We always knew we wanted to be off-grid, even though we had mains power to the front of the block. We decided to install a solar system on the shed, in part because it would make spending the odd weekend camping out easier, but also to see how it worked and what we could learn. The design brief was simple – cheap, something we could install ourselves, just enough to run a few lights, maybe run a very small TV to watch a footy game, maybe charge the camp water heater. In summer, we might be at the block for a week or two, but in winter we would never be there for more than two nights.
The first thing we learned was that most people who sold solar systems back then did not understand how they worked, or how to design them properly. All the companies that offered off-grid solutions came up with $25k – $40k designs, suitable for running a holiday home. Despite explaining the electrical load requirement, they didn’t understand how to size the system to match. Unfortunately, I didn’t either! I just knew that what they were proposing was not what I needed. And the internet wasn’t a much of a thing back then.
Understand your requirements (load list) and ensure your system is designed for them.
The key piece of information I was missing, which is obvious and common knowledge now, is that batteries have a Depth of Discharge (DoD) specification. Discharge too much and you seriously shorten their life and reduce their capacity. The lead acid batteries we were going to use had a DoD of 20%. Once I found this out, I could pick the required battery capacity. From the load list, I knew the solar panel size I needed.
After a fruitless search for an “off-grid” supplier, I called into a pool shop in Brighton (unfortunately not there anymore) who listed solar on their shop front. They were fantastic – they understood how to design a system from first principles, supplied all the equipment and even drew a single line diagram (electrical wiring diagram) for me so that I could wire it up correctly. Fully fused, sine wave inverter, 1 off solar panel, 2 off deep cycle truck batteries, and 12 volt lights, including outside flood light and bedside light. Total cost $5k. $20k cheaper than the “experts” had designed.
Don’t accept a design without understanding what it can and can’t do. You might waste a lot of money!
While things have certainly improved, we’ve found suppliers who still struggle to size appropriately. More on this later as we approach selecting our new system.
So how did it work? PERFECTLY.
It did everything that we needed it to do. In summer, when we might spend a week on the block back then, we never ran out of power. The batteries were typically fully charged by about 10:00 in the morning. Power usage was never an issue, and we didn’t have to think about what we used.
In winter, the story was a little different. We needed to be careful. We tended to use much more power – lights on much earlier, more time in the shed. We could watch the football, but the TV was limited to about 2 hours. We did run out of power a couple of times when we stayed for two nights, but only when we did more than we had said we would on the load list.
It really brought home to us the difference between summer and winter in both power generation and usage. I know its obvious, but its much more visceral when you’re living it.
Design your solar system for winter.
We’ve replaced the batteries twice over the years, and they’re well on their way out now. Having lived interstate for over 10 years, they have not been maintained. I’m sure we would have had better performance if we had maintained them. The new versions of lead acid are much more forgiving on this front….
The shed is just for storage now, but we’ll buy a new battery soon coz its nice to have the lights.