One of the most important concepts to understand when sizing a system or figuring out how much your panel produces is Energy and Power. Below you will be able to find a description about each along with some examples.
Power is defined as rate of doing work. It essentially tells you how quickly you can produce energy. Power takes on different forms, but when dealing with electricity or solar, you will define power as a Watt. As stated before, Watts = Volts x Amps. Multiplying the panel’s voltage by amperage will give you a wattage value. This is also true for an appliance. You can also think of power in terms of how much money you make hourly at a job, ie. $8/hour.
Energy is the capacity for doing work. It essentially tells you how much work can be done. Energy can take different forms, but when dealing with electricity or solar, you will define energy as Watt Hours. Watt Hours = Watts x Hours. Multiplying an appliances wattage, by how long it will run for will give you its energy value. Multiplying a panel’s wattage by the peak solar hours will give you its energy value. You can also think of energy in terms your paycheck, if you make $8/hour and work for 5 hours, you have $8 x 5 Hours = $40.
Energy in Panels
For Solar Panels, the energy produced is dependent on how much sun you get in your location. Sun hours will vary from state to state, but it is important to have an idea of what your states peak solar hours are. For example let’s look at a 100W panel in Texas vs. Nevada. Using Texas’s low value of 4.5 peak hours and Nevada’s low value of 6 peak hours we can calculate the energy or Watt-Hours produce by the panel. For Texas, 100 Watts x 4.5 Hours = 450 Watt Hours. For Nevada, 100 Watts x 6 Hours = 600 Watt Hours. As you can see the state location does have an impact on energy production, in this case by 150 Watt Hours.
Peak Hours Link: /template/files/Average-Peak-Sun-hours-by-State.pdf
Energy in Appliances
For appliances, the energy produced is dependent on the wattage value of the appliance along with the hours of run time. It is very important that you have the wattage, not just the voltage or amperage as those aren’t complete power values. For appliances, you can take the voltage and multiply it by the amperage. For example, an 8 Amp Fridge at 110V will be 8 Amps x 110 Volts = 880 Watts.
Let’s take two 35 Watt fans. One we will run for 2 hours and the other for 5 hours. The first fan consumes 35 Watts x 2 Hours = 70 Watt Hours and the second fan consumes 35 Watts x 5 Hours = 175 Watt Hours. As you can see, given the same fan, the second one takes more energy since it is ran for longer.
Energy in batteries
We can also relate energy to our batteries as well. Often times we get told that a customer has a 12V or 6V battery. As from what you saw earlier, this is not a complete form of energy, so just having this information is not enough to determine how much your batteries can store. We need to find the Watt-Hours value. Luckily most batteries are rated in a term called Amp-Hours. Although this has hours in it, it still isn’t energy. To get Watt-Hours we must multiply Amp-Hours by Volts.
Amp-Hours x Volts = Watt-Hours
For example let’s say we have two batteries, one 6V and one 12V. The 6V battery is rated at 100 Amp-Hours and the 12V battery is rated at 75 AH. The energy of the first battery is 6Vx100Amp-Hours= 600 Watt-Hours. The energy of the second battery is 12V x 75 AH = 900 Amp-Hours. As you can see even though the first battery has more Amp-Hours, it does not have more energy or storage.
Please view section 2.8 on sizing systems to learn how to relate all of this together.