One of my primary plans for the tiny house is to be completely off grid. I want to be able to park pretty much anywhere and not need to connect to anything or rely on another property for facilities. Ideally I’d like to be out in the country, away from everywhere and so to this end I’ve been designing the systems within the house to give me complete autonomy. I’ll cover the various systems and their designs one by one and today I’ll go over the power setup, as I have most of that already.
I picked up a couple of Kyocera photovoltaic panels from ebay. They’re 85w each. One of them is damaged, the glass is cracked and I need to fix this before I can use that panel outdoors. The glass is tempered, so when it breaks it’s like a car windscreen and just shatters. It’s also bonded to the cells underneath so not much comes out, just leaving it with a crazed appearance. However, this is enough to let air through to the cells and over time they’ll degrade because of it. Some online research suggests that automotive clearcoat, the stuff that’s sprayed over car paint to protect it, is good for sealing it, so I’ll need to get that done as soon as I can. I may be able to do that myself as I have a new compressor and spray gun to play with, amongst other air tools. More on that later.
Given that I effectively got the broken panel for free, I don’t mind if it doesn’t make quite as much power as the good one, anything extra is a bonus. A quick check with a meter when it arrived showed it to be putting out as many volts as the good panel but I’ll have to wait until there’s a proper load on it before I’ll know just how good it is. Fingers crossed.
Of course if you have panels you need batteries, and here I was lucky again as someone on an alternative energy forum I take part in was selling some. Most batteries that people use for small off-grid setups are either 12v deep cycle batteries or a number of 6v golf cart batteries. These are built to withstand repeated charging and discharging, which ‘normal’ car batteries aren’t. You’ll kill a car battery pretty quickly if you do that. Even these ‘deep cycle’ batteries have a limited lifespan, usually 2-5 years, depending on how heavily they’re used. For more serious battery backup setups, you want batteries that are designed for much longer life and much heavier discharge cycles. The problem with these is that they’re big, heavy and very expensive. Good options for second hand stuff is from fork lift trucks and large power backup systems in places such as telephone exchanges or power stations. I even know of people who’ve got hold of battery banks from decommissioned submarines, which have tens of years of life in them still. Not very practical for a tiny house that moves places.
What I’ve managed to get hold of is a set of second hand batteries from a power station backup. These are about 10 years old and absolutely immaculate, probably have a good 20 years left in them as long as they’re looked after properly. They’re about 25kg each, 2 volts per cell and 110ah. I have 14 of them which is enough to make up a 12v 220ah set with a couple of spares. Given that they weigh a little over quarter of a tonne, I’ll not be towing them in the house, they’ll have to go separately and, when parked, will live in a box on the back of the house with a bit of extra support under them. I’ll wire the house up using marine grade equipment which should ensure decent quality and levels of safety. I’ll cover the wiring setup in a later post when I’ve settled on exactly how I’m going to do that. I’ll get some photos up of the panels and batteries later.