I’ve got the power
Though technically it’s on loan from the sun.
My wife and I used to live in a small cabin on a farm at the edge of the woods a little more than a quarter of a mile from the road. We had a dedicated power line running from the street to the house and lots of trees along the road and driveway.
More than once while we were living there, large trees came down and knocked out our power. When this happened along the main road it usually didn’t take that long for a crew to come out and fix it. But when the power was knocked out by a tree in the driveway after a particularly large storm, it was 9 days before we had power again.
As someone who works from home and depends on reliable internet and electricity to earn a living the idea of 9 days mandatory vacation didn’t interest me too much. Fortunately the tin foil hat I have a tendency to wear around paid off, because we were able to power our home for the entire 9 days thanks to the small off-grid power setup I built shortly after we moved in. It has come in handy so many times over the years I’ve decided to finally write a blog post about it.
Power System Basics
A basic off grid setup includes the following critical pieces:
- A power input: PV Panel (solar panel), wind turbine, hydro turbine, or even the current grid I suppose
- Charge controller
- Battery bank
- Power inverter
The input allows you to charge your battery bank. I use a 130w PV panel which can be obtained for a couple hundred bucks online. But you could easily use a wind turbine, hydro turbine, or even your existing grid power, essentially turning the system into a giant UPS.
The charge controller insures that the battery bank is properly charged overtime. A quality charge controller will allow for different battery bank configurations. I have a TriStar TS-60 charge controller which can also be obtained for about a hundred bucks online.
The battery bank may surprise you, as it will likely be the most expensive part of this setup. When selecting deep cycle batteries for the battery bank you want to focus on the number of amp hours the battery provides. I use old Everstart Marine Maxx batteries which provide 125 amp hours. Each of these batteries brand new can be as much as $100. However, most batteries come with a two year warranty and a quality charge controller will ensure that your batteries continue to serve you long into the future. My bank of 6 batteries is over 5 years old.
Connecting the batteries in parallel gives you a capacity equal to the sum of the amp hours. An amp hour is essentially how many hours 1 amp could be drawn from the battery. As you remember from physics class Watts = Amps x Volts.
In ‘Merica we have 110 volts running through the walls. So an 80 watt laptop charger draws approximately .7 amps. Meaning a single battery from my bank could charge a laptop for more than 125 hours, or approximately 5 days.
There are lots of power inverters available. Power inverters do the important job of converting the stored DC electricity from the batteries into “normal” AC electricity that our everyday electronics can use. Some electronics, like stereos, really benefit from what’s known as “full sine wave” electricity. I don’t have a full sine wave inverter yet as I don’t have a major need for it. None of what I’m powering seems to mind the modified sine wave.
I’m using a very basic 1200w constant 2400w peak inverter that you might install in a car. Modified sine wave inverters can be had for well under a hundred dollars. The size of the inverter you’ll need will depend on your load.
Sizing your system
Figure out all the items in your home or your office that you’d like to power. Add the wattages together. This is the minimum inverter size you’ll need. Use the calculations glossed over in the battery section to figure out how many amps you’ll be drawing at any given time. Multiply that out over how long you’d like to power said load to figure out how much battery capacity you’ll need.
Ideally you want to ensure that your power input has the capacity to charge your battery bank up to full after each day of use. If you only intend to use this as a backup emergency power store this step isn’t a big deal you can simply run a power defecit and re-up the charge later.
My wife and I are into camping and getting out into remote areas so the idea of having a solar based system really appealed to us; as it’s not crazy to think at some point in the future we’d have a recreational property without grid access.
If you want to be able to power just your computer and internet routing equipment in a pinch you could probably do so with one or two deep cycle batteries, a $50 battery charger, and a cheap inverter. No need for a solar panel at all. Just plug the battery charger into the wall when you get power again.
Your mileage may vary
During the above mentioned 9 day outage we were able to power:
- A mid-sized chest freezer (protip: ice blocks in a large cooler are just as good as a fridge)
- A modem and router
- 3 laptops
- Two cell phones and other small electronics
Suffice it to say that the size of the battery bank has to match the intended load for this project to make any sense at all. Many solar power websites implement solar calculators which have a tendency to make it appear that without spending tens of thousands of dollars and tying into the grid to sell excess power there’s no benefit to setting up a solar power bank.
This simply isn’t true. I will say that it’s definitely something to look at as a fun project and not a way to “save money on your electric bill”. Electricity is CHEAP, and this project won’t pay for itself on the cost of the electricity it provides, but when the power goes out the value of the project definitely shines through.