As energy security becomes an increasingly prevalent issue new, technologies and products are being created to meet these new challenges. One particular problem is the “surge current” required to adequately start motor loads and keep them running.
One of these new technologies is Enphase’s Power StartTM. Combined with Encharge’s surge current capability, which temporarily increases the power rating of an Encharge unit for up to 10 seconds, both of these features, in tandem, help meet the requirements of starting certain loads. Examples of these heavy loads include heating, ventilating, and air conditioning (HVAC) units, refrigerators, or freezers. The feature can also help running appliances that do not always have a constant power draw over time. Here’s how it works!
Meeting Surge Current Demands
Have you ever had to jump-start your car to get it going again? That temporary jolt from another car (or a functional car battery) is needed to get the motor turning. Something similar happens for high load appliances in your home when they are turned on. Enphase’s energy storage product, known as Encharge, currently comes in two variants that can be combined for more backup capacity. As it relates to surge current, the Encharge 10 has a continuous power rating of 3.84 kilowatts (kW) and a surge power rating of 5.76 kW for up to 10 seconds. This means that one Encharge 10 unit can supply 24 amps of surge current for 10 seconds – a 50 percent increase over the continuous power rating.
Low Power Factor Appliances
In addition to surge current needs, some appliances use more power for certain periods of time due to the complexity of their alternating current (AC) power system and different power factors during startup and normal operations.
As a little background, AC is more dynamic than direct current (DC) and has characteristics beyond a continuous power rating that should be considered for off-grid situations. Some loads have a constant, or continuous, draw of power – such as hot water heaters and electric kettles. Other loads – such as HVAC systems or electric pumps – store some current and redeliver it back to the power system and react to changes in voltage and frequency of their supply. One difference is often denoted by an appliance’s power factor.
Simply put, if an appliance has a power factor of less than one, it actually requires more current and this situation should be considered when properly sizing a backup energy storage system. Another difference is the response of dynamic loads to the changes in voltage and frequency of their supply. This is where Enphase’s Power Start technology can help.
How this technology works
When an Encharge battery is providing surge current to meet a startup load, Enphase’s Power Start feature uses an algorithm that detects when the inverter approaches its maximum power limit and then begins to actively reduce voltage and frequency in order to maintain the inverter within its limits using active feedback.
Because many devices, such as pumps and compressors, will draw less power as the voltage and frequency reduce, this temporary reduction in power activated by Power Start technology is often enough to keep the inverter within its operating limits and ride-through a temporary power surge during the startup period of such loads.
The table below summarizes common surge current demands across a variety of devices and the number of Encharge units required to accommodate them during off-grid mode. You can also add a Hyper Engineering SureStart “soft starter” to reduce surge current needs and further extend Encharge’s ability to power essential loads.
Considerations for storage system design
Most solar plus energy storage systems do provide backup power for a limited period of time. However, they may lack the “surge current” and Power Start capability required to adequately start high load appliances like air-conditioning units and sump pumps. If you have any questions about which products have which features contact your local Greentech Renewables rep.
Enphase’s new Power Start feature is an added defense during appliance startup periods and can allow homeowners to run more essential loads during a grid outage. This can be very important if it’s the added difference to keep a sump pump or HVAC system working properly.
For more information about Enphase and their Encharge energy storage system, visit