Do you know how to use Ohms Formula with solar panels? Hi folks, in this video in the Solar Electric 101 series, I'm going to briefly cover concepts you need to understand when driving loads directly with PV DC solar panels, whether it is a fan, a heating element, an electric pump, hot water heater, and so on. This lays the groundwork for a deeper understanding of using solar power creatively to drive DC loads. If this video helps you out please leave it a thumbs up. Thanks for watching! DD
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The number one problem faced when driving a load from a solar panel directly, is impedance matching. Let's use a simple resistive heating element as an example.

Impedance means resistance to current flow.

Impedance / Resistance is measured in ohms.

Solar panels also have resistance, called internal resistance, much like batteries. But solar panels have a relatively high internal resistance. This is why the voltage range is so wide and the voltage drops under any load.

Let's continue with the example of a resistive hot water heater element. If you connect solar panels straight to the element, a voltage will be applied and some current will flow.

But this is governed by the voltage of the solar panel, and the impedance (resistance in ohms) of the element.

We can use a simple formula to estimate the performance of the solar panel and heating element.

Before starting, it's important to know what the solar panels you're using are actually capable of for power output. You need to know what their maximum power point voltage generally is under operation, and what the current (amperage)output is. It might be different in winter versus summer. For this example, let's say in good conditions our solar panels @ MPPT are known to put out 45V at 10Amps, or 450 watts. This math will change if you change the panels, for example by upgrading them or adding some extra panels.

I've found it's a great idea to go ahead and calculate the ideal impedance (resistance in ohms) of the load beforehand. For the example, how many ohms would we need the heating element to be, to get about 450 watts?

We use the simple formula: R = V/I
So 45 Volts over 10 Amps: we get 4.5 ohms
So our HWH element ought to be 4.5 ohms when hot.

But here is where it gets tricky. The following points should be kept in mind:
1) The element will probably increase its resistance as it heats up. How much depends on the type of element.

2) The solar panel will vary its performance based on temperature, age, time of day, and season.

Therefore it's probably best to slightly unload the panel. This means choose an element that is slightly less powerful than the panels maximum power output, to give some headroom.

Here are some additional points to keep in mind, if the heating element has a higher resistance, it takes more voltage to drive the same current through it.

If it has a lower resistance, and current flows more easily, so less voltage is required to flow the same current. Keep the voltage the same, and lower the resistance, you get current and therefore more power.

It's all interrelated. If your heating element resistance is too low and is drawing too much current, it will pull the solar panel voltage down below their maximum power point, maybe even to near zero volts. So to drive a heating element directly from solar panels with good results, one must properly match the impedance of the heating element to the solar panels. It's simple math.

One of the most useful things you can do with the knowledge presented here is to run heating loads directly off solar panels. It is clean, efficient and within reach of most DIY solar power enthusiasts.

As of now, I use several direct PV solar electric space heaters to heat various rooms in my home. I've been doing this for years with great success. I wish this technology was more commonplace.

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#solarheat #solar #offgrid #offgridsolarpowersystem #offgridsolar #offgridandongrid
#solarelectric #solarelectricity #pv2l #pvtoload


Music and image credits: by TuneTank, Pixabay