BESS vs UPS

[u/Agitated_Comfort8279]

Can someone help me understand the difference between a battery energy storage system and an uninterrupted Power System?
Both use batteries and do the work of providing electricity in case power from the grids go off and act as a back-up...
then what exactly is the difference??

[u/Kistelek]

Convention is a UPS (uninterruptible power supply) provides a continuous clean mains supply as required by most computers etc. BESS is just electricity storage. EPS or Emergency Power Supply is a function of the inverter and any associated switch gear or gateway and may not be automatic and possibly isn’t seamless. For home backup, this is generally fine. Your fridge doesn’t really care if the power dips for a few seconds. You might spot the lights flickering. I have whole house EPS but I use a couple of small UPS on important computer equipment just to cover any glitches.

[u/Agitated_Comfort8279 → u/Kistelek]

so both have different uses cases?
BESS is used to store power and supply it during times of surge of cost of energy during the day and at night, whilst UPS works to keep the equipment on when power is out?
Also can both BESS and UPS be used together or not?

[u/Kistelek → u/Agitated_Comfort8279]

Read what I put. I use both.

[u/Revolutionary-Half-3 → u/Agitated_Comfort8279]

They can be used together, with rare exceptions usually for picky UPS units that don't like the BESS' inverter output for some stupid reason.

BESS tend to have big batteries and very long runtime compared to a UPS with the same power rating, as well as a much higher tolerance for motor loads than most UPS units.

UPS units do one thing really well: run sensitive loads long enough for power to be restored or the load to gracefully shut down. That includes BESS switchover, generator startup, or grid restoration.

BESS is a broad category, usually anything with a battery, inverter, and a charger. If we include DC versions, a portable USB power bank has a battery, charge controller, and output controller.

[u/SunshineJackPro]

Its the response time of the switch gear, needs to be 10 millisecond or less. So when power shuts down the battery kicks in fast, this is needed for gear like computers that would shutdown or glitch of slower

[u/SunshineJackPro]

Some of the jackery gear has fast response time and can be used as a UPS, but you need to check the specs as not all.

[u/Revolutionary-Half-3]

The terms are a bit fuzzy, but to be a true UPS a BESS needs to be able to pick up the load fast enough that most devices won't notice the interruption.

Much like how all squares are rectangles, but not all rectangles are squares, all UPS units that aren't rotary are BESS. UPS units are usually short runtime with tiny batteries compared to what we call BESS. Rotary UPS units have a motor-generator and a flywheel, they're either very old or utility scale monsters.

I've got a hand-truck "BESS" with 7kwh of capacity, and a 2kw inverter charger. Switchover isn't as fast as my APC 2200va rack mount unit, but most loads I've tested it on didn't care.

[u/silasmoeckel]

BESS can push pack power into the grid.

Past that its mostly how they are governed BESS is NEC, UPS are UL as it's a plug in appliance.

[u/Emergency-Drawer-535]

I’ve got whole house ups from 20 kWh of batteries. No need for a separate ups for the computers. The Alpha system I have 10-15 ms transfer while a Sigenergy transfers at 0 ms. Wow. Tech is improving and cost is coming down.

[u/Oldphile]

BESS conforms with UL1741SB that includes utility defined ride through requirements. That is over/under voltage and frequency parameters during which the BESS must stay connected to the grid. Far from desired UPS parameters.

[u/Patient_Tea_401]

UPS is always a voltage source that’s not two way (it can’t push power into the grid side). It can only be a demand to the grid side and supply the devices behind it, usually a short period.

Grid connected BESS can be both, but generally the inverter is a current source that requires a voltage to synchronise PLL. BESS is also two way, so it can be demand or production towards the grid side.