Integration of Renewable Energy on Farms

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Interconnection Issues

Alternative energy systems installed on the farm may offer many advantages but it is necessary that they are installed and operated correctly. The principle issues to consider for possible interconnection of an alternative energy system to the grid are outlined below:

Proposed electricity production has to be discussed with the Local Distribution Company (LDC) to ensure that all safety and other concerns are addressed. If a Net Billing arrangement is in place, the utility will advice on the optimal capacity, voltage level, generator type, electronic power conditioners, and other issues. The LDC will want to have access to the safety disconnect at all times and they may put their lock on it.
All equipment used has to meet proper standards as developed by CSA and ULC. Procedures for automated shut down of generator(s) and overall protection of the system have to be incorporated into the system. The utility protection engineers have numerical codes for protection functions that do not mean much to others. These must be shown on diagrams
As well as approaching the LDC with your proposal you must get approval for the new construction from your local township offices and any government offices that may be involved. This may include building permits, water rights, clearance of tower height for air traffic, environmental impact, noise study etc. All installations must meet the requirements of the Canadian Electrical Code
The new generating facilities likely will require an amendment to the existing farm insurance policy
A stand-alone electrical system far away from the grid will need to have an electric storage device such as a battery that is fed by one or more renewable energy based generators such as a photovoltaic array, which is optimum for a summer cottage. A gasoline-powered generator could provide power when demand is high and must have adequate capacity
Where there exist Power Purchase Agreements (PPA), they will be the legal document between the owner of the new system and the LDC. Each utility company would have their own format and it covers the commercial, legal, technical and communication aspects. The finalized PPA may take a long time to issue but in all likelihood you will be allowed to connect to the grid and generate upon technical acceptance of the equipment. Payments may be retroactive. In a net billing situation there is no actual purchase of energy. Whatever you generate is for your own use and any surplus will in effect be “stored” by the utility to be withdrawn by you when needed. The bi-directional energy meter will keep track of this and in most cases it will be best to opt for a long billing period so that any surplus energy credit can be carried over several months. At the end of the billing period any surplus credit will be set to zero
Commissioning of the generator is performed when the installation is complete and the visual inspections have been carried out. The Electrical Safety Authority inspector will/may require a demonstration of the proper functioning of the utility protection systems. It will be useful to agree on test criteria and methods beforehand to have a clear picture of what is to be done. A test to demonstrate the anti islanding protection should be performed. Alternatives to the inspector witnessing the test may be written documents that the equipment manufacturer or an engineer at the site has performed the tests and prepared reports
Specific issues related to the renewable energy system may include:
- Wind turbines and photovoltaic arrays are powered by intermittent sources of energy and thus will go through many start and stop cycles that have to be automatic to maximise energy capture. This is normally done with a programmed sequence that monitors wind speed and grid parameters, lifts the brakes, monitors the speed and energizes the generator through a soft start circuit to minimize inrush current to the generator. The control logic can be programmed onto proprietary chips where the owner has little chance to interact or it can be on a commercial programmable controller with a keyboard or similar
- Hydraulic generators usually run all the time and for the occasional start require some manipulation of gates to allow water to flow. The start sequence usually is done manually in part. When a grid disturbance causes a trip there has to be a safety routine where stored energy, for example in a battery will drive the wicket gates shut and thus limit the speed of the turbine generator on run-away. When grid power returns, power will be available for a normal restart
- The controls of the microturbines and Stirling engines are highly refined and possibly only need the push of a button after all the external requirements have been met. An electronic power conditioner controls the output of the microturbine by setting its operating speed. When speed is reduced the compressor will pick up less air and less fuel will be required for combustion. Power will decrease and the power conditioner will draw less current while following the grid frequency
- In the case of biogas, it is necessary to ensure proper fuel quality, otherwise the generator will shutdown. When the fuel supply fails, the power output will drop and in the extreme case the generator will become a motor with the engine acting as brake. A reverse power-sensing relay will detect the condition and quickly open the main contactor. If an induction generator is in use, the main contactor is closed when a speed pickup senses running speed. For stand-alone operation, a synchronous generator will be required as well as a speed control loop for governing and an automatic voltage regulator