GE ECOmagination Challenge Powering Hour Home

The Requirements To Build Green Homes

In order to create zero energy buildings are 3 main factors: 1. The design and the materials of the green home; they determine the comfort and the insulation. 2. Energy efficiency of appliances and other energy users; conservation is the strategy of choice 3. Renewable energy generation; to offset the energy consumption and make it zero energy

The design and the materials of the green home. More and more architects are designing energy efficient houses. Very good insulation and controlled ventilation are key elements. Personally, I am in favor of ICF blocks, which have a similar shape as hollow concrete blocks -but are bigger- and consist of expanded polystyrene foam. Similar to hollow concrete blocks, they are filled with steel -horizontally and vertically- and are then filled with concrete. As they are larger, they hold more concrete so the resulting building is stronger. However, to create an energy efficient house, it is of decisive importance to have a very high insulation value. That is the reason why ICF blocks are my favourite, because no other building material beats their insulation factor. Trivial is to use well insulating doors and windows in green homes.

Energy efficiency. Space heating and space cooling combined with hot tap water are the biggest electricity users in most households. As shown at the General Electric ECOmagination challenge best efficiency will be offered by solar water based space cooling and heating systems. Currently, they are not on the market yet, but this will change soon as companies have made announcements and will get financial support from GE. The energy usage of "pure solar" A/C systems is extremely low as they just use small pumps and fans.

The efficiency of these systems can be further improved by installing seasonal water storage. In the late summer, all excess capacity can be used to store hot water in well insulated storage tank(s). Even in autumn -before the heating season starts- excess capacity can be used to maintain the temperature of the water in the seasonal storage tank. This hot water is then used for space heating during the heating season, as a supplement to the solar capacity on the roof during less sunny days. After the seasonal tank's temperature has dropped below a useful level (typically in the middle of winter) the water can be cooled by circulating water from the seasonal storage tank to a heat exchanger in the ground. During the cooling season this water can then be used to cool the house.

Renewable energy generation. A well insulated green home and energy conservation are the base conditions, but to make it zero energy renewable energy is the only way to go. Unfortunately, they are also the most expensive of them all. On the long term you are always better off by insulating your residence well and conserve energy. Then, you calculate your desired renewable energy generation capacity. If you are tied to the grid and have a "net metering" arrangement where you only pay for the net energy you are taking from the utility -but not get compensated when you supply more than you use, then the rule of thumb is to dimension your renewable energy capacity to 80% of your average energy usage. If you benefit from a subsidized "feed-in" tariff then you may want to install more than the capacity you need for your green home. It's just a matter of math.

Wind energy. Wind turbines are currently the cheapest approach but their aesthetics and zoning requirements and/or building permits are drawbacks. New designs are being made to compensate this and once production quantities increase, the lower their cost will be.

Solar energy. Solar photo-voltaic (PV) panels are aesthetically accepted and usually do not require permits. They are the safe choice, but at a higher cost. The price of solar PV is continually going down, especially now that a new generation of CPV (concentrated photovoltaic voltage) is now emerging.

Inverter. Both wind and solar systems generate a DC voltage. To connect to the grid and feed your appliances and equipment you need an inverter. There are inverters that just connect to the grid, those that can work stand-alone with batteries or those that combine these functions. If your utility has unfavorable feed-in tariffs you may want to opt for an inverter that uses renewable energy until (batteries are) depleted and then switch to the grid with a so called transfer switch.

Readers are recommended to check out entries at the ECOmagination contest to see in more detail what the very near future has to offer.


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Dutch technologist James Post is one of the top contenders in the GE ECOmagination contest and would appreciate when you would use the links below and if you agree the entry is good, vote and place comments or ask questions, which would all be answered by him. He currently resides in Grenada.

These are the links (made short to fit): http://tinyurl.com/smartwind & http://tinyurl.com/smartsolar