For some time now, we have been considering ways to reduce our carbon footprint while living here in Mexico. We already do this in some ways. We live in the historic centro of Merida–meaning we can walk to get most things we need for daily living. We do still travel by car once or twice a week for vet visits, larger purchases, etc. But we have dramatically reduced our driving (in the first year we drove about 3,700 miles versus 12,000 miles per annum while living in Minneapolis.) This reduces the C02 produced annually by 2.48 tons. In addition, we walk more. Having said that, we still have to fly to places which expends more C02 per mile. CO2 emissions in air travel vary by length of flight, ranging from 0.277 kg CO2 per passenger mile to 0.185 kg CO2 per passenger mile, depending on the flight distance. A car is 3.211 kg CO2 per passenger mile. Air travel is thus, on an individual basis, much more efficient. Note: this is a very oversimplified calculation since car travel average decrease based on number of passengers, etc. But, you get the point I hope.
In Merida, Mexico, the price per KW of electricity is “tiered.” The base rate (referred to as 1C) is roughly $0.5o pesos per kilowatt. However, if your monthly average (averaged on a rolling basis every two months) exceeds 850 kWh then you are kicked into the DAC tariff (De Alto Consumo, which means “of high consumption”)–and you loose your government subsidy. Once this happens, your rate climbs in three ways. First, DAC customers are charged a minimum of $65 pesos per month. Secondly, the Basico (basic) charge for DAC consumers increases from about $0.5 to $2.5 pesos per kilowatt hour (summer prices). The third way is that the government does not give you an Aportación Gubernamental (Government Subsidy). That aportación can underwrite more than two thirds of your bill every month, which is certainly not trivial. Note also that the government rates, tiers and subsidies vary by region–depending on the climate zone of your domicile.
Our house was designed to be as “naturally” cooling as possible. You can see from this chart that it can get hot here in Merida. April, May and June are the hottest months with an average high of 35+ degrees C or about 100 degree Fahrenheit. With this in mind, in 2010 I took a master class with Glenn Murcutt in Australia while we were beginning to design the house. This helped me tremendously in thinking about the design of the house to ensure natural cooling. We also were particular about our lot–meaning we insisted on a north-south orientation with enough depth to enable us to create positive and negative pressure on each side of our buildings. We have lived in the house since October of 2013 and have only a few times had to resort to air conditioning. This has meant that we have stayed in the 1C rate for the year.
Currently our average monthly use is 842 kWh. Our average, as you will detect, is very close to the 850 limit for going into the DAC charge. My wife has a weaving studio that requires continuous dehumidification in order to preserve her yarns, threads, fabrics and equipment. We actually do not even like the feeling of air conditioning and only use it when the temperature and humidity curves intersect to create extreme discomfort. Using our Panasonic Inverter Air Conditioning units has, as I mentioned, been rare for us.
After much discussion about further reducing our negative impact on the environment (first order) and saving money (second order) we have decided to install an array of 16 solar panels. These will be mounted to true south (our house runs 20 degrees west of south). Because of the high side walls, some of the panels will be elevated to maximize the solar exposure. This array will result in a 60% reduction in our average monthly consumption and an 83% monetary savings. The panels will produce about 394 kW each per year or a total 6,304 kW. We will feed back into the grid during the day and draw from the grid after dark. We are currently on track to consume 10,104 kW per year if we do not install the panels. This installation will reduce our monthly average consumption to about 316 kWh versus 842 kWh. We are hopeful that we can continue to reduce this difference through our conservation habits. It would be great to get this to 0.
The pay-back will be about 7.4 years. Of course, having these installed will not, we believe, alter our dedication to further reducing our carbon foot print. But this will go a long way since our array will reduce our carbon footprint by 3,670 KG or 4.05 tons of carbon dioxide. This is the amount of carbon monoxide that 112 mature trees remove from the atmosphere per year (32.85 KG per tree per year.) We will post progress photos and more commentary as we go along.