The Solar Power Expert Blog

Choosing Your (Solar) Path In Life

by Chris - August 25th, 2011.
Filed under: Solar Education. Tagged as: , , , .

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If you’re new to the whole ‘solar thing’ and are looking to get started, there are two important decisions that you need to make before investing in any solar technology. These choices will set the course of your solar life, so choose wisely.

First however, I want to point out here that this article (and this site for the most part) will focus on solar electric panels and not solar thermal panels. Solar thermal panels are used to heat water and use completely different technology. Other than using the sun as their source of energy, they don’t have much in common with solar electric panels.

So what are those two important decisions? They are these:

  • To implement a grid-tie system or an off-grid system.
  • To use 12 volt panels or a system that uses higher voltages.

Grid Tie vs Off Grid Systems

The term grid-tie means that your solar system is attached to the power grid through a grid-tie inverter. The purpose of a grid-tie system is to sell unused electricity back to the power grid. It’s very popular right now and most appropriate for people who live in a home tied to the power grid, which would include most people.

The term off-grid is the opposite of grid-tie. It means the energy from your solar system is stored in batteries, to be used only by your home when needed. This setup is most appropriate for remote buildings and cabins where grid power is not available or is overly expensive to install.

While it may seem like a no-brainer to implement a grid-tie system rather than an off-grid system, there are pros and cons to each. For example, off-grid systems do not need to meet any building or electrical codes. They are considered a hobby/custom installation. You are the designer and the buck stops with you because the electrical grid is not involved (other than maybe a battery charger). Conversely, you’ll need to get an electrical permit at a minimum and probably need to hire a professional to install a grid-tie system. If you don’t have thousands of dollars to invest in the beginning to install a complete system, you may need to hire someone or get a permit every time you want to add more capacity to your system.

domestic solar power

Schematic for Domestic Solar Power House Using Net-Metering

There is a middle ground. Using a grid-tie micro-inverter you can install a simple and basic system, powered from a small battery bank. You can use the batteries to isolate the solar panels from the inverter. From the panels to the batteries you have a basic off-grid system. The micro-inverter and a low voltage disconnect is used to upload stored energy in the batteries to the grid.

The point is that you need to be aware of the difference between grid-tie and off-grid architectures before starting in your own venture with solar power for homes. Many people opt for complete grid-tie kits and don’t realize that they may be pigeon-holing themselves into a corner if the system is not designed for adding additional solar panels later.

12 Volt vs Other Voltages

When solar panels weren’t as popular (10+ years ago), most solar panels were designed to operate with 12 volt systems. The reason for this is that grid-tie systems didn’t exist and neither did the concept of net-metering. Solar electricity was almost exclusively used in off grid living plans. With the advent of these new ideas, the majority of solar panels produced today generate electricity at voltages far higher than 12 volts.

The advantages of using higher voltages is a reduction in electrical current for a given power rating. This reduces transmission loss, sometimes referred to as I2R losses. To figure it out for yourself, play with the power equation and ohms law until you get this equation:

P=I^2 * R

Higher voltages mean smaller wires can be used and the system is more efficient. This saves money and energy. What could be wrong with that?

The disadvantage is that there is no standard for solar panel voltages. Panels from one manufacturer probably won’t be compatible with those from another manufacturer. Also, equipment like charge controllers and grid-tie inverters have their own voltage requirements which differ from manufacturer to manufacturer.

In contrast to this, 12 volt systems are well understood, standardized, and the equipment is widely available and cost effective. If the solar panels are mounted far from the load, the transmission losses can be elimiated by stepping the voltage up to 120V AC with an inexpensive inverter. At the load, this voltage can then be converted back to 12 volts with a standard power supply.

Additionally, solar panels are made from several solar cells strung in series. It takes approximately 36 cells to create a 12 volt panel. Panels using higher voltages need hundreds of cells. Since cells in a panel are in series, it means that if one cell gets shaded it will block power from all the rest of the cells in the series. Running multiple panels in parallel is more robust than running panels in series, so there are significant reasons to prefer 12 volt panels over high voltages from the perspective of shading effects.

DIY Solar vs Consumer Solar

Deciding on a grid-tie vs a off-grid architecture and weather to use 12 volt panels vs other voltages leads up to one important question: Are you a DIY solar enthusiast? If the answer is yes, or I want to be, then I strongly recommend installing a system that is modeled after an off-grid architecture (but may utilize a grid-tie inverter for uploading power to the grid) and operates at 12 volts (nominal). This is the best system for the do it yourself minded person. The system will be scalable, which means you’ll be able to add more panels and grid-tie inverters later on. Most components like wires, fuses, disconnect switches, and inverters will be available from local hardware or auto parts stores.

To get more information on how to install a DIY solar system, check out our educational articles. Also, be sure to check out the Grid-Tie Kits for getting a starter system.

1 Response to Choosing Your (Solar) Path In Life

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