Installing solar panels on my house in Tenerife

4 February, 2023

Background: energy use in Tenerife

In 2021, the average use of renewable energy in the Canary Islands was 19.9%, up from 17.5% in 2020, and 16.4%. in 2019. Per island use of renewable energy in 2019 was: 

55% Hierro
20% Tenerife
16% Gran Canaria
11% La Palma
10% Lanzarote/Fuerteventura
0.2% Gomera

Wind and sun is so abundant in Tenerife. So why is only 20% of the energy used in Tenerife renewable?  (See tables below.) Apparently the wind turbines need to be turned off sometimes because we don’t yet have a good way to store the excess energy. They implemented what sounded like a good solution in Hierro: using a higher reservoir as a means to store energy. Use excess energy to push the water up, then use turbines when bringing the water back down. I’m told the theory didn’t translate to reality so perfectly.  The rest of Spain actually subsidizes energy use in the Canary Islands, otherwise the electricity bills would be higher. Since 90% of our water comes from the four desalinization plants (desaladoras) which is energy-intensive, that means a lot of oil is being burned in order to water our gardens, pools, and the seven golf courses in Tenerife. In Hawaii, of all the cargo ships coming in, the majority of cargo is fossil fuels. One can assume the same is true in the Canary Islands. 

My house

I thought I was early in the game, but now I see a quarter of my neighbors already have solar panels. I checked the web and sent emails to 3 companies: Eave, Holaluz, and Sunhero. They ask for my factura de luz and review the top of the house with Google Earth, then send the proposal. I ruled out Eave — too long to reply. Holaluz requires me to switch to Holaluz as an electric provider (comercializadora). Holaluz sent a person to my house. Holaluz looked great at first: a certified B-Corp. But then I then saw all the bad google reviews they have as a provider — it scared me away. So I chose Sunhero — run by German owners. Their proposal was good. 

On-grid or off-grid: The first decision is whether to buy a battery for 1500€ or sell back to the grid. At first, I was assuming I would buy a battery, but I learned that a battery only lasts 10 years or so, and it’s an ecological disaster to get rid of. I realized that selling back to the grid is how things really should work (though “the grid” has to figure out its own way of storing energy).  So the next question was how does that work? I learned that in Germany, the energy “buy rate” is the same as the energy “sell rate”, but in Spain, the “sell rate” is one-third of the “buy rate”. (Is that possibly related to unemployed Spanish politicians always going to Endesa for a job? Enough speculation.) That means that it behooves you to use up as much of your solar energy when you can: run your dishwasher, water heater, etc. during the daylight. Because of this buy/sell difference, it’s not worth installing more panels than the actual amount of energy you need. Ideally, the panels should provide 90% of your actual energy use. The solar providers will look at your invoices and figure this out.

On-grid buyback rates: I currently use Som Energia as my electricity provider in Tenerife. They are a cooperative based out of Barcelona and I love them. They charge a bit more for electricity than Holaluz because they are smaller, but according to their website, as of January 2023, they buy back energy at a rate of  17 cents per kWh (compensation autoproduccion).  The guy from Holaluz said that Spain has dictated a maximum rate of 11 cents, so I don’t yet know what is true. I also read that it is important to get a variable buyback rate in the contract since the rate will probably go up.  Reading Som Energia´s great articles, I learned that they offer group sign-ups (compra colectiva): once 50 people sign up to buy solar installations, they get a discount rate on the panels, then in Tenerife contract out to cooperatives AEATEC y Ecooo. Sounds like a great idea, but there was no planned date for the next sign-up, so I decided to go ahead with Sunhero, though I probably should have gone with these coops directly.

The costs: Sunhero gave a final price of 8942€ for installation of 15 panels without a battery. I currently pay about 3500€/year in electricity bills (10,600 kWh/year). Sunhero estimates electric bill savings of 3000€/year. In Santa Cruz, there is a subsidy of 50% of IBI during 5 years (even if I already received a past subsidy for a solar water heater). In my case, that’s 2500€. So the installation cost with subsidy is 9000€ – 2500€. If I save 3000€/year, then in only 2.2 years, I recover the cost. Sounds way too good to be true, but even if it’s 8 years, it will still be worth it. Other notes:

  • The panels have a guarantee of 15 years. Their expected lifetime is 25 years. 
  • I need to clean off the panels a few times every year. Sunhero offers annual maintenance and cleaning for 100€.

Installation: The installer came to the house. Sunhero actually subcontracted someone from Eave to handle the installation. Once the panel positions are clear, you need a place for the inverter, then a way to get the cable from there to the fusebox. I was told my house didn’t have standardized three-phase voltage, so I would need to have a transformer installed (an additional 840€).

Sunhero answered all my questions in English. I signed the contract and paid 10%. Sunhero got the building permit and crane permit.

I was very happy with Eave’s installation. The panels didn’t quite fit, so they installed them in a way that hung over the roof. The installer himself said that looks ugly from the street. They took the initiative and time to move half the panels another way. I was very happy with Sunhero’s support too. The dedicated support person answered all my questions fast.

Legalization: They told me “in order to be able to sell the surplus to your electric company, it is necessary to carry out the legalization process. This process is carried out before Industria and we usually have the process finished between 1 and 4 months.” Once I receive the legalization papers, I pay the remaining 90% to Sunhero. I then send the legalization papers to Som Energia. 

Maintenance: The installer said don’t bother paying for maintenance. Just clean the panels myself: wash off the panels with a hose once every few months (or after every calima). Pour water on them, take a dust mop and clean them. Don’t do it when they are hot — do it in the morning or evening.

More to follow when this is all completed. After that comes the electric car.

 

 

My water heater struggle (an unrelated rant): Som Energia gives a graph of energy use during each day. When my electricity bills got huge, I discovered that my electric water heater (calentador) raises my daily use from 10kWh to 40kWh or more! That’s 30kWh/day. Endesa says normal kWh use of a water heater is 12-24 kWh / day.  A typical water heater runs 3-5 hours/day. This one is 1500W: 1.5 x 4 hours — should be 6 kWh / day. If the heater is covered in calcium deposits, the heater may run almost always but work poorly. I thought this was the problem or that the thermostat was burned out and it was running 24hours/day. So I bought a new one. But my bill stayed high. I just don’t get it. 

You might ask why the heck do you have an electric water heater if you have a solar water heater on your roof. Well, my wife, con razón, wants a guaranteed hot water shower, and some days it’s cloudy. But if nobody uses water, the electric water heater just keeps heating its tank of water regardless of whether the solar heater tank has hot water. Seems stupid. The solution is to get a gas water heater (using a butane tank) with a thermostat so it only fires when the water is cold enough. That setup will cost 1000€.  That seems kinda stupid too if I’m buying solar panels to give me free electricity. Currently, I have a timer on my electric water heater so it can only turn on for 8 hours per day. Hopefully, my wife won’t shower at 4 pm. I’m kinda stuck here…