How many amps does a 100w solar panel produce? This is an important question when calculating how much solar power you need when charging batteries. But it is not an easy question to answer as might first appear
There are lots of factors to take into consideration. Like the weather, the time of day and how efficient the solar charge controller is. The answer can only be given with known variables which are at full power output. These conditions occur during the middle part of the day when full sunlight is usually available.
The answer does have a small amount of calculation involved. So please be patient. It really is a very simple division and you will be able to calculate the amps any solar panel produces. Because the equation is always the same.
How Many Amps Does A 100 Watt Solar Panel Produce?
“To find out how many amps a 100w solar panel produces. We need to divide the maximum power rating by the maximum power voltage (VMP). You can find the VMP of a solar panel in the manufacturer’s specifications or on the rear of the panel. We already know the power rating is 100w and we will assume a VMP of 18.6 volts. So 100 ÷ 18.6 = 5.38. So this 100 watt solar panel will produce 5.38 amps at full power.”
How Many Amps Will Other Wattage Solar Panels Produce?
At this point I thought it would be handy to produce a table of solar panel wattages and amps they produce. But remember this is at full power under standard test conditions (STC). No other variables like weather or time of day are taken into consideration. The figures are taken from different manufacturers of solar panels.
|Solar Panel Watts||Solar Panel VMP||Amps Produced|
How Do I Find The Amps Produced By A 100 Watt Solar Panel At Any Given Time?
To measure this you will need a digital multimeter and Ohm’s Law. This is because the voltage needs to be divided by the electrical circuit resistance. This calculation will find the actual number of amps the 100 watt solar panel is producing.
Don’t worry I am not going to go into an explanation of Ohm’s law. If you want to know more about it follow this link (Source; Wikipedia).
How To Measure The Voltage The 100 Watt Solar Panel Is Producing
The multimeter should be set to direct current (DC) volts. You should measure the voltage between the + (positive) and – (negative) solar panel terminals. This should be done while the panel is live. Be aware it may create a spark but it isn’t anything to worry about.
Write down the number of volts the meter shows for example 17 volts.
By the way, the figures I am quoting are not real, they are for illustration purposes only. Measuring a single solar panel’s live voltage is ok. But measuring multiple solar panel voltages hooked up in series or parallel should be done by an expert.
How To Measure The Resistance Of The Circuit In Ohms
To measure the resistance in the electrical circuit, disconnect the multimeter. Then switch it to measuring resistance or Ohms depending on your meter it may share a function button. Make sure the solar panel isn’t live, turn it away from the sun or cover it. Connect the multimeter in the same way as before
Write down the number the meter displays for example 3.9 ohms.
How To Calculate The Actual Amps Being Produced by The 100 Watt Solar Panel
In our fictional example the number of volts the solar panel is producing is 17V and the resistance is 3.9 Ohms. We now divide 17 by 3.9 this equals 4.36A this is the actual amount of current the solar panel is producing.
What Conditions Can Affect How Many Amps A 100 Watt Solar Panel Can Produce?
There are several factors that can affect a 100 Watt solar panel amp production.
Solar Panel Placement
If you are using a portable solar panel it is quite easy to follow the sun around the sky during the day. All you have to do is move it to point it directly at the sun. But what do you do if you have a fixed installation to a recreational vehicle or roof?
The easiest way to collect the most sunlight is to try to orientate the panels as near south as possible. Solar panels work best when at a 45° angle to the sun this is achievable on a sloped roof. But not so easy with a flat roof or surface.
Consider mounting the panels in a frame that can be adjusted to a 45° angle. I know this seems like an extra step but you will find it is one worth taking.
I know this seems an odd thing to talk about but you might not know that solar panels lose efficiency when they become too hot. This will affect the amount of amps produced. So to help alleviate this problem try and have them at an angle. This will create airflow behind them keeping them cooler on a baking hot day.
Again you might not know but shade will stop sunlight collection altogether. This can be a problem with overhanging trees, buildings and other obstructions. This isn’t a problem with a recreational vehicle because you can move it. But if you are installing on a structure’s roof you will need to make sure your placement takes shade into account.
Obviously the weather will affect solar collection. Clouds, rain, snow and all manner of conditions will affect amp output. You need to be careful near the sea because of reflection from the water. This is called the Albedo effect and can be combated by placing the solar panels slightly off direct south.
Fog, haze and the output of light energy from the entire disk of the sun which is called Irradiance. Can all affect solar collection as can how clean the panels are.
Time Of Day
If the solar installation is fixed to a flat surface. The best opportunity to capture sunlight is going to be for about 4 hours per day when the sun is directly overhead. At these times under full sunlight maximum amp output will be achieved.
The rest of the time you can expect 1 or maybe 2 amps. Unless you are using a portable solar panel that can be moved to directly face the sun at all times of day. The point being that the sun is weaker in the mornings and evenings.
The best time to harvest sunlight is going to be between late spring and early autumn. Unless you are fortunate enough to live in a part of the world that has sun all year round.
During the winter the sun is not as strong and there is less of it. So if you are planning to use the solar panels all year around. You need to make sure your solar array is large enough to compensate for this.
Is The Type Of Solar Charge Controller Used With A 100 Watt Solar Panel Important?
The solar charge controller used with a 100 watt solar panel is important from an efficiency point of view. Some experts say that you do not need a MPPT solar charge controller in a smaller system. Because a PWM controller will do the job just fine.
But did you know that even in a smaller system like a single 100 watt solar panel. The MPPT controller is up to 40% more efficient than using a PWM controller. You don’t have to splash out on a Victron controller; there are plenty of alternatives that are just as good.
Taking into consideration all the different conditions that can affect solar collection. A good solar charge controller is a must to help offset them. Because every little helps when it comes to squeezing out those extra amps.
The Differences Between MPPT and PWM Solar Charge Controllers
Without going into a long technical explanation MPPT and PWM controllers work in different ways. You just need to know that an MPPT controller is more efficient than PWM. They provide the right protection for your batteries and use the panels’ available maximum power potential.
They can also be matched with different solar panel and battery voltages whereas a PWM controller cannot. Having said all that, a PWM controller will do an effective job. You can pick up a quality 10A PWM controller for around $20.
How Long Would It Take A 100 Watt Solar Panel To Charge A 100Ah Battery?
Under STC conditions by dividing the solar panel 100 watts by the VMP. We can find the number of amps that will be produced at full power. This means we can effectively calculate how long it will take to charge a battery. To achieve this we need to convert to amp hours (Ah) to do this we simply multiply the amps by 1.
You will remember that our example amps were 5.38 multiplying this by 1 equals 5.38Ah. If we use a 100Ah battery. Dividing 100 by 5.38 it will give us the amount of time a 100 Watt solar panel will take to charge it. This equals 18.59 hours.
But lead acid batteries should only be discharged by a maximum of 50%. This means with a discharge of 50Ah it will take half that time 9.47 hours. A 100Ah lithium Iron Phosphate battery can be safely discharged by 90% of its capacity.
As you can see a single 100w solar panel is probably not suitable to charge a 100Ah battery. It is probably best suited to charging a 50Ah battery or less . Remember these calculations are based on STC conditions.
Once you take into consideration all the other factors which can affect solar collection. It will probably take 200 to 300 watts of solar power to charge a 100Ah battery in a timely manner.
My Closing Thoughts
Finding out how many amps a 100 watt solar panel will produce is a simple affair. If the calculations are done under maximum power conditions. When it comes to real world conditions, finding the answer becomes a little more tricky.
It can be done using a multimeter and it will give an accurate reading using the method I have described. Having said that, the reality of achieving the best amp output is down to the panel’s positioning. The weather, the time of day, the season, heat and environmental considerations.
Some of these considerations can be offset by using a quality controller and monocrystalline panel. On an average day I would be working on 2.5 to 3 amps per hour of sunlight. That’s between 25 and 30Ah per day during the summer and less in the winter.
For further reading about 100 Watt Solar Panels check out this post
I hope you enjoyed this post and have found it helpful. If you have any questions about how many amps a 100 watt solar panel produces. Or want to leave your own personal review, please feel free to leave a comment below.