Monitoring Energy

By Jefferson Goethals

An energy monitoring system gathers, stores and presents data. Gathering the right data is important; storing it and organizing it is important. Extracting meaning from the data is the key to any energy monitoring system. Only then does the data become information that we can use. Here are some principles to guide that project.

1. Monitoring energy is monitoring economic value. The principal reason to meter energy is to understand its value. Electricity meters exist for billing. Performance monitors (e.g. miles-per-gallon monitors in a Prius) help to get the most out of energy systems. Monitoring for research is ultimately aimed at generating more energy or identifying energy potential (e.g. wind site monitoring).

2. Time is a critical element in all meaningful energy monitoring displays. Time helps us understand energy in several ways:

a. Presenting power vs. energy. Sometimes it is important to know power, or rate of energy (e.g. watts, joules-per-hour) at a point in time. Other times it is important to know accumulated energy (e.g. watt-hours or joules) over a time span.

b. Real-time and historical information. It is often important to know the real-time states of energy systems. Sometimes it is important to know how that state compares to previous states in that system. Accumulated energy over different historical time-spans is also useful.

c. Energy has different values at different times. For example, electricity that is available during peak load times is more valuable than electricity available off-peak. A good energy monitoring presentation will show that difference.

3. Accounting systems are very useful in tracking value over time. Since we are dealing with value in different time measurements, it is worth examining data tracking systems that already do that: accounting systems. Energy is produced, consumed and stored, and so is money. Stored energy depreciates just like capital invested in a fixed asset. Designs of databases that store data about complex energy systems should be informed by the designs of accounting databases.

4. Assigning value and cost to energy is the value-add. Assigning different values at different times, as described above, is one way. Here are two others:

a. Hidden cost and value. For example, wind energy in the US is eligible for production tax credits, and Renewable Energy Certificates in some states. Attaching these values to wind-generated kilowatt-hours gives a truer picture of their value.

b. Displaced Energy. Much of the value of renewable energy lies in the fact that it replaces energy generated by burning fossil fuels. For example, solar hot water could displace an electric hot water heater or a propane heater. Assigning an accurate value to solar HW depends on the type of fuel displaced and the efficiency of the system that uses that fuel. Carbon credits also depend on the type of energy displaced. For example, burning coal generates more greenhouse gas per kWh than burning natural gas.