Off-Grid/Mobile/Portable Solar Power Fundamentals - [Part 1/6]

Off-Grid/Mobile/Portable Solar Power Fundamentals [Part 1/6]

We've created a 6-part off-grid/mobile/portable solar power mini course to help you better understand the fundamentals of solar power and all of the parts and pieces that go into building a solar power system that meets all of your needs.

In part 1 of 6, we are going to explore some of the definitions and fundamentals of stand alone solar power systems.  Before building your own off grid, mobile, or portable solar power system, it is important to understand the basics behind solar energy.  

What is an Off-grid, Portable, or Mobile Solar Power System? 

Off grid, portable and mobile solar power systems are all considered “stand-alone systems.”  Stand alone systems are PV solar energy systems that operate completely independent of the power grid. Simply put, an off-grid system has it's own battery bank for solar to store the power being generated from the panels.

Off grid, portable and mobile solar power systems enable the use of electricity generated from solar panels to be used immediately, or to be stored and used later from the battery bank.  Some of the most common applications for stand-alone solar power systems include:

• Off Grid Homes and Cabins
• Boats 
• Campervans
• RVs
• Backpacking, camping and outdoors
• Agricultural Uses

How does an Off-grid, Portable, or Mobile Solar Power System Work?

An Off Grid, Portable, or Mobile stand-alone solar power system is simple:  It uses solar energy to power household devices. The system is able to accomplish this by allowing energy to flow through 3 separate blocks:  Production, storage, and usage.  

The Production Block

In the production block, sunlight is harnessed from the individual solar cells of a PV solar panel to create DC electricity.  All of the energy produced by your solar array is then sent to be stored or used immediately in either your battery bank or a solar generator.

The Storage Block 

In a standalone system, the solar energy is sent from the panels to a charge controller and battery bank or directly into a solar generator (which has a charge controller inside of it).  The charge controller is set in place to prevent damage to the batteries, where the solar energy is stored for later use.  

The Usage Block 

Most home appliances are run on alternating current, or AC electricity (standard wall plugs).  In off grid solar systems, the DC electricity from the battery is sent through an inverter to modify the current into appliance-friendly AC electricity.  From there, larger systems are sent to a home switchboard, or appliances are plugged directly into the inverter’s output interface. If you are powering DC appliances, then it is possible to bypass the inverter to run those particular devices directly off of the solar power. 

Again, a solar generator has everything inside of it (battery + charge controller + inverter) so that you can simply plug-in your panels and plug-in your appliances and away you go. 

Grid Tie vs Off Grid Solar Power Systems: The Main Differences

Off grid solar power systems are, by definition, entirely separate from grid tie solar power systems.  Grid tie, Grid-tied, or on-grid solar power systems are generally found on residential homes. These miniature green energy power plants generate electricity and send it directly back into the utility grid.  

During the evening and on days without direct sunlight, homeowners with grid tie power systems are still able to run their home’s electricity by using utility power from the grid, rather than their solar energy systems.  Some of these systems, known as “hybrid systems” include battery back-ups to store (extra) solar energy in the event of grid failure.

Off grid solar power applications rely solely on what is harnessed and stored within the energy system, without the luxury of additional utility power.  This means that depending on the amount of "things" you want to power, you will need to build the battery bank accordingly. Some off grid systems will have 1 or 2 batteries and some will have dozens. Either way, an off grid system means that you generate and store your own power. 

A solar generator kit is also technically an "off grid" solar power system but that is more portable since they weigh anywhere from 5-60 lbs and can be put in the back of your vehicle or on a boat quite easily. The power you harness from the panels is stored directly in the power station/generator and used whenever you need. 

Pros & Cons of Off-grid, Portable, And Mobile Solar

When comparing standalone (off grid) systems to grid tie solar, there are a certain number of advantages and disadvantages to using an off-grid, portable or mobile solar application.

Pros

• Completely Independent of the Power Grid - Stand alone power systems will still be running if there is grid failure.  Plus, off grid solar users never have an electric bill!
• Installation Anywhere - Off grid solar power systems generate electricity anywhere the sun shines.  In the case of an RV or van, you can bring a portable, mobile electricity power plant anywhere you go. 
  
• Infinite Applications - Solar energy is a renewable resource with an infinite supply.  Off grid power systems can run anything from small hand held devices to large agricultural operations. 
  
• Portable - You have the ability to build a portable power system that can be taken anywhere. Perfect for outdoors, camping or bug-out situations.

Cons

• High Startup Costs - The number one reason most people delay in building their off-grid solar system is because of the high start up costs.  Batteries can be extremely expensive and usually make up over 70% of total system expenses.
  
• Low Power Efficiency - Affordable off grid solar components can have relatively low efficiency ratings.  One of the biggest issues people have with solar energy is that rapidly advancing industry still has room for improvement.
  
• Battery Replacement - Solar panels are generally rated to last over 25 years, however most solar batteries will need to be replaced in as little as 5 years.  Although lithium ion batteries will last much longer than cheaper, lead acid batteries, they will still need to be replaced during an off grid systems lifespan. 
  

Basic Power Concepts & Units 

Power can be defined as “the amount of energy transferred per unit of time.”  In the case of an off grid solar system, the power is measured in watts. To understand what a watt is, you will need to know that “electric current” is the flow of an electric charge through the movement of electrons, and “voltage” is the electric pressure that is moving the electrons.  

Watts, Watt Hours, and kWh 

One watt is generated when 1 Amp of current flows through one volt of potential difference.  Solar panels are rated in watts, which refer to the peak amount of power a unit can generate.  

Watt hours are a unit of energy to measure the amount of watts that are generated or used in one hour.  In larger systems that generate a lot of electricity, most solar energy is measured in kilowatt hours (kWh).  A kilowatt is equal to 1,000 watts, so a kilowatt hour (kWh) is equal to how many thousands of watts of electricity are generated or used in one hour.  

Amps and Amp Hours

As mentioned above, current is measured in Amps.  Amp Hours (Ah) are the measure for units of energy that can be generated or consumed over a period of time.  In an off-grid solar system, the usable energy stored in a battery is measured in Amp hours.  

Energy Needs vs Solar Energy Production  

The delicate balance between the energy you produce and the energy you consume is the crux of sizing, building and using an off grid solar power system.  In an RV, van, or off-grid cabin, some of the luxuries of everyday grid-tie electricity life may have to be sacrificed in order to conserve energy and live off the grid.  

Obviously, solar energy is produced during the daytime.  On typical days, potential solar energy production follows a bell curve, peaking around midday for optimal electricity production.  Users can use solar electricity directly as it is produced, or as it is pulled from the battery during morning or evening hours.  

As we’ve mentioned, batteries can be quite expensive, so in order to make your off grid solar system cost effective, you will want to calculate the minimum size of storage you may need in order to run your essential electric devices when the sun is not shining. 

This is truly the first step in planning any off grid/mobile or portable solar power system.

What Are Peak Sun Hours?

As alluded to above, Peak Sun Hours (PSH) are the hours of a day in which solar energy can be generated at peak efficiency.  The amount of PSH (peak sun hours) your solar panels will receive varies depending on the part of the world in which the system is located.  

How are Peak Sun Hours they Calculated?

A Peak Sun Hour is achieved when one square meter of space receives 1000 watts of solar irradiance in one hour.  Throughout a day with 10 hours of sunlight, there is usually about 5 or six peak sun hours. This resource from NREL, can be used to estimate the PSH of anywhere in the United States throughout the calendar year. 

Why Are Peak Sun Hours Important?

Peak Sun Hours are extremely important in determining the size of your solar array.  If you are in an area with less PSH then average, then you will likely have to install more solar panels in order to generate the same amount of energy as a location with more PSH. So in simple terms, if you live in an area with less sun, you'll want more solar panels but if you live somewhere with lots of sun, you might be able to get away with less panels (hypothetically speaking).

Conclusion 

Ultimately, before you build your first DIY off-grid solar power system, it is important to know the concepts and terminology used in solar applications worldwide.  In our next lesson, we will focus on the most visible and widely known portion of solar energy systems as we explore everything you need to know about solar panels.  

If you still have questions, don't hesitate to reach out or give us a call today at 877-242-2792!

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