The Power of Time

15 Nov 2019

By Erik Anderson

Power vs energy. kW vs kWH. Inverter capacity vs battery capacity. Do you know the difference? A sustainable future featuring solar power plus energy storage should be getting more transparent and less confusing. But, as you can tell, that’s not always the case.

If we are to truly witness a paradigm shift in how we create and consume energy using solar and storage technology, we must first understand a few basics. This will help minimize confusion and friction that would otherwise slow widespread and rapid deployment of new technologies critical to transforming our future in eco-friendly renewables.

Power vs. energy explained

To understand the difference between power and energy is to understand the effect of time on the units of measurement, which we rely on to measure the flow of electricity. These two terms are related, but unique. Utility companies use both to plan and operate our grids, as well as bill us for our monthly power usage. 

If a 100-watt light bulb is used for 10 hours, it will have consumed a total of 1,000 watt hours (WH) of energy (10 x 100 = 1,000), or 1 kilowatt hour (kWh). We can think of watts as the size of a bathtub faucet, or its power potential. At any single point in time, you can measure how much water is flowing through it. When that flow accumulates in the tub, you end up with a volume of water you can measure differently, just like with energy. 

To further clarify, a watt is a static instantaneous measure of moving electrons - also known as “electricity”. With each passing second, minute, and hour, those individual measurements add up to a cumulative measure of energy. A watt is a two-dimensional measure of power; time adds the third dimension of power’s cumulative effect, describing energy as a function of power over time. 

Variable power consumption in the home

This concept is further complicated when power usage is variable. A home does not have a steady continuous usage of power. It varies and spikes from one moment to the next, and tells us an important story of how electricity is being used in the home at any given point in time. But, it is ultimately variable. 

When we adjust for the cumulative effect of time on power usage throughout each day, and add up the power being consumed every second in a home for a day, week, month, and year, we discover that home’s energy requirements. (By the way, both are equally important in sizing an energy storage system.)  

Battery storage & net energy metering

Cue the batteries. Lithium-ion (Li-ion) batteries, that is (as opposed to the NEM-facilitated grid ‘battery’).

Li-ion batteries are finite in their capacity to hold energy. Contrary to popular belief, they are not 100 percent efficient. However, they do facilitate onsite storage of energy, which is perhaps our most potent antidote to avoid higher electricity costs from disappearing net energy metering (NEM) policies, and the implementation of time-of-use rates. 

Given that Li-ion batteries have a finite capacity to store energy, the importance of energy and power becomes even more significant. In a world where energy storage is growing increasingly popular and affordable, understanding this point is essential for solar professionals.

When we talk about solar plus storage systems, it is important to understand that the power rating of the system is dictated by the kilowatt (kW) size, orIn order to make smarter decisions for our companies and our customers, all of us in the solar industry need to be on the same page. Take the time to really understand the power behind our technology. Remember, when talking energy storage systems, the power is in the inverter, and the energy is in the batteries.


Erik Anderson is a Regional Sales Manager with Panasonic Life Solutions and has been a strong advocate and promoter of renewable energy and home solar power for over a decade.

Panasonic Life Solutions |

Author: Erik Anderson
Volume: 2019 November/December