Photovoltaic solar panels come in different wattage sizes and are designed to supply energy to your home. Generally, solar panels are classified by their rated output power which is given in WATTS. This wattage rating is the amount of power that a single solar panel can produce in one peak hour of sunlight. One of the biggest technical challenges to overcome with all photovoltaic installations, regardless of configuration, is the correct sizing of the system to meet the demands of the household.

The size of the photovoltaic system required varies from home to home as each homes energy usage and energy efficiency will be different. But determining the optimum number of panels and total wattage of your solar system on requires knowledge of your household usage and some simple maths. To help you overcome some of these challenges, we have put together an easy-to-follow, step-by-step guide that will assist you to easily size your photovoltaic system.

Step 1. – Determine the Suns Peak Hours Available Per Day

Solar panels are typically sold by the peak watt. When the sun is at its strongest or peak intensity usually at midday on a clear day, it produces about 1000 watts per m2 of solar radiation directly onto the Earth’s surface. One hour of maximum, or 100% sunshine received by a solar panel equals one equivalent full sun hour. So if a solar panel is rated at say 100 Wp (peak watts) it would supply 100 watts of peak power at the brightest part of the day. If the average peak sun hours for a particular location is given as 4.5 hours, this means then that our solar panel will provide 450 watt-hours a day of peak electricity.

Obviously the sun shines longer than 4.5 hours a day. Climate data given for a particular location on the Earth’s surface would give the solar intensity data in terms of peak sun hours, so the suns intensity from sun rise to peak hours and back down to sunset throughout the day will be a percentage of the peak hours and therefore the power output from a photovoltaic cell will also be a percentage of the maximum during these times. For example, early in the morning a 100W solar panel may only be producing 25 watts, then midday it produces the full 100 watts, and in the afternoon only 25 or 30 watts again.

Step 2. – Determine Your Energy Needs In Terms Of Watts Per Hour

To determine the required overall power rating of a photovoltaic solar system required to power a home, the electrical energy needs in terms of watts per hour should first be evaluated. To work out your homes power requirements, you need to do some homework first. Everyone’s power consumption is different so by listing and adding together the appliances, lights and TV’s with their hourly power requirements in terms of watts you will arrive at the total watt-hours per day you need.

The final power rating of the solar system can then be calculated and sized, based on the portion of the homes electrical energy consumption to be supplied by the system. So for example, a system that is required to supply 100% solar electricity would be twice the size of a system designed to supply only 50% of the consumption. Then a photovoltaic system can be sized to provide part or all of your electrical consumption.

Step 3. – Optimize Your Power Demands and Usage

The ability of a photovoltaic solar system to produce free electrical energy is not unlimited. It is limited by the number of hours a day the sun shines and it is limited by the physical area available to install the solar panels. Accidentally leaving on a light bulb on during the day can easily consume and waste unnecessary amounts of energy. Saving and reducing your energy needs by using energy-efficient light bulbs and appliances not only saves you money but done correctly can reduce the final size and cost of your new solar photovoltaic system.

Solar systems are designed for a certain amount of energy consumption, and if the home exceeds the planned limits this additional energy will need to come from the utility grid costing you money. An energy-efficient home reduces the number of solar panels required making the installation of the system cheaper, less complicated and reducing its payback period so lower your power consumption and reduce your power needs as much as possible.

Step 4. – Determine The Type of Solar Panels You Wish To Use

There are many hundreds of different size solar panels available to choose from ranging from 50 watts to 250 watts per panel at 12, 24 or 48 volts and all with their own set of advantages and disadvantages. The number and type of solar panels required to capture enough solar energy to support your electrical consumption plays an important role in the design, sizing, operating voltage and cost of your solar photovoltaic system.

A typical solar panel is made up of a grid of individual solar cells. There are different types of solar cells to consider. Monocrystalline silicon solar panels are the most efficient at converting the suns solar energy to free electricity, but they are also the most expensive. Polycrystalline silicon panels are slightly less efficient than monocrystalline, but they tend to be cheaper since they are cheaper to produce. Thin film solar panels are the least efficient, but they are also the cheapest. Thin film solar panels are uniquely versatile as the silicon film is thin and flexible. Shop around the market to find the best panels that suit your needs.

Step 5. – Size Your Solar Array

To estimate the size of your solar array, you’ll need to divide the previously calculated total watt-hours by the peak sunlight hours you should get the total wattage of solar panels that you will need and then add a little extra to make up for cloudy days. This gives us the total number of solar panels we need to generate a given amount of Watt-hours (or kWh) for our home in our given location. For example if we need a 1000 watt system, that’s 10 x 100 watt panels or 5 x 200 watt panels.