Zero Carbon Home

by / Monday, 15 June 2015 / Published in Blog
zero carbon home

When most people are asked about climate change and what is causing it they can easily point to the obvious sources of carbon emissions such as cars and airplanes. Electric cars are beginning to gain some attention, in particular the new disruptive carmakers such as Tesla in the move away from fossil fuel consumption. Another area that has big part to play in reducing carbon emissions is buildings and what most people want to know is how can they reduce their homes’ carbon emissions to zero.

A zero-carbon footprint house supplies more energy to the energy grid than it takes. It generates enough energy to run the building and in many countries any excess electrical energy can be sold back to the grid. In Spain Photovoltaic, also know as PV (electricity production from the sun), cannot be sold back to the grid. This is why solar thermal is a better choice of renewable energy generation. The hot water can be stored for a reasonable amount of time and directly offsets the energy that would be consumed to heat the water. Typically this is either electricity or gas in southern Spain.

The first step to make any building zero-carbon—new construction or an existing building—is to do as many things as possible to lower the building’s energy consumption so less energy is required to power the building. This is often referred to as “reducing the load.” It’s possible to build super-efficient new homes fairly economically by using high levels of insulation and high quality windows. With existing construction, you can reduce loads by adding insulation wherever possible and by reducing air leaks.  Once you’ve reduced the load, it’s time to add some alternative energy system—in our case, solar thermal panels for hot water and/or photovoltaic panels to make electricity. You should implement conservation strategies such as increasing insulation and reducing energy use before investing in solar thermal and photovoltaics; it’s less expensive to buy the most energy efficient lights or add insulation than to buy and install more solar panels. Once you’ve done all you can to conserve, you may find you need fewer panels than you thought.

There are two basic types of solar panels. Solar thermal panels are used to heat water, whereas photovoltaics produce electricity for the home. Solar thermal panels are composed of three parts: a solar thermal collector; a fluid system to move heat from the collector to its point of use; and a tank for heat storage. Solar thermal panels are particularly cost-effective for heating spas and swimming pools, which require huge amounts of heat. Spain requires new and renovated buildings to obtain 30 percent of their hot water from a renewable energy source, easily achieved by installing a solar thermal system.

The most widely available photovoltaics (PVs) are thin strips of silicon, sliced up and glued onto glass, which generate electricity when the sun shines on them. One of the great things about PVs is that their life span appears to be very long. We see very small drop-offs of only around 10% in their production after 20 or 30 years of use.

What would it cost to install PVs on a 250m2 house? Let’s assume you have tidied up your energy consumption by getting an Energy Star refrigerator, replacing all your light bulbs with LED’s, and turning off your TV and satellite box with a plug strip so they aren’t running all the time. A 3-kilowatt (or 3,000-watt) system will handle the needs of most families; the national installed price of PV is currently about 2€ per watt if you include the total costs of panels, mounting structure, inverters and cables. At this price the system will pay for itself at the current utility rates in about six to seven years. It’s difficult to say what future electrical rates will be, but once you install PV you’ve essentially paid for all of your home’s electricity upfront.

I believe we can and must reduce the carbon emissions in the world by at least 90 percent in the next 15 to 20 years and it’s going to take a tremendous effort to do so. The problem is that each of our individual actions seems so miniscule compared with the overall amount of CO2 going into the atmosphere. But when large masses of people participate, it absolutely makes a difference. The key is to make changes that enhance people’s lives while also making their energy use more efficient.

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