Grid interactive systems
- Grid interactive solar
- Grid interactive wind and hydro
- Cost effectiveness
- Who can have grid connected solar power systems?
- Power companies
- Case study
A recent development in renewable energy technology is 'grid-interactive or two way grid interconnection. These systems use sophisticated control equipment so that when your renewable energy system produces more power than you need, the excess power is fed back into the grid. When your system doesn't produce enough power, then you get power from the grid. Some electricity retailers offer 'net billing' arrangements, so that they buy the electricity you produce at the same price as they sell their electricity to you. The renewable electricity is produced as Direct Current (DC). The DC electricity from the panels passes through a grid-interactive inverter, which converts the DC electricity into Alternating Current (AC). Electricity supplied by the grid is AC.
This AC electricity is then used by any appliances operating in the house. If more electricity is produced than the house needs then the excess will be fed into the main electricity grid. Conversely, when the renewable system isn't generating enough electricity to power the house, the house will draw power from the grid. Grid interactive systems eliminate the need for a battery backup for when the sun doesn't shine (if it's a solar system) or the wind doesn't blow (if it's a wind turbine). In effect, the grid serves as your battery. This means that maintenance costs for your system will be less. It should be noted that without battery storage a grid connected system will shut down when there is no power on the grid.
Another advantage with a grid interactive system is that you can start with a small renewable system and add to it over time as finances allow, thus reducing the need for large initial capital expenditure. Since the renewable system is connected to the grid, it will not provide electricity in the event of a blackout. For that you need a system with a battery, similar to a RAPS system, even if you do link it to the grid.
Grid interactive solar
In a grid-interactive solar system, electricity is generated by solar panels. Many houses in Australia have north-facing roofs, with space (5m2 to 30m2) to support a solar system. Such systems are usually sized so that the panels generate approximately the same amount of electricity consumed by the house over the period of a year, but this is not always the case.
Grid interactive wind and hydro
It is possible to use wind turbines and micro-hydro turbines in a grid-interactive system. These are less common than solar, however, as they are generally not as practical to install in built-up areas.
Cost effectiveness
The current cost of solar panels, and other renewable energy systems, means that grid-interactive systems are not as cost effective as relying purely on the grid for electricity. In spite of this, many people are choosing to install grid-interactive solar systems, as they do not create any greenhouse gases when generating electricity, unlike coal-fired power plants. Numerous studies have demonstrated that the equivalent amount of electricity used to make a solar panel is generated by the panel within the first two years of operation, hence a solar panel will repay its greenhouse gas 'debt' within this time.
Prices for grid interactive systems can start from as little as $2000 for a pair of solar panels and a small inverter. A system capable of running an average suburban home would cost around $20,000 to $25,000, and would include a solar array of 1.5 to 2 kilowatts and an inverter to suit.
Who can have grid connected solar power systems?
Generally, if you have a grid-connected house with a structurally sound north-facing roof, then you can install a grid-interactive PV system, providing your power utility allows it. In Australia, a growing number of electricity utilities are supportive of grid-interactive systems, and will pay you for your electricity if the amount you generate exceeds the amount you use during the billing period.
Power companies and Grid interactive systems
Most utilities now provide support for customers who want to install photovoltaic power systems on their houses or in commercial premises. Arrangements differ for either buying the electricity generated or deducting the value of the electricity produced from your regular bill.
Office of the Renewable Energy Regulator
When you install a photovoltaic system a number of Renewable Energy Certificates (RECs) are created through the Office of the Renewable Energy Regulator. The RECs are created on the basis of a formula that estimates the amount of electricity your system will produce in its lifetime. Each REC is saleable, effectively helping to subsidise the cost of your system, however different utilities treat RECs differently. In some cases the manufacturer of the system may wish to buy the RECs. Remember to ask you utility how they deal with the RECs created when you install a photovoltaic system.
Web: Office of the Renewable Energy Regulator - www.orer.gov.au
CASE STUDY
This system is located in West Brunswick, seven kilometres north of Melbourne's CBD. The family who own the house heard about an offer from their local electricity retailer to subsidise solar electricity systems in the area. They were keen to reduce their personal greenhouse gas contributions, so went ahead with the offer.
The power system
The system consists of twenty-four 83 watt Solarex photovoltaic panels, mounted on the north facing roof of the house, covering an area of 18 square metres. The solar array has a generating capacity of about 2 kilowatts. The array is connected to a 2.2 kilowatt CSA inverter that converts the electricity to 240 volts AC for use in the house, with the surplus feeding back into the grid. The system cost around $26,000 in 1996.
Energy savings
The house is a 1929 Californian bungalow style weatherboard. A family of four lives in the house, and have been impressed with the system's performance. Since it was installed in 1996, it has produced more electricity than they have used, and they are credited for the surplus on their electricity bill. Converting from an electric water heater to a solar water heater with gas boosting has reduced the household's electricity consumption dramatically.
The family and their electricity retailer have monitored the system's performance closely. The graph below shows cumulative electricity generation from the solar panels and consumption by the household. The power generated by the system to date exceeds 6000 kilowatt-hours, which has resulted in a saving of around 9 tonnes of greenhouse gas emissions.
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