Green Energy

How to design a solar pv system

In order to design a solar pv system, you need to follow following steps:

1. Determine the amount of electricity (kWh) consumption and the electricity rate

It is important to determine the amount of electricity consumption per year for better understanding the economics of installing a solar system. On your utility bill, your electricity usage is summarized wherein natural gas usage should be excluded. As the path of the sun varies with the seasons, a solar PV system would offset your electricity demands mostly in the summer months. It should be also considered that most utility companies have a tier rate structure based on consumption patterns and state mandates. A small PV system significantly helps to reduce your electricity demands for moving you to a different tier, minimize your rates and saves your money.

2. Determine your available roof space (sq-ft)

Knowing your available roof space is crucial for determining the quantity ofsolar panels you can actually use. Based on the size of your house, you should draw a diagram of your roof on a piece of paper. You can also use the free tool Google SketchUp or a free CAD program DraftSight. After determining the size of your roof, it is important to know how much of your roof faces towards the equator (South in the northern hemisphere [USA, Canada, etc.], north in the southern hemisphere [Australia, South America etc.]). Solar irradiance is strongest coming from the equator and you will want to maximize your system efficiency.

3. Determine your solar radiation data and calculate the amount of energy you could produce

In this case, you should use the official government statistics available on your area. PV Watts’ or Solmetric's solar calculators also can be used.

4. Determine shading issues

You should be careful if there are obstacles like trees or buildings in the vicinity of your roof which may cause shade. Shading decreases the output of your system and may also damage the solar cells. Solar Pathfinder or Solmetric Sun Eye should be used for detailed shading analysis.

5. Choose an appropriate solar panel

Various types of solar panels are available in the market. Therefore, it is very important to choose an appropriate solar panel carefully. The solar rating and the size (surface area) of the module are the most important factors. Although the solar ratings might be the same for some modules, the voltage and current output might vary. Therefore, it is advised to choose a lower voltage module for smaller projects having capacity less than 4 kW. Factors like financial limitations and color are also should be considered.

6. Choose an inverter

It is very crucial to choose an inverter out of the many available in the market. You can consider to use micro inverters which are easy to install and can generate AC power directly from the solar panel. If you want to use a central inverter, you should use the string sizing tools. The most important factors for choosing appropriate sized inverter are:

The number of strings in the system.
The maximum input current.
The voltage on a string.
The minimum ambient temperature during day light time when the system is supposed to run.
The maximum ambient temperature of the location.

7. Select a racking system to mount your solar PV system on your roof

It should be remembered that the racking system will consist 10% to 25% of the total costs. You should decide carefully which racking system is most suitable for your budget and for your roof. The racking system is one of the key components which protects both the roof and the modules and may last for at least 20 years. A minor mistake with the racking can permanently damage the roof or injure people or property.

Different types of racking and mounting systems are available in the market for roof mounted solar systems. Check the manufacturer's websites, read the installation manual. Be aware of the plan and codes how you are going to mount the racking system on the roof. Know about flashing solutions.

Using an inexpensive racking solution does not mean lower quality, it might require more effort to install it or the materials may be different. Additionally, as the solar PV field matures unique racking solutions, such as hanging panels vertically along an exterior wall, become more applicable.

8. Know your local and state incentives; calculate how much money you could save

You should check the websites of your local and state incentives provider. There are also a number of other financial calculators available online. Most importantly, you should estimate your electricity generation and compare it to your utility rate. It should be remembered that different tier rates might apply based on your energy consumption. Know about solar programs of your local utility company and their applications process. Implement the benefit of tax cuts and incentives.

9. Prepare your documents

There are different permitting processes in different location. In order to receive a construction permit or to apply for an incentive, you must obtain the equipments' (solar panel, inverter, racking) data sheets, submit a roof drawing and electrical drawing. You can draw those on your own using the programs mentioned above, or ask a professional to draw them for you. In order to determine the wire sizes, voltage drops, AC and DC disconnect, electrical background and knowledge is required. If you are not confident enough to do so, you should contact an electrical engineer.

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