Solar Power Glossary

Please note this glossary of solar energy related terminology and jargon is a work in progress and we are adding to the dictionary gradually.

AC coupling: For home energy storage this means the connection from the solar panels to the batteries is 230 volts AC. i.e. the DC from the solar first gets converted to AC, before the AC is then converted back to DC to charge the batteries. Like this:

AC isolator: A handy ‘off’ switch for your solar system. It will either be an isolator near your inverter, or in your switchboard with the label “Main Switch Inverter Supply”. Your rooftop solar system will have multiple isolators – You always switch the AC one off first, get the order wrong and it can go BANG!

activated stand life: How long a battery can be stored within a specific temperature range before it goes flat. More commonly referred to as shelf life. Also known as activated shelf life.

AGL Energy: AGL is Australia’s second largest electricity retailer with over 3.7 million customers.  In addition to selling electricity retail they also generate electricity for sale on the wholesale market.  They own the 3.15 gigawatt Loy Yang lignite power station in Victoria, which is Australia’s largest power station and one of the world’s largest sources of carbon dioxide emissions.

alternating current (AC): The type of current that is used in our homes and most transmission lines. Rather than just flowing in one direction, the current rapidly moves back and forth 50 times a second, which is the standard in the majority of countries. But most of the Americas, half of Japan, a couple of Koreas, Philippines, Saudi Arabia, Madagascar, and Liberia wiggle it back and forth 60 times a second.

alternative energy: Sources of energy that are an alternative to using fossil fuels or nuclear power. The big three are solar, wind, and hydroelectricity. Other types are geothermal, biomass, tidal, and wave power. While nothing lasts forever, these sources of energy should be good to go for at least one billion years. But note the earth only comes with a 5 billion year warranty which doesn’t apply if we break the planet ourselves through misuse.

ambient temperature: Basically, how hot or cold it is outside. This affects how well your solar panels work, as panels love light but hate heat. Really hot days can cause solar panels to lose aout 10% of their energy output. 

ampere (A): The unit of electrical current which refers to the rate of flow of electricity. A normal Australian power point can supply 10 amperes. An electric stove will normally have a 32 ampere connection which means it can draw a lot more power than if it was plugged into a standard power point. In Australia ampere is almost always shortened to amp. The number of watts is equal to amperes multiplied by volts, so a 10 ampere power point at 240 volts can supply 2,400 watts.

ampere-hour (A·h or A h or Ah): A current of one ampere produced for one hour. Lead-acid batteries used for home energy storage often have their capacity measured in ampere-hours. To determine its capacity in kilowatt-hours, multiply the ampere-hours by its voltage and then divide by 1,000. So a 100 ampere-hour 12 volt battery can output a maximum of 1.2 kilowatt-hours.

ancillary services: These are services that provide the electricity grid with stability and allow it to continue to operate smoothly. They include frequency regulation to keep the grid operating between 49.9 and 50.1 hertz, voltage regulation which can involve the use of spinning or non-spinning reserve, and the ability to restart the grid after a complete or partial blackout.

angle of incidence: The angle sunshine hitting a flat surface makes with an imaginary line rising straight up from that surface. If the angle of incidence is 0 degrees it means sunlight is hitting head on, while 90 degrees is a complete miss. The lower the angle of incidence the more electricity a solar panel will generate.

annual solar energy yield: This is the total energy output of your solar system in a year in kilowatt-hours.  Something that’s vital for calculating your solar system’s bang for buck.

anode: The anode is the electrode from which lithium ions move away during discharge and towards during charging.

anthropogenic: Caused by humans. For example, anthropogenic carbon dioxide is added to the atmosphere through human activity such as burning fossil fuels and land clearing rather than natural processes.

anti-islanding: An essential safety feature that severs a solar system’s connection to the grid during a blackout, preventing you from exporting energy into the grid and giving line workers a nasty shock.

arc fault: If a DC cable on your roof is damaged, blue crackling electricity can leap between gaps in the cable.  This miniature lightning is called an arc and is dangerous because it can start fires. Get a good install – please!

array: A collection of connected solar panels that work together which can range from 2 panels to over one million. Array is definitely not what killed Steve Irwin.

array over-sizing: Array oversizing might sound like an “uh-oh”, but it’s actually more of an “oh yeah”! It’s when your solar panels can pack more punch than your inverter’s rating. solar panels spend most of the day generating below their full capacity.  Without a battery your panel capacity can normally be a maximum of one-third greater than the inverter capacity.  With a battery it can be much higher.

Australian Energy Market Operator (AEMO): The mob of bureaucrats and engineers in charge of the electricity and gas markets for everywhere in Australia except WA and the NT. 

Australian Standards: the Australian Standards relating to solar installations are:  

avoided cost: A cost saving that occurs in the future. For example, if you install rooftop solar the avoided cost is the grid electricity you don’t have to pay for.

azimuth:  Picture azimuth like a compass for your solar panels. It’s all about degrees: Zero for true north, 90° for east, 180° for south, and 270° for west. But here’s the kicker for us Aussies: aiming them north is like a bullseye for max power generation. 

backup: Something you fall back on when things don’t go as well as you hoped. An off-grid household will usually have a backup generator for use when the weather is bad and/or electricity consumption is high.

balance of system (BOS): Refers to all the components of a solar PV system, excluding the solar panels. This includes wiring, switches, mounts, inverters, and other equipment.

baseload: The lowest amount of electricity used by a grid or or electrical system, generally over 24 hours. The baseload demand in South Australia’s electricity grid yesterday was 950 megawatts because at no point did the state use less than that much grid power. A baseload power station is one that operates at a high capacity factor and continues to operate during periods of minimum demand. Baseload power stations are not required, as South Australia’s grid has demonstrated by operating without any.

battery: A specially constructed case containing potential chemical energy. When a chemical reaction occurs electricity is generated and can be used to do work. In disposable batteries the chemical reaction cannot be easily reversed, so avoid using them. In rechargeable batteries the chemical reaction can be reversed by supplying electrical energy. (Or in some rare cases sticking part of the battery in a really hot oven or other weird behaviour.)

battery bypass switch: A physical switch that allows you to turn your essential circuits back onto the grid if your battery is flat or misbehaving. 

battery capacity: The total amount of electrical energy a battery can provide before it is completely discharged. Battery capacity is often higher than usable capacity because many types of batteries will be damaged if they are completely discharged.

battery case: The tough protective case that protects the battery cell or cells inside. It is part of the battery and doesn’t need to be purchased separately.

battery cell: A battery can be made up of many individual units called cells. Or a battery can be a single cell, such as the small batteries you might put in a remote control or toy. Very rarely you will come across a person who will insist that a single cell cannot be referred to as a battery, but that person is a dick and can be safely ignored.

battery cycle life: This is the number of times a battery can be fully discharged before it becomes so degraded it can only operate at 80% of its original capacity. Because a full discharge is very hard on most types of batteries the number of cycles that are typically given for home energy storage systems are not for 100% discharges and will usually be for 80-90% depth of discharge instead.

battery enclosure: A cabinet or structure that holds batteries. This is important for lead-acid batteries used for home energy storage as they can take up a lot of space, require a lot of cabling, and both children and batteries operate better when kept separate from each other. Modern home energy storage systems normally do not require an enclosure as they are designed to be less dangerous and less infested with cabling.

battery inverter: An inverter designed for use with batteries.  This is required for home energy storage if the solar inverter is not a multimode solar inverter that is compatible with the batteries used.  (Multimode inverters are also known as hybrid inverters.)

battery management system (BMS): The software and electronics that control how a battery charges and discharges. Some batteries come with a built in BMS. This is good, because the BMS can act as a ‘gatekeeper’ to the battery and stop the battery inverter doing things that would damage the battery, such as charging/discharging too fast or too much. The Powerwall and ZCell are examples of batteries with a built in BMS. Batteries without a BMS are trusting the battery inverter not to do anything stupid.

bayonet fitting: a light fitting common in many older buildings where a light bulb has to be pushed in against a spring and then slightly rotated to seat it in place, similar to a bayonet. The name has nothing at all to do with the fact that it is possible for the bulb to break and stab you in the hand.

bifacial solar panels: Unlike regular panels, they can capture sunlight from both their front and back sides, like a white rooftop or the ground. They’re much more useful in ground-mount applications than for residential rooftops.

bird poo: This substance is sometimes called white dielectric material by American engineers and bird shit by Australian ones. It can cause a significant reduction in the output of solar panels. The white portion isn’t actually poo but concentrated uric acid, which is handy to know if you are ever caught short of uric acid.

black start: In the context of solar batteries, this is when a flat battery can be re-started purely from solar, instead of needing the grid or a generator.

blocking diode: This diode prevents current flowing in a specific direction, which is perfectly normal behaviour for a diode. They prevent solar panels that are connected to a battery from draining the battery at night.

break-even point: The moment when the savings from your solar system equal its cost. This is typically between 3-7 years, depending on how much energy your home uses during the daytime.

brightness: How well lit things appear to the human eye. Luminance is how much light there really is. They are not the same thing which is why photographers use light meters. Because the human eye is so adaptable we are very bad at judging absolute light levels.

brownout: Not as severe as a blackout, a brownout is a temporary reduction in voltage in the electrical power supply. 

Btu (British Thermal Unit): Also referred to as BTU. A kilojoule wearing a top hat and monocle and just different enough from a plain old kilojoule to be annoying. One Btu is 1,055 joules. It is an old term that is outdated. Please let it die.

busbar: Found inside a solar panel, these are thin wires or ribbons that carry electricity from the solar cells. More busbars can mean more efficient energy transport, but design matters too.

building-integrated photovoltaics (BIPV): When solar panels don’t just lay on top but become part of the building itself, like solar roof tiles or solar windows. 

by-pass diode: Quality solar panels have by-pass diodes that prevent a part of the panel that is suffering from shading, bird poo, or other problems, from affecting the performance of the rest of the panel and so improve the overall output from what it would be otherwise.

calendar fade: The slow degrading of performance that occurs with many types of batteries even when they are not used. As a result, even a lightly used home energy storage system is likely to have suffered a significant amount of deterioration by the end of its warranty period. Some battery types, such as zinc-bromide, don’t suffer from this problem.

calendar life: How long a battery can survive unused on the shelf before it is unusable. Because warmth causes things to decay faster, it is dependant upon temperature. Note this is different from activated stand life or shelf life which is how long it takes a battery to go flat rather than become completely useless.

capacity factor: The portion of electrical energy a generator produces compared to if it ran at its nameplate capacity all the time. It is often given as a percentage. If the wind blew strongly all the time a magic wind turbine that never needed repairs or maintenance could operate at a capacity factor of 100%. But because the wind is not constantly strong and wind turbines aren’t quite magical enough, they tend to operate at capacity factors from 30-42% in Australia. Because of things such as clouds and the rotation of the earth, a north facing rooftop solar system in Hobart may have a capacity factor of 14% while one in Darwin could have a capacity factor of 20%.

carbon dioxide (CO2): A greenhouse gas that is released from burning fossil fuels. Human activity has increased its level in the atmosphere by over 40% since the start of the industrial revolution. This results in global warming which has contributed to disastrous environmental effects such as floods, killer heatwaves, bushfires, and extinctions. Global warming kills humans and will greatly increase in severity unless we dramatically cut carbon dioxide emissions starting now.Currently 87% of human CO2 emissions result from burning fossil fuels, 9% from land use changes, and 4% from industrial processes such as cement making.

carbon price: The most economically efficient method of reducing carbon dioxide emissions. Carbon prices come in two types, a carbon taxes and emission trading schemes. They are the most efficient method because they directly discourage the undesired activity by making people pay to release CO2 and other greenhouse gases into the atmosphere from activities such as burning fossil fuels. A common mistake made in regard to carbon pricing is to regard it as a cost. It is not a cost, but a transfer and money raised from a carbon price is available purposes such as lowering taxes, paying for government spending, or distributing equally amoung citizens as part of a guaranteed income.

cat: Not a dog.

cathode: This is the electrode in a battery which positively charged cations move towards and negatively charged anions moves away from. 

central inverter: usualy refers to a large (MW scale) inverter that thousands of solar panels will be connected to in a very large commercial or utility-scale installation. They are usually big boxes, the size of a small shed. Some people will refer to the single inverter in a residiential installation as a central inverter, but the proper designation for this is a string inverter 

charge: usually this refers to putting energy into a battery. For example, “I need to charge my phone or I’ll die from Flappy Bird withdrawal.” It can also refer to the basic electrical property of matter. All matter contains tiny little positive things called protons and tiny little negative things called electrons. If an object has the same number of protons and electrons its charge is neutral. If it has more protons than electrons its charge is positive and if it has more electrons than protons its charge is negative. And when it comes to charges, just like Paula Abdul and a cartoon cat, opposites attract.

charge controller: A device that regulates the charging and discharging of batteries. They generally operate to maximise battery life and prevent the depth of discharge being too great and prevent overcharging. In modern home energy storage the charge controller is often an integrated part of the system and not a separate item that needs to be worried about. Charge controllers are also referred to as charge regulators or battery regulators.

charging: Putting energy into a battery. Technically we should say energising instead of charging because the amount of charge in the battery is always the same, it is only the type of charge that changes, and what matters is how much usable energy there is in the battery that can do work for you. But no one really cares about this, so go ahead and charge away.

circuit: A loop that electricity travels through. A circuit can have one or many electrical components on it.

conductance: How well something conducts electricity. How poorly something conducts electricity is resistance.

conductor: Something that carries electric current. A good conductor will only lose a small amount of electrical energy when current is passed through it. Electrical cables lose little electrical energy as heat when used properly and so are good conductors. A stove element loses a lot of electrical energy as heat and so is a bad conductor. People are bad conductors and enough current can cause significant heating both externally and internally, so try to avoid having current pass through you whenever possible.

cost-effective: If something is worth the money you spent on it, it is cost-effective. The accounting methods businesses use to determine if something is cost-effective vary and can be quite complex.

cost of money: When you borrow money from a bank or other financial institution they will want you to pay interest. Even if they say you don’t need to pay interest they will still get you in some other way and make you pay. If they didn’t, they wouldn’t be able to put bread in the mouths of their children or Ferraris in their garages. So the cost of money is the interest you pay plus the cost of any fees, charges, or tricks. Because inflation reduces the value of the money you use to pay them back, the real cost of money is the interest rate they charge you after it has been adjusted for any any fees, charges, and tricks; minus the rate of inflation. So if you borrow money at 5% with no other costs and inflation is 2%, the real cost of money in this instance is 3%.

C-rate: A measure of how much power a battery can provide and how long it takes to discharge. A C-rate of one means a battery can provide enough power to discharge its capacity in one hour. A C-rate of 2 means the battery can discharge its capacity in half an hour. And a C-rate of 0.5 means a battery can discharge its capacity in 2 hours. So if a 4-kilowatt battery has a C-rate of 1 it can output an average of 4 kilowatts and will be discharged in one hour. If it has a C-rate of 4 it can output an average of 16 kilowatts and will be discharged in 15 minutes. And if it has a C-rate of 0.2 it can output 0.8 kilowatts and will be discharged in 5 hours.

cut in: The point at which a controller activates a device. For example, my refrigerator’s thermostat will activate the heat pump to cool things down when the temperature inside rises to 4 degrees Celsius.

cut off voltage: As a battery becomes discharged the voltage of the current it supplies decreases. The cut off voltage is either the voltage at the point where the battery is fully discharged, or when a charge controller stops the discharge at a pre-set point. Most home energy storage systems have cut off voltages which prevent their batteries from being fully discharged to prolong their lives.

current: A flow of electricity. There are are two types. Direct current (DC) where electricity flows through a conductor in one direction. And alternating current (AC) where electricity rapidly flows back and forth in a conductor.

datasheet: These provide technical information on solar panels, inverters, and other items as well.  They can be found online.  If you can’t find the datasheet for a solar panel or inverter online then that’s the internet’s way of telling you not to buy it.

DC Converter: This is a device that changed DC current from one voltage to another.  A battery DC converter can allow batteries to be connected to a rooftop solar system.

DC Coupling: When there is one inverter used for both the solar and batteries. DC from the solar panels is used to charge the batteries via a DC charger.

If you have a separate regulator and inverter it might look like this:

Or if you have a grid connect solar system with a single ‘hybrid’ inverter it might look like this:

 

DC optimiser: This is a small device that is either attached beneath a solar panel when it is installed or comes already integrated with the panel.  They maximise the output of panels and if one suffers from poor performace due to shade, bird poo, or other reasons it will prevent it from affecting the performance of other panels on the string.  They increase the output of solar panels by around 5-15%.  In this respect they are similar to microinverters, but do not convert the panel’s DC to AC and instead rely upon a string inverter.

deep cycle battery: A battery that is designed to be deeply discharged regularly and suffer less degradation than a normal battery of its type when doing so. Usually only used to describe lead-acid batteries and the depth of discharge they are designed for generally ranges from 45-75%.

depth of discharge: How much of a battery’s total capacity is depleted before it is recharged again, expressed as a percentage. For most battery types the amount of deterioration the battery suffers becomes progressively greater with the depth of discharge, which means two 40% discharges will result in less total deterioration than one 80% discharge.

dielectric: A material that is dielectric is an electric insulator. The plastic coating around electrical wiring is an example.

diode: An electronic component. A semiconductor that only allows the flow of electricity in one direction like the valves in your heart only allow blood to flow in one direction. (If they didn’t, it is be unlikely you would be reading this.)

direct current (DC): Electricity that flows in only one direction. Solar panels produce direct current. Before it can be used in our homes it has to be converted into alternating current by an inverter. Batteries can only be charged with direct current.

discharge: When a battery outputs electrical energy it discharges and the energy stored inside it decreases. When a battery is fully discharged there is no usable energy left.

discharge rate: How rapidly a battery is discharged.  This can be measured by C-rate.

discount rate: In general, people regard $1 gained now as more valuable than $1 gained in the future. In other words they discount the value of future money. Human beings are complex and fickle creatures and their discount rates can vary wildly from situation to situation. But when it comes to making decisions about investments it is generally assumed that people have a single discount rate. A person who requires at least $109 in one year’s time in order to forgo receiving $100 now has a discount rate of 9%. A person with a lot of money sitting in the bank at 2% interest is going to have a low discount rate as any guaranteed return over 2% is going to look good to them, while a person who has large credit card debts at 15% interest will have a high discount rate, as any investment would need to have to have a guaranteed return of over 15% to be better than using the money to pay off their debts.

All else equal, people with low discount rates will regard buying rooftop solar as a better deal than people with high discount rates. But people with high discount rates could benefit from leasing rooftop solar, even though in the long term they will end up paying much more than if they had just bought the system outright. In addition, they could also benefit from putting their credit cards through a blender.

distributed solar: This is small scale solar generation that first meets the electricity needs of a home or business before any surplus is sent into the grid. It is extremely cost effective in Australia. The opposite of distributed solar is utility scale solar which consists of large solar farms where the electricity generated is sent directly into the grid.

DNSP: Distribution Network Service Provider. The company that owns and operates your local distribution network. i.e.the local poles and wires that connect up all the homes and businesses (but not the long distance wires that connect remote generators to the towns and cities). 

This table shows you your local DNSP:

dopant: A very small amount of a substance added to a solar cell or other semi-conductor to give it specific electrical characteristics. Boron and phosphorus are the two dopants normally added to silicon solar cells. Boron is about as toxic as table salt and is an essential plant nutrient, while phosphorus is an essential us nutrient, even though I don’t recommend trying to eat pure phosphorus. And while I also don’t recommend eating solar cells, the large majority of them are not toxic.

Doping: Adding a dopant to a solar cell or other semiconductor during production.

dry cell: A battery cell that does not contain any liquid but instead has a solid or paste electrolyte.

duty cycle: The percentage of time that a machine or system is active. If a backup generator is used for 48 hours a year its duty cycle is 0.55%.

east facing: Solar panels mounted on east facing roofs will generate more electricity in the morning and less in the afternoon. Placing some or all panels facing east can improve the self consumption of homes and businesses that use large amounts of electricity in the morning. For example, they can be useful for warming the house on cold winter mornings.

edison screw: a screw lightbulb fitting that is becoming standard in Australia only 140 years after it was invented. Apparently it has taken us this long to work out they are actually better. Note the edison screw is not what Edison did to Nikola Tesla.

efficiency: The universe is very strict about requiring more energy go into a system than useful energy comes out. The ratio between useful energy coming out and energy going into a system is its efficiency and is usually given as a percentage. For solar panels, the higher its efficiency the more sunlight energy will be converted into electrical energy. High efficiency panels are more expensive but take up less space, and so can be useful for people with limited room on their roofs.

earth: Electrical items with metal exteriors must have an earth or ground wire which is the bottom pin on an electrical plug. The earth wire is connected to the earth itself, usually by attaching it to a building’s cold water pipes. This is done so that if there is a dangerous fault, electricity will flow into the ground rather than people touching the faulty item. Appliances with a plastic outer case are considered safe enough not to require an earth wire and so their plugs only have two pins.

electrolyte: A substance inside batteries though which charged particles called ions move and this movement of ions allows current to flow externally from one battery electrode to the other. And this external flow of electricity can be used to do something useful such as power a flashlight or a home

electromagnetic radiation: This includes radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays. Sources vary in the type of electromagetic radiation they emit. Light bulbs give off infrared and visible light, while x-ray machines emit x-rays. Most of the energy in sunlight is visible light. It is possible to be harmed by electromagnetic radiation, as anyone who has used a microwave oven or gotten a sunburn probably knows. High energy radiation known as ionizing radiation is particularly dangerous to living things and is released by nuclear materials. We are constantly exposed to a very small amount of ionizing radiation and suffer very little harm from it, but trust me, you really want to avoid going around peeling open containers of nuclear waste or fooling around with x-ray machines.

electron: A very very very small negatively charged thing that hangs around atoms. Direct current is a flow of electrons in one direction through a conductor. Alternating current is electrons rapidly moving back and forth in a conductor. Electrons are attracted to positively charged protons and vice versa.

electricity: A phenomenon involving the movement of electrons or charged particles called ions. What we pay for on our electricity bills is electrical energy measured in kilowatt-hours and when we say a solar panel is 300 watts it refers to electrical power.

embodied energy: All the energy consumed in the production and delivery of an item. The embodied energy payback time is how long it takes generating capacity to produce as much useful energy as was used to make it. In Australia the energy payback time for a solar panel can be much less than one year and the period for a compete rooftop solar system can be under two years.

emissions: This often refers to greenhouse gas emissions from burning fossil fuels, but can also refer to other pollutants. For example, burning coal releases carbon dioxide, sulphur dioxide, nitrogen oxides, particulate matter, mercury, lead, carbon monoxide, hydrocarbons including carcinogens and volatile organic compounds which contribute to ground level ozone formation, and arsenic. None of this is good.

energy: A common definition is energy is the ability of a system to perform work. Energy can be converted from one form to another, such as when a solar panel is used to used to convert sunlight into electricity. However, converting energy always results in some waste heat, so unless your goal is to generate heat, there is nothing we can do with 100% efficiency.

energy audit: Inspecting a home or business to determine how energy is consumed, usually to determine ways in which energy efficiency can be improved or to determine that a particular standard has been met.

energy density: The higher the energy density of a battery the more energy it has per liter of volume. This is different from specific energy which refers to energy per kilogram. The higher the energy density the less space a battery will take up per kilowatt-hour. And the higher the specific energy the less a battery will weigh per kilowatt-hour.

energy efficient: The more energy efficient something is, the less energy is required to produce one unit of output. For example, LED lights use much less energy than incandescent light bulbs or compact fluorescent lights to produce the same amount of light, and so are more energy efficient.

energy management relays: Switches that allow loads such as hot water to be turned on when there is excess solar power and turned off when there isn’t.

energy storage: A method of storing energy for later use. For home and business energy storage this is normally done using batteries to store solar electricity generated by rooftop solar during the day. Other methods include storing hot water for later use, storing ice to be used for air conditioning during the day, and lowering the temperature inside freezers.

Large grid scale energy storage in Australia consists of three hydroelectric pumped storage systems. One large one that is part of the Snowy Mountains Hydroelectric Scheme, a medium sized one in Queensland, and one that is so small I’ve forgotten where it is.

equinox: Twice a year, during the and autumn and spring equinoxes, day and night are the same length. They occur around the 20^th of March and the 22^nd of September.

escutcheon: Sounds like something out of a medieval fantasy, but in the realm of Aussie switchboards, it’s a modern necessity. An escutcheon is a hinged plate that covers the wiring behind your circuit breakers or fuses. It’s your switchboard’s own personal security guard, keeping prying fingers and curious eyes away from the live wires.

ESOI: Energy Stored On Invested. The ratio of electrical energy delivered by a solar panel or battery over its lifetime vs. the energy required to mine and manufacture it.

feed-in-tariff: The rate you are paid for the solar energy you produce. Under a net-metering scheme you are paid for only the solar energy exported to the grid. In a gross-metering scheme you are paid for all the energy produced by the panels.

frameless panels: These are solar panels without a metal frame around the edge.  Normally they are made of solar panels sandwiched between two sheets of tough glass instead of having a sheet of plastic on the underside.  As a result they may be called double glass or glass-on-glass panels.  An advantage of framless panels is that when they are set at a low angle water can’t gather at the bottom of the frame and collect dirt or seep into the panel and damage it.  Their drawback is they currently tend to be higher both in price and weight.

gigawatt: 1,000,000 kilowatts.  It takes 1.21 gigawatts to send a DeLorean through time.

gross-metering: A way of measuring and paying for solar electricity where all the solar electricity generated is metered and paid for, whether that electricity is used on-site, or exported to the grid. So you will be paid for all the solar you generate, but will also have to pay grid rates for all the electricity you consume.

Heterojunction Cell Technology (HJT): The cool kid on the solar cell block. HJT cells marry two types of silicon: amorphous and crystalline, forming a union that boosts solar cell efficiency. The amorphous silicon acts like a bouncer, keeping naughty electrons in check, helping to reduce energy loss. This union doesn’t just shoot up the efficiency but also performs better in higher temperatures. Handy for Australia.

hybrid inverter : an inverter (see next entry) that has both solar and battery supply, from which it can draw energy to create 240 volt AC power.

Hybrid inverters can also draw 240-volt AC from the grid to charge a battery if programmed to do so. This may be triggered by a price signal from an electricity retailer or scheduled for a time of day when grid-supplied electricity rates are exceptionally low. With the right electricity retailer and the right hardware, there’s potential for those brave enough to get paid to both charge and discharge a battery.

IEC 61701: This is the standard a panel needs to meet to be certified salt mist corrosion resistant and suitable for installation near the beach.  Generally, panels installed within 200m of the beach must meet this standard. 

inverter: These convert direct current (DC) to alternating current (AC). The most common type in Australia are string inverters, which send DC produced by solar panels along one or more cables called strings to a single inverter.  Another type are microinverters, which consist of a small inverter attached to each panel that directly converts its DC to AC.

junction box: This is a box in which wires connect.  A small one can be found on the back of solar panels.  It is normally well sealed to prevent water seepage, corrosion, and to prevent people who lack adequate caution from licking the electrical connections.

kilowatt (kW):  A measure of power equal to 1,000 watts.  If I have a bar heater that has two 1,000 watt heating elements and I turn one element on it will draw 1 kilowatt of electrical power.  If I turn both elements on it will draw two kilowatts of electrical power.  It doesn’t matter how long I leave the two elements on, whether it is one second or 10 days, when they are both on the power drawn will always be 2 kilowatts.  Kilowatts are measured in an instant. 

kilowatt-hour (kWh, kW·h) A measure of energy. If I turn on one a 1,000 watt element and leave it on for one hour it will consume one kilowatt-hour of electrical energy.  If I leave two elements on for one hour they will consume two kilowatt-hours of electrical energy.  And if I leave two elements on for three hours they will consume six kilowatt-hours of electrical energy.  Kilowatt-hours are measured over time and are equal to the number of kilowatts of power multiplied by the number of hours. 

While they are related, kilowatts and kilowatt-hours are very different things.  Kilowatts are a measure of power and kilowatt-hours are a measure of energy.

Levelised Cost Of Energy (LCOE) The cost of energy from a system, as calculated by dividing the total cost of the system, including operating and maintenance costs by the number of units of energy (usually in kWh) that the system is expected to produce over its lifetime. 

Lithium Iron Phosphate (LiFePO4)  A type of Li-ion battery. This chemistry is safer and has a longer life than NMC batteries, so is better for stationary storage.

Megajoule (MJ) A unit of energy. 1 million joules. In the context of home energy use, MJ is most often used to show how much gas you’ve used on your gas bill. 1 MJ is the equivalent of 0.277778 kWh of electrical energy. And 1kWh is equivalent to 3.6MJ of gas.

megawatt (MW): A unit of electrical power. A megawatt is one million watts, or one thousand kilowatts.  1.5 kilowatts of electricity is enough to power an electric kettle.  2.6 megawatts is enough to power the electric motor of a mining truck carrying 290 tonnes of ore uphill.

megawatt-hour (MWh): A unit of electrical energy. If you use one MW of power for 1 hour, you will use 1MWh of energy. When describing battery storage capacity, a MWh of batteries is enough batteries to store 1 MWh of energy at any one time. i.e about 150 Powerwalls.

microinverter:  A small inverter that is attached beneath a solar panel and directly converts its output from DC to AC.  They maximise the output of each panel and operate independently so if one panel suffers from poor performance due to shading, bird poo, or other reasons it won’t affect the performance of other panels.

monocrystalline silicon: There are two main types of silicon used to make solar cells.  Monocrystalline solar cells are made from wafers cut from a single large crystal of silicon while polysilicon solar cells are cut from a solid silicon ingot that is made of many smaller crystals.  Because monosilicon is mostly free of defects solar cells made from it have higher efficiency than polysilicon cells.  At the time of writing, polysilicon is about 12% cheaper per wafer.  Polysilicon is sometimes called multicrystalline silicon.

multimode inverter: This is an inverter that can operate both on-grid and off-grid and can allow compatible batteries to be added to a rooftop solar system.  They are also known as hybrid inverters.  If you are on-grid and want to use battery storage if the grid fails, a multimode inverter is the only practical way to do it at the time of writing in September 2016.  Their disadvantages are they cost more than a standard, single mode inverter and the types of batteries or battery systems they are compatible with can be limited.

Maximum Power Point Tracking or MPPT: This is a method inverters use to get the most power out of solar panels.  Older inverters, and currently some small ones, only have one Maximum Power Point Tracker.  This means all the panels connected to the inverter need to be facing the same direction and if there is shading, suffer from the same amount, to prevent losses in output.  Most modern inverters of 3 kilowatts or more have two Maximum Power Point Trackers.  This allows them to accept two different strings of panels that can be facing different directions or under different conditions without suffering losses resulting from the differences between the two sets of panels.

net metering: a way to measure, and be paid for, solar electricity exported to the grid. Simply put a ‘net meter’ subtracts the energy used by the home from the amount of solar energy being generated at any moment in time. The result is the amount of energy that is fed into the grid and credited on your bill at the prevailing Feed-In-Tariff. If the result is negative (consumption is greater than generation), then you are importing energy from the grid and will be charged at standard rates for the electricity imported. Solar energy used on-site is not metered by a net meter. To track self consumed solar energy you need to buy a third party meter.

NMC:  A specific type of Lithium Ion (Li-ion) battery: It stands for Nickel Manganese Cobalt. The cathode is approximately a third nickel, a third manganese and a third cobalt. It is good for electric vehicles, not so good for stationary storage because it has a shorter cycle life and degrades faster than many other chemistries such as Lithium Iron Phosphate (LiFePO4).

nominal capacity: the amount of kWh that a battery can store in theory. In practice most batteries only allow you to discharge a fraction of this in order to prolong their lifespan. This practical limit is called the usable capacity.

Origin Energy: Origin Energy is Australia’s largest electricity retailer with over 4.3 million customers.  In addition to selling electricity on they retail market, they also generate electricity for sale on the wholesale market.  They own the 2.88 gigawatt Eraring Power Station in NSW and claim it is Australia’s largest power station, but that is only true when Loy Yang Power Station in Victoria is feeling a bit crook (as opposed to making people around it feel crook) and not operating at full capacity.

panel mismatch: Because manufacturing processes aren’t 100% accurate, solar panels will vary slightly in their performance even if they are made on the same production line on the same day.  Currently, most solar panels end up being attached to a string inverter and this arrangement the weakest panel can pull down the performance of the others.  This panel mismatch is typically estimated to reduce the output of solar systems by around 2%.  A dedicated installer can minimise this loss by testing the performance of each individual panel.

Photovoltaic (PV): Photovoltaic materials generate electric current when exposed to light.  Solar panels are contain photovoltaic materials and so are able to generate electricity without any moving parts.  Silicon PV is the most common type, but others include, cadmium telluride (CdTe), copper indium gallium selenide (CIGS), copper indium diselenide (CIS), and organic.

polysilicon (multicrystalline silicon):  There are two main types of silicon used to make solar cells.  Monocrystalline solar cells are made from wafers cut from a single large crystal of silicon while polysilicon solar cells are cut from a solid silicon ingot that is made of many smaller crystals.  Because monosilicon is mostly free of defects solar cells made from it have higher efficiency than polysilicon cells.  At the time of writing, polysilicon is about 12% cheaper per wafer.  Polysilicon is sometimes called multicrystalline silicon.

power density:  How much punch a solar panel can pack in a given area. Its units are watts per metre squared (W/m²). Imagine having a tiny patch of roof, but you want to rake in as much solar goodness as possible. A solar panel with higher power density is your go-to mate, as it cranks out more electricity per square metre. It’s like having a Nissan Leaf with the motor of a Cybertruck. 

Renewable Energy Target (RET): This is a scheme designed to increase the amount of new renewable generation in Australia.  It was first introduced by the Howard Government in 2001, expanded by the Rudd Government in 2009, and reduced by the Abbott Government in 2015. 

round trip efficiency: When a battery is charged some energy is always lost.  And when a battery is discharged some energy is also always lost.  The combined loss of energy going into a battery and going out, expressed as the percentage of energy that was put in, is the round trip efficiency.  A lead acid battery will typically have a round trip efficiency of around 75%.  A lithium-ion battery can have a round trip efficiency of 96% or higher, but in practice it is usually lower than this.  For example, the Tesla Powerwall, which uses lithium-ion batteries, has a round trip efficiency of 92.5%.

self consumption: When a home or business consumes electricity produced by its own rooftop solar system that is referred to as self consumption.  Because feed-in tariffs for new rooftop solar are now much lower than the price of grid electricity, maximising self consumption of rooftop solar power increases the economic benefit of a system and shortens its payback time.  Solar electricity that is not self consumed by an on-grid home or business is exported for use by other people on the grid, which displaces polluting and environmentally dangerous fossil fuel generated electricity with clean solar electricity.  One way to increase self consumption is to orientate panels in a way that maximises their output when the household daytime demand for electricity is highest.  Another method is to shift consumption to when rooftop solar production is high.  For example, hot water systems, dishwashers, air conditioners and so on can be turned on, or placed on timers that turn them on, when rooftop solar output is high.

single phase power: Single phase power is a form of alternating current.  In alternating current electrons wriggle back and forth 50 times a second.  In single phase power all the electrons do this at the same time, so at the point where they change direction the power supplied drops to zero.  This is why you can sometimes see lights flickering because the power supplied is not constant.  In three phase power there are three wires in which the electrons wriggle back and forth 50 times a second, but at slightly different times so that constant power is supplied.  Most home in Australia have single phase power and it is sufficient for most people’s needs.  But buildings with large central air conditioners, heavy tools, or other devices that draw a lot of power usually have three phase power.  Three phase power is becoming more popular for homes in Australia. 

STC (Small-scale Technology Certificate): These certificates are created when a rooftop solar system or other small-scale renewable energy system is installed.  They are part of Australia’s Renewable Energy Target which is designed to increase the amount of renewable energy generation in the country.  Because electricity retailers are required to hand over a certain number of them each year to show that the amount of renewable genertion is increasing, there is a market for these certificates and they can be turned into dollars.  Normally solar installers use the STCs created from installing rooftop solar to reduce the cost of the system to the homeowner (popularly referred to as a “solar rebate“), but people are free to keep them for themselves if they wish. STC’s can be created for up to 12 months after the installation takes place.

string: The cable on which solar panels are attached to a string inverter.  The panels are attached in series and the string delivers high voltage direct current to the string inverter.

string inverter: An inverter that has one or more strings of solar panels attached to it.  It converts direct current from the solar panels into alternating current that is used in our homes and business or exported to the grid.  They are by far the most common type of inverter in Australia. 

temperature coefficient: As the temperature of a solar panel rises above standard testing conditions (ambient 25C), the power output starts dropping below the module’s nameplate wattage rating. The temperature coefficient of panels can vary widely, so it’s a number to take note of. A typical value is 0.4% per °C. The lower a temperature coefficient rating is, the better. Bear in mind also that in real-world sunny conditions, the air temperature may be 25°C, but the panel will be hotter.

tier 1: Tier 1 is a measure of the ‘bankability’ or financial strength of a solar panel manufacturer. It is not a measure of quality of a particular panel model. But it is often used as a proxy for quality. The general idea being that if a manufacturer makes crappy panels, they won’t be successful financially, and they won’t be bankable. A red flag for a crap installer is that they advertise ‘Tier 1 panels’ without disclosing the brand. Most panels from Tier 1 manufactures are good, but some Tier 1 manufacturers do not have an Australian presence and instead export panels into Australia through a local importer. These panels may be their bottom-end panels that they don’t want to sell in countries where they have a stronger brand to protect. If you buy these panels and they fail, you should first go to the installation company. If they have disappeared you have to go to the importer. If the importer is the same as the installation company and they have disappeared you are royally screwed. We only recommend panels with a proper Australian presence. Finally – there are some good panels out there that are not Tier 1, because the manufacturer is not big enough. Tindo is an example.

three phase power: This is form of alternating current.  In alternating current electrons are made to wriggle back and forth 50 times a second.  In single phase power all the electrons do this at the same time.  So at the point where they change direction the power supplied drops to zero.  This is why you can sometimes see lights flickering as the power supplied is not constant.  In three phase power there are three wires in which the electrons wriggle back and forth 50 times a second, but at slightly different times so that constant power is supplied.  Most home in Australia have single phase power and it is sufficient for most people’s needs.  But buildings with large central air conditioners, heavy tools, or other devices that draw a lot of power usually have 3 phase power.  It is becoming more popular for homes in Australia. 

usable capacity: The amount of kWh that you can store in a battery in practice, without killing it prematurely. As opposed to the nominal capacity which is often the number advertised by the marketing department and/or Elon Musk.

Voltage Rise Calculations (VRC): This are calculations often performed by installers in regional areas of Australia to determine if a household is permitted to export solar electricity to the grid, and if so, how much.

watt: The amount of electrical power consumed by an appliance, or produced by a solar panel / inverter / battery is measured in watts.  Every electrical applicance in Australia you can plug into a normal power point should have the watts it consumes written on it somewhere.  For example, on the bottom of my toaster it says 750 watts.  The capacity of solar panels is number of watts of DC power they will produce under standard test conditions.  The capacity of inverters is the maximum amount of AC power they will consistently produce when supplied with sufficient DC power.  At the moment my rooftops solar system is producing 2,344 watts which is enough to power 3 toasters at once with a little left over.  Watts are a measure of power.  Watt-hours are different and are a measure of energy.  A kilowatt is 1,000 watts. 

wholesale electricity: Large electricity generators sell electricity on the wholesale market.  The wholesale price they receive per kilowatt-hour is much lower than what households pay per kilowatt-hour because it does not include the extra costs of transmission, distribution, or retailing.  The average wholesale cost of electricity varies from state to state, but the average for Australia overall is around 4 cents a kilowatt-hour.  Australia’s wholesale electricity prices are among the lowest in the developed world.