Intro: DIY Grid Tied Inverter (using UPS)
Many people want to have solar panels to reduce their impact on the environment or reduce the cost of their electricity and there two ways about doing this, going fully off grid that requires a large bank off batteries and a decent inverter or subsidising your electricity with both grid and and renewable energy using grid tied inverters that feed your power back into the grid.
The problem is that going off grid is not always possible, designing a system that would power everything you want without issue would be very difficult and unreliable. and with grid tied inverters you would need a qualified electrician to install the inverter so it conforms to regulations when feeding back into the grid which is not very cost effective for everyone or ideal for your application.
so my solution is a small scale solar system with a "grid tied non feedback inverter" using uninterruptible power supply and basic components that are easily available. this allows you to produce and use your own electricity without feeding into the grid but still able to use the grid power when you run out.
Step 1: Converting the Ups
This is very straight forward, get your hands on a ups to convert, you could buy one new or get one for free from a company just throwing it out because the batteries needs replacing. since you want to run this off a more powerful battery bank long term remove the old battery from a ups most are 12v some are 24v deppending on your system depends on the type of ups you want i run both 12v and 24v systems ( story for another time) so i did not run into any problems.
Step 2: Creating a Switching System That Controls the Ups
The way my switch works is that it makes the ups work in an opposite way. it uses a relay to turn on and off the main power. the relay is connected to a load controller that provides power to a second relay (which is open) when the voltage off my battery bank reaches 11.5v the load controller cuts power to the second relay (closing the contacts) this allows power to the solid state relay and turns on 230v from the grid power and turns off the 12v from the bank (to stop the ups charging the bank). when the bank is recharged the load controller turns back on automatically turning off grid power resulting in less grid consumption.
Step 3: What You Will Need
an ssr (solid state relay) this requires a low voltage to turn on and off high voltage and current
2 12v relays (one to turn on and off the ssr and one to disconnect the 12v supply from the ups
wire, and some crimps and IEC cable and a load controller (most cheap charge controllers have this)