The energy efficiency and renewable energy technologies currently available have created the possibility of net-zero and net-positive energy buildings:
It is important to note that these types of buildings are not necessarily off the grid - they may consume energy from the electric utility on occasions, but the energy they export to the grid equals or exceeds their consumption. Upgrading a building into a net-zero or net-positive energy building is a step by step process that should be carefully planned. Simply installing a lot of solar panels until you exceed consumption is not the most cost-effective approach: the PV system size can be reduced drastically if an intensive energy efficiency retrofit is carried out first.
In commercial buildings, the three modifications that tend to have the highest impact on energy efficiency are the following:
This is recommended as the first step because all subsequent upgrades benefit from it. For example, if the building envelope is upgraded, air conditioning needs are reduced: once the A/C is upgraded it can be changed to a higher efficiency model and downsized in terms of capacity. Some of the main modifications that can improve the building envelope are the following:
LED lamps save over 80% of the energy compared with incandescent lamps, and 30 to 40% of the energy compared with fluorescent lamps. They also reduce indoor heating, which leads to cooling load reduction. The cooling savings can be significant in buildings with thousands of lamps, possibly representing thousands of kilowatt-hours each month.
Just like with building envelope upgrades, it is smart to upgrade lighting before carrying out any HVAC upgrades: the reduced cooling load may allow AC equipment to be sized smaller.
A building that is well insulated will have much lower heating and cooling requirements. For the particular case of air conditioning, lamp upgrades also reduce load since the heating effect of lighting is minimized. Some upgrades that can have a significant effect are:
At this point, the total energy requirements of the building will have been reduced considerably. For old and inefficient buildings, potential savings may be in the range of 50 to 70%.
Installing renewable energy sources makes sense once energy efficiency has been optimized. If renewable energy is implemented as step 1, the result is a system sized for the original and inefficient building, which requires a much higher investment. The cost of ownership of the overall project is much lower if efficiency goes before renewable energy.
The main options available for residential, commercial and industrial buildings are the following:
At the moment, this renewable energy technology is the most viable for small-scale system to be used by homes and businesses. Solar power has several characteristics that make it one of the most versatile renewable sources:
Among all renewable sources, solar PV systems are currently the most likely candidate to become a mainstream energy source.
Wind energy also uses a free energy source, but is more limited than solar power with respect to location because a minimum average wind speed is required for the project to be viable. Wind energy tends to benefit greatly from scale, since output is proportional to rotor diameter squared.
There are some cases where regulations may limit the deployment of wind power in urban areas. Unlike solar panels, wind turbines have parts moving at high speed and their use may be restricted for safety reasons.
This energy source tends to be viable for companies in the food industry, who have access to large amount of organic waste to produce bio-fuels. Alternatively, a company with plenty of land available can plant and harvest crops for the sole purpose of using biomass energy. Biomass is typically processed as bio-diesel or bio-gas, depending on the needs of the user.
Once the energy needs of a building have been reduced, and then renewable sources have been implemented to cover 100% of consumption, a net-zero energy building has been obtained. If renewable sources manage to produce more energy than what is needed, the result is a net-positive energy building, which can sell its surplus to the electric utility company or to other buildings.