Designing Grid Tie Photovoltaic Systems

By Author: Peter Clarck
Total Articles: 19
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Because many governments now offer generous subsidies toward the implementation of energy efficient solar systems, the grid tie system has increased in popularity in the United States, as well as in European countries like Spain and Germany. As you examine your options, let us first consider a sample project: a grid tie solar electric system which does not need to be connected to the national grid. There is little difference in the scope of a grid tie system and a grid fallback system; the same procedures must be followed. The only major difference is the battery efficiency of a grid fallback system.

The batteries in the grid fallback system are used for storage of excess electricity - when the system output exceeds the total electricity requirements for your home. These batteries can then be used to power your home when your home needs more electricity than your solar electric system can provide.

In the basic grid tie system, you draw backup power from the national grid to support your demand for extra electricity, rather than from batteries.

A power analysis is helpful for determining the size of the ...
... required grid tie system, even if there is no requirement to generate all the necessary power. You can also opt to be “carbon neutral” – by which you can achieve zero carbon output - with the buy-back option offered by the national utility grid.

A standard grid tie system is designed to generate more than enough power for the summer season, and less in the winter. The objective of a solar electric system should be to generate the maximum quantity of power in a year; more than necessary so that some of the power is stored for days in which power is not being supplied by solar energy alone.

The design considerations for the grid tie/grid fallback system will allow you to implement your solar system on a small scale and expand as funds allow, without the necessity of investing a huge sum of money in a large number of solar panels from the start. A carbon neutral grid tie solar system requires fewer solar panels than an off grid, or stand-alone solar system.

Now, let’s put more specifics around the requirements to improve our scope. The original scope took this form:

Install an off-grid holiday home with a “complete electricity” requirement.

We can enhance this to:

Install an off-grid holiday home that can power everything required, including lighting, television, refrigerator, laptop computer and other small appliances, with a total daily electricity consumption of 695 watt-hours. The solar system has to supply sufficient power for the residents’ stay during the months of March through October, with several winter weekends. With the above enhanced project scope, the focus is now more defined. A clearer understanding of what is to be achieved sets us on the right path to implementing the required solar system.

Summary

1. Get the project scope right from the start.
2. Keep the scope simple before adding the correct computation of energy requirements, taking into account all of the electrical devices that will be used.
3. Factor in any “phantom loads” (i.e., electricity leaks, or standby mode electronics).
4. Design the system to run electric appliances at low voltages, rather than by using inverters for high voltage mains power.
5. Use 12V appliances, which are plentiful due to ample supply for the camping and boating communities. They make a stand-alone solar system or a grid tie/fallback solar system more efficient than a connection to the mains.
6. It pays to run through a detailed power analysis for any kind of solar electric system you plan to implement.
7. Take into consideration battery and inverter inefficiencies.
8. Consider the time of year when the solar electric system is to be used.
9. When this stage is completed, you will have a better understanding of how to move your project forward to success.

About the Author

Peter Clark is an energy and water management specialist guiding others to save energy and water. Check Solar365.com if you like to know more about solar energy or solar photovoltaic systems.