There are multiple things to consider for a new solar powered system, one is the wattage of the panels. Since this is first element of a solar set-up, I decided to do a little research, and here is what I’ve found.
How much wattage do I need for my off grid solar panels? The amount of wattage you need from your solar panels depends on a few various factors, but a good rule of thumb is to have a minimum of twice as many watts as the total maximum wattage you plan to be using during peak times. Below, I’ll go into more detail without getting too technical.
If you are going off grid, and are on a budget, you’ve probably already considered some of the merits of downgrading your lifestyle to a simpler style of living. When considering moving away from a grid tied lifestyle, and completely cutting the chords, this can be an important but intimidating first step. But what comes next?
What Factors Go Into Determining My Solar Panel Wattage?
First, you’ll want to determine what electronic devices you plan to use in your off grid set up, and what you can live without. This varies from person to person and region to region. Can you live without a Microwave, air conditioning, electric heating, computer, fridge, or dishwasher? Those choices are up to you, only you can decide these things for yourself and your situation, but they are vital in deciding your solar needs.
When you have determined what you are not willing to live without in your new off grid haven, you can start to determine what kind of wattage you will actually be consuming during “peak hours”, which basically is the time you are awake, and physically in your off grid home.
Most every device you own has an output wattage ratting printed right on the power plug, or the back of the device. Add all these up, and you can determine what your maximum energy usage is. We’ll discuss how to do this in a bit.
Here’s an example of what you’re off grid power usage might look like:
- Small Refrigerator: 50w
- Window Air Conditioner: 900w
- LED Lighting (60w Equivalent): 13w
- Laptop Computer: 100w
- Cell Phone Charger: 15w
- Internet Router: 7w
- 19 Inch LCD TV: 16w
- Total: 1101w
With this example, you will need at least 2200w, or 2.2kw (1101w x 2) to maintain your system. Keep in mind, this is everything you own running at the same time and consuming the maximum amount of power, which will not always be the case, but this number will give you enough overhead to power everything while still charging your battery bank.
You may also want to consider how your power needs, and daylight hours, change with the different seasons of your location. For example, during winter your solar array might get 2 hours less light, however you are probably using your wood burning stove for heat and not running your air conditioner, so your overall power consumption will decrease quite a bit.
How to Determine Your Energy Usage
We’ve already discussed a quick way to take a look at your maximum energy usage through out the day, but what if you want a little bit more exact of a number, and determine your total daily and monthly usage? This will take a little time, but you can easily figure this out with a simple formula, and here’s how:
Every electronic device has a label on the back with some information about the power ratings required to run it. For some items, they will have a Wattage rating clearly listed, or sometimes it’s labeled as “Output Wattage”.
Many items will have a label that looks like this: “DC Rating: 19V – 3.42A” This is the voltage rating with the amperage of current. To convert this to wattage, all you have to do is multiply them together: 19V x 3.42A = 65W.
For smaller items, the amperage might be rated in milliamps (mA). One thousand milliamps equals one amp. So for example, if you have a camera battery charger that’s is labeled with a rating reading “DC 8.4V – 500mA”, you would multiply 8.4 by .5 to find a wattage of 4.2, since 500mA is half an Amp.
Take a moment to find the wattage of all the devices you plan to have hooked up to your system, and write them down.
Once you have the wattage, the next step is to estimate how long you use each one everyday, and multiply the time by the wattage. For example, lets say you have an LCD TV that is rated at 16 watts, and you typically watch 3 hours of TV a day: 16w x 3 hours = 48w of power every day.
Do that for every device, and ad the answers together. That is your total Watt Hours per day. That wasn’t too bad huh? If you take the daily number and multiply that by 30, of course you’ll get your monthly wattage use. Multiply that by 12 and you’ll find your yearly use.
There are multiple calculator tools online, where you can do this easily. Here is one I found pretty helpful.
Differences in Solar Panels
There are many options out there for solar panels, so how do you know which one is right for you, and how many panels of each you will need? Lets take a quick look at this to help you decide.
The information you need to decide on a solar array is:
- Your total usage
- Hours of direct sunlight in your area
- Output Wattage of the Panels
- Efficiency Rating
If you have determined that your total usage is about 9kWh per day, or 9000 watts, you’ll need enough panels to generate this amount of power. To figure out how to do this, you need to know how many average hours of daylight your panels will get on any given day; for many places, its 4-5 hours of direct light.
There are many websites that will calculate for you the exact number of daylight hours where you live. Here is one.
If you divide 9000w into 5 hours of time, this will tell you that you need to generate 1800w (1.8kW) per hour. Knowing this, you can now look at the ratings on the different solar panels available on the market.
Many panels come rated at 100, 250, or 300 watts. How many panels you need will be determined by this rating. Divide the 1800w by the number of watts the panel produces to figure out how many of the various types of panels you’ll need to cover your usage.
For example, lets say you are looking at 300w panels. Divide the 1800w by 300w, and you’ll get 6. So of the 300w panels, you’ll need 6 of them to produce enough to meet your needs. If you are looking at 250w panels, 1800w divided by 250w is 7.2, so in this case you could either go with 7 or 8 panels, but having 7 panels will be slightly under powered.
The other factor to look at is the efficiency rating. Panels will have an efficiency rating of 8-20%, which refers to how well they are able to collect energy, and usually correlates with the physical size of the panel as well. When comparing two different 300w panels, one with a 10% efficiency, and one with a 20% efficiency, the one with the lower efficiency will be larger, because it needs a greater space to collect the same amount of energy.
Other Factors That Affect the Wattage
There are a few other factors that will affect the amount of wattage you will be able to collect.
Orientation of your panels is important. The panels will need to be set up in a place that gets the most sun throughout the day, without having shadows cast upon them. Many people use rack systems to mount them on the roof, others use free standing pole racks mounted in the ground.
Temperature can also affect the output. In hotter weather, the amount of collected energy can decrease. If you live somewhere with a hotter climate, its important to have your array mounted in a way that the air can move across it, so it doesn’t get too hot.
The charge controller you select is also important. The charge controller manages the flow of power from the panels, into and out of, the battery bank, and to the load (your lights, computer, etc.) You’ll want to make sure you’ve selected the correct controller with sufficient wattage and amperage for your system.
Make sure to clean the panels from time to time. Dirt and dust can collect on them, and will block out how much sun they will be able to collect.
The wiring you use between the panels, controller, and batteries can also have an affect on how much power you will be able to collect. You will need wire thick enough to handle the max amperage , and efficiently carry it over the distance between the components.
What To Expect In Price
Luckily, the panels themselves are the cheapest part of a system. The best way to compare prices of panels is to compare the cost per watt. You can expect to pay $.50 to $1 per watt for the panels alone.
After you ad the cost of batteries, charge controller, mounting, wires, and basically everything else you need for the set up, you can expect to pay somewhere between $3-5 per watt for the entire system.
These prices will vary a bit of course, especially if you compare a professional installation, and a DIY setup. Having a professional set up the system for you will cost more, but they will help you avoid any possible mistakes you might make as a DIY setup. Make sure you shop around and get multiple quotes before deciding on installer though, prices between company’s can vary by thousands of dollars.
Related Questions
How Do I Connect My Solar Power System to The House Wiring? From the solar panels, you will need to run first through a charge controller, then to your battery bank. From the batteries, you will run into a power inverter, which changes the current from DC to AC. The AC line out of the inverter will hook up to your main input on the breaker box.
Can I Grid Tie My Solar Panels as a Backup? Grid tying your off grid system can be beneficial. Several days or weeks of cloudy days may drain your battery bank significantly, and you will need an extra source of power to keep from damaging them. Having your system tied to the grid is one way to back it up, while using a gas or diesel generator is another option.
Are Solar Panels Easy to Install? Solar Panels are relatively easy to install for anyone with a basic knowledge of carpentry and wiring skills, who is also comfortable with being on a rooftop. You’ll need to have an understanding of local building and safety codes that may apply to your area. The project can typically be completed in 1-2 weekends, depending on the scale.
