid having to take it down again. To do this, turn it over and lay it on the ground face up. Make sure you have enough people helping to avoid twisting or dropping the solar array.
Using a multimeter set to an appropriate DC Voltage range, measure the voltage between the two cores of the output cable. It should be equivalent to the open-circuit voltage of one solar panel multiplied by the number of solar panels in series. That is, about 20 V for a 12 V system, 40 V for a 24 V system and 80 V for a 48 V system. 80 Volts is a dangerously high voltage, and 40 Volts is enough to give a nasty shock in the wrong circumstances; take care when performing these measurements and cover the solar array with an opaque material before connecting the meter if in any doubt.
Once this test is complete it is advisable to make the solar array safe before lifting it into place. There are two ways of doing this; either cover it with an opaque material or connect the cores of the output cable together to short-circuit the solar array. This will not cause any damage and is my preference.
5.2.4 Mounting
Once you are certain that the solar array is correctly assembled it is time to lift it into place and secure it. Usually there are a number of rails to be mounted to the roof or foundations first. Ensure that these are orientated correctly so that the solar array will point towards the equator once mounted; that is towards the south in the northern hemisphere and towards the north in the southern hemisphere. Use appropriate fixings and follow safe working practices for working on roofs where appropriate.
Assemble a team of sufficient number to lift the solar array into place without bending it. Often the best method is to place two ladders parallel to each other and walk up them with the solar array in between. Often there is only one ladder in the village though, so you may have to improvise.
Carefully lift the solar array into position on the mounting rails. Assemble using the correct nuts and bolts. If the mounting structure is adjustable for tilt, now is the time to set it. Support the solar array whilst making any adjustments and set the tilt based on the latitude of the location as follows:
- Optimised for winter, e.g. lighting systems in temperate zones: Angle of latitude +15º from the horizontal.
- Optimised for summer, e.g. holiday homes: Angle of latitude -15º from the horizontal.
- All year round performance, e.g. medical systems in the tropics: Angle from the horizontal equal to angle of latitude.
Do not set the tilt to less than 10º from the horizontal whatever the latitude, as a tilt of less than this will allow dirt to build up on the solar array which will reduce its performance.
5.3 Battery
Installation of the battery may be as simple as taking a wet-charged or sealed battery out of a box and placing it on a firm and level surface. Alternatively it may involve mixing acid to the right concentration and filling the batteries on site.
5.3.1 Siting
The batteries need to be mounted such that they are secure, i.e. they can’t fall over, they are protected from unauthorised access and away from sources of ignition. The room or container that they are in should be ventilated so as to allow the hydrogen produced by charging to escape. This applies even to sealed batteries as they are able to vent excess gasses should the charging system malfunction.
Practically this is most likely to mean one of two things:
- On a solid floor or racking within a locked and well ventilated room.
- In a purpose designed battery box.
It is important that it is possible to gain access to the batteries in order to perform maintenance. In the case of a sealed battery this means the terminals, but for a vented battery it may mean access to the level markings on the side and the filling caps.
5.3.2 Commissioning
It may be necessary to commission the batteries either before taking them to site or once at site. Always follow the manufacturer’s instructions and, if it is not possible to do exactly as instructed, ask the manufacturer or supplier for advice. Correct battery commissioning is vital to the proper performance of the battery. General instructions are as follows.
5.3.2.1 Sealed batteries
Sealed batteries of both gel and AGM types are always supplied filled and usually charged. It may be necessary to give them a refresher charge before putting them into service. This should be performed with a regulated mains charger if possible. If this can’t be done for any reason then the system should be used as little as possible for the first 24 hours in order to allow the batteries to become fully charged.
5.3.2.2 Wet batteries
When batteries are supplied already filled with electrolyte, they are usually charged and are treated in the same way as described for sealed batteries.
5.3.2.3 Dry-charged batteries
Some wet batteries are supplied dry-charged. This means that they have been charged, the electrolyte emptied out and the battery dried and sealed. It is important that it remains sealed if it is to be stored before being put into service. Once it is required, the seals should be removed and dilute sulphuric acid of the correct specific gravity used to fill the cells to the filling mark. The acid will usually be supplied with the battery. The battery should then be allowed to stand for a period of time to allow any air to escape.
A dry charged battery, once filled, will achieve about an 80% state of charge. For this reason it must be charged before putting into service. Normally this will be specified by the manufacturer as being at a specific voltage for a particular amount of time. Again it should be accomplished by means of a mains operated charger if possible, although it may be possible to use the solar system to provide this charge if the loads are disabled for a certain amount of time.
5.3.2.4 Dry uncharged batteries
Sometimes batteries, normally large cells, are supplied in a dry uncharged state. It is critical that the manufacturer’s instructions are followed to the letter as the initial charge is important to the formation of the plate structure. Normally they will be filled as with dry-charged batteries and then subjected to an extended charge, often taking some days. This must be performed with the correct type of charger and it is advisable to avoid purchasing batteries in this state if possible. If wet batteries have to be transported by sea or air the best option is to obtain them in a dry-charged state with the acid in suitable packaging as advised by your shipping company.
5.3.2.5 Mixing acid
It may sometimes be necessary to mix your own electrolyte from concentrated sulphuric acid and distilled water. This should be avoided unless absolutely necessary, for instance in developing countries where it may be impossible to purchase ready made electrolyte and shipping it from the manufacturer is impractical. It is essential that the sulphuric acid and distilled water are of the highest purity.
Before you start collect together the following items:
- Safety clothing, including a chemical splashes apron, face shield and suitable gloves.
- A suitable non-metallic mixing vessel and stirrer. Glass is ideal although you may have to use whatever is available such as a plastic bucket and wooden stick. I write from experience on this.
- A glass thermometer calibrated from at least 10 - 80º C.
- A battery hydrometer, which can be bought from a battery specialist or tool shop.
- A container to hold the finished electrolyte. A plastic drum is ideal and should be marked “Sulphuric acid. Highly corrosive.”
It is important that you always add acid to water and never the other way round. In this way, you are never diluting concentrated acid, which can cause it to boil explosively with very serious consequences. Mix a little at a time, add the acid in small amounts and stir thoroughly. Bear in mind that it will become hot.
Each time you add some acid, check the specific gravity by drawing a little electrolyte into the hydrometer and expelling it, then drawing in enough just to lift the float. Read off the specific gravity from the scale and record. Then measure the temperature of the electrolyte and add 0.001 to the reading on the hydrometer for each degree Celsius above the specified temperature.
For example:
The battery manufacturer calls for an electrolyte with a specific gravity of 1.240 at 25º C. The hydrometer reads 1.230 and the thermometer 35º C. The electrolyte is therefore correctly mixed; 1.230 plus 10 (35-25) times 0.001 is 1.240.
If at any time the electrolyte reaches a temperature of 60º C, go and have a cup of tea until it cools down again. You really don’t want it to boil.
Once each batch of electrolyte is mixed, add it to the waiting container until sufficient has been mixed. Allow to cool to room temperature before using. Ensure that it is all mixed thoroughly so that there is no variation between the strength of electrolyte across the cells of the battery. I have achieved this in the past by an eight-hour canoe journey; you may choose to invert the (sealed) container a few times. Store the container securely if it is not to be used immediately.
5.3.3 Connection
Once the battery has been put in place, the individual batteries or cells can be connected together to form a single battery. If possible use battery interconnect cables supplied by the battery manufacturer or supplier; if you have to make your own then use the thickest cable that is practical.
Take great care when connecting the batteries; remember that they are never switched off and the current from a single cell can be sufficient to heat tools to red heat in moments. Remove all metal jewellery before starting and use insulated tools where available. Do not connect the output cables at this point.
5.3.4 Earthing
Provision should be made to earth the battery negative terminal. If no suitable earth is available, then an earth rod must be driven into the ground outside as near as possible to the battery. This is connected to the battery negative terminal via green and yellow earth cable of at least 2.5 mm2 and preferably 6 mm2 cross-sectional area.
5.4 Control equipment
The controller, inverter and any other control and monitoring equipment can now be installed.
5.4.1 Mounting
The control equipment is generally mounted on a vertical surface to aid cooling. See the instructions for your particular units. In a building, the normal position is on the wall above the batteries. Bear in mind that inverters in particular can be very heavy, and ensure that the wall is strong enough to support the weight.
5.4.2 Wiring
The wiring may now be put in place, following the diagram and cable sizes arrived at in section 5.6. Take great care to observe the correct polarity, and ensure that all connections are well tightened. Use crimp eyelets to connect to stud terminals, and attach them with the correct crimp tool, not a pair of pliers. Clip the cables securely to the wall where possible to keep them out of harm’s way and make them look neat. Do not make any of the final positive connections to battery, solar array or load at this stage.
All wiring must be installed in conformity with local electrical regulations, by a qualified electrician where necessary. See section 5.6.1.7 for recommendations for DC wiring.
5.5 System Commissioning
System commissioning is the process of checking and testing the installation and putting it into service. It may be tempting to hurry this procedure; time may be running short and the user may be impatient to see the system working. However, the future reliability of the entire system depends on careful commissioning. If the equipment you are using has any specific commissioning instructions then follow those in preference to the instructions below.
5.5.1 Visual check
With the wiring diagram in your hand, carefully examine the system to ensure that everything is as it should be. Pay particular attention to the polarity of connections and don’t forget the battery earth.
5.5.2 Connections
Check the security of all the connections to the control gear and any other connections that have been made already, such as the battery negative and earth connections. Even if you’ve just connected them, check them again.
5.5.3 Applying power
With any load isolators or circuit breakers switched off, connect the loads to the controller and / or inverter.
Next, measure and record the battery terminal voltage and connect the battery positive terminal. Insert the battery fuse if fitted. Be aware that a spark is likely to occur, so ensure that the room is well ventilated and blow across the battery caps first to clear any hydrogen if the battery is of the vented type. Measure the voltage at the battery connections of the controller and inverter. This should be the same as the battery terminal voltage. If not, check all the connections and the battery fuse.
Finally, connect the photovoltaic array. Before you do this you may want to cover it with an opaque material if possible; remove this as soon as the connection is secure. Measure the voltage at the input terminals of the controller – this should be the same as or slightly higher than the battery terminal voltage.
If there is a reasonable amount of daylight then the controller should show that the battery is charging. If it’s gone dark already then you really need to come back tomorrow. Check that the battery is actually charging by measuring the terminal voltage, which should be higher than that initially recorded and rising.
Now switch on the loads. Go round and test them all, if there are more than one, to make sure that they all work. Make sure you switch off anything that is not in use afterwards.
The commissioning process is now complete.
5.5.4 Handover
If you are not to be the eventual user yourself, then an explanation of the operation of the system should be given to the end user before leaving the site.
This explanation should cover the following:
- Principles of operation
- Effect of weather and season on available energy
- Importance of keeping energy usage to a minimum
- Operation of low voltage disconnect
- Meaning of indications on control equipment
- Safety aspects of batteries
The user should also be given copies of the instruction manuals for the components.