Calculating Solar Panel Output

The usable power from the sun depends on many thing such as weather conditions, time of year and latitude. When determining how to figure solar panel output, there are other inefficiencies that should be taken into account. This will help you to decide whether solar power is a good option for powering your home. Whether you want complete solar home heating or are only looking for a smaller system such as solar water heating, it's useful to know what affects solar panel output.

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How Much Energy Comes From the Sun?

More solar energy is delivered to earth in one day then all energy produced by humans in one year. Most energy from the sun is absorbed by the oceans and land to drive the wind, water and weather cycles.

Factors that Affect Solar Panel Output

Solar panels are a collection of solar cells connected together to create a panel that's rated according to power output. Larger panels have more solar cells than smaller panels, and therefore produce more current and power. However, inefficiencies in and around the system will reduce this rated power quite drastically. For instance:

  • Bright sunshine on a clear day will produce more power than on an overcast day. Commonly known as the intensity of solar radiation, a panel can output its rated power when the sunshine is at its brightest. Clouds can reduce the power output by as much as 70-80%. A covering of snow and leaves on top of the panels has to potential to completely stop them from producing any power at all.

  • Solar panels should be kept clear of dust and debris, whenever possible or practical. A layer of dust on the panel may reduce the output power by up to 30%, even in bright sunlight.

  • The sun's rays are more intense in the summer than in the winter. The lower solar intensity and the shorter number of daylight hours during the winter months will reduce the power production.

  • The time of day also affects the efficiency of the panels. When the sun is at its highest point, the rays are most direct to the earth and the panels produce the most power.

  • The length of wire from the panel to the batteries also makes a difference. The longer the wire, the more resistance will be present in the electrical circuit which results in less power being sent to the batteries. Use the appropriate gauge wire for the peak amount of current expected from the panels. All wires should be as short as possible.

  • Select a charge controller with maximum power point tracking (MPPT). This device adjusts the voltage and current from the PV cell and will extract the maximum amount of power.

Solar Panel Output

The amount of power a solar panel can generate depends on the voltage and current. For these devices, the voltage doesn't vary much (10 V - 16V), but the current increases with more solar cells. Power is calculated by multiplying the voltage by the current, ie. power = voltage * current. So the more solar panels you have, the more current your system generates, and therefore provides more energy for your home.