If the power grid goes down in the middle of the day, almost everyone “loses power” regardless of whether the home has solar panels or not. I note most households will lose power but not everyone. For the majority of systems, the sun could be blazing away at 1 pm on a cool, sunny afternoon but should the grid go down, the majority of households will lose access to their electrical energy supply. When the grid goes down which we call a “power outage” or a “blackout”, a safety feature referred to as “anti-islanding protection” results in an electrical supply source ceasing to feed into the grid. All grid-tied supplies must automatically cease exporting energy when grid power goes down so that technicians can safely work on the lines to undertake repairs without the risk of being electrocuted from active supplies keeping the system “live”. When an electrical supply is “islanded”, that is, separated from the main supply, “anti-islanding protection” stops the systems from feeding energy into the grid. Because of this necessary safety feature, when the grid goes down, not only does the excess energy a home’s solar panels generate cease to feed into the grid but you can no longer use the power generated from your solar panels to run your household. Your rooftop solar system, regardless of size or quality ceases to supply energy that you can access. For most households, electricity supplied by solar panels is only of use when the grid is functioning. What can be done to “keep the lights on” in the middle of the day should a blackout occur? Let’s have looky … The energy supplied from solar panels is in the form of Direct Current (DC). Since our homes run on Alternating Current (AC), an inverter is required to change the electrical supply from DC to AC which allows use of the collected solar energy to be consumed in the house and the excess to be exported into the grid. Yes, there are inverters that have the capacity to operate the legally required “anti-islanding protection” during “power outages” and still allow the use of the energy collected from solar panels at the time of collection to be used within the home. The reason these are not supplied as standard in the majority of homes is because they are expensive and very rarely needed. Further to that, should cloud cover reduce the electrical collection from your 6kW system down to only 2kW at a time when your household appliances may need 3kW; that serious shortage of required energy may cause some unwanted and possibly serious damage to your electrical appliances. Switching to battery system during a blackout occurring during daylight hours allows for a consistent electrical supply even when clouds periodically cover the solar panels. Of course you need an inverter that can change your DC supply from the solar panels to AC because home appliances are manufactured to run on AC. This is an expense most households probably don’t need and there is a significant reduction in efficiency, that is energy losses, when high DC electricity from the panels is “transformed” into the 12, 24, 36 or 48 volts to charge the battery system and then changed back into AC electricity for household use. There is a plethora of combinations and permutations of energy setups and supplies for homes which may include other energy sources such as wind, water turbines or petrol or diesel generators.
The most common set ups are the most practical and meet the requirements of the general public’s needs best. Most people live in cities or towns so a simple “grid connected” system is most common where a household accesses all of its electrical energy from the grid. The next most common set up which continues to grow in popularity is a “grid interactive” system. Grid-interactive systems have solar panels and uses the energy generated from the panels through the day exporting excess energy to the grid or importing any shortfall energy required. At night the household exclusively uses energy from the grid. Should there be days or even weeks of wet weather the household operates as a normal grid-connected home. Grid-interactive solar systems generally pay themselves off in 3 to 5 years and have a life expectancy of 20 to 25 years making them an economically viable option in today’s market.
A third option, less popular because it is not an economically viable option for most homes, is an interactive system with battery backup or “hybrid” electrical system. That is, a grid connected solar system where the energy collected from the solar panels is used at the time of collection and the unused energy is used to charge the battery bank with any excess energy exported to the grid. Should more energy be required that is being produced from the solar panels, energy is pulled from the battery bank. If the battery bank is depleted, energy is pulled from the grid. This system keeps “the lights on”, metaphorically speaking, during a power outage at any time of the day or night. Because it is still less expensive to pull a kilowatt hour of energy from the grid than it is to source it from a battery, these systems are more for convenience than for economic reasons.
The fourth option is to be “off grid“. That means that the household has no access to grid supply electricity and all energy for the home is supplied onsite. Solar panels are the most common source of off-grid energy. As energy obtained from battery storage is a much more expensive option, off-grid systems are generally reserved for people who live far from where mains power or grid power can be readily accessed. Homes that operate on off-grid systems generally have to be very energy-efficient as a kilowatt hour of electricity may easily cost four to six times as much as that supplied from the grid. Obviously the most economically viable option is the second option using a grid interactive system. For homes that need energy security for medical reasons or for the peace of mind of protecting food in freezers, a small generator such as a 2.4 kVA unit will be suffice to keep the household running with plenty of headroom for general appliances to turn off and on at will.
John Lynn
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Moreton Bay residents can access weekly tips from John on Community Radio 101.5 FM Friday Mornings at 10:10am