Units and quantities
kWh (kilowatt-hour)
Also known as: kilowatt hour, consumption in kWh.
Definition
The kilowatt-hour is the unit of energy that appears on your electricity bill: it measures how much electricity you consume or generate over time. A solar system is sized from your monthly consumption in kWh, and the saving is also measured in kWh.
A kilowatt-hour is the energy a 1,000-watt appliance uses running for an hour. Ten 10 W LED bulbs on for ten hours use 1 kWh; a 5,000 W electric shower uses that same kWh in twelve minutes. That is why consumption depends not only on how many appliances you have, but on their power and how long you use them.
On the bill, consumption for the period appears in kWh and is multiplied by a tariff in pesos per kWh. That tariff changes according to the retailer, the stratum or the type of user and the applicable subsidies or contributions, so two households with the same consumption can pay different amounts. For sizing a solar system what matters is the kWh; for calculating the saving in pesos, both the kWh and the tariff matter.
The recommended approach is to take the average of twelve months of bills, not a single month: consumption is seasonal and an atypical month distorts the calculation. That average, divided by thirty, gives the daily consumption used for sizing.
The essentials of kWh (kilowatt-hour)
- 1 kWh = a 1,000 W appliance running for one hour.
- It is the figure your electricity retailer bills you for.
- Average daily consumption = monthly consumption ÷ 30.
- To size well, use the twelve-month average, not a single month.
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Frequently asked questions about kWh (kilowatt-hour)
Where do I find my kWh on the bill?
In the consumption detail for the period, usually identified as 'consumption kWh' or 'active energy'. Many bills also include a history of recent months or a bar chart: that history is the best source for working out your annual average without hunting through bill after bill.
How many kWh does a solar panel produce per day?
It depends on its capacity and on the peak sun hours at the location. A 550 Wp panel in an area with 4.5 peak sun hours generates on the order of 2 to 2.2 kWh a day before system losses are deducted. Multiplying by the number of panels gives the installation's estimated daily output.
Can I size a system from the peso value of the bill?
It is an unreliable shortcut. The peso value mixes consumption with the tariff, subsidies, contributions and other charges unrelated to the energy consumed. The kWh is the only stable figure for sizing; the peso value comes in afterwards, to estimate the saving.
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