top of page
Search
  • Writer's pictureKerry Lipp

Load Shifting Simplified, getting the most out of your system

WHAT IS LOAD SHIFTING?

Load shifting is changing the time of day at which high powered loads are running. For example, running the washer or dryer at midday while the sun is high and the solar is producing max power instead of in the morning or evening. Another example would be putting your electric water heater on a timer so that it only turns on during midday. You are shifting the time of day at which the load is on.


HOW DOES THIS SAVE MONEY/ENERGY/GREENHOUSE GAS EMMISSIONS?

When you load shift, you use solar energy directly and there is no need for using grid or battery power at all. This saves money since you don't pay for the kWh cost of that energy. It also reduces the need for grid power which also saves emissions of greenhouse gasses and reduces the need for other problematic sources of energy such as nuclear power. It is always cheaper to use solar power directly rather than exporting it to the grid.


GRID-TIED LOAD SHIFTING

In the following screenshot of a system's daily output, the green represents solar production exported to the grid, the red represents grid power used, and the blue represents self-consumed solar power, or power used before it is sent to the grid.


The red spikes are loads that could have possibly been shifted to midday. Th


You may think that it is an even trade to use grid power at non-sunny times as long as you are exporting solar power to offset it. However it is always better to use your solar energy first. Here is why:

  • Line Loss..... Using energy at the site of production eliminates losses from long distance transmission and will always be more efficient

  • Transformer Loss....When you send solar energy out onto the grid the voltage must be stepped up to be able to send it long distance and vice versa. Transformers are not 100% efficient and some of the energy is lost to heat dissipated into the air.

  • Grid Power Is Dirty..... Most grid sources are not efficient and produce heat and carbon pollutants as by products. Sources are 40% gas, most of which is derived from fracking which comes at an enormous cost to water tables, health care costs, climate instability, and property values. 19% comes from coal, another contributor to the climate crisis, human suffering, health care costs, water contamination, etc. 20% comes from nuclear power plants. This is an abysmal choice of energy production since there is not a safe way to dispose of spent fuel rods. The disaster at Fukushima has contaminated much of the Pacific Ocean. Do we need to play with this dangerous technology any more while safer alternatives exist?

  • Climate Crisis.....We have already reached warming of 1.2 degrees C and at current rates of carbon emissions will easily surpass the 1.5 limit set at the Paris Climate Accord.

These reasons take into account the long term costs. If all that we value are short term costs, then, no, there is no reason to load shift with a grid-tied PV system other than to minimize rate hikes due to increasing demand. But in doing so we risk losing everything. We must prioritize non-monetary costs and hidden costs if we are to continue living on this planet as a species. What good will the economy be if our planet is uninhabitable?


OFF GRID LOAD SHIFTING

With off grid systems, surplus energy is stored in batteries and the grid is not an issue. During daily charging, as the batteries become full they take less and less current so it is probable that on a sunny day, as the batteries reach capacity, only a small portion of the array's potential is being utilized. For example, I can run my electric water heater, induction cooktop, or toaster oven during midday if the batteries are in absorb and the current going into the batteries will not change. This is all surplus energy that I would not have been able to use. If I had waited until sundown to use the oven, let's say, it would have taken the energy out of the batteries, possibly necessitating the use of a generator. This can be avoided by load shifting.

Another example: Let's say it's a sunny day and you have a 2kW array and your batteries are in absorb or float. They are probably taking in only 100-200 watts. Look at the current going into the battery bank. The rest of that PV energy from the array is ignored by the charge controller so as to not overcharge the batteries. It is free energy that is never used. By turning on loads during this scenario, you will be utilizing the full power of your array/system, otherwise it is solar power that never gets used, and could cause the need for a generator later. Just don't over do it and end up needing to start a generator later anyway.


SUMMING UP

Load shifting is just one technique that can save energy, money, carbon, and raise awareness. It will help us get the most out of PV systems and reduce the demand on an aging grid. It can also extend the life of battery systems by reducing the # of charge cycles needed.





16 views0 comments

Recent Posts

See All

Comments


bottom of page