Context

other than the upfront hardware cost for a homelab, i wanted to figure out roughly how will it cost monthly to keep it running.

i took some time to figure it out and i don’t want to forget how to do it, so here it is.

Side note

this guide focuses on the maximum possible power draw, because it’s an amount we can reference from (power adapter, PSU, graphics card power and so on).

Units

Here are a few units relevant to calculate electrical bill

Ampere (A)
Voltage (V)
Watts (W)
kilowatts (kW)

kWh / per hour is associated to a cost, and we’ll use this unit to figure out much our bill will be

We can calculate watts and kilowatts like so

Watts (W) = Ampere (A) x Voltage (V)

kiloWatts (kW) = Watts (W) / 1000

kiloWatts per hour (kWh) = kW * 1 hour

1kW = 1000W, so we need to divide Watts by 1000 to get the correct denomination

The kWh cost

In Singapore, price of electricity will change depend on your utilities provider. In this case, lets take a look at SP Group.

On this page, it shows a few other costs but we’re mainly interested in the electricity cost. har

SP Group has a rate of 34.78 cents / kWh (SGD). We’ll use this number as a reference moving forward to calculate our cost

The 24/7 Soft Router

The zimablade looks like a good choice for a soft router alongside with openwrt

The Blade 7700 starter bundler includes a 16GB ram, the server and a power adapter.

Scrolling down to the specification sheet, the adapter specification shows us what’s the maximum possible draw for this server if it’s on full load

The power adapter can draw up to: 12V / 3A

The steps

derive watts
- 12V x 3A = 36W
convert watts to kilowatts
- 36 / 1000 = 0.036kW
factor in price from utilities provider
- 0.036kW x 34.78 cents = 1.25208 cents / kWh
- it costs 1.25 cents to run the soft router on maximum load per hour
calculate the potential maximum monthly electrical cost
- 30 days x 24 hours = 720 hours
- 1.25208 cents / kWh x 720 hours = 901.4976 cents / kWh
- 901.4976 cents / kWh = SGD $9.01 / kWh

If the router is on full load every month, it can cost up SGD $9.01 to keep it running

So for a year it can potentially cost up to

$9.01 x 12 = $84

Pre Built NAS

zimaspace has a NAS offering.

The Creator pack includes a i5-1235U CPU, 64GB DDR5 RAM, 1TB NVMe SSD Storage and RTX Pro 2000. It has a built in PSU (power supply unit)

Scrolling down to the specification sheet, it shows us what’s the maximum possible draw for this NAS if it’s on full load The PSU can draw up to: 19V / 13A

The steps

derive watts
- 19V x 13A = 247W
convert watts to kilowatts
- 247 / 1000 = 0.247kW
factor in price from utilities provider
- 0.247kW x 34.78 cents = 8.59066 cents / kWh
- it costs 8.5 cents to run the NAS on maximum load per hour
calculate the potential maximum monthly electrical cost
- 30 days x 24 hours = 720 hours
- 8.59066 cents / kWh x 720 hours = 6,185.2752 cents / kWh
- 6,185.2752 cents / kWh = SGD $61.85 / kWh

If the NAS is on full load every month, it can cost up SGD $61.85 to keep it running

So for a year it can potentially cost up to

$61.85 x 12 = $742.2

Conclusion

For day to day use, we’ll probably never reach the maximum costs we see here. Day to day or burst workloads should cost much lesser.

Now this leaves me to wonder how much does it actually cost to run those AI servers, they’re potentially on 80% load half the time and the compute power draw should be quite high.