How many solar panels do I need? Variables that affect system output

When beginning to plan each system, our engineers need to answer two fundamental questions:

  1. How high is the electric bill and what is the house’s energy consumption??
  2. What is the maximum output that solar panels can produce according to the structure and surroundings of the house

One of the best ways to answer the question “how many solar panels does my house need” is to invite one of our solar experts for a free consultation visit, so our engineers can prepare a simulation of the house and the desired number of solar panels.

1. What is the electricity consumption of the house?

o understand this, all you have to do is look at the electric bill.
At the bottom left corner there is a graph showing the electric consumption in kilowatt-hour per month over the past year. The consumption during the summer and winter months is probably higher than during the transitional seasons.
We care about the annual consumption. Within the net metering regulation  he surplus electricity produced in the summer can be used during the less sunny winter days.

2. How much electricity can be produced by solar panels on the roof?

In order to answer this question, we need to examine several different parameters:

  • The location in Israel: different areas of the country enjoy different amounts of sunlight. In general, it can be said that all the population centers in the country are very attractive for installing a solar system. However, some population centers have an exceptionally high level of profitability.
  • The type of roof: on flat concrete roofs the energy output can usually be maximized by precisely positioning the solar panels to face south at the correct angle, with a ratio of 1 installed kilowatt per 10 square meters. On slanted tiled roofs, the output depends on the direction of roof and its angle, with a ratio of 1 installed kilowatt per 7 square meters. Roughly calculated, the annual amount of energy that can be produced per square meter in an optimal environment: South facing: 1700 kWh, East and West facing: 1550 kWh, North facing: 1250 kWh. Of course, the numbers can vary significantly depending on the unique characteristics of each roof.
  • What shading factors exist near the roof: solar panels produce less output when shaded by nearby objects, so the ground coverage around the house affects the amount of electricity the system can produce. Nearby trees, adjacent houses that are taller than the roof, the water boiler – all of these should be considered when designing the system. The technology we use prevents a shaded panel from affecting the entire system, so that the output is optimal at any given moment.
  • Panel type: different panels produce different outputs and are measured in watts. We typically install either 325-watt or 340-watt panels. This means that when the conditions are optimal, and the panel is exposed to the sun, it can produce the amount of energy indicated.
  • The size of the roof: the larger the roof, the more panels that can be installed. Using a drone, some measurements and simple math we can examine the maximum number of panels that can be installed on the roof.

How does this mean for the average Israeli family?

For the sake of demonstration, we can examine an Israeli family of five with a standard private home in Pardesiya. The house has a tiled roof, facing east and west with a total available area of 50 square meters. The family consumes 12,500 kWh per year (annual electric bill of about 7,000 shekels). Let’s divide the annual consumption by 1,550 kWh according to the roof direction, and we get a recommended system size of 8 installed kW. Approximately 3 panels combined equal 1 installed kW. Accordingly, we would need 24 panels to achieve 8 kW and eliminate the household’s electric bill. Since the area of the tiled roof is 50 square meters, we can install only 21 panels, which is equal to about 7 kW. This will cover about 85% of the house’s electricity consumption.

You can calculate for your own home in the solar calculator  or contact us to perform a simulation specific for your home at no cost.