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This question already has an answer here:

How many Watts DC are equivalent to 1,000 Watts AC?

For instance, my load in AC is 1,000 Watts 220V. Then, how much DC watts would an equivalent load dissipate in 12V or 24V DC system?

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marked as duplicate by pjc50, Nick Alexeev Jul 17 '14 at 16:15

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

ummm..... 1000? – markt Jul 17 '14 at 10:40
What's heavier, a pound of feathers or a pound of rocks? – Olin Lathrop Jul 17 '14 at 13:16

Simple answer watts are watts whether DC or AC.

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To amplify AndyA's answer a little.

Watts are a measure of power, that is energy consumed or delivered per unit time.

1000 Watts is 1000 Joules every second.

To provide that power at a lower voltage you increase the current (or vice versa). Power is voltage multiplied by current.

1000 Watts can be 250 volts RMS AC x 4 amps (i.e. 250 x 4 = 1000).
1000 Watts can be 12 volts DC x 83.3 amps (i.e. 12 * 83.3 = 1000).

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It does not matter whether you apply AC or DC, 1kW is 1kW. The difference between AC and DC is that DC only produces a real power P, whereas AC produces a reactive power Q on capacitors and inductors as well. But if you only apply ohmic devices there is no difference whether you apply AC or DC (in that respect).

To answer your question though, if you assume that there is a purely ohmic load that dissipates \$P=1kW\$ at \$U=220V\$ AC then you could simply calculate its resistance \$R= \frac{U^2}{P}\$ and then calculate the power \$P_2 = \frac{U_2^2}{R}\$ generated by the same load on a DC source (\$U_2 \in \{12V, \quad 24V\}\$).

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