Can a district energy system help to keep your electricity rates low? It does at Princeton University!

By Paige Davis posted 07-31-2017 14:58


Paige Davis, IDEA
July 31, 2017

Summertime is synonymous with school vacations, beach days, and summer bbq’s. For those in the utility business it also means high electricity demand driven by high temperatures and heat waves. July 2017  has seen new peak records in Texas and Alberta as well as year-to-date highs in the Northeast, Mid-Atlantic, and Central US.

These high load days, or ICAP days, are used by the Independent System Operator (ISO) to help determine how much customers contribute to the peak demand on the grid. This peak load contribution (PLC) is taken into account to determine rate schedule, load profile, and eventually the billing rate for the customer. In order to get the best electricity rate possible, customers need to minimize their PLC. Limiting how much you buy from the grid, especially on ICAP days, can go a long way in lowering electricity costs.

On Wednesday, July 19th Princeton University experienced one of these ICAP days and even though the campus peak demand exceeded 19MW, they were able to purchase an average of less than 1MW from the grid. Reducing their demand on the grid allowed Princeton to avoid peak prices that reached more than 3 times the average rate and will also help them the next time their capacity charges are determined. But how did they manage to avoid more than 18MW of demand on the grid – without causing campus customers to suffer? With a flexible district energy system powered by CHP.

Courtesy of Princeton University Facilities Engineering; Princeton University energy use on July 19, 2017
During the peak hours of 4:00pm-6:00pm Princeton was able to keep the amount of electricity purchased from the grid below 1MW (indicated by the black line above) even though the campus was using 18-20MW (indicated by the orange line above). This helped them to save money by avoiding peak electric rates of over $250/hr (indicated by the bright green line above).

The Princeton Energy Plant has a variety of electric, steam and renewably-powered equipment used to produce heating, cooling and electricity for their campus. The variety of equipment and fuel inputs gives Princeton the flexibility to choose the best combinations at any given time to make sure that they provide for the campus’s energy needs at the lowest cost possible while simultaneously helping to reach sustainability goals. During the extreme temperature conditions on July 19th,, Princeton used their cogeneration plant to provide 15MW of their peak load. The rest came primarily from their solar farm,  leaving less than 1MW of demand to purchase from  the grid. They were also able to reduce the campus demand by activating technologies like Thermal Energy Storage which uses electricity purchased during off-peak times to produce chilled water to be used to cool the campus when there is stress on the grid – and avoid the most expensive electricity.  Informing these decisions is a sophisticated system of instrumentation, controls and modeling that is constantly feeding energy and economic information to the Energy Plant. It also helps to predict extreme conditions, like it did for the July 19th ICAP day.

Activating and balancing this network of assets helps Princeton save money and reduce their environmental footprint. The whole system at Princeton reaches efficiencies of up to 80%, compared to a traditional power plant which is typically around  33% efficient. This in combination with highly energy efficient buildings and dozens of Energy Conservation Modifications to the energy plant over the past several years minimizes the total energy use at the university and provides countless economic, reliability, and environmental benefits.

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