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What Can A 100 Watt Solar Panel Run?
What can a 100 watt solar panel run? This is a typical question from newcomers in the world of solar power. Generally, when we design a solar power system, we start with a load list. We determine what you are trying to power. From there, we figure out what size solar panels you need. But for this scenario, we will be doing things in reverse. What can you power with a 100W solar panel?
A solar panel is rated by the amount of power it creates at Standard Test Conditions (STC). These conditions include:
the intensity of the sun, 1000 watt per square meter
the angle of the light hitting the panel directly
the temperature, 25℃ or 77℉
other criteria.
So the actual output from solar panels may vary, based on these factors in the real world. We generally reduce the calculations based on the difference between the lab setting and your actual installation.
When a 12V solar panel is rated at 100W, that is an instantaneous rating. If we meet the test conditions, when you measure the output, the voltage will be about 18V and the current will be 5.55A. Since watts equals volts times amps (W=V x I), 18 volts x 5.55 amps = 100 watts. To figure out how much power is generated over a period of time, you can multiply the watts times the number of hours it is running. So in one hour, 100W x 1 hour = 100 watt hours (WH).
Take a look at the Renogy 100 Watts 12 Volts Monocrystalline Solar Panel. This is Renogy’s most popular product. It has an Optimum Operating Voltage (Vmp)=18.9V and an Optimum Operating Current (Imp)=5.29A. 18.9V x 5.29A=99.98W (100W).
Now, we need to figure out how many hours to plug into the equation to determine how much power the solar panel will generate in a day. How many hours of sunlight that is equal to the intensity of standard test conditions? This is basically the sun at noon.
How many hours will the solar panel be exposed to during the day? The number of hours of sunlight equal to noon is called effective sun hours (ESH). As you well know, even though the sun is up at 8 in the morning, it is not as bright as it is at noon. You can’t say that the sun is shining for 10 to 12 hours and multiply 100W x 10 (or 12). This is not the way it works. The hour between 8AM and 9AM is probably only half as strong as the sun from 12 noon to 1PM. The morning hour would probably only be equal to ½ sun hour. The number of sun hours would be dramatically different throughout the year.
Your location also determines the amount of effective sun hours you will get in a day. I live in the Philippines, where we get an average of 4.28 ESH/day according to NREL’s PVWatts Calculator. Looking at two major cities in the Philippines, the amount of sunlight I would get in Baguio City (5.52 ESH, average) would be different than the amount of sun hours I would get in Cebu City (4.8 ESH, average).
From the pictures, the ESH is broken down by month and even the tilt angle that the panels are mounted. Looking at the charts, if I have a 100W solar panel, in Baguio City, installed facing directly south, on annual average, I’d get 5.52 sun hours a day. Likewise, if I took that same solar panel in Cebu City, installed it facing directly south, I would have an annual average of 4.8 sun hours.
I want to make sure that you see, during the month of April, I am going to get more power out of that solar panel in Baguio City than I will in Cebu City. For your specific location, play around with the solar panel direction to get the best ESH for your planned installation.
Back to the question at hand, what can a 100 watt solar panel run? Will I use the solar power for a specific period or do I plan to use it the whole year round? If the plan is to use it the whole year round, I need to figure out my worst case scenario. This is the worst performing month that I will be using the panel.
Let us assume that the panel will be used in Cebu City. I need to use the data for December which has the lowest projected ESH for the year. So how can I squeeze out as much power as I possibly can in December? Based on the solar panel direction choices from the chart, no matter how I tilt my panel, I will still get an ESH of 4.05 sun hours. We will use what is in the picture, panel facing directly south for our example. 100W x 4.05H = 405WH. Our panel can produce a minimum of 405WH/day. Let’s move on to the next step.
Nothing in real life is perfect, so I have to figure in losses that I’ll likely incur, such as voltage drop across the wire, dirt accumulating on the solar panel, losses through the charge controller, etc. We are going to multiply the 405WH by 0.7 (30% loss factor). It is like losing ⅓ of your power, that is the reality. We have to compensate for losses all the time. I now end up with 283.5WH of power that I have made with my 100W solar panel on a December day. What can I do with that power?
First, I need to store it in a battery so that I can use it later when I need it. Before doing so, I need a charge controller (SCC) to manage putting the power into a deep cycle battery that can be charged and discharged on a regular basis. WIth our 100W panel and system voltage of 12V, 100W / 12V = 8.33A. We need an SCC of at least 10A for this purpose. The Renogy 10 Amp 12V/24V PWM Negative Ground Solar Charge Controller is an example. The Renogy Adventurer – 30A 12V/24V PWM Flush Mount Charge Controller with LCD Display is a 30A PWM charge controller, a good option if you plan to expand your system up to a maximum of 400W. If you have a plan to expand in the future, you only need to buy more panels instead of buying a new charge controller.
What size battery do I need? I have my 283.5WH that I am producing. I am also putting it in a 12 volt battery. Because watts divided by volts equals amps, 283.5WH divided by 12V equals 23.63AH.
Even though I will be using a deep cycle battery, most batteries still don’t like being drained down more than half way, so I’m going to make sure I get a battery that can hold at least twice as much power I will be using, so I’ll only use half of the power in it ===>>> 23.625AH x 2 = 47.25AH.
The amount of power a battery can store changes depending on the temperature of the room it is in. If my battery is going to be as cold as 60 degrees Fahrenheit, I need to increase the size of my battery by 11% to accommodate the cooler temps.
This applies to installations in very cold areas. 47.25AH x 1.11 = 52.45AH. DO NOT FORGET THIS IF YOUR INSTALLATION SITE WILL HAVE CLOSE TO FREEZING TEMPERATURES. But in our example, since this is a tropical location, we don’t need to compensate for this and we will continue our calculations using 47.25AH.
We are also going to use an inverter to convert the DC power from my battery to AC. I am going to lose about 5% of my power through that conversion, so 47.25AH / 0.95 = 49.74AH. Bestek inverters are a good choice. To save on money, some will opt to use 12VDC appliances. You may skip this step if that is your plan.
The sun doesn’t shine every day as we have to compensate for cloudy days and rain (or snow). So I need to figure out how many days without sun that I need to store the power for me to get through those sunless days. This is called days of autonomy (DOA). Let us say I need it to last at least two days without sun. 49.74AH x 2 days = 99.47AH. So finally, I am going to get myself a deep cycle battery that is 100AH at 12V. The Renogy Deep Cycle Pure Gel Battery 12V 100AH is a good choice. The Renogy Deep Cycle AGM Battery 12 Volt 200Ah is also another option.
I can finally figure out what I can do with that power. I can run my Macbook Pro that uses 61W for 4 hours and 40 minutes. Because 283.5WH Watt hours/61W = 4.65 hours. Or I can power 3 of my 10W LED lights for 9 hours, and still have a little power left over. Or I could watch TV, listen to the radio while reading a book with a 10W light on for 3 hours, and use my laptop for 2 hours.
This should give you enough information so that you can figure out how to fit this into your situation. You can change the numbers to fit your area, and your power needs.
You can make a load list to figure out what you can use per day, just do not exceed the calculated 283.5WH. This is so that you still have left-over power for the next day in case the battery does not fully charge because of cloudy conditions or rain. It is all up to you.
NOTE:
If you are in a hurry and don’t want to go into the math of solar power design, here is a good starter kit:
There you have it. I hope I was able to help you with this article. Watch out for more! If you want to be updated when I post a new article, please sign up in the subscription box below. Thanks!
I’m very impress with your expertise information on what can you use with 100 watt solar panel I’m trying to develop off grid solar power generation . I have issues like you have highlighted in your information.. Like seize of the battery’s and panels etc.
At last!! A clear, concise, detailed explanation of solar power, and all that it entails, written in a way that I (a nubie) can understand! If you’re not a teacher, you should be. Thanks alot!
This was a fantastic article!! Very informative but simply explained for beginner like myself. Best one I’ve come across in the field thus far. Thankyou!!
Hi Mike, great blog! Found it via pinterest after wading through reams of postings that had great titles but no content. Yours was excellent, clear, concise and even though my experience with electronics is from high school (30 years ago) i feel confident to get to work on the calculations for my first steps into solar power.
Previous comments say you should be a teacher…. You already are.
Thanks for your help and chalk me up as a new subscriber.
Thanks again
Thanks so much for the info. I was planning on trying to play with solar power after I retired on my land. So now I understand that I should build double to way over what I expect to use for backup.
This was a totally wasted part of my day! Someone looking for the answer doesn’t want a 4 page dissertation on the hows and whys along a list of formulas. inverters ,agm batteries and the hrs of daylight in Cebu City.
A simple list:
A a nuclear power plant
B 100 watt light bulb
C A cell phone charger
D A book deal
Spot on mate.
A 100w solar panel won’t produce 100watts unless you strapped it to a space shuttle and sent it to the Sun.
Fucking 5 amps lol
You can’t calculate solar panels as there is too many factors and no constant.
Good afternoon
please help me.
I was looking for Solar irrediance figures for Croatia, as you gave for Cebu City Effective Sun Hours and Baguio City Effective Sun Hours. Can you even tell on which website you found those two graphics. I am interested in Croatia. Thank you very much.
Best regards from Croatia.
I am in a paid home with alot of southern sunlight, could u help me find out how to do this, I would love to put few panels on roof my home is setting perfect for solar, please help me do this, could u please give me a estimate ty mike
Hi Mike, excellent article that will help me install a couple of panels on my UK canal boat.
On the fuse calculation, what does “panel lsc”stand for?
Cheers
John
Well crap you know your stuff and me following that was like triganomatry lol i cant even spell it. No i never made it through algeabra. But i no what i want. A lot of help. Just make it work. GODBLESS YOU have a wonderful brain. And you use it its a gift to those of us who dont get it. Just do it!
Ugh. Sudda started with…. I’m not actually going to just give a simple list. But sit load of techno dance ….. I got a 100 watty and was curious what I can slap on her. I did learn how she could dance in the first cupla paragraph before I realized I got swallowed up by your green machine. Someday soon I’ll come back and read this with vigor and make my own gosh darn list. No need to reply, this can’t help me today. Next month it might.
Great Article!
I need to make a load list and figure out how to scale up to max energy absorption and storage and then load and how to pass along the savings.
I’m very impress with your expertise information on what can you use with 100 watt solar panel I’m trying to develop off grid solar power generation . I have issues like you have highlighted in your information.. Like seize of the battery’s and panels etc.
At last!! A clear, concise, detailed explanation of solar power, and all that it entails, written in a way that I (a nubie) can understand! If you’re not a teacher, you should be. Thanks alot!
Very informative and well explained. Thank you!
This was a fantastic article!! Very informative but simply explained for beginner like myself. Best one I’ve come across in the field thus far. Thankyou!!
Hi Mike, great blog! Found it via pinterest after wading through reams of postings that had great titles but no content. Yours was excellent, clear, concise and even though my experience with electronics is from high school (30 years ago) i feel confident to get to work on the calculations for my first steps into solar power.
Previous comments say you should be a teacher…. You already are.
Thanks for your help and chalk me up as a new subscriber.
Thanks again
Thanks a lot…
Thanks so much for the info. I was planning on trying to play with solar power after I retired on my land. So now I understand that I should build double to way over what I expect to use for backup.
This was a totally wasted part of my day! Someone looking for the answer doesn’t want a 4 page dissertation on the hows and whys along a list of formulas. inverters ,agm batteries and the hrs of daylight in Cebu City.
A simple list:
A a nuclear power plant
B 100 watt light bulb
C A cell phone charger
D A book deal
Spot on mate.
A 100w solar panel won’t produce 100watts unless you strapped it to a space shuttle and sent it to the Sun.
Fucking 5 amps lol
You can’t calculate solar panels as there is too many factors and no constant.
Good afternoon
please help me.
I was looking for Solar irrediance figures for Croatia, as you gave for Cebu City Effective Sun Hours and Baguio City Effective Sun Hours. Can you even tell on which website you found those two graphics. I am interested in Croatia. Thank you very much.
Best regards from Croatia.
There is a link on the post on where to get solar irradiance figures.
http://www.solarelectricityhandbook.com/solar-irradiance.html
Very informative and well explained. Thank you! Would love to subscribe but don’t see the subscrition box.
Thank you so much this information was certainly helpful. Such a compact solar panel allows me to install on my RVs and utilize it with ease.
I am in a paid home with alot of southern sunlight, could u help me find out how to do this, I would love to put few panels on roof my home is setting perfect for solar, please help me do this, could u please give me a estimate ty mike
Just follow the steps in the article.
Hi Mike, excellent article that will help me install a couple of panels on my UK canal boat.
On the fuse calculation, what does “panel lsc”stand for?
Cheers
John
Isc=Short Circuit Current
Well crap you know your stuff and me following that was like triganomatry lol i cant even spell it. No i never made it through algeabra. But i no what i want. A lot of help. Just make it work. GODBLESS YOU have a wonderful brain. And you use it its a gift to those of us who dont get it. Just do it!
Ugh. Sudda started with…. I’m not actually going to just give a simple list. But sit load of techno dance ….. I got a 100 watty and was curious what I can slap on her. I did learn how she could dance in the first cupla paragraph before I realized I got swallowed up by your green machine. Someday soon I’ll come back and read this with vigor and make my own gosh darn list. No need to reply, this can’t help me today. Next month it might.
Hi Mike,
Happy New Year to you and your loved ones; may it be safe and full of life’s ups and downs that helps us grow without too much drama.
Superior article Mike…The information,calculations and resources are Spot on.
I would like to put together a Renogy 100 Watt system . Can you recommend any sources for parts near Cebu City…. Trying to minimize shipping.
Thanks for the time, energy and TLC.
Trane
Thanks for the feedback. My apologies. I don’t know any local sources in Cebu City. My suggestion is Lazada and Shopee.
Great Article!
I need to make a load list and figure out how to scale up to max energy absorption and storage and then load and how to pass along the savings.
Moody sends