How do I calculate my electricity consumption

Many of us are already looking forward to implementing solar energy in our homes, cottages, businesses or companies. Before moving forward, do we know how much consumption we have? How many solar panels do we need?

There are 5 crucial parts in a house’s solar panel system: solar panel, power inverter , solar battery, solar charge controller, and also other cable connection accessories. We know that a solar panel system will allow us to save electricity substantially and even solve problems such as power outages or have service in remote locations. The first question that usually arises is how much it costs. That’s when we are tempted to enter the shopping sites to see what they offer us in terms of solar energy and find a lot of options. After seeing so many options, we choose one and post the question: “I have a house with a TV, a refrigerator and some lights, is it useful? How much does it cost?

The reality is that before we can evaluate what we are going to install we must know our electrical consumption, since we can have the same appliance and have completely different consumptions from another person. The electrical consumption is measured in Watts per hour (Wh), that is to say that, to know the electrical consumption that we will have, it is enough to multiply the consumption by the amount of hours used in the day.

Let’s say for example that we have 2 equal houses, with the same appliances and lights, let’s call them houses A and B. The owner of house A keeps his TV constantly on from 8 am to 11 pm, while in house B he only uses it for about 3 hours during the day, during lunch and dinner. This TV is LED type and consumes according to its information label about 100 watts while it is running.

House A – Tv Led 100W x 15 hours = 1500 Wh – Per day

House B – Tv Led 100W x 3 hours = 300 Wh – Per day

As we can see, the consumptions are completely different, and even more if we project it over 30 days. House B could perfectly operate with a solar energy system more economical than house A since it has a much lower consumption. That is why a consumption analysis is the first step we have to take. For that we will look for the items that we consider most important or with the highest consumption. The ideal is to make a table like the one shown here:

Daily consumption spreadsheet

A quick way to have a consumption parameter, if we already have electricity service, is to look at our last bills where it indicates the amount of Kwh (1 Kwh = 1000 Wh) that we have consumed in the billed period. With this data we can now define the right system for us, or request the development by a suitable professional as we do here at Renogy. In another post of this blog we will discuss the different types of solar panel installations, advantages and disadvantages. We hope we have been helpful, any questions you may have about your solar project we are here to help you. Leave your comment right here or write us.

What factors influence the number of solar panels that a home needs?

  • Annual home consumption (We’ve outlined in detail above)
  • Plate quality and performance
  • solar panel type(including solar battery type)
  • Installation power
  • roof orientation
  • Geographic situation

Quality and performance of solar panels

The quality of the solar panels is critical to their performance in producing energy. Higher quality systems have a slightly higher cost. However, they make better use of sunlight and are capable of producing more electricity.

The right choice of solar panels for the house allows us to reduce the number of solar panels we need to install. In addition, with higher performance panels, the investment of the installation is amortized faster.

It is always advisable to use panels from manufacturers with experience and reputation in the production of photovoltaic panels. For example, at Endesa X we only use solar modules from CanadianSolar, one of the most innovative companies in this type of system.

Type of solar panel by cell type

The yield is the capacity of the panel to produce electricity when sunlight strikes it. The technology used to manufacture the cells contained in the photovoltaic panel will influence its performance, with three main types of panels being distinguished.

Crystalline plates (poly- and mono-) are the ones that show the best performance results and are currently used for photovoltaic panel installations in homes. The amorphous ones, being more economical, are currently in disuse due to their low performance and shorter useful life.

Power of the installation

The power of the solar panels will indicate the amount of electrical energy that our domestic installation is capable of producing. The power is generally indicated in Wp units (peak power in Watts). Thus, the total power of the installation is the sum of the power of all the panels that form it.

Number of panels * power of each panel (Wp) = Power of the installation (Wp).

For example, an optimal solar panel has a power of 300 Wp. If our installation consists of 6 solar panels, we have a total power of 1800 Wp. This power value corresponds to 1800 kWh of electricity per year in theoretical conditions. It should not be forgotten that the Wp value of the manufacturers is measured in optimal conditions of solar radiation (Solar radiation = 1000 W/m2 and Temperature = 25 °C). Therefore, in order to correctly calculate how many panels our house needs, it is also necessary to make a study of both the orientation of the installation surface and the geographical location of our house.

Roof orientation and inclination

The optimal orientation for solar panels is south facing. It is the arrangement that makes the best use of solar radiation for the production of light in our domestic self-consumption installation. There is no need to worry if you cannot have that particular orientation. In the case of southeast or southwest orientations, the efficiency loss is only between 1% and 4%, which is perfectly acceptable.

In the case of east and west orientations, the drop in efficiency can reach 20 to 30%, so it may be necessary to install more solar panels to achieve the required power production. In the case of north orientations, it is important to make a very thorough preliminary study to evaluate whether it is worthwhile to install the panels. Regarding the inclination, to calculate how many solar panels we need, we will be somewhat limited by the structure built. However, the panels are installed on their own supports in order to have the most adequate inclination. Generally, the optimal tilt for solar panel installation on a house is related to the latitude of the location.

Table for calculating the angle of solar panels on a house

For example, the city of Toledo is at a latitude of 39.8568. If we multiply by 0.9 we get a value of 35.87112. Thus, the optimal tilt angles for the solar panel system would be: 64.9 degrees in winter, 37.4 degrees in spring/autumn and 12.4 degrees in summer.

Since changing the tilt of the system is a cumbersome and costly process, it is generally decided in the preliminary studies of the installation to choose a tilt angle for the panels that will work optimally during all seasons of the year.

Geographical location of the house

When calculating how many solar panels a house needs, it is essential to take into account the geographical location of our house. In Spain each province receives a different amount of solar radiation so, depending on the area where we live, we will need to install more or less solar modules.

For example, in the province of Malaga the average energy value that falls throughout the year is 1700 kWh per m2, while in the province of Lugo it is 1270 kWh per m2. Thus, in Lugo we would need between 1 and 3 additional modules to obtain the same energy as in Malaga. The general recommendation is to request a personalized study to ensure that the installation of solar panels in your home fits your energy needs taking into account all these factors.

Limitations on the number of solar panels on a house

Available square footage, With the new higher efficiency solar panels, the surface area of the roof or where we intend to install the solar panels is not usually a limiting factor.

However, it is important to keep in mind that if we want to produce a large amount of energy, we may be limited by the available surface area. In such cases it is better to have more powerful panels that generate more energy in the same number of square meters.

Hours of sunshine versus hours of consumption

The central hours of the day, when there is greater light intensity, are the hours in which more energy is produced in our solar panels. If these hours coincide with the hours when we consume the most electricity, we will get the most out of our installation. However, if we need to spend more energy at other times, a traditional off grid solar system may not be as profitable. In this case we have two solutions:

To have an electric accumulator: these devices store the surplus electricity generated by our solar panels to be used at another time. Currently they are expensive devices with short life times, so they are not recommended unless you want to make a large investment.

Compensation mechanism: these are electricity tariffs that compensate the surplus energy generated by the solar panels, deducting the money from the bill. All the electricity we use during the hours when the solar panels are not producing is compensated for the energy we did not use when they were producing electricity, saving on our bill. In single-family homes, it is generally advisable to take advantage of this compensation mechanism to make the most of the energy production of the solar panels.

How much does a solar panel installation cost depending on the number of panels?

Currently the price of a photovoltaic electrical installation in a house is between 0.8 € per kWh and 1.2 € per kWh of annual electricity consumption. This is approximately between 500 and 600 € per solar panel or module in the complete installation.

Annual consumption Number of panels Price of installation

3300 kWh 6 4000 € – 5000 € – 5000

5000 kWh 9 5000€ – 6000€ – 6000€

6600 kWh 12 6000€ – 7000€

9900 kWh 18 7000€ – 10000€ – 10000€

As always, these prices are approximate and it is best to make a personalized study according to your needs. Also not included in the prices are possible discounts and subsidies to which you have access in the different plans to promote the use of clean energy. Well, if you still have any questions about measuring power consumption and estimating how many solar panels you need, please feel free to contact Renogy for a free consultation.Renogy is a supplier of excellent quality solar panels, inverters, Solar batteries, solar generators, battery charging items, and especially supply top efficiency solar panel for sale and also solar generators available for sale all over the world. Renogy deals solar panels that vary in dimension from 10W Watts to 300W Watts, excellent for both tiny scale applications and also big power projects.