How do solar panels work?
Short answer – Solar panels convert the sun’s energy into useable electrical energy. In the first instance this is Direct Current (DC) that is converted into Alternating Current (AC) by an inverter. AC power can then feed into the electrical circuits of a household or business premises to power appliances and lighting. Most solar systems in Australia are connected to the electricity grid, so if the panels are producing less power than is being used, the balance is drawn from the grid. Alternatively, if the solar system produces excess power, that is fed back into the grid. This process requires a ‘smart’ meter. These can measure both electricity drawn from the grid, and excess power fed back into the grid for other consumers to use.
Long answer – A solar panel is also referred to as a photovoltaic (PV) module. These modules consist of multiple solar cells that employ a ‘photovoltaic effect’, which is where solar radiation is directly converted into an electrical current. Several PV modules are usually connected in series called a ‘string’. An array is either a single string or a collection of strings which feeds the generated electrical current to an inverter, which converts DC into AC – the more useable form of electrical current that powers most houses and appliances.
For those of you interested in more technical depth, such as the nature of the semiconductors used in PV modules and conversion efficiencies, Wikipedia is a good place to start. Search ‘Solar Power’ and ‘Photovoltaic System’ and follow the links.
How does shade affect a solar array?
Solar panels operate at maximum efficiency in full sunlight. However, if even one panel is shaded this can lower the output of all the panels in the series. It’s the old ‘weakest link in the chain’ principle.
So how can this problem be solved? There are technical solutions and physical solutions. For example, micro-inverters allow for each panel to work independently. There are also output monitoring systems that will shut down a poorly performing panel and allow the rest of the series to work at maximum efficiency. The problem with such solutions is that they add both expense and complexity to the solar array.
The best solution is the best design. A good designer will perform shade analysis and calculate the best position and layout for the panels. The electrical design can also allow for a partially shaded section to be wired as a separate ‘string’ so it will allow the full sun section to work at maximum efficiency. Needless to say, a good designer will present you with the best, customised solution for your needs – not the biggest, most expensive system they can sell you.
What’s an inverter?
Short answer – An inverter changes the Direct Current (DC) produced by the solar panels to Alternating Current (AC) used in grid connected domestic and commercial premises. This can be the 240 volt single phase power used in most households or the 400 volt three phase power used in many commercial and industrial buildings. The inverter feeds this useable power into the buildings circuits via the meter. If the solar power exceeds the usage, then the excess power is fed back into the grid.
Long answer – Modern inverters have many functions besides the simple DC to AC process. Typically they also measure and record the performance of the system. They have many inbuilt safety functions and can shut the system down if necessary. Many have web connectivity, either inbuilt or by a connected module so the system can be monitored remotely. This can be on a computer at the premises, or even via an app on a mobile device.
While solar panels are very simple and robust, inverters are now complex devices that require careful selection for the individual application.
How do feed in tariffs work?
The feed in tariff is the rate that a grid connected solar system will get paid for excess power exported to the grid. This power will be sold to other grid connected households and businesses by their retail energy suppliers. The meter at a grid connected premises will measure both power imported (for which you pay) and power exported (for which you get paid – or at least credited against your usage).
The confusion about this issue is largely the product of government intervention, which varies from state to state. In SA, those who connected some years ago receive over 60 cents per Kwhr, guaranteed for many years. Over time both the rate and the time have steadily reduced. Currently (in SA) there is no government supported feed in tariff for new connections. However, the power retailers are obliged to pay a minimum of 7.6 cents per Kilowatt Hour. This is referred to as the ‘Retailer Contribution’ but for simplicity we’ll refer to any payment for exported power as a feed-in tariff.
While the reduction of feed in tariffs has reduced the demand for solar systems, over this period the cost of those systems has fallen dramatically. So it still pays, given that solar power is cheaper than grid power and self-consumption is money saved. It does, however, change the payback calculations and therefore the design of a system. Ask how this works.
Will a solar system protect me from a grid blackout?
Short answer – No. A typical grid connected solar system will automatically shut down if there is a blackout. This is a legal requirement as it protects the grid workers from power feeding into the system.
Long answer – As stated above, a grid connected system can feed power into the grid and must shut down in a blackout. This means that even if the solar panels are pumping out DC power, this is not being converted by the inverter and therefore not available for use in the building. Frustrating? You bet. However, there are solutions.
There are now various energy management systems that can allow the system to work on a stand alone basis during blackouts. These are often incorporated as a function of the inverter. Ideally, these will incorporate a battery bank, so the system can supply the building’s full power needs even if the solar array is not producing enough power at that time. The critical system is an energy management system that will shut down any feed into the grid during a blackout, while allowing the solar power generated to feed the current use. Typically, these systems prioritise the use of power generated. First priority is to feed the current usage. Second priority is to charge the batteries. Finally, excess power is exported to the grid. A good system will recognise a blackout and not allow export for that time.
The catch is, such a system must be approved of by the network operator. In South Australia, this is SA Power Networks (previously ETSA). If you are considering being energy independent and purchasing such a system, ensure that your proposed device will be approved.