Guide
Two numbers decide whether a system works: power and energy. Getting either wrong produces a different kind of failure.
Power (kW) is the rate at which the system can deliver energy at any instant. It must exceed your largest simultaneous load, including the surge when motors start. If power is undersized, the system trips — immediately, and regardless of how much energy it holds.
Energy (kWh) is how much it can deliver in total before it needs recharging. It sets your runtime. If energy is undersized, everything works perfectly and then stops early.
A useful way to hold the distinction: power is the size of the pipe, energy is the size of the tank.
List every load that can run at the same time, with its rated power. Add them up. Then add the starting surge for anything with a motor or compressor — air conditioning, refrigeration, pumps, some tools — which can be several times running current for a short period.
The result is your peak kW. The system's continuous rating should cover your sustained simultaneous load, and its peak rating should cover the surge. A PulseTrek Performance, for example, provides 8,000 W continuous against 20,000 W peak — that gap is what absorbs motor starts.
For each load, multiply its power by the hours it actually runs, then add them up. Be honest about duty cycle: a 2 kW heater on a thermostat is not drawing 2 kW all day, and a kettle is a very large load for a very short time.
The result is your kWh per run. Then add margin for the state-of-charge cutoff — PulseTrek systems reserve 20%, so a 30 kWh pack gives you roughly 24 kWh usable.
| Load | Power | Hours | Energy |
|---|---|---|---|
| Two site cabins, lighting and sockets | 600 W | 10 | 6.0 kWh |
| Cabin heating (thermostatic, 50% duty) | 2,000 W | 10 | 10.0 kWh |
| Kettle and microwave (intermittent) | 2,000 W | 0.75 | 1.5 kWh |
| Tool charging station | 400 W | 8 | 3.2 kWh |
| Security cameras and floodlights (overnight) | 350 W | 14 | 4.9 kWh |
| Total energy per 24 hours | 25.6 kWh | ||
| Peak simultaneous draw | ~4.2 kW |
That compound needs about 25.6 kWh per day against roughly 24 kWh usable from a 30 kWh pack — so it needs a daily recharge, and the question becomes whether there is a window and a source. Shore power overnight solves it. So does a generator running two hours to recharge. So does a solar array sized for 26 kWh/day.
If there is no recharge source at all, you need enough energy for the whole deployment, which is when multiple units or a containerised system enters the conversation.
Questions answered
You need power (kW) greater than your largest simultaneous load including starting surge, and energy (kWh) greater than your total use between recharges. A site drawing an average 3 kW for 8 hours needs roughly 24 kWh of usable energy.
kW measures power — the rate energy is delivered at any instant. kWh measures energy — how much is delivered over time. Power determines what you can run; energy determines for how long.
Multiply the loads you need to keep running by the hours you need them, then add margin for the state-of-charge cutoff. Backup sizing is usually driven by a short list of critical loads rather than the whole site.
Sum each load's power multiplied by its operating hours, accounting honestly for duty cycle, then divide by the usable fraction of the pack — typically 80% after the state-of-charge cutoff.
Get in touch
Tell us the site, the load and the runtime you need. Our Austin engineering team comes back with a configuration, a runtime estimate and a price.
+1 512-316-7347
info@pulsar.industries
WhatsApp +1 512-585-8293
