Solar Panels: How much Solar Power do I need?
Posted on December 14 2018
How many solar panels should I buy?
This is a very frequently asked question as more and more people are trying to use some form of solar power in their daily use. Of course, it is not as straightforward as to say "ok, one solar panel for one smartphone"; that is precisely why we are here to help. In this article, SUAOKI will describe the basics of the solar system and how the setup works. You can find more about how solar panels work here. A solar calculator is basically your calculation of how many solar panels do you need for your house, farm, boat or any other place that you want to be run on solar energy. Furthermore, you can also calculate for any specific electrical appliance that you want to run on solar power, e.g., if you only want to run your air conditioner on solar energy.
The basic solar system structure
A solar system is primarily made of PV cells combined and exposed to high-intensity sun rays to generate electricity from it. You can use the energy from the solar panels directly, or you can store it first in batteries and then use it when required. So, battery cells are an optional choice, but it is highly recommended as batteries can give you safe and uninterrupted power whenever you need it.
Basic solar system setup. via equatorenergycorporation
What do you need your solar system for?
The first question you need to ask yourself is that what is your goal for a solar system. As we know, solar panels cannot generate electricity at night, or even when its cloudy - snow and rain is a step-ahead hurdle. So, if you want to get off the national grip and require uninterrupted power, then you need to store the energy generated from the solar panels in batteries and then use it to power up your appliance. But, you can also have direct electrical energy from a solar system if you live in a place which sees many sunny days with little or no interruption in weather conditions. This is best when you only want to use the solar generated electrical energy occasionally for some appliances only. However, we strongly recommend using batteries with your solar system even if you're going to use it sometimes, as batteries provide uninterrupted constant power which is safe for your devices; for more on why you should include batteries in your solar system click here.
Household solar power system. via solarpowerauthority
That being said, in this article, we will consider a solar system without storage batteries (Yes we just told you it is not recommended). However, this is the first article in the series of Solar Panels, so we need to start with the basics and beginners.
How much energy will your appliance(s) use?
The first step is to calculate how much energy will your appliances use over an entire day. Electrical power is calculated in watts, and almost all your electrical devices are labeled with or imprinted on with watt-hours (that is the amount of electrical power it needs to operate in one hour). However, if it is not marked already you can still calculate it by simply finding the current in amperes (A), and the voltage in volts (V) that the device needs, and multiply them together to get the power in watts. For example consider a 12v LED bulb that uses 5A current, it will require 60 watts of power every hour to operate, or in other words 60 watt-hours (Wh).
An electric oven consumes a lot of power. via elleci
Peak sun-hours, what? So not all the daytime sunshine is the same?
Yes, all that glitters is not gold. Before we go to the next step, you need to understand the essential concept of peak sun-hours. We all know that the sun only shines for some time in a day and thus solar panels cannot generate energy all day long. However, even during daylight, just a couple of hours of the sunshine are actually worthy of generating electrical power via the solar panels, which is called the peak sun-hours. Scientifically speaking, the peak sun-hours in a day is the time when the sun’s intensity reaching the solar panel on ground and STC is equal to or more than, 1000 watts per meter square.
For example in summer, the state of New York receives an average of 14 hours of daylight, but only about 5 hours of all the daylight time are the sun peak hours. Therefore you have to consider your location, and find out the sun peak hours online and then proceed to the next step.
Peak sun-hours in July in Mississippi. via mssolar
What is STC?
STC or Standard Testing Conditions is a strictly controlled environment under which performance of PV modules (solar panels) is analyzed and calculated in terms of how much energy it generates in one hour. Then it is labeled on the solar panel as the "solar rating". The test environment specifies the solar cell temperature of 77°F (25°C) and an irradiance of 1000 W/m2 with an air mass 1.5 (AM1.5) spectrum. These correspond to the irradiance and spectrum of sunlight incident on a clear day upon a sun-facing 37°-tilted surface with the sun at an angle of 41.81° above the horizon - via sinovoltaics.
Calculating solar power. via solarprofessional
So how many solar panels do I need?
Solar panels are rated in watts, for example, the SUAOKI Solar Panel Charger rated as a 100W solar panel means that it can produce 100 watts of energy in one hour (but in optimal conditions that is the STC). To calculate the total energy from a solar panel in a day, you simply have to multiply the solar panel's rating with the time (in hours) it was exposed to peak sun-hours. Let's say the SUOKAI 100W solar panel was exposed for 5 hours to solar energy during the sun peak-hours; then you will get a total of (100*5W) = 500 watts of energy form it.
So now you know all the basics: energy your appliances need in a day and the energy a solar panel can produce in a day. Then calculating the size of your solar system is very easy. As in the earlier example, we found that our devices need 3,800 watts of power in a day, but hold on one last thing. To account for line losses, inefficient and of course not having STC conditions at your disposal it is safe and wise to add 10-15% to your power requirement so that when you put these theoretical values to practical use, everything goes smoothly. More on this in the next geeky blog. So with a 15% increase due to the inefficient system, we have then a total power requirement of 4,370 watts per day.
Large scale solar power generation. via harmonysolar
Back to our example, so we have the SUAOKI 100W solar panels in store, and we are in NY conditions during summertime, i.e., 5 sun peak-hours; so we can produce a total of 500 watts from one solar panel in one day. To meet our demand of 4.37kW we then need (4,370W/500W) = 8.7 solar panels, in this example then we need to get 9 times 100W solar panels and run them for 5 hours together during the sun peak-hours to get our required demand of electricity. This will then be sufficient for us to run our air conditioner for 4 hours and the washing machine for 2 hours.
The last piece of the puzzle is a regulator (that works as an inverter). A regulator is connected between the solar panels and the appliances, and it controls the amount of current flowing from the solar panels to your appliances. It keeps the flowing current in a steady and stable condition to protect your devices. Also, the current produced by solar panels is a Direct Current (DC) whilst our appliances work with Alternating Current (AC), therefore, this regulator also does the conversion job and converts the DC into AC so we can then directly use the power from the solar panels.
Solar cells are only about 20% efficient, what? Yes! And to add more, the power generated from these 20% efficient photovoltaics is still not utilized at a 100% rate. Batteries are one of the primary sources of power losses. Hold tight for the next blog in this series which will go into details of should you get batteries for your system or should you just used the power from the solar cells directly.
A 60-watt light bulb. via newssupersite
I know this was a lot to digest for some of you people. Don't worry, if you still have any questions, please do leave us a comment below and we will help you with your queries. And for some, it was fundamental knowledge - for you guys more geeky information in the next blog.