Parts of a Solar Power System
Note: Not all parts are required in all systems
Solar Module - Is basically an electrical device made from silicon, which is grown into ingots, and are then cut into slices to make solar electric cells. These cells are then soldered together to make an electrical circuit which when exposed to sunlight produce a voltage and current. The cells are then encapsulated between a tempered glass face and a weatherproof backing and placed into a aluminum frame. Modules are then wired into an array to provide you with the charging capacity you need. You normally would like to produce more power than you use on an average day to make up for cloudy weather.
Charge Controller - is a component whose function is to regulate the amount of charge going into the batteries. It prevents the solar modules from over charging your batteries by limiting the amount of current flowing into them. Some controllers can also have a low voltage disconnect which prevents the batteries from being over discharged. They can also have meters to show battery voltage and the amount of current flowing into and out of the batteries.
Safety Disconnects - are circuit breakers or fuses which are placed into each current carrying conductor in the system to protect the system in case of short circuits or overloads, they also act as an emergency shut down switch.
A MUST IN EVERY SYSTEM.
Battery Bank - is a group of batteries wired together to store your power in a solar electric system. They allow you to use this power at any time day or night. The battery bank is usually sized to give you between 3– 10 days of power storage. Batteries MUST be placed into a box and vented to the outside for safety.
DC Load Center - contains fuses or circuit breakers to which all your 12 or 24 volt lights and TV’s, etc. are wired to.
Inverter/Chargers - converts DC battery power into standard AC power, which allows you to run regular 120 volt AC appliances. Some inverters also contain battery chargers which when used in conjunction with a gasoline generator will automatically charge your batteries when the generator is running, and transfer any extra power to your house to power your loads.
AC Load Center - contains fuses or circuit breakers to which all your 120 volt AC appliances are wired to.
Charge Controller - is a component whose function is to regulate the amount of charge going into the batteries. It prevents the solar modules from over charging your batteries by limiting the amount of current flowing into them. Some controllers can also have a low voltage disconnect which prevents the batteries from being over discharged. They can also have meters to show battery voltage and the amount of current flowing into and out of the batteries.
Safety Disconnects - are circuit breakers or fuses which are placed into each current carrying conductor in the system to protect the system in case of short circuits or overloads, they also act as an emergency shut down switch.
A MUST IN EVERY SYSTEM.
Battery Bank - is a group of batteries wired together to store your power in a solar electric system. They allow you to use this power at any time day or night. The battery bank is usually sized to give you between 3– 10 days of power storage. Batteries MUST be placed into a box and vented to the outside for safety.
DC Load Center - contains fuses or circuit breakers to which all your 12 or 24 volt lights and TV’s, etc. are wired to.
Inverter/Chargers - converts DC battery power into standard AC power, which allows you to run regular 120 volt AC appliances. Some inverters also contain battery chargers which when used in conjunction with a gasoline generator will automatically charge your batteries when the generator is running, and transfer any extra power to your house to power your loads.
AC Load Center - contains fuses or circuit breakers to which all your 120 volt AC appliances are wired to.
DC Power Systems
Solar electric power systems must include a means of storing the electrical energy that the solar modules produce if they are to operate loads at night and during cloudy weather. Batteries which are able to store the electrical energy generated by the modules provide this source of power. The system loads can then draw power from the batteries during the day or night and
during clear or cloudy weather. This system’s basic components include solar module(s), a charge controller, safety disconnect, storage batteries and a DC load center, which the systems loads will be wired to. The battery bank can range from small golf cart batteries (cottage systems) to large capacity heavy-duty industrial batteries (home systems). Special batteries, designed to withstand being deeply discharged are more appropriate than conventional automobile batteries. These batteries are known as "deep cycle" batteries. The size of the battery bank depends on the size of the loads to be run and the amount of power usage. In addition, local weather conditions and patterns such as the amount of solar insolation, cloudy weather and temperature must be considered in battery sizing design. The number of modules must be chosen to adequately recharge the batteries during sunny weather. DC solar electric power systems are mainly used for cottage applications where the loads are small. These would include such items like lights, TV’s, radios and small water pumps.
AC Power Systems
In a full time residence AC power is a must. This is so that anything purchased in a store can be run on the system, and also because DC equipment is expensive and limited. Since solar modules produce DC electrical power and store that power in batteries an inverter is required to
provide the high quality, alternating current. Inverters convert DC power into AC 120 volt power. Inverters and a properly sized battery bank also have the capability to supply high surge currents. This gives the system the flexibility to start large motors or to perform other "high power" tasks. Inverters provide convenience and flexibility in a solar power system but also add complexity and cost. If conventional alternating current loads are required, an inverter is a
necessity. High quality inverters are now available and are very efficient (90%+) resulting in very little power losses. These losses although small must be calculated into system design. Also phantom loads must be looked at and eliminated if possible. Phantom loads are loads which use power even when the appliance is turned off (TV’s, VCR’s, stereos, microwaves, etc.). One might
think these are small draws but they add up quickly when on 24 hours a day, adding cost to the system. Using power bars or switched outlets is recommended. A good metering system should also be considered and is recommended. Without a system meter determining the state of charge of your batteries is difficult, and this will usually result in draining your batteries to low, causing damage.
Solar Modules
Introduction
Solar cells, modules and arrays utilize the photovoltaic effect to produce DC electricity from the sun and have the potential for producing a significant amount of DC electricity. An example of this is that a 50 watt module can produce in access of 2,000,000 watts of power over its design life. Solar modules have proven to be a reliable source of electricity, but systems must be
properly designed to be effective. Below I will discusses the basic physical characteristics of solar modules and explains how some climate and site factors will affect their performance. System designers and users should be aware of these factors when choosing panels and designing a solar electric power system.
Photovoltaic Effect
The basic part of a solar electric system is the solar cell. The cell has no moving parts and uses sunlight to produce DC electricity. It generates this electricity because the cell’s materials give it an electrical potential when sunlight strikes it. Made from silicon, one of the earth’s most abundant elements, which is purified and grown into a crystalline or poly-crystalline structure to make the solar cells. Silicon’s natural properties as a semiconductor of electricity make it an ideal material for solar cells. A solar cell is a semiconductor device. Because of its atomic structure, a semiconductor has special electrical properties. Its electrical properties are modified by two other elements, boron and phosphorous, to create a permanent imbalance in the molecular charge of the material. A solar cell is made up of two layers of semiconductor material and is about 1/l00th of an inch thick. Two regions are created – a positively charged region and a negatively charged region. The negative region lies at the top surface of the cell where phosphorous has been added to the silicon. The positive region lies below the cell’s front surface. These layers create an electrical potential within the cell. When sunlight strikes the cell it frees electrons from some of the atoms in the cell material. The cell’s internal potential then pushes these free electrons toward the negative layer. When one end of a wire is attached to this layer and the other end is attached to the second layer, the free electrons will flow through the
wire, creating an electric current.
Solar Modules
A solar module is a number of cells wired together in series and/or parallel to produce a desired voltage and current. The cells are then encapsulated between a tempered glass face and a weatherproof backing and placed into a aluminum frame. Modules are then wired into an array to provide you with the charging capacity you need. Solar modules are available in a variety of sizes from 5 watts to 120 watts.
Factors Affecting Solar Module Performance
Load resistance
A load or battery determines at what voltage the solar module will operate at. In a 12 volt battery system, battery voltage is usually between 11.5 – 15.0 volts. Therefore in order to charge that battery the module must operate at a slightly higher voltage. That is why most modules are rated at between 16.0–17.0 volts. This higher voltage is also necessary because there is always a small loss in the wire run from the modules to the batteries. Be careful when choosing a solar module, some modules are rated at too high a voltage (18.0+ volts) and should be avoided in battery charging systems unless used in conjunction with a Maximum Power Point Tracking, MPPT, controller. Since this voltage will never be reached and voltage X current = the power output of the module, one will never see the rated output of the module. Looking at a modules
rated current output is a better indication of its power output. (while having a high enough voltage to charge batteries and to overcome wire losses).
Intensity of Sunlight
A solar module’s output is proportional to the amount of sunlight it is subjected to. More intense sunlight will result in greater current output. Lower sunlight levels result in lower current output. Voltage is not changed appreciably by variations of sunlight intensity. Solar modules are therefore still charging batteries on cloudy days just at a reduced rate. I have also
heard some people tell me that their solar modules are so good that they charge at night under a full moon, don’t believe this, solar modules are good but they are not magic, they need some amount of sunlight to produce power.
Cell Temperature
Solar modules operate less efficiently at higher cell temperatures. Heat, in this case may be thought of as an electrical resistance to the flow of electrons. Generally a module will lose approximately 1/2% efficiency per degree centigrade temperature rise between 80 and 90 degrees C. Therefore it is important to remove heat from the modules. Using a mounting
scheme which permits module cooling, such as a stand-off roof mount or more preferable a ground mounted rack, is an easy way to address this problem.
Shading
Even partial shading of solar modules will result in dramatic reduction of a module’s output. By this I mean even a leafless tree will reduce the output of the module dramatically. Therefore siting of solar modules is very important. In an open field it is very easy to decide where to locate the module rack but once you get into the bush it can become very difficult. Too many times we have been called by customers who have purchased their system elsewhere and said their batteries were always at a low state of charge in the winter time, even though they have had nice sunny days. On arrival the solar module rack was totally in the shade. The answer to the question, why was the rack located there?, was always the same. It was a sunny location in the summer when we installed it. Don’t let a solar system installer install a system without a complete site evaluation using a siting device of some kind. We have also heard of the system
installer asking the customer where the sunniest spot on the property is. Don’t hirer these people, they don’t know what they are doing, and this will cost you a great deal of money in the future.
What Direction Should Modules Face?
In Canada, solar modules should face true south. But if you are shaded through part of the morning or afternoon, it may be of benefit to shift the array more to the west or the east to take advantage of the afternoon or morning sun. Again hiring a professional who uses a solar siting device can save you a lot of time and money.
What Angle Should The Rack Be Mounted At?
A solar module produces the most power when it is perpendicular to the sun. In the summer the sun is high in the sky, so a shallow mounting angle is good, about 30 degrees. In the winter, the sun is closer to the horizon so raising the panels to a steeper angle of 60 degrees improves output. During the spring and fall panel angle should be 45 degrees. Therefore, if you adjust your solar module rack angle by season, 4 times a year, you will gain about 10% more power
from your modules compared to a stationary rack.
What About Snow?
In areas which experience a lot of snow, consider mounting the solar panels on a ground mount, this will shed the snow better. Mounting a roof array close to the eaves so snow won’t accumulate on the panels may also be an alternative. Solar panels may accumulate ice and snow when there is freezing rain or when its snowing, but because the solar cells are dark, they absorb heat which usually melts the snow or ice shortly after the sun comes out. Having a ground mount is a benefit because it will allow you get at the rack to clean off the snow if necessary.
Solar electric power systems must include a means of storing the electrical energy that the solar modules produce if they are to operate loads at night and during cloudy weather. Batteries which are able to store the electrical energy generated by the modules provide this source of power. The system loads can then draw power from the batteries during the day or night and
during clear or cloudy weather. This system’s basic components include solar module(s), a charge controller, safety disconnect, storage batteries and a DC load center, which the systems loads will be wired to. The battery bank can range from small golf cart batteries (cottage systems) to large capacity heavy-duty industrial batteries (home systems). Special batteries, designed to withstand being deeply discharged are more appropriate than conventional automobile batteries. These batteries are known as "deep cycle" batteries. The size of the battery bank depends on the size of the loads to be run and the amount of power usage. In addition, local weather conditions and patterns such as the amount of solar insolation, cloudy weather and temperature must be considered in battery sizing design. The number of modules must be chosen to adequately recharge the batteries during sunny weather. DC solar electric power systems are mainly used for cottage applications where the loads are small. These would include such items like lights, TV’s, radios and small water pumps.
AC Power Systems
In a full time residence AC power is a must. This is so that anything purchased in a store can be run on the system, and also because DC equipment is expensive and limited. Since solar modules produce DC electrical power and store that power in batteries an inverter is required to
provide the high quality, alternating current. Inverters convert DC power into AC 120 volt power. Inverters and a properly sized battery bank also have the capability to supply high surge currents. This gives the system the flexibility to start large motors or to perform other "high power" tasks. Inverters provide convenience and flexibility in a solar power system but also add complexity and cost. If conventional alternating current loads are required, an inverter is a
necessity. High quality inverters are now available and are very efficient (90%+) resulting in very little power losses. These losses although small must be calculated into system design. Also phantom loads must be looked at and eliminated if possible. Phantom loads are loads which use power even when the appliance is turned off (TV’s, VCR’s, stereos, microwaves, etc.). One might
think these are small draws but they add up quickly when on 24 hours a day, adding cost to the system. Using power bars or switched outlets is recommended. A good metering system should also be considered and is recommended. Without a system meter determining the state of charge of your batteries is difficult, and this will usually result in draining your batteries to low, causing damage.
Solar Modules
Introduction
Solar cells, modules and arrays utilize the photovoltaic effect to produce DC electricity from the sun and have the potential for producing a significant amount of DC electricity. An example of this is that a 50 watt module can produce in access of 2,000,000 watts of power over its design life. Solar modules have proven to be a reliable source of electricity, but systems must be
properly designed to be effective. Below I will discusses the basic physical characteristics of solar modules and explains how some climate and site factors will affect their performance. System designers and users should be aware of these factors when choosing panels and designing a solar electric power system.
Photovoltaic Effect
The basic part of a solar electric system is the solar cell. The cell has no moving parts and uses sunlight to produce DC electricity. It generates this electricity because the cell’s materials give it an electrical potential when sunlight strikes it. Made from silicon, one of the earth’s most abundant elements, which is purified and grown into a crystalline or poly-crystalline structure to make the solar cells. Silicon’s natural properties as a semiconductor of electricity make it an ideal material for solar cells. A solar cell is a semiconductor device. Because of its atomic structure, a semiconductor has special electrical properties. Its electrical properties are modified by two other elements, boron and phosphorous, to create a permanent imbalance in the molecular charge of the material. A solar cell is made up of two layers of semiconductor material and is about 1/l00th of an inch thick. Two regions are created – a positively charged region and a negatively charged region. The negative region lies at the top surface of the cell where phosphorous has been added to the silicon. The positive region lies below the cell’s front surface. These layers create an electrical potential within the cell. When sunlight strikes the cell it frees electrons from some of the atoms in the cell material. The cell’s internal potential then pushes these free electrons toward the negative layer. When one end of a wire is attached to this layer and the other end is attached to the second layer, the free electrons will flow through the
wire, creating an electric current.
Solar Modules
A solar module is a number of cells wired together in series and/or parallel to produce a desired voltage and current. The cells are then encapsulated between a tempered glass face and a weatherproof backing and placed into a aluminum frame. Modules are then wired into an array to provide you with the charging capacity you need. Solar modules are available in a variety of sizes from 5 watts to 120 watts.
Factors Affecting Solar Module Performance
Load resistance
A load or battery determines at what voltage the solar module will operate at. In a 12 volt battery system, battery voltage is usually between 11.5 – 15.0 volts. Therefore in order to charge that battery the module must operate at a slightly higher voltage. That is why most modules are rated at between 16.0–17.0 volts. This higher voltage is also necessary because there is always a small loss in the wire run from the modules to the batteries. Be careful when choosing a solar module, some modules are rated at too high a voltage (18.0+ volts) and should be avoided in battery charging systems unless used in conjunction with a Maximum Power Point Tracking, MPPT, controller. Since this voltage will never be reached and voltage X current = the power output of the module, one will never see the rated output of the module. Looking at a modules
rated current output is a better indication of its power output. (while having a high enough voltage to charge batteries and to overcome wire losses).
Intensity of Sunlight
A solar module’s output is proportional to the amount of sunlight it is subjected to. More intense sunlight will result in greater current output. Lower sunlight levels result in lower current output. Voltage is not changed appreciably by variations of sunlight intensity. Solar modules are therefore still charging batteries on cloudy days just at a reduced rate. I have also
heard some people tell me that their solar modules are so good that they charge at night under a full moon, don’t believe this, solar modules are good but they are not magic, they need some amount of sunlight to produce power.
Cell Temperature
Solar modules operate less efficiently at higher cell temperatures. Heat, in this case may be thought of as an electrical resistance to the flow of electrons. Generally a module will lose approximately 1/2% efficiency per degree centigrade temperature rise between 80 and 90 degrees C. Therefore it is important to remove heat from the modules. Using a mounting
scheme which permits module cooling, such as a stand-off roof mount or more preferable a ground mounted rack, is an easy way to address this problem.
Shading
Even partial shading of solar modules will result in dramatic reduction of a module’s output. By this I mean even a leafless tree will reduce the output of the module dramatically. Therefore siting of solar modules is very important. In an open field it is very easy to decide where to locate the module rack but once you get into the bush it can become very difficult. Too many times we have been called by customers who have purchased their system elsewhere and said their batteries were always at a low state of charge in the winter time, even though they have had nice sunny days. On arrival the solar module rack was totally in the shade. The answer to the question, why was the rack located there?, was always the same. It was a sunny location in the summer when we installed it. Don’t let a solar system installer install a system without a complete site evaluation using a siting device of some kind. We have also heard of the system
installer asking the customer where the sunniest spot on the property is. Don’t hirer these people, they don’t know what they are doing, and this will cost you a great deal of money in the future.
What Direction Should Modules Face?
In Canada, solar modules should face true south. But if you are shaded through part of the morning or afternoon, it may be of benefit to shift the array more to the west or the east to take advantage of the afternoon or morning sun. Again hiring a professional who uses a solar siting device can save you a lot of time and money.
What Angle Should The Rack Be Mounted At?
A solar module produces the most power when it is perpendicular to the sun. In the summer the sun is high in the sky, so a shallow mounting angle is good, about 30 degrees. In the winter, the sun is closer to the horizon so raising the panels to a steeper angle of 60 degrees improves output. During the spring and fall panel angle should be 45 degrees. Therefore, if you adjust your solar module rack angle by season, 4 times a year, you will gain about 10% more power
from your modules compared to a stationary rack.
What About Snow?
In areas which experience a lot of snow, consider mounting the solar panels on a ground mount, this will shed the snow better. Mounting a roof array close to the eaves so snow won’t accumulate on the panels may also be an alternative. Solar panels may accumulate ice and snow when there is freezing rain or when its snowing, but because the solar cells are dark, they absorb heat which usually melts the snow or ice shortly after the sun comes out. Having a ground mount is a benefit because it will allow you get at the rack to clean off the snow if necessary.
Charge Controllers
Is a component in a solar electric system whose function is to regulate the amount of charge going into the batteries. It prevents the solar modules from over charging your batteries by limiting the amount of current flowing into them.
Controller Types
Shunt - This type of controller prevents over charging by "shunting"or by-passing the batteries when they are fully charged. The shunt controller's circuitry monitors the battery voltage and switches excess current through a power transistor when it reaches a pre-set full charge value. This acts like a resistor and converts the excess power into heat. Shunt controllers have black
fins which help to dissipate this heat. A shunt controller also incorporates a blocking diode to prevent current from draining back from the batteries through the solar array at night. Inexpensive, but also inefficient.
Single Stage - This type controllers prevent battery overcharging by switching the current off when the battery voltage reaches a certain pre-set value called the charge termination set point, usually between 13.8 –14.6 volts. The array is then automatically reconnected when the battery reaches a pre-set lower value called the charge resumption set point usually between 13.0 – 13.5
volts. The controller goes through this on/off cycle a number of times a day to fully charge the battery. Inexpensive, but it also takes a long time to fully charge the battery.
Pulse Width Modulation Constant Voltage - This type of controller allows the full array current to flow into the batteries when the battery is at a low state-of-charge. As the battery
approaches full charge, the controller cuts back some of the array’s power so that less current flows into the batteries while keeping them at a constant voltage. This "trickle" charge tapers off as the battery bank slowly approaches a fully charged state. Very good controllers, but tend to boil away a fair amount of water from the batteries. Check batteries monthly. Since heat is
generated by the dissipation of power, this type controller needs to be properly ventilated. Most of these controllers have a relay type switch that opens to prevents reverse "leakage" at night.
Pulse Width Modulation Three-Stage Charging - This type controller automatically establishes different charging currents depending on the battery’s state-of-charge. The full array
current is allowed to flow into the batteries when the battery is at a low state-of-charge. As the battery bank approaches full charge, the controller cuts back some of the array’s power so that less current flows into the batteries while keeping them at a constant voltage. This "trickle" charge tapers off as the battery bank slowly approaches a fully charged state. After an preset time or current set point has been reached the controller goes into what is called a float setting. This lowers the voltage to a value where the battery is no longer gassing but still high enough to keep the battery full. This approach usually increases battery life and results in less water loss from the batteries. Usually requiring water only about every 6 months. Since heat is generated by the dissipation of the extra power, these controllers need to be properly ventilated. These controllers have a relay type switch that opens to prevents reverse "leakage" at night.
Maximum Power Point Tracking (MPPT) – This type controller takes the extra voltage from a solar module(s) (eg. 12 volt modules rated between 17.0 – 18.0 volts and a full battery needs only about 14.6 volts) and turns it into extra charging current. This means more usable amp/hours per day from the same size solar array compared to a regular controller. Another feature is that the solar array and battery voltage do not always have to be the same. Depending on the controller, the solar array is wired between 30 – 120 volts to charge a 12/24/48 volt battery bank. This is a great advantage if the solar array is a long distance from the batteries, smaller wire size is normally used which saves money. To take advantage of this type controller the wire from the solar modules must be sized correctly so that there is very little voltage drop between the array and the batteries.
Batteries
Is a component in a solar electric system whose function is to regulate the amount of charge going into the batteries. It prevents the solar modules from over charging your batteries by limiting the amount of current flowing into them.
Controller Types
Shunt - This type of controller prevents over charging by "shunting"or by-passing the batteries when they are fully charged. The shunt controller's circuitry monitors the battery voltage and switches excess current through a power transistor when it reaches a pre-set full charge value. This acts like a resistor and converts the excess power into heat. Shunt controllers have black
fins which help to dissipate this heat. A shunt controller also incorporates a blocking diode to prevent current from draining back from the batteries through the solar array at night. Inexpensive, but also inefficient.
Single Stage - This type controllers prevent battery overcharging by switching the current off when the battery voltage reaches a certain pre-set value called the charge termination set point, usually between 13.8 –14.6 volts. The array is then automatically reconnected when the battery reaches a pre-set lower value called the charge resumption set point usually between 13.0 – 13.5
volts. The controller goes through this on/off cycle a number of times a day to fully charge the battery. Inexpensive, but it also takes a long time to fully charge the battery.
Pulse Width Modulation Constant Voltage - This type of controller allows the full array current to flow into the batteries when the battery is at a low state-of-charge. As the battery
approaches full charge, the controller cuts back some of the array’s power so that less current flows into the batteries while keeping them at a constant voltage. This "trickle" charge tapers off as the battery bank slowly approaches a fully charged state. Very good controllers, but tend to boil away a fair amount of water from the batteries. Check batteries monthly. Since heat is
generated by the dissipation of power, this type controller needs to be properly ventilated. Most of these controllers have a relay type switch that opens to prevents reverse "leakage" at night.
Pulse Width Modulation Three-Stage Charging - This type controller automatically establishes different charging currents depending on the battery’s state-of-charge. The full array
current is allowed to flow into the batteries when the battery is at a low state-of-charge. As the battery bank approaches full charge, the controller cuts back some of the array’s power so that less current flows into the batteries while keeping them at a constant voltage. This "trickle" charge tapers off as the battery bank slowly approaches a fully charged state. After an preset time or current set point has been reached the controller goes into what is called a float setting. This lowers the voltage to a value where the battery is no longer gassing but still high enough to keep the battery full. This approach usually increases battery life and results in less water loss from the batteries. Usually requiring water only about every 6 months. Since heat is generated by the dissipation of the extra power, these controllers need to be properly ventilated. These controllers have a relay type switch that opens to prevents reverse "leakage" at night.
Maximum Power Point Tracking (MPPT) – This type controller takes the extra voltage from a solar module(s) (eg. 12 volt modules rated between 17.0 – 18.0 volts and a full battery needs only about 14.6 volts) and turns it into extra charging current. This means more usable amp/hours per day from the same size solar array compared to a regular controller. Another feature is that the solar array and battery voltage do not always have to be the same. Depending on the controller, the solar array is wired between 30 – 120 volts to charge a 12/24/48 volt battery bank. This is a great advantage if the solar array is a long distance from the batteries, smaller wire size is normally used which saves money. To take advantage of this type controller the wire from the solar modules must be sized correctly so that there is very little voltage drop between the array and the batteries.
Batteries
To begin with, one of the most common questions, "Do I need batteries?" The answer is yes, most systems are installed and used in conjunction with a battery bank of some sort. Exceptions to this rule are utility interactive systems where a back-up is not required or direct water pumping systems.
Battery Safety
Batteries which are used in solar electric systems are potentially dangerous if improperly handled, installed, or maintained. Dangerous chemicals, heavy weight, high voltages and currents are potential hazards and can result in electric shock, burns, explosion or corrosive damage to your person or property.
Safety rules which should be followed to insure safe and proper handling, installing, checking and replacing of batteries include:
Remove any jewelry before working starting work.
Proper tools should be used.
The battery area should be properly ventilated.
Wear protective clothing including eye protection.
Have baking soda easily accessible to neutralize acid spills.
Have fresh water easily accessible in case electrolyte splashes on skin or eyes.
Flush with water for five to ten minutes. Contact physician.
Keep open flames and sparks away from batteries.
No smoking near any battery.
Disconnect battery bank from all sources of charging or discharging before working on batteries.
Do not lift batteries by their terminal posts or by squeezing the sides of the battery. Lift from the bottom or use carrying straps.
Use tools with insulated (or wrapped) handles to avoid accidental short circuits.
Follow manufacturer's instructions.
Use common sense.
Battery Operation
Batteries chemically store direct current electrical energy for later use at night or during periods of cloudy weather. Since a solar electric systems power output varies throughout any given day, the battery storage system must be able to provide a constant source of power during these periods. Batteries also can provide large amounts of surge power. Since batteries are not 100% efficient (efficiency about 80-90%) when converting input energy into actual output power,
the system must be sized to compensate for these losses.
Types of Batteries
The battery most commonly used for solar applications is the lead acid battery, which closely resembles an automotive battery. Automotive batteries are not recommended for solar applications because they are designed to discharge large amounts of current for a short period of time to start an engine and then be recharged immediately by the vehicle’s alternator. Solar power systems require a battery to discharge small amounts of current over long period of time and to be recharged under erratic conditions. If an automotive battery was used in this way it would only deliver about 30 charge/discharge cycles. In contrast, lead acid batteries suitable for solar applications can tolerate these conditions and if properly sized and maintained, will often last from 3 to 10 years, 20 years if heavy duty industrial batteries are used (between 400 – 3000
cycles depending on battery type). A battery is charging when energy is being put in and discharging when energy is being taken out. A cycle is considered one charge/discharge sequence.
Battery Capacity Ratings
Most battery manufacturers specify battery capacity in amp-hours (AH) In theory, a "200 AH Battery" will deliver 1 amp for 200 hours or roughly 2 amps for 100 hours. But since even deep cycle batteries should only be discharged about 50% of their capacity to get their maximum life, a "200 AH Battery" will deliver about 2 amps for 50 hours. Battery capacity is affected by many factors including rate of discharge, temperature, controller efficiency, age and recharging characteristics.
Since it is easy to add solar modules to an existing system, we often think the entire system as being modular as well, this is not always the case. I generally advise against adding new batteries to an old battery bank if the batteries are more than a year or two old. Older batteries will degrade the performance of the new batteries. It's also advisable to minimize excessive
"paralleling" of batteries because in so doing, you increase the number of cells, thereby increasing the potential for failure from a bad cell, as well as having a large amount of cells to look after and water. Using a battery with a higher amp/hour rating is advisable in larger systems. Initially specifying slightly larger battery capacity than is required will result in the batteries being cycled less, therefore increasing battery life. On the other hand greatly over-sizing the battery bank is inadvisable, since the battery bank may remain at a state of partial charge during periods of reduced charging. This state could shortened battery life, reduced capacity, by causing battery sulfation to occur.
Temperature Effects
The speed of the chemical reaction occurring in a lead-acid battery is determined by temperature. The colder the temperature the slower the reaction. The warmer the temperature the faster the reaction and the more quickly the charge can be drawn from the battery. The optimum operating temperature for a lead-acid battery is around 77 degrees Fahrenheit. For this reason I like to see batteries placed indoors or in a heated and ventilated space with a temperature between 55 and 80 degrees. If we do install them in a unheated space, battery
capacity must be increased to compensate for this derating. On the other hand high temperatures can drastically shorten the life of the battery and should be avoided.
Determining Battery State of Charge
Battery state of charge is determined by reading either battery voltage, using an Amp/Hour meter or reading the specific gravity of the electrolyte. The density or specific gravity of the sulfuric acid electrolyte of a lead-acid battery varies with its state of charge. The density is lower when the battery is discharged and higher as the cells are charged. Specific gravity is read with a hydrometer. A hydrometer reading will tell the exact battery state of charge. A hydrometer cannot be used with sealed or gel-cell batteries. Another important point is freezing. At low
densities, the electrolyte contains enough water that the battery can freeze. This is not a problem with PV systems where the batteries are kept both warm and charged. Batteries can survive and operate in a cold location, but the state of charge level should not be allowed to get too low or the battery will freeze and need to be replaced.
Batteries are the heart of every solar electric power system. I recommend you buy the best battery you can afford. Don’t buy used batteries unless they are properly tested. Only batteries of the same type and capacity can be used together to build a battery bank. Choose batteries carefully to give a long and efficient life.
Battery Safety
Batteries which are used in solar electric systems are potentially dangerous if improperly handled, installed, or maintained. Dangerous chemicals, heavy weight, high voltages and currents are potential hazards and can result in electric shock, burns, explosion or corrosive damage to your person or property.
Safety rules which should be followed to insure safe and proper handling, installing, checking and replacing of batteries include:
Remove any jewelry before working starting work.
Proper tools should be used.
The battery area should be properly ventilated.
Wear protective clothing including eye protection.
Have baking soda easily accessible to neutralize acid spills.
Have fresh water easily accessible in case electrolyte splashes on skin or eyes.
Flush with water for five to ten minutes. Contact physician.
Keep open flames and sparks away from batteries.
No smoking near any battery.
Disconnect battery bank from all sources of charging or discharging before working on batteries.
Do not lift batteries by their terminal posts or by squeezing the sides of the battery. Lift from the bottom or use carrying straps.
Use tools with insulated (or wrapped) handles to avoid accidental short circuits.
Follow manufacturer's instructions.
Use common sense.
Battery Operation
Batteries chemically store direct current electrical energy for later use at night or during periods of cloudy weather. Since a solar electric systems power output varies throughout any given day, the battery storage system must be able to provide a constant source of power during these periods. Batteries also can provide large amounts of surge power. Since batteries are not 100% efficient (efficiency about 80-90%) when converting input energy into actual output power,
the system must be sized to compensate for these losses.
Types of Batteries
The battery most commonly used for solar applications is the lead acid battery, which closely resembles an automotive battery. Automotive batteries are not recommended for solar applications because they are designed to discharge large amounts of current for a short period of time to start an engine and then be recharged immediately by the vehicle’s alternator. Solar power systems require a battery to discharge small amounts of current over long period of time and to be recharged under erratic conditions. If an automotive battery was used in this way it would only deliver about 30 charge/discharge cycles. In contrast, lead acid batteries suitable for solar applications can tolerate these conditions and if properly sized and maintained, will often last from 3 to 10 years, 20 years if heavy duty industrial batteries are used (between 400 – 3000
cycles depending on battery type). A battery is charging when energy is being put in and discharging when energy is being taken out. A cycle is considered one charge/discharge sequence.
Battery Capacity Ratings
Most battery manufacturers specify battery capacity in amp-hours (AH) In theory, a "200 AH Battery" will deliver 1 amp for 200 hours or roughly 2 amps for 100 hours. But since even deep cycle batteries should only be discharged about 50% of their capacity to get their maximum life, a "200 AH Battery" will deliver about 2 amps for 50 hours. Battery capacity is affected by many factors including rate of discharge, temperature, controller efficiency, age and recharging characteristics.
Since it is easy to add solar modules to an existing system, we often think the entire system as being modular as well, this is not always the case. I generally advise against adding new batteries to an old battery bank if the batteries are more than a year or two old. Older batteries will degrade the performance of the new batteries. It's also advisable to minimize excessive
"paralleling" of batteries because in so doing, you increase the number of cells, thereby increasing the potential for failure from a bad cell, as well as having a large amount of cells to look after and water. Using a battery with a higher amp/hour rating is advisable in larger systems. Initially specifying slightly larger battery capacity than is required will result in the batteries being cycled less, therefore increasing battery life. On the other hand greatly over-sizing the battery bank is inadvisable, since the battery bank may remain at a state of partial charge during periods of reduced charging. This state could shortened battery life, reduced capacity, by causing battery sulfation to occur.
Temperature Effects
The speed of the chemical reaction occurring in a lead-acid battery is determined by temperature. The colder the temperature the slower the reaction. The warmer the temperature the faster the reaction and the more quickly the charge can be drawn from the battery. The optimum operating temperature for a lead-acid battery is around 77 degrees Fahrenheit. For this reason I like to see batteries placed indoors or in a heated and ventilated space with a temperature between 55 and 80 degrees. If we do install them in a unheated space, battery
capacity must be increased to compensate for this derating. On the other hand high temperatures can drastically shorten the life of the battery and should be avoided.
Determining Battery State of Charge
Battery state of charge is determined by reading either battery voltage, using an Amp/Hour meter or reading the specific gravity of the electrolyte. The density or specific gravity of the sulfuric acid electrolyte of a lead-acid battery varies with its state of charge. The density is lower when the battery is discharged and higher as the cells are charged. Specific gravity is read with a hydrometer. A hydrometer reading will tell the exact battery state of charge. A hydrometer cannot be used with sealed or gel-cell batteries. Another important point is freezing. At low
densities, the electrolyte contains enough water that the battery can freeze. This is not a problem with PV systems where the batteries are kept both warm and charged. Batteries can survive and operate in a cold location, but the state of charge level should not be allowed to get too low or the battery will freeze and need to be replaced.
Batteries are the heart of every solar electric power system. I recommend you buy the best battery you can afford. Don’t buy used batteries unless they are properly tested. Only batteries of the same type and capacity can be used together to build a battery bank. Choose batteries carefully to give a long and efficient life.
Inverters
Purpose of Inverters
The main purpose of an inverter is to change the DC electricity produced by the solar modules and stored in the batteries into AC electricity so that loads that require AC can be operated. In the past inverters were a weak link in a solar power system. They were unreliable and very inefficient, thereby imposing large penalties on the overall system. This is no longer the case. High quality, reliable inverters are now available and are very efficient (90%+) resulting in very little power losses. These losses although small must still be calculated into system design.
Inverter Types
Basically there are two categories of inverters. Synchronous (also called grid-tied) inverters require utility power and are used with grid connected solar power systems. The second category is a "stand alone" inverter. These are designed for the independent "utility free" power systems with batteries and are used in remote solar power installations. Some inverters may have features from both types to facilitate back-up power when the utility fails.
Common Wave Forms
Square wave inverters - inexpensive, square wave inverters switch the direct current input into a step-function or "square" alternating current output. They provide little output voltage control, limited surge capability, and considerable distortion, causing a lot of interference is some loads. Consequently, square wave inverters are only appropriate for small resistive heating loads, some small appliances and incandescent lights. They are not recommended to be used in homes.
Modified sine-wave inverters - use transistors or silicone-controlled rectifiers (SCR) to
switch direct current input to alternating current output. These complex circuits can handle large surges and have much less distortion in their output. This type of inverter is more appropriate for operating a wide variety of loads including motors, lights, and standard electronic equipment (ie. televisions and stereos, etc.). This type inverter is rarely used in systems nowadays.
Sine-wave inverters – are used to operate the more sensitive electronic hardware, found in some computer equipment and higher quality sound equipment, also some new type furnaces fridges, TV‘s, Etc. These inverters are specifically designed to remove most unwanted harmonics so they can operate delicate equipment that requires a high-quality wave form. All equipment will work better and last longer when powered by this type inverter. Grid-tied systems all use sine-wave inverters. Not that expensive any more, most off grid systems now use these inverters.
Choosing an Inverter
Output - This figure indicates how many watts of power the inverter can supply during standard operation. It is important to choose an inverter that will meet a system’s peak load requirements. The inverter must have the capacity to handle all the alternating current loads that could be on at one time. For example, a system user may wish to power a 800 watt microwave and a 1500 watt power saw at the same time. Therefore, a minimum of 2300 watts output would be required. So choosing an inverter of 2400 watts would do the job. However
over-sizing an inverter a little to allow for system expansion is not a bad idea.
Voltage Input or Battery Voltage - Indicates if the inverter is set to run on 12, 24, 48 volts. The inverter voltage must match the nominal solar system voltage. As an inverter’s maximum
rated wattage increases so does its DC input current. Therefore larger wires and circuit breakers need to be installed to carry the greater currents. That is why most of the higher power inverters have higher input voltages.
Surge Capacity - Most inverters are able to exceed their rated wattage for limited periods of rime. This is necessary since motors may draw 5 to 7 times their rated wattage during start up. Surge requirements of specific loads should be determined by consulting the manufacturer or measuring with an ammeter.
Efficiency - If you plan to operate your whole home on an inverter, a high efficiency unit is a must. Many inverter manufacturers claim high efficiency. However, some inverters may only be efficient when operated near their peak output. Check inverter specifications. Most of the time the inverter is powering loads at less than its rated capacity. Therefore, it is usually wise to choose a unit rated at a high efficiency over a broad range of loads. Also choosing an inverter that has a search mode in recommended. A lot of inverters use a lot of power when they are on even if they are not powering a load. Good inverters go into search mode when no loads are being powered, this saves a great deal of power. Then when a load is turned on the inverter automatically comes on to power that load.
Inverters with Chargers - Having the option of having a battery charger as part of the inverter is a good idea. Most good inverters have an excellent three stage charger as part of the unit. This allows you to use a fuel powered generator as a back-up during long periods without sunshine. Inverter/chargers are also used as part of utility back-up systems.
Inverter Sub-system Checklist
While the inverter is one of the main components in an AC solar electric power system it must be installed properly and safely.
Inverter to battery cabling - Because of the high current required on low voltage circuits, the cable from the inverter to the battery is large, commonly 2/0 to 4/0 in size. Using smaller conductors is unsafe and will not allow the inverter to perform to its full output rating.
DC input disconnect and over-current protection - It is very important to have a safe installation with a properly sized DC rated, CSA approved safety disconnect. Typically the
disconnect works in conjunction with a over-current protection device such as a fuse or breaker. These components are installed in an enclosure which can also house the solar input breaker and/or DC load breakers or also shunts.
AC output disconnect and over-current protection - If the AC load center, which is fed from the inverter, is adjacent to the inverter, then the main breaker can serve as the inverter output disconnect and over-current protection. If, however, this panel is not grouped with the inverter, then a separate unit should be installed. This also holds true with AC circuits coming to the inverter from a generator or utility source. Using the inverter by-pass switch on the "additional products page" is a good and inexpensive way to address both these issues.
Shunts - Used in conjunction with an amp/hour meter to read the amperage flowing into and out of the batteries. This device is installed in the negative conductor. It is usually, and easily housed in the disconnect enclosure.
NO system should ever be installed without safety disconnects with properly rated and sized breakers and the properly sized cabling. Protect yourself and your property.
Note all system must be inspected by the Electrical Inspection Authority.
Purpose of Inverters
The main purpose of an inverter is to change the DC electricity produced by the solar modules and stored in the batteries into AC electricity so that loads that require AC can be operated. In the past inverters were a weak link in a solar power system. They were unreliable and very inefficient, thereby imposing large penalties on the overall system. This is no longer the case. High quality, reliable inverters are now available and are very efficient (90%+) resulting in very little power losses. These losses although small must still be calculated into system design.
Inverter Types
Basically there are two categories of inverters. Synchronous (also called grid-tied) inverters require utility power and are used with grid connected solar power systems. The second category is a "stand alone" inverter. These are designed for the independent "utility free" power systems with batteries and are used in remote solar power installations. Some inverters may have features from both types to facilitate back-up power when the utility fails.
Common Wave Forms
Square wave inverters - inexpensive, square wave inverters switch the direct current input into a step-function or "square" alternating current output. They provide little output voltage control, limited surge capability, and considerable distortion, causing a lot of interference is some loads. Consequently, square wave inverters are only appropriate for small resistive heating loads, some small appliances and incandescent lights. They are not recommended to be used in homes.
Modified sine-wave inverters - use transistors or silicone-controlled rectifiers (SCR) to
switch direct current input to alternating current output. These complex circuits can handle large surges and have much less distortion in their output. This type of inverter is more appropriate for operating a wide variety of loads including motors, lights, and standard electronic equipment (ie. televisions and stereos, etc.). This type inverter is rarely used in systems nowadays.
Sine-wave inverters – are used to operate the more sensitive electronic hardware, found in some computer equipment and higher quality sound equipment, also some new type furnaces fridges, TV‘s, Etc. These inverters are specifically designed to remove most unwanted harmonics so they can operate delicate equipment that requires a high-quality wave form. All equipment will work better and last longer when powered by this type inverter. Grid-tied systems all use sine-wave inverters. Not that expensive any more, most off grid systems now use these inverters.
Choosing an Inverter
Output - This figure indicates how many watts of power the inverter can supply during standard operation. It is important to choose an inverter that will meet a system’s peak load requirements. The inverter must have the capacity to handle all the alternating current loads that could be on at one time. For example, a system user may wish to power a 800 watt microwave and a 1500 watt power saw at the same time. Therefore, a minimum of 2300 watts output would be required. So choosing an inverter of 2400 watts would do the job. However
over-sizing an inverter a little to allow for system expansion is not a bad idea.
Voltage Input or Battery Voltage - Indicates if the inverter is set to run on 12, 24, 48 volts. The inverter voltage must match the nominal solar system voltage. As an inverter’s maximum
rated wattage increases so does its DC input current. Therefore larger wires and circuit breakers need to be installed to carry the greater currents. That is why most of the higher power inverters have higher input voltages.
Surge Capacity - Most inverters are able to exceed their rated wattage for limited periods of rime. This is necessary since motors may draw 5 to 7 times their rated wattage during start up. Surge requirements of specific loads should be determined by consulting the manufacturer or measuring with an ammeter.
Efficiency - If you plan to operate your whole home on an inverter, a high efficiency unit is a must. Many inverter manufacturers claim high efficiency. However, some inverters may only be efficient when operated near their peak output. Check inverter specifications. Most of the time the inverter is powering loads at less than its rated capacity. Therefore, it is usually wise to choose a unit rated at a high efficiency over a broad range of loads. Also choosing an inverter that has a search mode in recommended. A lot of inverters use a lot of power when they are on even if they are not powering a load. Good inverters go into search mode when no loads are being powered, this saves a great deal of power. Then when a load is turned on the inverter automatically comes on to power that load.
Inverters with Chargers - Having the option of having a battery charger as part of the inverter is a good idea. Most good inverters have an excellent three stage charger as part of the unit. This allows you to use a fuel powered generator as a back-up during long periods without sunshine. Inverter/chargers are also used as part of utility back-up systems.
Inverter Sub-system Checklist
While the inverter is one of the main components in an AC solar electric power system it must be installed properly and safely.
Inverter to battery cabling - Because of the high current required on low voltage circuits, the cable from the inverter to the battery is large, commonly 2/0 to 4/0 in size. Using smaller conductors is unsafe and will not allow the inverter to perform to its full output rating.
DC input disconnect and over-current protection - It is very important to have a safe installation with a properly sized DC rated, CSA approved safety disconnect. Typically the
disconnect works in conjunction with a over-current protection device such as a fuse or breaker. These components are installed in an enclosure which can also house the solar input breaker and/or DC load breakers or also shunts.
AC output disconnect and over-current protection - If the AC load center, which is fed from the inverter, is adjacent to the inverter, then the main breaker can serve as the inverter output disconnect and over-current protection. If, however, this panel is not grouped with the inverter, then a separate unit should be installed. This also holds true with AC circuits coming to the inverter from a generator or utility source. Using the inverter by-pass switch on the "additional products page" is a good and inexpensive way to address both these issues.
Shunts - Used in conjunction with an amp/hour meter to read the amperage flowing into and out of the batteries. This device is installed in the negative conductor. It is usually, and easily housed in the disconnect enclosure.
NO system should ever be installed without safety disconnects with properly rated and sized breakers and the properly sized cabling. Protect yourself and your property.
Note all system must be inspected by the Electrical Inspection Authority.