How To Calculate Your Solar Power Needs

If you’re thinking of setting up an off-grid solar power system but you’re not sure exactly how much power or how many watts and/or how many solar panels you require. In addition, what kind of batteries and what kind of inverter you will require. This can all be very confusing at first so keep reading and we are going to explain how to calculate your solar power needs.

To calculate solar power needs, you will need to consider a few key factors. Here’s a step-by-step guide to help you determine your solar power requirements:

Determine your average daily energy consumption

Begin by understanding how much electricity your household or facility consumes on an average day. Check your utility bills to find the monthly or yearly consumption in kilowatt-hours (kWh). If you don’t have this information, you can estimate it by listing all the electrical appliances you use and their power ratings (in watts). Multiply each appliance’s power rating by the number of hours you use it per day, and sum up the values for all appliances to get the total energy consumption in watt-hours (Wh). Convert Wh to kWh by dividing by 1,000.

Calculate daily energy generation

Multiply the average daily sunlight hours by the solar panel’s capacity in kilowatts (kW) to estimate the daily energy generation in kilowatt-hours (kWh). Keep in mind that solar panels rarely operate at their maximum capacity due to factors like shading, panel orientation, and system inefficiencies. A conservative estimate assumes solar panels operate at 70-80% of their rated capacity.

Daily energy generation (kWh) = Average daily sunlight hours × Solar panel capacity (kW) × Efficiency factor

Account for losses and efficiency

Solar systems experience losses due to factors like shading, dust, temperature, and system inefficiencies. It is advisable to add a buffer or safety margin to account for these losses. Multiply the system size (kW) by a factor between 1.1 and 1.3 to accommodate these losses and improve the overall system efficiency.

Adjusted system size (kW) = System size (kW) × Buffer factor

Consider roof space or available area

Assess the available roof space or area where you plan to install solar panels. Determine how many panels can fit based on their dimensions and orientation. If the available space is limited, you may need to adjust the system size accordingly.

Determine the system size

The most important thing is to figure out what you want to use your solar system for so what appliances and electronics are you going to be using for example are you going to be using a small fridge maybe with a few LED lights running seven days a week all day or maybe you want a solar power system just to run a few lights when the sun goes down for a few hours at night so this makes a big difference and how are you going to calculate everything?

Divide your average daily energy consumption (kWh) by the daily energy generation (kWh) from the solar panels. This will give you an initial estimate of the system size required.

System size (kW) = Average daily energy consumption (kWh) / Daily energy generation (kWh)



In our case, we want to power two laptops one small USB fan and camera batteries. In addition,  every once in a while we also wanted to charge our iPod Touch and some double-a batteries and we wanted to make sure that we could power all these electronics for about eight hours a day seven days a week.

Assess your desired level of energy independence

Determine how much of your energy consumption you want to meet with solar power. Some people aim to cover 100% of their energy needs, while others may choose a lower percentage. This decision will impact the size of the solar power system you require.



Secondly, we have to determine what was the energy consumption of each item every electronic device every appliance every item has a power consumption rating it’s often on the power adapter itself.

Sometimes it can also be directly on the item there’s a little sticker in the back and this can be found on every single item that you look at what is most important is that you want to find the output wattage of every item so in this case it clearly says output sixty watts and if you look at the fan it also says clearly 2.5 watts but for some items like camera battery charger doesn’t actually provide the output wattage of the item.

Unfortunately it’s only giving the output volt and milliamps so there’s an easy conversion for this all you have to do is do volts times amps and you get the wattage.

In this case it is milliamps. A thousand milliamps gives you 1 amp so in this case 500 milliamps means that it’s point five amps so you’re going to do 8.4 times 0.5 and you’re going to get a total of 4.2 that means that this item takes 4.2 watts so we figured out that our first laptop would take 60 watts our second laptop would take 45 watts.

Our camera battery charger would take 4.2 watts charging our iPod would take about 4 watts and our little fan would take 2.5 watts so that would give us a total of 115 point 7 so we rounded it out to 120 just to be safe side. Now, we have to figure out for how long we wanted to use all of this

So, we wanted to use everything for about eight hours a day seven days a week we probably wouldn’t actually use all of this eight hours a day seven days a week but that gives us a little bit of leeway in case we want to use other things like an electric shaver anything like that once.

Now, you have figured out all those numbers all you have to do is input them into a solar power calculator which you can easily find anywhere.

So, what is the total wattage that we’re thinking of using as in our case like we mentioned earlier it was 120 so we are going to input here then for how long are we planning on using these devices in our case it’s approximately 8 hours a day so we are  going to put 8 the charge controller there’s at PWM and MPPT they have different efficiency numbers so in our case we have an MPPT charge controller so we are  going to input 92 percent right here then you have to figure out approximately for how many hours of sunlight you get in your area per day.



Where we live we get about five hours a day of sunlight so we have just input five in this box right here and once we have all these numbers inputted we just press calculate right here and we get our totals so you can see minimum system size so how many watts of solar panels do I need they recommend about two oh eight point seven recommended battery size if it’s 12 volt 160 amp hours and recommended battery size if it’s two if they’re 24 volts 80 amp hours so as you can see it’s not very complicated once you figure out the output wattage of every item and for how long you want to use them?

In our case we actually didn’t do exactly what the calculator was telling us to do we had some restrictions in terms of budget and available space so we altered things a little bit we actually got 300 watts of solar panels and only a hundred fifty amp hour battery but for our needs the system is working really well.

Consider your location

The amount of sunlight your location receives affects the efficiency and output of solar panels. Areas with more sunlight will generate more electricity. You can find data on the average daily sunlight hours for your location from weather websites or solar resource maps.


The amount of electricity your home solar system will likely produce will directly depend on the peak sunlight hours for your specific region. For instance, Phoenix residents can anticipate more peak solar hours than those who reside in Seattle. Even yet, a household in Seattle could still go solar; they would just need additional panels.

Our case vary the results a little bit but one last thing to keep in mind for your solar power system is the inverter and in the case of the inverter bigger is not actually better usually smaller is better so again we ‘ll use our system as an example we figured out that we would use about 120 watts at a time.

So, when you’re trying to pick an inverter you have to figure out what is the maximum amount of wattage that you’re going to be using at the same time.

For instance, if you have a 500 watt inverter and you’re thinking of using a thousand Watts all at the same time while your inverter the fuse in it is going to blow and it’s not going to work you’re going to need a 1500 watt inverter or anything above a thousand.

In our case we knew we were only going to need 120 watts so we picked a pretty small inverter our inverters 500 Watts that gives us some room to add some more electronics on there and we were comfortable with that but we probably could have went down to even 300 watts this is more efficient because your inverter actually takes power it’s a machine that’s running off your solar system also so the bigger it is the more power it takes and if you don’t need that amount of power you’re actually wasting energy.

Consult a solar professional

It is recommended to consult with a solar professional or an installer to validate your calculations and obtain a more accurate assessment of your solar power needs. They can also provide advice on system design, component selection, and any specific considerations for your location.

By following these steps, you can estimate the solar power needs for your home or facility. Remember that this is a general guide, and professional assistance can help you make more precise calculations and determine the most suitable solar power system for your requirements.

Thanks for reading.  We hope this helps you calculate how much you need for your solar Power system.


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