# kW and kWh Explained – hopefully.

What’s the difference between a Kw and a Kwh? When your local solar contractor is tempting you to buy a complete solar solution, you're probably trying to understand as much as possible before making the plunge. This question is one that puzzles many people, so here’s the scoop:

First, ‘kilo-Watts’ are a *power *measurement, while ‘kilo-Watt-hours’ are an *energy *measurement. Huh? Well, ‘energy’ is referring to a measurement of how much fuel something contains or may use or generate over a period of time, just like when people on diets talk about calories (another measurement of energy). ‘Power’ measures the speed at which energy is used or made. This can be a bit confusing, but read on.

For the purpose of conversations relating to solar energy, that energy is typically measured in kWh (kilo-Watt-hours) – sometimes mWh’s (for mega-Watt-hours in big installations).

And power is typically measured in kW (kilo-Watts).

A simple example will help to illustrate the difference: A solar panel may generate 250 Watts (or 0.25kW) of *power* when the sun shines on it. No matter how long the sun shines, 250 Watts will be the power output from the panel (more or less – this is a complicated area, but for now we’ll just say it’s 250). When the sun goes down, the panel stops functioning and 0 Watts are produced. However, if you want to know how much *energy *this same panel will produce, we need to consider a time factor – how many kWh’s can the same panel deliver in, say, 1 month? To answer this, we need to know how many hours the panel is generating power for each day during the month. Let’s estimate 5 hours per day, for 30 days. This means the panel will deliver 250 (Watts) x 5 (hours) x 30 (days) = 37,500 Watt-hours in a month – we can divide this big number by 1,000 so it's easier to read. This makes it kilo-Watt-hours – the panel makes about 37.5 kWh’s of electrical energy per month.

Simple, right?