Off-grid Solar basics
Updated: Nov 25, 2020
Renewable energy is a super cool topic, but speaking from experience I know it can feel a little complex with a substantial barrier to entry. Over the next few months, I am going to share what I have learned about a variety of different renewable energy options and hopefully, you can pass on what you learn and help increase our society's energy literacy.
The first topic I'd like to start off with is off-grid solar. When it comes to installing solar panels, there are generally two options. The first being; you generate electricity and basically put it back into the powerlines at which point your utility (BC Hydro, Hydro Ottawa etc.) will generally give you credits towards your energy bill. The second option is off-grid, where you are responsible for everything from generating the electricity to storing it, and finally to using it. Seems simple, and at the end of the day, it is fairly straightforward, however, there a few key steps aside from just throwing a solar panel on your roof - some of which I had to learn the hard way.
Step 1: Finding how much energy you need
The first step to your off-grid solar system is to find out what you want to power. Whether you have 4 TVs, a fridge, and a kettle, or you just want to charge your phone a few times this is crucial.
Doing a little research will tell you the power rating of your appliances, which you should write down, along with an estimate of how long they will run every day. For the purpose of this let's say we have a TV used for 4 hours a day, a total of 5 lights used for 8 hours a day, a hot plate that we use for an hour a day, and a phone charger used for 8 hours per day.
TV 100 watts
5 LED lights 20 watts
Hot plate 1200 watts
Phone charger 6 watts
Multiply the power rating by how long it's used each day will give you the energy need in watt hours.
TV 400 watt hours
5 LED light 160 watt hours
Hot plate 1200 watt hours
Phone charger 42 watt hours
Total 1802 watt hours
For completeness, you want to turn this number into "amp hours" because that is how battery sizes are measured. To do that you divide it by the voltage of the system. Modern systems can be 12, 24 or, 36 volts depending on what they are being used for. We can talk later about why 24 or 36 volts are being used but for the sake of this example, we will use a classic 12-Volt system. That gives us a total of 150 amp hours per day.
Step 2: Sizing your battery bank
Now you know how much energy you're going to use every day. Perfect, now we can figure out how big of a battery you need. There's a couple of rules of thumb when it comes to batteries that are important to keep in mind, the first is you don't want to discharge them to less than 30% of their capacity, and secondly, you want them to hold more than just one day worth of energy. If the sun doesn't come out you don't want to be hooped.
Knowing this, let's get ourselves a size. Let's say we want two days of autonomy, which means you'll have enough energy stored to run your system for two days without sun. Take your total from Step 1 and multiply it by 2.
300 amp hours
Now we want to make sure the batteries won't go below 30% capacity, so we take the 300 amp hours and divide by 1 minus the minimum capacity (in this case 1-0.3=0.7). 300/0.7 gives us
430 amp hours
Recommended battery types to look for are lead-acid glass matt and lithium-ion. Lead-acid will be your cheaper option but lithium-ion will last longer and you can discharge to below that 30% marker.
Step 3: Sizing your solar panels
Now we know how much energy we need for our battery bank, we can determine the size of your solar array. To do this, first, find the average number of sunlight hours per day. A google search of your location will find you a good rough number. If you are using this only in the summer then you can use average, however, if you will be using it year-round, find the minimum number of hours because you want to size to the worst-case scenario to make sure you never run out of electricity.
For this example, I will use my home town Terrace BC which gets about 1.6 hours per day of sunlight in the middle of winter - the struggles of living up north. If you were to live in say Kelowna BC you'd get about 3.3 hours per day in the middle of winter or 2.9 in Ottawa Ontario. For a summer cabin, the number would be up to 9.1 hours per day in Ottawa, and you could size to that. But for now, we want the worst-case, middle of winter scenario so we will stay with the low number.
We want to be able to make enough electricity to run the system in one day so we take the total our total from step 1: 1802 watt-hours, and divide it by the minimum hours of sun per day (1.6 hours). This gives us the sizing for worst-case scenario which turns out to be:
if you are not designing an essential system that will be used every day - like a vacation cabin perhaps, then this number can be much smaller, usually just above half. But if you want to live off this system you should not go below this final number.
YOu can find solar panels in a variety of sizes but for bigger systems you usually want to go with the 300 Watt panels so you don't have to get as many. In this case, we'd get 4 300 watt panels.
Challenges and things to keep in mind
Now that you know how big of a system you need, you need to know where and how to mount it. This can be tricky. Your roof is almost always the easiest option, however, some houses are tight in the trees- bad for the system because you want as little shade as possible - or have very complicated roof structures. If this is the case, you could consider a pole mount or even a ground mount.
No shade is very important. If any section of the solar panel is covered in shade it will reduce the output of the entire panel. This is because inside the panels, the systems are connected to together so slowing one down will prevent others from outputting to their maximum potential. It's like one car in traffic moving slowly and creating a bumper to bumper pile up for hundreds of meters behind it.
When installing your panels, you should have them at an angle that matches the latitude of your location (54 degrees for Terrace). FACING SOUTH. The further north you go the more you have to tilt them so they stay facing the sun.
This is because in the Northern hemisphere the sun stays below the apex of the horizon but will always be to your south, rising in the east and setting in the west. The earth is also tilted, and as far as I know, it is not flat meaning that if you laid the panels flat on the ground and looked at it from the sun, it would actually be pointing upwards and not directly at you. When the sunlight hits the panel directly it excites the electrons in the panel and creates a current to make power. If the sun isn't hitting it directly, it will be more likely to bounce off and won't make as much power. Think of a head-on car crash vs getting sideswiped. You're gonna feel a head-on way more.
Finally, try to have the panels close-ish to the battery bank. This isn't a huge deal, if you have a big field a couple hundred feet away and you are in the forest it is worth it to move the array to the field. But you do lose some power while transmitting the DC current over longer distances, so avoid it if possible.
Other equipment you will need include a charge controller, fuses or breakers, a racking system and an inverter.
The charge controller takes the energy from the solar panels and feeds it to the battery bank while making sure that the battery bank does not overcharge which would be detrimental to its longevity.
The fuses or breakers are used to make sure the system is safe and will not catch fire if there is a short somewhere.
The racking system is used to install the panels and is specifically designed to make life much easier.
The inverter will take the direct current (DC) power that is created by the panels and stored in the batteries and turn it into alternating current (AC) power that most conventional devices plug into. DC is what you find in your car like the cigarette plug and AC is your conventional household plug-in.
Thank you for reading all the way through, I hope I was able to answer some of your questions and open your eyes to the one of the many renewable options.
Please send any feedback, or reach out if there is another type of system you would like to hear about. I am going to try to get into video format aswell so if you are more of a visual learner, watch out for that!
As always, get out there, appreciate the world, and rep the step