The nickel iron (NiFe) batteries used in our Iron Sun Boxes are incredibly tough and durable compared to other batteries, but how you use them is what matters. If you try to use nickel iron batteries to power heavy loads, like refrigerators, motors, and inverters, you will need a very large battery set, and that will be expensive. If you shift your big loads to daylight drive systems (like the Sundanzer refrigerator), then you can power the rest of your life with modest energy sources at a modest cost.
In the battery world, lead-acid batteries are the cheapest. Lithium batteries are lightweight. But both of those batteries will degrade quickly if drained deeply. Over time, this essentially renders the “amp-hour” rating of the batteries meaningless. For any battery other than nickel iron, they will perform as rated the day you buy them, but not much longer.
The power source in a nickel iron battery is fine powder inside perforated sheet metal pockets. Electrochemical reactions occur as the electrolyte circulates into and out of these pockets. This happens at a modest rate. Have you ever had the experience of walking along with a flashlight as it runs out of power? The flashlight will get a bit dim, and then suddenly, it goes out completely. That experience of “going over a cliff” does not happen with nickel iron batteries, as long as you maintain a modest draw rate. Let’s say you get our Iron Sun Cabin Kit. It’s been very cloudy all day, you have been running your light bulbs, and charged up your tablet, and then you notice the voltage dropping. At that point, you turn off a load, and watch the voltage. Let’s say you drop back to 2 bulbs and notice the voltage stabilizing. Once you get within the optimum draw rate, the voltage will likely start increasing, even with no charge coming in! The optimum draw rate is the rate at which the electrolyte can move into and out of the fine perforations in the plates inside the battery. At this optimum rate (which is lower than the full power rate), a nickel iron battery can sustain output for a very, very long time. There is no “cliff.” For living off-grid, the fact that there is no cliff, no point where our batteries just give up, is a lifesaver.
On a graph of battery output over time, at a high draw rate, NiFe batteries will perform like other batteries, and power output will decline quickly. If you drop to the optimum draw rate, then every other battery goes over a cliff while the nickel irons keep performing for a long, long time. This is true whether the time scale is hours (daily use) or decades. At low draw rates, NiFes are amazingly tough. When partnered with super-efficient modern electronics like smart phones and LEDs, they are almost miraculous in performance.
All of that said, nickel iron batteries are not really miracles, they are machines, and our smallest kits are very small. Our Cabin Kit is the absolute cheapest system we could build that will provide decent lighting services for low income people living involuntarily off the grid. (Link to LEF’s climate justice campaign.) For most Americans, this kit is too small for anything other than emergency back-up. It will light 4 bulbs (in the 3 – 5 watt range) for a few hours in the evening, most of the time, and charge phones and small devices. If the voltage falls below 10.5, you can reduce loads on the system, and the system will not turn off.
Our Small House Kit is much stronger. Particularly if you are powering a computer, the Small House Kit will work better than the Cabin Kit. Under extended cloudy conditions or if users leave lights on all the time, any of these kits will lose power.
You get the most power for your dollar with the Homestead Kit. Even our Homestead Kit is “small” compared to the kits sold by other off-grid suppliers, but we have lived with 10 people or more using our Homestead Kit daily, winter and summer, and you just don’t need a bigger kit if you have daylight drive systems for heavy loads. Learn more about DC Microgrids and the science behind our Iron Sun boxes.
A big advantage of our systems is that they are tenacious, but they teach people to conserve. You will need to turn the lights off when not in use, and particularly with the smaller systems, pay attention to the timing of your energy use. We think it’s a small price to pay for our children to have a future on this sacred Earth.
Please e-mail us at firstname.lastname@example.org if you’re still not sure which size Iron Sun is right for you. We wish you many years of grid free, pollution free, power bill free living!