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A 170W solar panel is a good choice for RV and off grid applications. Most of these panels have a 25 year warranty, testament to their quality. But the one question that often comes up is its amp output. This is something you need to consider especially if you are going to use it in an off grid setup. By reading this guide you will know the answer and a lot more.
A 36 cell, 170W solar panel has an output of 9. 4 amps. If the panel has 60 cells, its amps will be 5.6. Divide the solar panel voltage by 170 and you get its amp output.
How Many Amps Does a 170W Solar Panel Put Out?
Before we proceed to the calculations, there are a few terms you need to get familiar with. This will make it easier to understand how solar panel power and output is calculated.
Watts. Watts (W) is used to determine the maximum power output of a solar panel. A 170W solar panel can generate up to 170 watts an hour. If the weather condition is not ideal, the output will be lower.
Amps. Amp or amperage measures how fast electricity moves in a conductor. Deep cycle battery capacity for solar is measured in amp hours (ah).
Volts. Voltage is the pressure that makes current flow through wiring. A 170W solar panel can produce up to 18 volts.
Cells. Solar panels are available in 32, 36, 48, 60 and 72 cells. Most 170W solar panels are sold as 32, 36 or 60 cells.
|Solar Panel Size||Cells||Volts||Amps|
To calculate the amp output of a 170W solar panel, divide voltage by watts. A 36 cell, 170W solar panel can generate up to 18 volts, the calculation looks like this:
170 / 18 = 9.4
Under ideal conditions, the solar panel can generate up to 9.4 amps. If your solar panel has 60 cells, its voltage can reach 30 volts. Using the same calculations:
170 / 30 = 5.6 amps
The higher the voltage, the lower the amp output. If you want to increase the amp production, buy two solar panels and connect them in parallel. Two 170W solar panels in parallel will give you 18.8 amps but keep the voltage at the same level.
12V Nominal Voltage vs. 18V Actual Voltage
One thing that often confuses people is the voltage on solar panel specifications. If a 170W solar panel like the Zamp Solar Legacy Series can produce up to 18 volts, why it is classified as a 12 volt?
The 12V label is a nominal voltage and used for classification purposes only. A 12V solar panel is designed to work with 12V batteries, 12V inverters and so on. A 24V solar panel is for 24V inverters, batteries etc.
In truth though, all 12V solar panels can produce 17-18 volts depending on the weather. You can find its actual voltage on the specifications sheet. Look at its VMP or VMPP, which states its actual voltage. This is the voltage you will see on a charge controller hooked up to the system.
So do not be confused by 12V solar panels. It only means they are compatible with 12V batteries such as the Expert Power LifePO4. In fact, 12V batteries charge up to 14.4V, so its 12V rating is also nominal.
How Long Will a 170W Solar Panel Charge a 100ah Battery?
A 170W solar panel produces 9.4 amps an hour, so it will take about 11 hours to fully charge an empty 100ah battery.
The formula is:
Solar panel amp output x required battery amps = charging time
To recap, a typical 170W solar panel has a maximum power point voltage (VMPP) of 18 volts. Some panels might have a VMPP of 17 or 18.8 volts, but for the sake of simplicity let us use 18 volts.
So 18 volts / 170 watts = 9.4 amps
That is 9.4 amps an hour. If there are 5 hours of peak sun in your area:
9.4 x 5 = 47
The solar panel can output 47 amps with 5 hours of sunlight. So if a 100ah battery is empty, it will take 11 hours to fill it up.
For a general guide on how many amps a solar panel can put out, check this out . But as the next section shows, a lot of factors can affect the charging sped of a solar panel.
Factors That Affect Solar Panel Charging Speed
The calculations above are based on the specifications provided with solar panels. However those numbers are based on ideal or laboratory conditions. There are a lot of factors that determine how fast or slow your 170W solar panel will charge.
- Number of peak hours
- Battery depth of discharge
- Solar panel efficiency
Let us take a look at each one and how it affects battery charging time. As you will see, these are applicable to all solar panels, not just 170 watt units.
Peak Sun Hours
Sun peak hours refers to how much sunlight is available in your area. Use this to find out the average.
The more sun hours available, the faster a solar panel can charge. Using our example of a fully discharged 100ah battery and 170W solar panel again:
If you live in Arizona and get 6-8 hours of sunlight per day, you can charge the battery in just over a day.
9.4 amps x 8 = 75
At the end of day one the battery already has 75ah. You only need 25ah the next day to fill it up. That should take only 3 hours or so.
If your area only gets 4 hours a day, the amp output drops:
9.4 x 4- 37.6
To fully charge a 100ah battery you will need three days:
37.6 x 3 = 112.8
So the number of sun hours available makes a huge difference. The more sunlight available, the faster your battery gets charged.
The depth of discharge (DOD) refers to when you should recharge the battery. For example, a 100ah lead acid battery has a 50% depth discharge. This means that when capacity drops to 50ah, you should recharge it.
In effect you can only use 50% of its capacity at a time. If you need the full 100ah you should buy a 200ah deep cycle battery.
AGM and gel batteries have a 70-75%, while lithium batteries are at 85-100%. As you might guess, this affects battery charging time.
A 170W solar panel can charge a 100ah lead acid battery at 50% DOD in 6 hours, under ideal conditions.
If the battery has a 70% DOD, the charge time will take about 8 hours.
The formula is:
Solar amp output x sun hours = daily amp output
If your solar panel produces 9.4 amps and there are 5 hours of peak sun, you get 47 amps a day.
From there it is easy to figure out how many hours are needed to fully charge a battery.
A 100ah battery with a 50% DOD needs 50 amps, so it will take your solar panel about 6 hours.
If the DOD is 70%, the battery needs 70 amps. Assuming a 47 amp daily output, the solar panel will recharge it in two days.
Solar Panel Efficiency
Solar panels are not 100%. Factors like the weather, the sun intensity, solar panel shading and many others affect its output. A 170W solar panel can theoretically generate 850 watts with 5 hours of sun, but that is under the best scenario.
In reality, solar panels produce less power, because their rated output is for the maximum. A 170W solar panel can give you a maximum of 170 watts, but under certain conditions the output will be less than that.
This applies to amp output too. The output you see (the LMPP on solar spec sheets) is the maximum. If the voltage drops, the voltage goes down, the amp increases. This will fluctuate throughout the day, so you will not get a consistent 18 volts.