Cooling with the heat of the sun: How many solar panels for a refrigerator?

It is possible to make your fridge consume less on a regular basis. These tips will make your refrigerator more energy-efficient and lower your electricity bill:

1.Keep the refrigerator full. A refrigerator needs more energy to cool itself when it's empty than when it's full.

2.Move the fridge away from the stove and radiators.

3.Defrost your freezer from time to time – it improves the efficiency of the unit. When the thickness of frost reaches 1/4", it is time to get to work.

4.Clean the doors and sides of the fridge. Dirt and dust makes it harder for a fridge to cool down.

5.Cover all the liquids and soups that you put in the fridge. They release moisture and it increases the burden on the fridge compressor.

6.An old fridge draws more energy than a new one. Make an upgrade to make your home more energy-efficient! Look for Energy-Star labels on devices – it assures low energy consumption.

7.Don't set the temperature inside too low. The lower the temperature to be maintained, the more energy it takes. 37 °F is ideal for a fridge and 0 °F is perfect for a freezer.

Now that we have some numbers to work with, let's figure out how many panels we need for a refrigerator. Let's say it needs approximately 1.5 kWh daily to function. Across the USA there are 5 peak sun hours on average, during which panels perform at their maximum. Therefore, to power a refrigerator, our array has to generate

1.5 kWh ÷ 5 h = 300 W

As you can see, we can actually support our fridge with one 300 W solar panel. We can add 25% to our energy needs, assuming that panels are going to perform at 75% of their maximum capacity due to imperfect weather, angle and positioning. In this case we'll need

1.5 kWh * 1.25 ÷ 5h = 375 W

To be safe you can get one 380 W or 385 W solar panel. Should it produce a little extra, this energy will come in handy someplace else.

While solar panels don't work at night, a fridge usually does. The way you will feed it depends on the type of the solar system you have:

• With a grid-tied system you can rely on the utility grid. The night rate is usually lower, so it won't cost you much.
  
  
• With an off-grid system the batteries will do all the work.
  
  
• With a hybrid system you can choose either the grid or the batteries to power your fridge, whichever is cheaper.

Using the utility grid is pretty straightforward: you just pay for a fridge at nighttime in accordance with the established tariffs. What about batteries? Figuring out the exact battery capacity for running a fridge at night is tricky and even pointless. First of all, in the night-time a refrigerator consumes less electricity: we hardly ever cook or eat at night, don't we? So, it's easier to maintain low temperature then. At the same time, you probably wouldn't purchase a battery just for your refrigerator only. If you want exact numbers for your refrigerator's night consumption, use an electrical meter.

However, it makes sense to demonstrate how to size a battery not only for a night support, but also for an emergency situation. Let's calculate the size of a battery that would support the refrigerator on its own all day and night long. Assumed daily consumption of a refrigerator is still 1.5 kWh.

If the battery is lithium-ion, its capacity is measured in kWh as well. Its efficiency is close to 100%, so we won't take it into account. However, you don't want to discharge it further than 80% on a regular basis. Therefore you need at least

1.5 kWh ÷ 0.8 = 1.875 kWh

If you have a lead-acid battery, its capacity is measured in Amp/hours. Its depth of discharge is around 50%, so the capacity should double the needs of your fridge. Plus, efficiency of lead-batteries is considerably lower – at around 80%. Power = Voltage * Amps, so assuming we'll get a 12V battery, its capacity should be bigger than

1.5 kWh * 2 ÷ 0.8 ÷ 12V = 312.5 A/h

We've calculated the minimum capacity for two types of batteries to run a refrigerator without any support for 24 hours. The same principle can be used for other appliances. We hope that these calculations give you an idea of how to figure out the energy needs of your refrigerator, the number of panels to support it and the battery capacity to run it independently.