You probably heard about the blackout in Spain & Portugal that happened more than a month ago at the time I’m writing this, and is still under investigation to find out the root cause.

It inspired me to do the following test: how long will my fridge run when powered by my power station. I own a portable power station (Ecoflow Delta EU), its batteries have a total capacity of 1260 Wh.

My fridge consumes 1,72W in standby and about 27W when the motor is running. Here is a graph of the power it consumes while running over a period of 24 hours:

On average, it requires 529 Wh per day to run.

So I was thinking, theoretically, it should run a bit more than 2 days (1260 Wh / 529 Wh per day = 2,38 days) when powered by my power station.

In practice, it ran just shy of 24 hours before my power station was depleted:

It consumed 266 Wh. Which is far less then the capacity of the batteries in the power station (1260 Wh).

How can this be explained?

My first idea was maybe it’s because of the inductive load (it’s a motor). The power factor is very low (0.06):

I was thinking: maybe the 230V inverter in my power station is not efficient at handling inductive loads.

So I tried with a pure resistive load (an incandescent light bulb of 60W):

I got 595 Wh. Which is still far less than 1260 Wh.

Then I tried with a fan that requires 21W at a power factor of 0.70:

I got 362 Wh:

I started to reformulate my hypothesis: me it’s not the low power factor that make the inverter inefficient, but maybe it’s inefficient at low power demands.

Because while this fan requires 21W, the power station was displaying 31W :

So I did run the fan again, but now with the resistive heating element powered on, so that it would consume a large amount of power (around 1 kWh, that’s the maximum sustained load my power station can handle):

I got 778 Wh out of it:

So that’s the best my power station can deliver at a maximum sustained load of 1 kWh and a nearly pure resistive power factor of 0.99.

Which is only 62% of the rated battery capacity.

Conclusion: I can power my fridge for 1 day in case of a power outage, which should be ample enough in case of a power outage similar to the Spain & Portugal incident. But it’s far from efficient. Inverters seem to very less efficient at very low loads.