The most crucial step for achieving a cost-efficient sizing of your off-grid and RV solar power systems is the correct determination of the electricity usage.
Our AC and DC load calculators have been created to help you estimate your solar power consumption fast and easy!
We highly recommend you to read the quick start guides for using AC/DC load calculators below before starting your calculations.
Table of Contents
AC Load Calculator
DC load Calculator
Quick Start Guide for the AC Load calculator
The blue cells, where you enter your input data, are editable:
- AC device – you find a list of AC devices you can have at your home, RV, or boat. Also, you are free to add devices missing from the list.
- Rating, W – the power rating (wattage) you can find on a device’s label. You may modify the wattage of any of the listed devices, if you need to.
- Qty (quantity) – the number of devices of the same type you use simultaneously. If you don’t use a device, you should either enter ‘0’ in the cell or just leave it blank.
- Use hrs/day – the number of hours a day you use a device.
- Use days/week – the number of days a week you use a device.
The yellow cells, where you get the calculated results, are non-editable:
- Total Watts – the power of all the plugged-in devices of a certain type. At the bottom, you have the Total AC wattage of all the devices plugged in at the same time.
- Watt-hours – the energy consumed by a device for its period of use.
- Average AC Daily Consumption – the daily consumed energy, averaged on a weekly basis. It is calculated upon inverter efficiency = 0.9.
- Max AC Daily Consumption – the maximum energy consumed per day by the devices plugged in simultaneously.
You get a recalculation by clicking on the Update button.
The Reset button clears the input data.
The Print button helps you get a printout of the calculated results.
Quick Start Guide for the DC Load Calculator
The blue cells, where you enter your input data, are editable:
- DC device – you find a list of DC devices you can have at your home, RV, or boat. Also, you are free to add devices missing from the list.
- Rating, W – the power rating (wattage) you can find on a device’s label. You may modify the wattage of any of the listed devices, if you need to.
- Qty (quantity) – the number of devices of the same type you use simultaneously. If you don’t use a device, you should either enter ‘0’ in the cell or just leave it blank.
- Use hrs/day – the number of hours a day you use a device.
- Use days/week – the number of days a week you use a device.
The yellow cells, where you get the calculated results, are non-editable:
- Total Watts – the power of all the plugged-in devices of a certain type. At the bottom, you have the Total DC wattage of all the devices plugged in at the same time.
- Watt-hours – the energy consumed by a device for its period of use.
- Average DC Daily Consumption – the daily consumed energy, averaged on a weekly basis.
- Max DC Daily Consumption – the maximum energy consumed per day by the devices plugged in simultaneously.
You get a recalculation by clicking on the Update button.
The Reset button clears the input data.
The Print button helps you get a printout of the calculated results.
Essential Things You Need To Know About Solar Loads And Their Impact On Solar System Performance Overall Price
Before to proceed with solar system sizing, you have to select among 3 options available.
Option 1: Maximum daily use.
With this option, you have your daily consumption calculated for ‘the heaviest day of the week’, that is, when you use the maximum number of devices, and all of them are on during the hours you have entered in the ‘Use hrs/day’ column.
In such a case, what you need to further calculate the size of the battery and the solar array, is the Max Daily Consumption (AC + DC).
As a result, you get the most expensive solar power system.
Option 2: Average daily use.
With this option, you get the energy drawn by each device averaged on a weekly basis.
Therefore, you practically ignore the risk of ‘overloading’ the battery in case of plugging too many appliances simultaneously.
Thus, your battery is exposed to the risk of over-discharging and reduced lifespan. The worst situation can occur if your battery gets drained by too many appliances operating at the same time.
Such a situation means both a power outage and a risk of battery damage. With this option, what you need to further calculate the size of the battery and the solar array is the Average Daily Consumption (AC + DC) value reported by the tool.
Although found somewhat risky, this is the most widely used option for system sizing. As a result, you get the least expensive solar power system.
Have you managed to get the difference between Option 1 and Option 2? Here is an example.
Suppose, you have a 1-hp well pump (1,000 W) and you use it for half an hour a day, three days per week.
For the day you use the pump, it consumes a total of 557* Wh – this is the Max Daily Consumption. Such a value averaged over 3 days per week, gives 238* Wh of consumed energy, which is twice less!
This is the Average Daily Consumption.
Obviously, if you use the pump every single day of the week, the Max Daily Consumption would be equal to the Average Daily Consumption, or 557 Wh.
*10% inverter losses are taken into account i.e, the solar power generation must be increased to compensate for these losses.
Please, do not mistake Max Daily Consumption with Peak Power. Peak Power is the Total AC/DC Wattage of the devices operating simultaneously, while Max Daily Consumption is the total energy consumed throughout the day by devices that might not be plugged in simultaneously. When sizing and selecting the inverter for your off-grid solar power system, you need the peak power or the Total AC Wattage.
When you size the battery and the solar array, you need energy rather than power – the Average Daily Consumption or Max Daily Consumption.
Option 3: Selected maximum daily use.
This is a less expensive version of Option 1 but still more expensive than Option 2.
Unlike Options 1 and 2 above, here you don’t have a value that is directly reported. Instead, you are supposed to enter combinations of appliances you might possibly use at the same time and the hours you use them.
For every combination of simultaneously plugged in devices, you are supposed to note the Max Daily Consumption.
When you have entered all the possible combinations of simultaneously plugged-in appliances, you should compare the Max Daily Consumption values and choose the highest ones to further use it for sizing the battery and the solar array.
Obviously, it is recommended to choose the combination with fewer appliances working in parallel.
This combination has to be a trade-off that suits your needs.
The drawback is that it requires self-control to follow it.
If you are not sure in your self control abilities just choose the next higher wattage combination.
Why do you need to perform load analysis?
Load evaluation, also known as ‘load calculation’ or ‘load analysis,’ is an essential starting point of sizing any off-grid solar power system.
In most off-grid PV systems, you have a battery that stores the solar-generated electricity.
The solar panels generate DC power, which is conserved in the battery for later use.
The devices and appliances (whether DC or AC ones) in your home, RV, or boat draw power from the battery to operate. DC devices draw power directly from the battery, while AC devices need to be connected to an inverter that converts DC power into AC power.
If you don’t have enough electricity in your battery, your devices will probably soon go out.
Furthermore, your battery will get damaged if often discharged below 50%. A damaged battery cannot be used any longer and should be replaced with a new one.
As you know, however, the battery is the most expensive part of any solar system.
Therefore, above all, you need to know how much energy you need daily.
Once you have determined your daily electricity use, you will be able to evaluate out how big battery you need and how many solar panels you should have installed to get this battery fully charged.
It’s vital to fill in the loads’ spreadsheet as accurately as possible. You should include ALL the appliances you use in your home, RV, or boat and try not to ‘forget’ any of them.
A device used regularly or occasionally but missing in the list of the loads can bring you nasty surprises when you start using your solar power system.
The amount of power a device is consuming is rated in watts. Also, the rated power of a device is called ‘wattage.’
Your ultimate goal, however, is to find the energy this device consumes daily. Energy, electrical energy or electricity, is the power that a device consumes for a certain period during the day.
For example, let’s say that your plasma TV set has a power rating or wattage of 60 watts.
These 60 watts are the power your TV set is drawing at a given moment. Also, these 60 W alone don’t help you much upon solar system sizing.
What you need is how much energy your TV would draw per day from the solar battery. To find that, you should know how much time your TV set is on every day.
If you watch TV for 3 hours a day, then this TV set consumes 60W x 3 hours = 180 watt-hours (Wh) per day. These watt-hours denote the daily energy consumption of your TV set.
Next, if you have 2 LED lights of 2 watts each, and you have them on 4 hours a day, then these LED lights consume 2 x 2 watts x 4 hours = 16 watt-hours daily.
These 16 watt-hours should be added to the energy consumed by your TV set as calculated above: 180Wh + 16 Wh = 196 Wh of energy consumed daily by your TV set and the two LED lights.
Note that 2 watts (W) are different from 2 watt-hours (Wh). 2W is the power your LED light is instantly using.
These 2 watts are power, not energy. If you, however, have this LED light on for 1 hour, then the energy consumed is 2 watt-hours (Wh).
And these 2 Wh are essential for your battery. Your battery cares how long this light is on, not just how much power it is drawing right now!
Similarly, you have to the same for all the devices you use daily.
As a result, you get the total energy consumed by the devices you use every day.
Once you have your daily energy use, you can proceed with sizing the solar battery and solar panels.
Eventually, you have to sum the AC daily energy use and DC daily energy use.
Remember, to get the solar power system for your home, RV, or boat, you must know how much energy you need daily.
Otherwise, your system is going to fail since you will not be able to find the right battery size and solar panel size!
You can learn more about the fast and easy solar power system sizing and design in our best selling practical books and ebooks available in pdf, ebook(Kindle, Apple and all the rest popular ebook platforms) and paperback formats:
Off-Grid Solar and RV Solar Power For Everyone
The Ultimate Solar Power Design Guide-Less Theory More Practice
Other useful solar power calculators:
- Off-grid solar system calculator
- Solar panel output calculator
- Solar PWM charge controller calculator
- Solar DC Wire Sizing Calculator
- Solar Battery Calculator
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