5 Steps To Designing An Off Grid Solar Power & Energy Storage System
In the United States, at least 180,000 families are living off-grid, and that number increases each year, according to Home Power Magazine. Whether you’re looking to transition to full-time off-grid life, want to occasionally travel in your off-grid vehicle, or enjoy your vacation in an off-grid cabin, it can be daunting to know where to start, from meeting your water to your electricity needs. Fortunately, we have you covered when it comes to designing your off-grid power system from scratch, including determining your energy needs, solar and battery system sizing and the additional components you will need. Take a look below to learn the five steps you can take to power up your self-sufficient lifestyle today.
Step #1: Determine how much energy and maximum power you will need
Although many people often skip over this step and move straight to purchasing their off-grid solar-plus-storage system, this is one of the most important steps you can take to ensure you don’t waste your money on an oversized system or end up with a system that isn’t able to sufficiently meet your energy needs. In order to correctly determine your energy needs, you will need to use a load calculator or work directly with a representative from RELiON. Enter each appliance or item you will be powering with your energy system, how often you use it per day, as well as the item’s relevant specifications. Try your best to remember every item you will be using with your power system, as seemingly small edits to your load calculation can end up making a large impact.
If you would prefer to make this calculation manually on your own, note that every electronic device will indicate the electrical load it draws on its label or packaging. This load will be provided either in amps – the base unit of electrical current, or watts – the base unit of power. If it provides amps, then estimate – in hours – how long this device will be used each day and then multiply that by the current (amps). This will provide you with the daily amp-hour requirement. Alternatively, if the device lists watts, simply divide the watts by the voltage to get the amps. Again, estimate – in hours – how long the device will be on each day and then multiply that by the current in amps. Now you have the amp-hours for each device. Add them all up and you’ll have your daily energy load. This will help you determine how much battery capacity you need.
Next, determine your maximum power or maximum current requirement. This can be done in amps or watts. Since you already determined the amps above, you already have all of the information you need. Determine the maximum current needed by adding up all of the potential current draws that may take place at the same time. Now you know the maximum current requirements for your battery.
Step #2: Determine the number of batteries you will need
After you have determined how much energy and maximum current or power you need, you will need to figure out how many batteries you need to properly store all of that energy as well as meet your power and current needs. During this process, make sure to ask yourself questions like whether you only need enough storage for a day or two, or if you need to have enough storage for three or more days; whether you will incorporate another power source, such as a wind turbine or generator, to use during consecutive cloudy days; and whether you will be storing the batteries in a warm room or a cold location. Batteries are often rated for storage at higher temperatures because, in colder temperatures, the battery's ability to provide sufficient power is diminished. Therefore, the colder the room, the larger the battery bank you need. For example, in below-freezing temperatures, you may need over 50 percent more battery capacity. Note that there are few battery companies that do offer a battery that is designed specifically for below-freezing temperatures though. Factors such as those listed above all affect the size, and cost, of your battery bank.
An additional factor to consider is that lead-acid batteries can only be discharged up to 50 percent without being damaged, unlike lithium batteries - especially lithium iron phosphate batteries, which can be safely discharged up to 100 percent. For this reason, lithium batteries are an ideal choice for off-grid power systems, which often require the ability to discharge more deeply. You would also have to buy twice as many lead-acid batteries compared to lithium batteries just to reach the same usable capacity, after the depth of discharge, charge rates, and efficiency rates are factored in.
After taking into account these considerations, you will then need to determine what voltage battery bank you need, ranging from 12V to 24V to 48V. In general, the larger the power system, the more likely you are to need a higher voltage battery bank in order to keep the number of parallel strings to a minimum and reduce the amount of current between the inverter and the battery bank. If you just have a small system and want to be able to charge minor items like your tablet and power 12V DC appliances in your RV, then a basic 12V battery bank is suitable. However, if you need to power well over 2,000 watts at a time, you’ll want to consider 24V and 48V systems instead. In addition to reducing how many parallel strings of batteries you will have, this will allow you to use thinner and less expensive copper cabling between the inverter and the batteries.
Let’s say you decide a 12V battery bank is best for your needs and that you came up with a daily use of 500Ah in step #1. Looking at RELiON’s 12V batteries, you would have several options. For example, you could use five of the RELiON 12V 100Ah RB100 batteries, or two of the RELiON 12V 300Ah RB300 batteries. Of course, if you are unsure as to which RELiON battery is best for your needs, please contact us and we will work with you to find the right size bank of the right batteries to keep you powered up.
Step #3: Determine the number of solar panels you will need
The second part of your off-grid power system calculation involves determining how many solar panels you will need. After you know how much energy you need to produce per day from your load calculations, you need to factor in how much sunlight will be available for you to harvest from, otherwise known as “sun hours.” The number of “sun hours” is determined by how many hours the available sun in a given location shines on your panels at a specified angle throughout the day. Of course, the sun isn’t as bright at 8 a.m. as it is at 1 p.m., so an hour of morning sun may be counted as half an hour, whereas the hour from noon to 1 p.m. would be counted as a full hour. Also, unless you live near the equator, you do not have the same number of hours of sunlight in the winter as you do in the summer.
It’s also recommended that you base your solar power system size on the worst-case scenario for your given location, which includes basing your calculation off of the season with the least amount of sunshine in which you will be using the system. This way, you will ensure that you do not end up short on solar energy for part of the year.
Step #4: Select a solar charge controller
Once you have determined the number of batteries and solar power you need, you will need a way to manage the transfer of the solar power into the batteries. A very rough calculation you can use to determine what size solar charge controller you need is to take the watts from the solar, and then divide that by the battery bank voltage, and then add another 25 percent to be safe.
It’s important to also note that charge controllers are available with two major types of technologies: Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM). In short, if the voltage of the battery bank matches the voltage of the solar array, you can use a PWM solar charge controller. In other words, if you have a 24V battery bank and a 24V solar array, you can use PWM. If your battery bank voltage is different from the solar array, and can’t be wired in series to make it match, you will need to use an MPPT charge controller. For example, If you have a 12V battery bank and a 12V solar array, you will need to use an MPPT charge controller.
Step #5: Select an inverter and balance of system components
Please note that if you are only running direct current (DC) loads straight off of your battery bank, you can skip this step. However, if you will be powering any alternating current (AC) loads, you will need to convert the direct current from the batteries into alternating current for your devices. First and foremost, it’s important for you to determine what type of AC power you need. In North America, the standard is 120/240V split phase, 60Hz. In much of Africa, Europe, and some countries in South America, the standard is 230V single phase, 50Hz. In some islands, it is a mixture of the two. While some inverters can have their voltages and/or frequencies configured, many are fixed. Once you have determined the type of AC power you need, then verify through the inverter specifications that it matches your needs.
If you do have the North American standard, you must determine if you have any devices that use 240V, or if they are all just 120V. Some inverters are able to put out 240V, and you can wire the output to use either 120V or 240V. Other inverters are stackable, each one putting out 120V, but when wired together, or stacked, can create 240V. Others are only capable of putting out 120V, and cannot be stacked. Once again, verifying factors like this through the inverter’s specifications is key to deciding whether the inverter will be able to meet your needs.
You will also need to know how many watts total your inverter will need to power. Fortunately, you already have this information from step #1, in which you created a load list that determined both the power requirements as well as the constant watts of your loads. It’s important to also note that an inverter is designed for a specific voltage battery bank, such as 12V, 24V, or 48V, so you will need to know what voltage battery bank you are going to have before you decide on the inverter. Also, if you think you may expand your off-grid power system in the future, such as through the use of a higher voltage battery bank, the lower voltage inverter will not work in the larger system. You will therefore need to plan in advance and opt for the higher voltage from the outset or plan on swapping out your inverter at a later date.
In addition to the above-listed items, you will also have to select several small components that are needed for the balance of the system, including items such as the fuses and breakers that provide overcurrent protection. You will also need to decide what size wires you will need, which breaker boxes will be used, and what items you will use to mount the solar panels.
After you have completed all five of these steps, you will be well on your way to designing, and more importantly, actually using your new off-grid solar-plus-storage system! If you have any questions at any point along the way, please don’t hesitate to reach out to a RELiON representative to support you with your off-grid power system design.