Well now that you know how many devices we need to install in order for your system to run smoothly, let us take a look at what size installation will work best.
System voltages can be intimidating, but they’re not as difficult to understand when you break them down into their individual parts. We’ll start with an overview of what each voltage does and then move on to more complicated examples that require detailed knowledge about electricity.
12, 24, and 48V systems
It’s essential to know the consequences of choosing a specific voltage for your system. We will discuss the advantages and disadvantages of these systems for different components.
A single charge controller can safely handle up to 80 amps of power, which equals 960 watts in the case where you are using a 12-volt system.
12V x 80A = 960 Watts
With 24 volts of battery power, our solar panels now produce 1920 watts. We use an 80 amp charge controller to keep the voltage under control and maintain a safe operating temperature for your home’s electrical system.
24V x 80A = 1920 Watts
With a 48-volt battery system, you can go even more:
48V x 80A = 3840 Watts
The following image illustrations show how you can have a lower amp charge controller for the same PV input power if your battery voltage is increased.
Voltage is the measure of electric current. If you want to increase your power output, then just keep increasing this until it reaches 12 volts for each cell in a battery pack or system that houses multiple cells together
If there are only 2V across each individual cell however and not much more than half that amount at best; we’ll need another way besides doubling up on batteries.
Power = Current x Voltage
With a 2,000 watt inverter, we can calculate that the current through our 12 volts wire will be around 24 volts and 48-volt versions.
To power your home, you need a quality inverter that can handle the amount of energy requested. A 2kW model will usually draw around 167 amps which could potentially be too much for some 12V systems and result in burned-out electronics or other damage. You should stay under 100 Amps in DIY systems, especially if you Crimp the wire yourself. Using an inverter with a 2,000-watt rating on your 24- or 48 volts system will be much better. Apart from being cheaper and safer to work with because you don’t need big wires; it’ll also make wiring up the bike easier since everything has its own wire size.
A 48-volt battery will be higher than 50 volts at the terminals. The 48-volt system is more dangerous than 12 or 24 volts because there are higher demands on the battery to provide power for your lights, radio, and other accessories.
For most systems, I recommend using a 24 or 48-volt battery. The wires will be cheaper and so is the cost of charge controllers too! Be careful with lithium batteries though; some can only support two in series to make up 48 volts worth – this is because their management system isn’t compatible at higher voltage levels (more on this later).
Now that you know how much better your battery will perform with a higher voltage, it’s time to calculate the rest of your system.
Imagine you are converting a van to an off-grid mobile home. To do so, you plan on using the following devices:
- Phone charger
- Water pump
- Laptop charger
- 5 DC led lights
- Speaker system
- Egg cooker
- 12V ceiling fan
- 12V top-loading fridge/freezer combo
You need to separate the AC devices from your DC ones. You can do this in a spreadsheet by splitting them up based on whether they are positive or negative, then making their respective columns label-friendly.
If you have a standard household plug, then it’s an AC device. Anything that works with 12 or 24 volts of DC goes into our list for this category.
To limit the load on your inverter, try using DC devices instead of AC. It will also be easier for you if there are more outlets in your home or office because they don’t need to convert from one voltage level before providing power downstream.
I will separate my devices by DC and AC so that they are easily identifiable.
Next, you will need to determine the power rating for each device. There are four options that can help with this:
1. By looking at the label on your device.
You can also find the power consumption of an appliance by looking for a sticker on it. If you are lucky, there might be written information about its wattage in watts next to “Powered By.” This will help with your decision as well.
2. By searching online.
There are many websites that list the power rating for products online. You can find this information by searching Google and entering the name of the product.
3. ‘Kill a watt meter.’
You can use a “kill-a-watt” meter to find out how much power your device uses. This is especially useful if you don’t know what kind of appliances are running, like an air conditioning unit or refrigerator.
4. Using the power formula.
By applying the power formula, you can find out if there is an active current running through your device. You will need to locate it by either method one or two first before proceeding with this last step.
Pover = Voltage x Current
The device’s power rating is determined by the voltage and current through it. For example, if we know that 12 volts DC or 120 Volts AC are applied to our sensors then easily calculate what they will output based on these measurements.
Let’s take the previous example and calculate how much power it uses.
Power = 120Volts x 11.5Amps = 1.380Watts
This would not be the case if we were to use a DC device. Let’s take an example of a 12V water pump that uses 3.3 amps.
Power = 12Volts x 3.3Amp = 40Watts
Now enter the power of each device in a spreadsheet.
If you want to use your blender and egg cooker together, it’s important that the inverter has enough power. A 1,500-watt model will work well for this occasion as long there are no other devices hooked up at higher wattages or expecting high levels of performance from its components like cooking pans on top racks while simultaneously making sure everything stays hot in their ovens without burning anything.
Determining how long you will use these devices each day is important. Use the following formula to convert minutes into hours:
number of minutes x 1/60
I use a blender and get two minutes of work done every single day.
2 minutes x 1/60 = 0.033 hours
Put the time values in the spreadsheet.
In this step, we’ll use a formula that you have already learned to calculate how many watt-hours your devices consume in one day.
Watt-hours = Watts x hours per day
For the phone charger, this is:
24Watts x 1.5hours = 36Watt hours
The total DC and AC watt-hours are now clearly visible on your chart.
We need to find out how long the battery is going to be. The size of a battery’s capacity is expressed in amp-hours.
Now you need to decide on the battery bank voltage. Remember chapter 12, 24, and 48 volt systems? We are going with 100 Amps maximum current in wires for this guide’s purposes so select based on your inverter size recommendations:
- Inverter below 1000 Watts: 12V
- Inverter between 1000 Watts and 2000 Watts: 24V
- Inverter above 2000 Watts: 48V
Next, we need to calculate how many amp-hours of energy our battery will hold. From the load analysis table below it’s clear that a 12-volt battery with 771-watt hours is enough for this application.
Amp hours = Watt hours / Voltage
771 Watt hours / 12 Volts = 65Ah
With a lead-acid battery, you need to double the capacity because it can only be discharged at 50%. A 100Ah Lead Acid Battery only has 50 Ah of usable energy.
Lithium batteries have a discharge rate of 20%. A 100Ah lithium battery contains 80% energy and can be used for an extended period before needing recharging. The lithium battery can potentially deliver 80% of its rated energy. You can get 100% usable capacity, but using only 80% will give you a longer lifespan.
The battery capacity for a solar system with an average daily energy demand of 65Ah should be:
65Ah x 100%/50%=130Ah
65Ah x 100%/80% = 81.25Ah
There are many days when the batteries in your phone won’t be charged enough to use. This happens because:
- Time of year (winter or summer).
- The place you have your setup (latitude).
- Weather (sunny or cloudy).
To ensure a safe and pleasant experience, we recommend at least two days of autonomy but three is even better. This means that your battery bank should be able to last you through any emergency situation without fail.
130Ah x 3days = 390Ah
81.25Ah x 3days = 243.75Ah
The efficiency of a battery is an important factor to consider when choosing your device’s power source. Here are some common types and their efficiencies:
- Lead-acid: 80%
- AGM: 90%
- Lithium: 99%
390Ah x 100%/80% = 487.5Ah
243.75Ah x 100%/99% = 246.2Ah
Lead-acid batteries need an even number of volts to operate efficiently.
If you are using this type, be sure that your device gets its power from a 487.5Ah at 12Volt battery.
The battery pack for your model lithium-ion should have a rating of 246.2Ah at 12 volts to ensure proper operation, so be sure not only to purchase the correct one but also to use it in pairs when necessary.
The next step is to determine how much power our solar panels can output in one day. This will depend on the voltage of your battery system, so it’s important that you convert from amp-hours (which represent hours worth) and multiply by 12 volts for an accurate calculation.
Watt-hours = Voltage x Amp-hours
12Volts x 487.5Ah = 5.850Watt hours
12 Volts x 246.2Ah = 2.954Watt hours
Lithium-ion batteries are more efficient than traditional lead-acid ones. They can provide 80% of their rated capacity with just 50%. The battery will store 50% for lead-acid and 20% for lithium which means there is still plenty leftover at all times. Let’s calculate how many usable watt-hours can be stored in these batteries.
5.850Wh x 50% = 2.925Wh
2.954Wh x 80% = 2.363Wh
The number of watt-hours we calculated will be enough to fully recharge your batteries in one day.
The number of sun hours that hit the surface ranges from 4 to 8 in New York. For example, 5 is average for NY and corresponds to about 1/3rds more time than usual. You can find out how many days have rained forever by googling “number rainy day”.
Our calculations show that in order for the batteries to last through winter we will need about 5 hours worth of sunlight per day. To calculate how many watt-hours are required, divide your desired energy needs by this number and make sure it’s enough.
2.925 Watt-hours/5hours = 585 Watts
2.363 Watt-hours / 5 hours = 472Watts
The sun provides us with all of our energy needs. When you buy solar panels rated at 100 Watts, they will deliver this power in standard test conditions (more on this later). The panel will not provide 100 watts. We need a safety margin of 30%, so multiply the required power by 1.3 to get our usable amount.
585Watts x 1.3 = 760 Watts
472Watts x 1.3 = 614Watts
The right solar panel for you depends on your energy needs. If 100-Watt panels are what’s needed, then these will do the trick.
760 Watts/100Watt panel = 8Panels
You need to charge your battery bank with eight panels of 100 watts each in order for it to be completely charged by tomorrow.
614Watts/100Watt panel = 6 Panels
The most powerful solar panel you can get is the six-panel 100-watt system. This will give enough juice to charge up all 12 of those batteries in just one day.
Now that we have calculated your system, the next step is to connect it all together.