You have read Home Power Magazine and their articles on off-grid living, helped your friend install his solar panels on his RV and are thinking about building your own cabin in the woods where there is no utility power. What do you need to know to be able to build your own off-grid home to support your simple, yet semi-electronic lifestyle? This article will tell you what you need to know before designing your off-grid home, what considerations to take into account and how you go about creating your own bill of materials to get started.
Step Number 1
Figure out your loads! Often times the hardest part of sizing an off-grid system, but truly, the most important. If you do not know what you plan on running (electrically) how will you be able to know if what you have in mind is too much, or too little power? You can determine your loads by using a Kill-A-Watt meter, by referencing the manufacturers electrical specifications on the units themselves, or by taking a look at average wattages of household appliances. It is always best to get the electrical data from your equipment, but sometimes we have to use our best educated guess.
How many hours a day will you be drawing power? The next step is determining how many watt hours you use on an average day. This will allow you to size your battery bank, your solar array and even help determine your inverter size. You can use a LOAD WORKSHEET or LOAD CALCULATOR to help compile this data.
Step Number 2
What voltage system are you going to put together? Most common sizes are 12V, 24V and 48V. You can determine what voltage system you will need based on the electrical data that you collected about your system. So, what did those numbers come out to be? You can use this chart to get a gauge for your system size, but it always best to consult a off-grid contractor or specialist who can direct you accordingly.
|Amp Hours Per Day||Voltage|
|1200 watt hours or less||12V|
|1200 – 4200 watt hours||24V|
|4200+ watt hours||48V|
Where are you located? Your location will help you determine how many sun hours you receive on average throughout the year. This information is crucial to properly sizing your PV array. A good resource for this is PV Watts through NREL (National Renewable Energy Laboratory). Simply enter in your address and hit continue to get to a final landing page that summarizes the amount of solar irradiance you get. If your system is going to be running year round, you have to use the lowest sun hours available to make sure that even during the winter months, your solar panels will be producing enough power to properly charge your system. *Generators are a good supplementary power source to have on site for those cloudy months as well. (Just make sure your off-grid inverter has an AC input!)
Now that you know how many solar panels you will be using and how many solar panels you will be needing, you can choose your charge controller. A rough estimation to help you decide what size charge controller you will need will be to take the total PV watts and divide that by your battery voltage. You also will want to take into account the safety protection factor of 25%. We have included an example for a 12V system below.
500 watts solar / 12V battery bank = 41.66 amps Ideally you will round up and use a 45 amp charge controller. Keep in mind that if your solar panels are the same voltage as your battery bank then you can use a PWM charge controller. For solar panel inputs higher than your battery voltage, it is a good idea to use an MPPT charge controller.
If you are putting together a 12V DC system for an RV or marine application, you would not need an inverter and can skip past this step. For those who are looking to run AC loads, you will need an inverter for your off-grid system. There are a few key points that will help you determine which kind of inverter to choose for your system. Do you need your inverter to simply invert DC to AC? Or perhaps you want to be able to use a generator to charge your batteries as well. If you are looking for the latter, than you need to be looking for an inverter/ charger. (This is not a “charge controller” charger – it is the ability to take an AC input from either a generator or shore power to charge your batteries.) Another consideration is choosing either a pure sine wave inverter or a modified sine wave. If you plan on running some lights, a cell phone and minimal equipment, then a modified sine wave can be a great cost effective solution. Note that modified sine wave (also known as square wave inverters) will not power certain high frequency electronics such printers, digital clocks and even some computers.
Tying your system all together and choosing your balance of system components such as your racking system for your solar panels, breakers, wiring and combiner boxes. It is a good idea to consult the company that you are planning to purchase the equipment from to make sure that everything you have in mind is compatible and that you are not missing anything.
Alternatively, there are several pre-wired and complete off-grid system packages to choose from. For a custom quote, you can use the link below to have one of our off-grid specialists design a system for you.
Give us a call at 760.597.0498
Or visit our web site at www.ecodirect.com
Thank you and we look forward to speaking with you!