Loads List: Off Grid Solar Power System Design - Step 1

Loads List: Off Grid Solar Power System Design - Step 1

Hi. I'm Amy Beaudet from the altE Store. Thank you for watching the first of our video series on designing an off-grid solar system.This first video is appropriately called, Step 1 - Loads List. Figuring out how much power you need is a critical step that many people try to skip.

Designing a solar system without knowing your loads is like being asked how much gas do I need to drive, without knowing what type of vehicle or how far you are driving. Let's start at the beginning. Here's a basic schematic of a typical off-grid system.

You'll notice there is a generator in the drawing. That is there for instances when there is not enough sun to provide the power needed, generally Winter, and if you have an occasional load that requires more power than your system can provide.

For instance, if you needed to use a welder for a project, it may not make sense to design the whole system to be able to accommodate a tool that is used once a year. So having a generator available for occasional use makes good sense.

So keep this option in mind when designing your system. This video series will cover the major steps of designing an off-grid system. Let's start with step 1, analyzing your load.

So let's go over the steps to determine the amount of power you need. Start with a loads analysis. Unlike a grid tied system where you can just base the system on how much power you want to offset, an off-grid system needs to provide all of your power. With an off-grid system, you need to take a good look at what you are powering, and how long you need to power it. Going off-grid often takes changes to your lifestyle.

It's not as simple as just saying, "I'm tired of paying the electric company, I'm taking my whole house off grid and stick it to the man". You have to figure worst case scenarios; winter time, with little to no sun for days. Unless you are in a climate that has long sunny days all year round, most people who are doing a year round off-grid system will have a generator available to pitch in in the winter.

I read a quote from an off-gridder who said, "if it's going to be a sunny day, I can cook waffles for breakfast. If it's cloudy, I have cereal." When designing the system, you can't just say it's an "average" size system.

No such thing. You also can't base it on the square footage of the house or cabin. One cabin may have air conditioning, an electric stove and water heater, electric washer and dryer, a fridge and freezer, and the other may have LED lights and a laptop. Which one is "average"?

Who's to say? Do you think the same system will work for both cabins, even though they are the same physical size? You need to make a complete list of every electrical device you will be using, how much power it uses, and how long each day it will be on.

Don't forget anything. All UL listed equipment will have a power label on it.

Since volts x amps = watts, you should be able to get all of the information you need off the labels. Here's some examples from walking around my house. You can see some do list the watts, some list a voltage range, some and amps, and some list the DC voltage and amps used from a power block that is converting the AC voltage to DC. If the label only lists the volts and amps, but not watts, you can multiply the volts times amps to get watts. Once you have watts, you'd then multiply the watts x hours a day it is on, and you get watt hours a day.

This is not perfect, as it may just be listing the start up current, and not the continuous power, but it is a starting point. If the voltage listed is DC instead of AC, you would still multiply the DC volts by the amps to get watts. If the voltage listed is a range, like 100 to 240 volts, you would use the voltage that is used in your area, for instance, 120V for North American outlets. Some loads, like a refrigerator or a pump or furnace fan, are not on continuously and have a high surge when the compressor turns on, making it difficult to determine how much accumulated power, or watt hours, it uses throughout the day. If it is Energy Star rated, you can find the Energy Star Label, either on the appliance or on the Energy Star web site.

 

If it is not Energy Star rated, and you are looking to power it with solar, it may be worth it to replace it with an Energy Star fridge. The Energy Star label will tell you the average annual kwh used.

From there, you can simply divide it by the number of days in the years, 365, to see how many watt hours it uses in a day. In this example, 383kwh a year, divided by 365 days in a year = 1.049kWh a day.

You can multiply that by 1000 to determine how many Watt hours a day, as a kilo watt is 1000 watts. A more accurate way of determining the power consumption is to measure it with a device like a Kill-a-watt meter.

You plug the meter into the outlet, and then plug your device into the meter. It will show you an instantaneous wattage, volts, amps, and accumulated watt hours. It also shows how long the unit was measuring, so you can divide the watt hours by hours to see how many watts it is drawing on average.

Multiply that by 24 hours, and you have how much it actually used in a day. For example, if the Kill-a-watt says it used 1260 Wh over 30 hours, that averages 42W. 42W x 24 hours in a day = 1008Wh a day. Taking it one step further, 1008Wh / 1000 = 1.008kWh.

Alright, now that we know what each device is using, what do we do with that info? Using a load calculator can help you create the loads list.

This calculator is available on...

altE's website at altestore.com/store/calculators/load_calculator.

To use it, you enter the appliance name, quantity, how many watts it is in AC or DC .

You'll know it is AC if it plugs into a wall outlet. If it is DC, it runs off a battery, like your cell phone car charger. On at the same time indicates that the system needs to be big enough to power those devices that may be on simultaneously.

For example, you have no control over when your fridge compressor will turn on, or your well pump, but you can control when you turn on a light. So if there is a chance that multiple devices may be on at once, you must select On at Same Time.

That will help you determine how big of an inverter you need to handle that power if they all turn on at once.

Some devices also have a high momentary surge, like a fridge or motor. It uses 2 to 4 times as much power for a few seconds when it first turns on. You need to keep track of that as well, because if your inverter cannot handle that surge, the device may not be able to turn on, or you could damage the inverter. That's it for the first video in this series of designing an off-grid PV system.

You can go to our web site to use our Loads List calculator to calculator your own loads. Watch the next videos in this series for how to size the battery bank and the solar array , using the numbers we came up with from our loads list.

Also watch more of our various Video Series on our web site. We've got a team of highly trained Technical Sales Reps available to help you plan your system, give us a call..

http://gridmarketing.net/go.php?r=josebaezky&p=22

Thanks for your visit!

https://youtu.be/vdly8OhsdmI

https://bit.ly/3t0wA9p