Your big off-grid solar questions, illuminated.
Ever feel like harnessing the sun's energy is more magic than it is science? Our friend Garret Town of AM Solar is here to demystify the process with our "Solar Sunday" series to get you connected so you can start your off-grid adventures. In this article, he'll cover a series of frequently asked questions from how many batteries you need, basics for how to connect them, and if it's worth your time to clean your panels for a better charge. If you are new to solar energy or already warmed up to it, we hope this article sheds light on some of your questions!
Garret Towne has worked in the solar industry since 2009 starting with a company that developed dual axis solar trackers. After solar panel prices plummeted, making the ROI on trackers less attractive, Garret became a Senior Engineer and Technical Sales Manager for a solar panel distributor. Garret joined AM Solar in 2015 and became President in 2016. As President, Garret has grown AM Solar from 11 to 23 employees. Garret has a BS in Electrical Engineering and MBA from Oregon State University. When not at work, Garret enjoys studying foreign languages (Spanish, Portuguese & German), competitive archery, beekeeping, and raising chickens on his mini farm with his wife and son. His greatest joy in life comes from writing fake bios for his employees that get published on his website.
How many panels do I need?
It depends on the wattage. I wouldn’t recommend less than 400W for a simple DC fridge, LED lights, and fans. If you have a residential refrigerator, get at least 600W. If you want to run an air conditioner or minisplit, get as much solar as you can afford/fit.
How many batteries do I need?
If you just want lights and fans, you can get away with 200Ah of AGM. If you plan on using a microwave or blender, you’ll need at least 300Ah of AGM, or 200Ah of lithium. If you want to run an air conditioner or minisplit, get at least 300Ah of lithium, but plan to add-on.
What's the difference between AGM and lithium batteries?
This page goes into a lot of detail on that topic: https://amsolar.com/diy-rv-solar-instructions/edbatteries/
The main factors that I consider:
-Lithium batteries don’t need to be topped off weekly like lead-acid batteries and give you a little more flexibility in often you charge.
-Lithium batteries might twice as long as AGM batteries.
-Lithium batteries give you about 4x usable energy per weight and 2x per volume compared to AGM batteries.
-Lithium costs about 50% more than AGM.
Does tilting my panels towards the sun give me more power?
Yes, but maybe only 15%, and depends on the time of year. I would only consider tilting if you plan on parking for a week or more.
Should I clean my panels?
If you have a leaf or bird mess on a panel, the production of the panel will go down to about 0W. You’ll definitely want to clean anything like that. As for dust, it probably isn’t worth the effort.
If I have a 300-watt panel why am I only getting 175-250 watts when looking at my Victron Energy app?
It is unlikely that you will ever get the full rated output of your panels. That rating is meant to guide circuit protection decisions for system designers, not advertise real-world energy production. You will get 300W of power from a 300W panel, when you have 1000W per square meter solar irradiance at 25 degrees C, with no line losses. This isn’t practical for someone living in North America with flat panels, looking through a lot of atmosphere on top of a hot skoolie roof.
If my panels are a little in the sun am I getting the full charge?
You actually get a lot of solar production from a bright blue sky. You don’t need the full sun to generate watts. On the other hand, if you have shade close to the panel, it will dramatically reduce the output. I like to imagine that you have a fisheye lens on the panel looking upwards. How much of your view is obscured by shade? How much is bright blue sky and the sun? The ratio of shade to sun is roughly the percentage of rated output you will get. But, if there is a part of the panel that has zero light on it, that part will bring down the entire panel.
What are the standards you follow for fuse and cable connections?
Without going too deep, here are some standards we follow:
12V battery system, all parallel solar arrays:
Up to 200W of solar: 15A charge controller, 8ga cable, 20A fuse
Up to 300W of solar: 20A charge controller, 8ga cable, 25A fuse
Up to 450W of solar: 30A charge controller, 6ga cable 40A breaker
Up to 700W of solar: 50A charge controller, 4ga cable, 60A breaker
Up to 900W of solar: 70A charge controller, 2ga cable, 80A breaker
Up to 1200W of solar: 85A charge controller, 2ga cable, 100A breaker
Up to 1600W of solar: 100A charge controller, 2ga cable, 120A breaker
12V Inverter systems:
Up to 1200W, 2ga cable <10’, 150A Class T-Fuse
Up to 2000W, 2/0 cable <10’, 300A Class T-Fuse
Up to 3000W, 4/0 cable <10’, 400A Class T-Fuse
We are using Nissan Leaf or Tesla batteries. Can you answer our questions?
These systems are cool, but as a business with liability insurance and long term customer support, we can’t help with Nissan Leaf or Tesla-based battery systems. This is because they are typically used batteries. I don’t recommend this approach for the novice.
How do you know that it's electricity your bus is harnessing and not magic? (It's clearly magic.)
It is magic. You should see my old Electrical Engineering notebooks from when I was a student at Oregon State University. 500 years ago, I would have definitely been burned at the stake. That’s why this information is so hard to convey to the uninitiated.
Contact Garret and his team at AM Solar here.
Thank you to Stu the Bus for use of the image of their tilted solar panels. Watch a full tour of their bus here.
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