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How many solar panel watts for a house?

Posted on4 Years ago by

How many solar panels do I need to install as part of my solar photovoltaic kit?

In order to come up with a correct estimate, we need to answer the following questions:

  • What average kWh consumption will I have?
  • What is the solar irradiation (solar yield) in the Europe location where I will mount my photovoltaic modules?
  • What is the output power of the solar panels I need to install?

Next, we will provide some answers to all these points, so that you can better understand all points that need to be taken into account when designing your solar project.

We also encourage you to contact our specialist sales team should  you have any technical questions or want to receive a free quote.

What is my kWh consumption?

To proceed with the calculation of solar panels, the first and most important thing is to know the consumption that we are going to have in our installation.

One of the most common mistakes that people make at this point is thinking that just knowing the roof surface of the house will be enough, but this is not so.

For example, we could have a roof area of 60m2 and have the electricity consumption of only10 bulbs, or in a different case, we may have the same 60m2 surface but a larger utility consumption of 10 bulbs, a refrigerator, a microwave, etc. Therefore, the solar PV kit that we are going to need in the first scenario will be different to the solar PV components we will need in the later.

Elements to take into account when calculating my solar panel installation:

  • Lighting
  • Television
  • Computers
  • Washing machine
  • Dishwasher
  • Fridge
  • Microwave
  • Heating (if electric)
  • Dryer (a very demanding element)

Once you have listed about what these elements apply in your case, and their usage times, we can move on to the next point.

What is the solar irradiance of the Europe place where the solar panels are going to be installed?

Once we are clear about the consumption (Wh/day), the next important piece of information we need to know is the solar yield within our area. This information can be obtained through the PVGIS website (so as not to go into detail, in this example we will not vary any parameters, we will simply enter the location and calculate).

To choose one or another irradiance value, it is important to know the time of year in which it is going to be used. In case we have a steady consumption throughout the year, then we will take a conservative approach and choose the month of less solar radiation (December). If we only use it for a few months per year, then we will choose the irradiance among those months, the one with the lowest radiation.

What is the power of the solar panel we will need?

Another detail we will need is the power of the photovoltaic panel we want to install. In principle, we can choose any model we want, taking into account that the lower the panel’s W output, the greater area we will take up. 

Example of how the calculation of photovoltaic panels is done:

We suppose that we want to carry out a photovoltaic solar installation in Pamplona (Spain) for a weekend home (3 days/week usage) with a steady use throughout the year, with the following energy consumption



Power (W)

Time (h/day)

Energy (Wh/Day)

Led Light





Television A+










Fridge A+++ (162 kWh/year)





Microwave (10min/day)





Mobile Charger






If we add up all the Wh/day we are going to consume, we get a total of: 1214 Wh/day

The second step is to obtain the PV radiation of Pamplona (Spain), in this case, of the most unfavorable month (month with the least solar irradiance). If we carry out the procedure as explained above, using the PVGIS page, we see that we get a daily average of global irradiation (Hd) for the month of December of 2.49 kWh/m2. In the formula that we will use later, we need to calculate the solar peak hours (HSP), dividing that value by the solar irradiance 1 kW/m2 obtaining:

Solar calculate

Other data we will need for the photovoltaic installation are:

  • The working efficiency. Here we will take into account the losses that the different solar equipment (pv inverter, charge controller, Solar panles…) within our photovoltaic system will have. We will assume a working efficiency of 60%.
  • Peak power of the module. We can make our choice based on the price of the panel or on the available space on our roof. Depending on our choice of solar modules, we will need a greater or lesser number of solar panels to install. In our case we will choose a solar panel of 260W.

With all this data, we can already calculate the solar panels we need in the following way:

In this case, since we have 1.34 panels, we will round it up to 2 pv solar modules of 260W

If we assume, instead of weekend use (3 days), a daily use, we would have to replace in the formula the 3/7 by 7/7 staying as follows:

That is, if plan to live in the house on a daily basis, we would need 4 photovoltaic panels of 260W.

We hope that this practical post will be of great help to you and encourage you to buy a money-saving solar photovoltaic installation in your home.

And if you still have any questions, we remind you that our team of specialists is at your disposal to attend any queries that you may have.

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