I’ve been looking into solar a bit lately. Prices are starting to go down a bit and the new technology from Tesla looks pretty amazing. However, in my spirit of DIY, I’ve been looking at how to do parts of it myself. I’ve also seen some interesting articles about whole home DIY UPS systems. Of course now anyone with some cash can go out and just buy a Tesla Powerwall, but wheres the fun in that.
The core of these systems is pretty basic, power source, charging, storage, and distribution. In most installations this is the solar panels, some form of converter (12V to 120V) for a grid-tie (net-metering) system or you could keep it at 12V and charge a battery system to be converted back to mains at a later point.
Some areas have net-metering, some don’t. Net-metering allows your power meter to run in either direction. You get billed for the power you use, but get paid for any power you put back int the system. If you have the option, get net-metering.
In areas without net-metering, you can still do grid-assist. So you are tied into the power grid and will pull power from it when you system can’t keep up, so a rainy day or at night. This may also be what you end up with if your solar system isn’t big enough for your needs.
This is how I will start the design of my system. A very under-rated, grid assist system, with some extra batteries for solar storage. Why? I’ve got a few reasons. My area currently doesn’t let people install solar on their roof. Cost.
My thoughts for version one of this project will include 1-2 solar panels. Solar panels range in price from around $250-$450 depending on the wattage of the panel. Not much I can save here. At peak this will roughly give me 0.5kWh.
The power will then be stored in some 12V batteries. To get there though we will need to go through some sort of power conditioner to keep both the batteries and panels happy (more to it but I’ll get to that in a later post). Power then goes from those batteries through and inverter to get back up to 120V and then distributed to whatever circuits I plan on powering (hint: won’t be many at this point).
That last part will be DIY and will take some engineering. A couple double pole double throw relays should do the trick. When we have solar power, we want to use it. When we have battery power, we want to use it. After those are exhausted, we will resort to the mains. That relay circuit will look something like this:
The circuit I have in mind for this project is for my network stack (To be discussed in a later post). The typically runs around 60Wh, which isn’t too bad. The whole thing sits behind an APC UPS which should protect it a bit when the system changes power sources.
More on this project coming soon.