Off-grid solar design can be a very complex process. Many people are interested in the potential of operating electricity in an off-grid cabin with nothing but solar energy but don’t know how to get started. The good news is that the solar/battery storage industry is now mature enough that there are many affordable options available to consumers. However, since there are so many options, it can get very confusing very fast if you don’t know what to look for. So, I have created this list, based on numerous customer interactions that may help assist a novice client who is interested in going off-grid.
There are three questions you should be able to answer when looking for an off-grid PV system:
1. How much energy (measured in kWh or kilowatt-hours) does the house use per year?
2. Where is the house going to be located?
3. What is your budget for the project?
Being able to answer these three questions will get you started on the right foot toward designing and acquiring a suitable off-grid PV system for your home.
1. How much energy does the home use per year?
The easiest way to find this out is to look at your utility bill if you have one for the project home. This will provide the most accurate year-long data on how much energy (in kWh) you use each month of the year. Some clients wonder why we need to know how much energy in kWh/year you use when it may be easier to find out the kWh/month or kWh/day for the project. The answer is that energy use tends to change on a seasonal basis. For example, during the summer, we tend to cool our homes more with air conditioning, which increases the amount of energy used in the summer relative to the winter.
If a Utility bill is not available for the project, maybe because it will be for a new home, or the current home isn't connected to the grid, then it will be a good idea to estimate the energy that will be required for the electronics in the home. There is no one perfect way to estimate your energy use, as there are many options available and which one is best for you, may depend on the situation at hand.
You can use an online calculator tool to estimate how much energy your system will require. You can also look at each individual electronic device you plan to use, check its power rating in Watts and estimate how much time you plan to use each item per day. With this information, you can build a spreadsheet that will calculate your total kWh per day energy use. Note that this is generally fine with lighting, computers, televisions, and small electronics. However, for heating/cooling systems like toasters, dryers, and air conditioning units, this will be a more difficult load to estimate. This is because heating systems will require more energy in colder climates to reach a target temperature and vice versa. For example, an air conditioner in a hot climate like Florida will require more energy to cool a 1000 square foot area than it would in Maine most of the year because Florida is generally hotter than Maine. Other factors such as home insulation, volume, and other weather conditions can be taken into account, but it will be best to simply estimate these numbers to the best of your ability to move on with the overall system estimation.
Once an estimate of how the yearly energy consumption is known, now we can get an idea of what your off-grid PV system should be able to supply per day. You should be cautious, however, as most American homes can use somewhere between 20kWh and 200kWh per day. But a typical off-grid PV system in the $10-30k range would find it to be difficult if not impossible to supply a 200kWh energy load on a daily basis, as they generally range from 5kWh to 40kWh per day consumption depending on the setup. So finding ways of reducing energy consumption in the home with LED lighting, efficient electronics use, alternative heating/cooling systems, and better insulation can help a great deal to balance out the energy use.
2. Which part of the country is the home located?
A big part of an off-grid system sizing is looking to see how much solar insolation you have access to where the home is located. The basic idea is that Sunnier areas will be able to get more energy. Solar energy can be estimated based on the total sun hours per day in your area, but there are many online tools that can assist you with simply finding out how much energy you can expect to get from a typical PV system based on your zip code and a few details about the PV array orientation. PVWatts is a great example of a tool that can provide this information. Other tools exist of course, but I find this will allow you to get a good estimate of what an off-grid PV system could provide you based on your area. Note that this tool isn’t perfect and won’t take into consideration local shading such as other buildings and trees, so be sure to use your best judgment when making these estimates.
3. What is your budget?
One of the biggest factors in getting an off-grid system will be to determine your budget. PV systems are coming down in price every year, but if you plan to purchase one soon, you will want to set a realistic maximum price for the system. This way, we can focus on the best system that can be provided in your budget range, and not go overboard. Many prospecting clients will want to know what it would cost to run their system now, just to find out that it is far past their price range. If you wish to go off-grid, it may be best to set a budget first and stick with it by lowering your energy use down to what is really required (such as food refrigeration, lighting, and basic electronics). Air conditioning can tend to be a very heavy load, so it may be best to figure out how to go without it if possible.
Putting everything together:
Once this information is gathered, you will have a good idea of what type of off-grid PV system you will need. Typically Renvu will suggest a PV system such as the Outback Systemedge series equipment with PV modules and racking along with it for your given project. This will be a good system to start with during the design phase, as it provides everything necessary for an off-grid power electronic system such as charge controllers, an inverter, switchgear, batteries, and a controller. We can, of course, supply other off-grid systems from Schneider, Midnite, Morningstar, and SMA, but these systems tend to have to be designed from the ground up, which may increase the amount of time it takes to size your system correctly.
Any system that you choose to go with for an off-grid system will be fairly complex. Be sure to check with our sales team, the manufacturer, and any solar experts you may know to go over the details of the project and system design. You will want to familiarize yourself with as many aspects of the system as you can, as it will be the main source of electricity for years to come. The more information you have up front, the better you will be able to utilize and maintain the system in the future.