A little over two years ago, I put together a small powerwall (battery pack) to store solar energy in our caravan. Read more about the process of putting it together here. We have been off-grid for this entire time, with free power, no stress and an immense sense of connection with the sun! So, here’s an update:
Has It Worked?
Short answer, yes, like a dream. The powerwall, made of 180 18650 cells divided into 3 packs of 60 to give a 12v pack, hasn’t been amended since it was put together. We have depended on it entirely for all of our power in both the caravan and, more recently, in the strawbale house. It has been through extreme temperatures in both winter and summer, but has never let us down or shown any sign of overheating.
What Exactly Is The Set Up?
We have three 100w panels in parallel delivering just upward of 20 amps of 12v power in full sun. This is delivered to the battery via a solar charge controller and more recently a voltage cut-off relay to increase the battery life (more below). The load is also delivered to the positive fuse board via the solar charge controller and the negative terminals are all soldered to a copper bar, before entering the solar charge controller to complete the circuit. Every 12v light, pump and socket has its own dedicated solid-core copper insulated wire and fuse.
The shorter months of the year have been a problem, we have barely scraped by. However this is less to do with the battery and more to do with a lack of panels. In a setup which is in constant use, your battery, in a super slimmed-down system, only really needs to get you through the dark hours, and, in theory, your array will harvest just enough for the bare basics even on a cloudy day. In reality, you have a bit of both, so, our battery is ample for 3 days of no power, but we need more panels for the darkest month or so of the year.
A second significant problem has been the solar charge controller that allows the cells to reach capacity before cutting off charge from the panels, this dramatically shortens the life of the pack as it fatigues and stresses the cells, therefore reducing the number of cycles it can do during its lifetime. This has since been amended by adding a simple cut-off device which allows you to decide how full you want the battery to be, in our case, we limit the battery to 12v, rather than the full 12.6v capacity. This will dramatically reduce stress on the cells and extend the usable life of the pack. Unfortunately, the original battery has been filled to capacity for over 2 years, so it will probably go out of service soon, however, the latest pack will benefit from this new addition.
Any Changes Planned For The Future?
I have recently built a second pack, in the same way, but using cells already tested and cycled on ebay. This was much quicker, but they are not 100% reliable, it is definitely worth testing the cell voltage at the very least, to see if some have discharged, I ordered 200 and found 5 useless cells which could have ruined an entire pack if not weeded out beforehand. The reduction in voltage mentioned above causes a commensurate loss of capacity, so the second pack will solve this problem.
Also, we have ordered 2 more panels, figuring that if we struggled with 3, then an extra 2 should be fine (although we now have two 12v Surflo pumps to run, so we’ll see if this hunch is right). But, another hurdle, 5 panels in parallel would deliver around 35 amps in full sun, this is a lot, and would require fat wires and a new solar controller as ours is only rated up to 20 amps. Therefore, the two new panels will be wired up to the old pack (which is being put into retirement) exclusively, meaning we can effectively switch between two identical, independent systems, one with 3 panels, one with just 2. This will avoid the need for fat copper cabling, a hunt for a new solar controller (very difficult for a 12.6v 3S Li-ion cell, believe me!) and mean we can make changes / service one without interrupting our supply.
The batteries are currently housed inside the house, and seeing as we have taken every precaution we can think of (big wires, independent fuses, fused cells in the packs, exhaustive testing, low stress on the packs), it seems sensible to house them outside. So we plan to build a small hempcrete ‘battery house’ about 1.5 metres away from the external wall with wiring coming in under the house. It will be chilly, and damp, but hopefully the hempcrete will control humidity and the cold doesn’t affect them that much anyway, also, the wire runs will be a little longer, but certainly not long enough to cause resistance or draw problems on our ‘thirsty’ items (pumps and fridge). Above all, peace of mind is what we are after!
Being off-grid and completely power-independent is immensely rewarding. Whilst bills are a part of life for everyone we know, they don’t even cross our minds. Our behaviour has adapted to our reality, we simply don’t feel like we sacrifice anything and it’s hard to work out why everybody isn’t doing this. It is a little complicated, but perfectly achievable by a complete novice (like me), just keep it simple, keep it small and take every precaution to can think of.