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 use 100% renewable energy. They charge a bit more for electricity than Holaluz because they are smaller, but as of April 2023, they buy back energy at a rate of  13 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. 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 takes 8 years, it will still be worth it. The panels have a guarantee of 15 years. Their expected lifetime is 25 years. 

Update: The reduction of IBI can only be received once. The IBI subsidy can be received for solar heating of water (“termico“) or for solar electricity production. If you have already received a subsidy for termico, you cannot receive a subsidy for electricidad. I had called the Ayuntamiento twice and both times they confirmed that these are separate subsidies but it turns out this was not true. Also note that the reduction of IBI is up to 50%. However, Sunhero gave me the contact of a third party who applied for a “Next Gen” subsidy. The invoices are now coming in and showing 500€/year, as Sunhero said. So assuming I don’t get the Next Gen subsidy, I will have paid off the solar panels in 3 years.

Installation: The installer came to the house. Sunhero actually subcontracted someone from Eave to handle the installation. Once the positioning of the panels 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.

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.

Legalization: Sunhero 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.” After full payment, Sunhero handled the application. I received an email 31 days later from Som Energia approving autoproduction. I told Sunhero, and they flipped the switch. In the inverter app, I could then see the curve of the sun’s energy production. With real-time data, I can see exactly where the energy use in the house is.

Note that “Legalization” has nothing to do with getting the subsidy. 6 weeks after installation, Sunhero sent me the docs so that I can apply for the subsidy at my City Hall.

Conclusion: Overall I am very happy with the whole process. The only real problem is the app data going down sometimes. Sunhero has been good about fixing that. There is a buzzing noise from the transformer that can be heard inside the house. We might need to put some insulation under it.

In our house, everything besides the water heater (see below) has negligible electricity use when the sun is down. First, I set the water heater thermostat so that when the shower lever is on max, it is no hotter than necessary. Next, I plugged the water heater into a timer so we don’t heat the water during the night. We can ignore the electricity use directly from the panels during the day. The only important numbers are the kWh that we use from the grid and what we feed back to the grid.

  • Fed to grid: average of 24 kWh/day x 0,176€/kWh (Som Energia’s autoproduction rate)
  • Case 1) From the grid (with the water heater timer set to 7:00 – 18:00): average of 5 kWh/day x 0,28€/kWh (average rate of punto/llano/valle)
  • Case 2) From the grid (with the water heater timer set to 6:00 – 23:00): average of 15 kWh/day x 0,28€/kWh 

In Case 1: 24 x 0,13 is greater than 5 x 0,28: We are feeding more to the grid than we receive, so we pay nothing (but with Spain rules, we can’t get money back).
In Case 2: 15 x 0,28 – 24 x 0,13 = 1,08€/day. We spend 1,08€/day of electricity. So Sunhero was right. Our electrical bills will be very close to 0€, as far as actual use goes, though there is still a fixed cost on the bills of about 360€/year. It looks like we will pay off the investment in 3 years.

Electric car: As soon as the panels were installed, I bought a Nissan Leaf electric car. No need for a wallbox. No daily commute so our regular socket is enough. It’s a thrill to see the “gas tank” go up as I drive down the hill from La Laguna to Santa Cruz.  Since driving from one end of any island in the Canaries and back is no more than any electric car can handle, there is no reason for gasoline cars in the Canaries, as long as they build enough charging stations for those who don’t have their own garage. I would love to see the Canaries pass a law to only allow electric cars sold within 5 years. 


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…