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How much do solar panels save

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If you are interested in solar energy, I think the economic question is what commands and wants to know How much do solar panels save, in this article we will try to answer it.

The end of the month arrives, moment of the dreaded charge of the electricity bill. The electric company’s receipts rise unstoppably and, as savers we are, we have been thinking about the idea of ​​solar panels for a while.

How much do solar panels save

We have heard that tolls have to be paid, a sun tax, that there is a decree that regulates everything – and complicates it. Will it be worth installing panels? Do we disconnect from the power grid? Batteries? How many panels?

How much do solar panels save


Since 2000, developed countries have promoted the production of electrical energy by means of photovoltaic solar panels. In Spain they also opted strongly for this, with several decrees approved between 2004 and 2007 that granted premiums to producers.

So, “planting” solar panels in the Spanish fields was a round business. It’s not like that. But let’s put aside production and focus now on the Royal Decree of 2015.

To simplify the complex regulation on the self-consumption of the Royal Decree, we distinguish  two possible situations :

  • Self-consumption disconnected: we have solar panels installed and we are not connected to the power grid. We only consume our electricity production.


  • Connected self-consumption: we have solar panels installed and we are connected to the electricity grid to have conventional electricity   when we need it.

One factor to consider in both cases is that in the hours of more sunshine is when we need less energy: because we are not at home, or because we do not need lighting or air conditioning. This simple fact conditions the entire approach to domestic solar energy  and forces us to remain connected to the electricity grid and / or use batteries to accumulate energy, which makes the installation more expensive.

In the case of disconnected self-consumption, we forget about the electricity companies and we manage our production and electricity consumption ourselves, whether or not we have batteries. Then we see an example.

How much do solar panels save

On the other hand, if we choose to remain connected, the famous backup toll , introduced in this Royal Decree 900/2015 comes into play with a variable part, nicknamed “toll in the sun” and another fixed part. The controversy is unleashed when, to have the backing of the power grid if we do not produce enough with our installation, we must also pay for that energy that we have produced with our panels.

But beware, because by analyzing in detail the BOE of the decree, in the first transitory provision  there is an important exemption to tolls :

  • If we are consumers in type 1 self-consumption mode,
  • and we contract with the electric company a power of 10 kW or less (usual in homes):

So, we don’t have to pay those tolls, just the power we have contracted and the consumption we have of the electricity grid. Belonging to type 1 self-consumption adds two extra requirements:

  • We cannot sell the surplus electricity.
  • The installed power (in panels) must be less than or equal to that contracted (with the electric company), so we could not install more than 10 kWp (peak power of solar panels).

What if we install batteries besides being connected? That way, we would leave the consumption of the network in a third plane: first we would pull our production, if there is not enough, of the batteries and, finally, of the network. Well,  in this case there is no applicable exemption for the fixed part of the backup toll , which we would have to pay based on the maximum generation power of our panels.

How many solar panels do we have to install to save? Two examples

Determining how many panels to install is the task of each saver. There is no choice but to take out the calculator and start calculating. To consider:

  • How much energy do we need?
  • How much does the solar kit that gives us that energy cost?
  • How many panels does that kit have?
  • Do we have space to install all the necessary panels?
  • Are we still connected to the network? Do we use batteries?

First of all, it  is essential to calculate how much our electricity consumption is  in Wh / day. It is easy to measure with a sensor that is installed in the electrical panel of the house and costs about 70 euros.

According to IDAE, the average consumption per household is 3,487 kWh, a high figure that we could easily reduce if we know how to fight the electricity bill.

How much do solar panels save

First example: we buy a solar kit with batteries and disconnect from the power grid

Suppose we consume 3,487 kWh per year, equivalent to 9,553 Wh / day. To look for an appropriate solar kit, we look at those that allow to capture those 10,000 Wh on a winter day. The approximate price of the kit is around 6,500 euros, although it will be higher depending on the peak power chosen and the capacity of the batteries. If we add 3,000 euros of additional cost to replace the batteries (their useful life is lower than that of the panels) and some other possible breakdown, the total investment comes to us for 9,500 euros.

To calculate the savings with these panels, we approximate the average cost of kWh in Spain to 0.15 euros, which means an annual electricity outlay of 523 euros (3,487 x 0.15). Assuming that the price of that kWh in the coming years does not vary, we would  need 18 years to amortize the investment in the solar kit .

That is, after 18 years we would begin to save all electricity consumption. As the useful life of the solar panels is 25 years,  in those remaining 7 years we would save 3,661 euros . As the price of kWh will continue to rise in all likelihood, the amortization period will be cut and the savings will be even greater.

With so many numbers,  let’s not forget the most obvious: the necessary space . A solar installation of these characteristics requires six to eight solar panels and each measures approximately two meters long and one meter wide, in addition to a place to store the eight batteries. Therefore, it  is unfeasible for housing blocks and its use is practically reduced to  independent houses with their own roof and / or gardens.

How much do solar panels save

Second example: we buy a solar kit without batteries and we remain connected to the network

In order not to have to pay the backup toll, we have already seen that we must contract a maximum of 10 kW with the electric company, the peak solar power must not exceed that figure, and we cannot install batteries.

The key idea to save can be oriented to depend less on the network and pay a little less on the electricity bill. It is important to consider that the hours of more solar radiation do not usually coincide with those that consume more electricity.

A good strategy is to save part of the consumption of the devices that remain on during the daylight hours, especially the refrigerator , and those that are given occasional use such as the television, charging the mobile or the laptop.

For this we should choose between two or three solar panels of 250W each. This option is more feasible for savers who live in a building. The cost is around 1,100 euros for two panels and 1,400 euros for three.

In this example we assume the installation of 2 solar panels, with 6 hours of sunlight a day and that the 500W that are being produced is always consumed:

500W x 6 hours of solar radiation / day x 365 days = 1,095 kWh / year

If we assume a constant price of kWh of 0.15 euros, then  we will be saving more than 164 euros  from the sixth year, since, as we have spent 1,100 euros on the installation,  the amortization period will be 5 years .