Cut the electric wires off!

With the continuous changes in electricity tariffs (always against our pockets), many people are starting to look at that yellow ball up in the sky and mulling over if it could help in some way with our invoices. Do I unplug from the mains and produce my own energy with photovoltaic panels? Is the photovoltaic profitable? If only, to give a kick in the ass to my electric provider.


Let's start from the beginning.


First of all, let's talk about "toll backing" for those who do not know anything about it, let me explain that in a summary form, could only be interpreted as a recent joke from the Spanish Government with which the electric companies do charge between 4 and 9 cents for each kWh generated by our own photovoltaic installation (even if it is for own consumption), always and when your house is connected to the mains. Based on that, even if you are not using the mains, you have available those Kws. as backup, therefore you have to pay. (You don`t understand it?.... neither do I)


If you have an installation somewhere in a country home somewhere up in a rural area you will not have to pay anything , so it is normal that many people are thinking to install themselves an installation. Let's put a simple example of a house with a monthly electric consumption of about 1.61kWh which is a low consumption.


If we want to feed our house with a photovoltaic's system and disconnect from our supplier of electricity, we must be self-sufficient 100%, therefore we need to dimension the installation for the months with most unfavourable solar radiation, which in our example will be December and January.


This could be our consumer profile for these two months:

We are not going to enter into the calculations, but we have considered a depth of discharge of 50% from our accumulation batteries pack and other parameters that we are not going to analyse here. Therefore we would need a supply of at least:

  • Installed power: 2. 250W
  • Accumulation in batteries: 12kWh corresponding to 6kWh
  • An Inverter of: 4kW.

A kit may be sufficient if it: consists of 9 panels of 250W, built with support frame, an inverter of 4kW and 4 batteries 12V 250Ah. The price would be € 5,500 and the installation could come out approximately €1.500. Total to pay for the system  €7,000.


In addition this kit could be installed initially without disconnect from the mains and leave it at that time to test it, then once tested we would disconnect and be a fully autonomous "island" which is our final goal.


Doing a simulation, we check that the available energy accumulated in our batteries in the two toughest months always is positive; therefore we'll not stay without supply at any time.


With this measure we would save the full invoice from our power supplier, about €43 per month in this example, about €512 a year (with taxes). Energy wise we would save 161kWh per month or 1. 932kwh per year.


It should be noted that this facility allows us to feed ourselves fully in the month of January, therefore the rest of the months we would have more than sufficient, so we will generate more of what we consume. We can use any "energy dump" for these kWh leftovers, in an electric water heater for domestic hot water, for example, in this way would save even more since we would not pay hot water from April to November.


Profitability of photovoltaic panels.

If we take into account the savings made from prices of the kWh today, the simple return on investment time will be 13 and a half years, which is not bad and that does not include, the continuous escalation of the price of electricity.


We could make a more optimistic estimation of evolution of price of the kWh based on previous years. I say very optimistic because no one will believe is that in 2020 will only cost €0.2 kWh. It would be something like this:

With these data, the simple ROI is reduced, becoming little more than 10 years, which is much better. We have not taken into account for this calculation the savings obtained by the "energy dump" (Thermo or similar) making a saving on hot water for example, so the ROI would be quite possibly even less.



There is a movement in Spain called "Cut the wires dot com" which is an organisation that guarantee that with the exclusive use solar photovoltaic panels we can disconnect from the electric companies and could leave happily ever after, consuming green energy with 0 Co2 and giving a kick in the ass to all the Spanish electrical companies. So it could be very interesting if you pay a visit to http://www.cortaloscables.com/.

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