Incorporating renewable energy into a building’s electrical system is becoming an increasingly efficient and cost-effective option. Renewable energy (from photovoltaics, wind power, etc.) uses natural resources, reduces greenhouse gas emissions and minimizes dependence on a power grid – all benefits that can lead to long-term cost savings.
Grid-Connected or Independent
When integrating renewable energy, electrical engineers must first decide whether a building’s electrical system will be connected to the local utility or completely independent from it.
In a grid-connected system, a building is able to use the local utility to balance its electrical ebb and flow. If a building needs more power than it has produced from renewable sources, it draws from the grid in the standard way. If a building’s renewable sources produce more than its electrical demand, the excess goes back into the grid.
A building that isn’t connected to the local utility needs a battery storage system to manage its power excesses and deficits. Battery storage is often expensive and can reduce the overall system efficiency by up to 5 to 10%.
In general, if it is an option to connect to a local utility, it’s more cost-effective than operating independent from the grid. Many states have adopted interconnection standards recommending or requiring that utilities let customers connect on-site power systems to the electrical grid. In the absence of these standards, the interconnection is left to the local utility, and can be more burdensome and expensive for a building owner.
Net Metering & Submetering
Net metering is essential for a building producing renewable energy and connecting to the grid. Standard utility meters only move forward to measure the amount of electricity used by the building. Net meters, on the other hand, shows both the energy consumed and the energy produced. A meter spins both forward and backward, to and from the utility, depending on the power usage. A net metering system uses the utility as battery storage, saving excess produced power for a later time. An electrical system connected to the grid will carry a utility tariff or an agreement that defines the value of the energy the building feeds back into the grid.
Submetering also is a useful tool to measure the long-term efficiency of a building’s electrical system. A submetering system offers a more detailed view of energy consumption, for example, identifying the loads of lighting, mechanical and plumbing equipment in a building. This allows engineers to determine if certain areas are exceeding expected output.
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