Tracking Renewable Energy Sources

Tracking renewable energy sources requires an energy monitor to have a dedicated channel for that purpose. This channel must be in addition to those channels used to track total load or specific appliance loads.

When alternative power is tracked against total load the net  result is the number of kilowatt-hours that will be on your next electric bill.

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Each channel of the energy monitor will require a separate set of current transformers or CT's.  These CT's measure the current generated by the renewable energy source.  They must be located on the conductors coming from this alternate energy source prior to entering a transfer switch or circuit breaker in the distribution panel or else measurements will not be accurate.

Since wind speeds change, clouds pass in front of the sun and stream levels fluctuate alternate power generated by renewable energy sources is not usable in standard electrical distribution networks.  It must be rectified (AC to DC) and/or inverted (DC to AC) to become usable.  This power must have the proper voltage and frequency to compatible with standard household power.

Given these considerations, the best location to measure the true output of renewable energy sources is on the load side of the rectifier and/or inverter before power enters the main circuit breaker panel.  Alternative power can now be measured at standard voltage and frequency and includes any efficiency losses caused by the rectifier and/or inverter.

Metering Renewable Energy Sources
Metering Renewable Energy Sources

This diagram provides a generic description of where the CT's should be located when wiring an energy monitor to track alternate energy.  Be sure to follow the manufacturer's instructions when you go to install your own system.  Before you do, however, keep in mind there are some peculiarities associated with measuring each renewable energy source.

Solar power panels capture sunlight and convert it into direct current or DC. Sun angle, time of day and level of overcast all effect the amount of power that can be generated. Battery storage systems are generally used to stabilize this high degree of fluctuation.

Direct current (DC) must be converted to alternating current (AC) using an inverter in order for it to work with standard household power.  Inverter inefficiencies can be high robbing as much as 20 to 30 percent of the total energy generated by the solar array.  Be sure to take inverter efficiency into account when sizing a system for your home.

Solar thermal uses the sun's energy to heat water, or glycol, if a heat exchanger is used.  This heated water supplements existing hot water systems or can be used directly to warm swimming pools.  If a separate pump is used for circulation, be sure to include its energy consumption in your final energy cost calculations.

Measuring the amount of electrical energy saved by solar thermal should be done deductively.  Set up a baseline by logging the amount of energy required without solar thermal.  Measure again with solar thermal operating and net out the difference. Load profiling or sub-metering the hot water heater is a good way to do this.  Log outside air temperature and match weather conditions before and after for a more accurate comparison.

Wind power is generated by mounting a large propeller on a tower to capture energy from a steady air stream.  Due to the constant fluctuation in wind speed the AC power produced is erratic and cannot be used directly to power appliances.  It must be converted to DC through a rectifier and then converted back to stable AC at the proper voltage and frequency before it can be used.

Micro hydro turbines require an ample supply of flowing stream water and a reasonable amount of vertical drop to work.  Output is generally limited to 12, 24 or 48 volts as they serve to charge battery storage systems.  Producing enough alternate energy to power an entire home at the 120/240 volts - 60 Hz. level is possible but requires a dramatic increase in the amount of flow.

If you are fortunate enough to take advantage of renewable energy sources where you live, by all means do so.  But, sharpen your pencil before proceeding.  Know all the costs, the efficiency of the system as a whole including rectifiers and inverters, the expected output and the credit or rate your utility will pay you for the extra kilowatt-hours you send back to the grid.

Install an energy monitoring system to track system performance and verify you are being properly credited for any surplus kilowatt-hours.  The cost of monitoring equipment is very small when compared to the overall investment you will make in generating power from renewable energy sources.

As always, actual wiring of monitoring equipment should be done in accordance with the meter manufacturers instructions and comply with all NEC electrical codes for your area.  If you are at all uneasy with following these instructions, BE SAFE, and hire a licensed electrical contractor to do the work for you.

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