DIY Grid Tied Inverter (using UPS)





Introduction: DIY Grid Tied Inverter (using UPS)

About: I am an apprentice electrician, DIY'er and renewable energy hobbyist

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)

Step 4: Video Coming Soon



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    10 Discussions


    Question 27 days ago

    Hi Kieran. Am keen to hear about your new system when you're ready. I liked your last one.

    Hi Kieren. Is there any "blip" in mains power supply to any downstream devices during the switching process from grid to battery / UPS and visa versa ?

    1 more answer


    Not that i had noticed,The whole point of a ups is to have seamless transfer from battery to grid so not to cause disruption. To be honest, I am using a different kind of system now and will be doing an update post soon to show my changes :P

    Hi Kieren, In the situation described on the picture (system off grid) shouldn't the top-right relay be closed - providing 12V to UPS? Also, is your UPS working correctly being not able to charge battery? Thanks

    1 reply

    Yes the relay should be closed, as far as the ups it does require a little tinkering since it beeps when there is no power and beeps when there is no battery, the simple fix is to remove the buzzer for that, i did find that the relay switch on the 12v supply to the ups causes the ups to turn off, to fix that i put a blocking diode to across the relay, the ups then thinks its got a battery and it still cant charge the batteries, while the blocking diode fixs the problem the relay is still required due to the current it pulls :p hope this helps


    10 months ago

    This is not a grid tie system.

    Since its not feeding power back into mains. Its just a relay system that cuts mains when batteries have sufficient charge. I have the same at my office.

    That is awesome. I have been trying to come up with something like this to set up as a solar system.

    1 reply

    This is great and I will build one of these . Have 2 UPS put aside for the job . I just would like some clarification of terms used . What do you mean by non feedback ? Do you just mean no input to the grid from the ups ?

    What does the load controller do ? Does it simply cut the power going out if a set low voltage is used?

    1 reply

    great to see people like my idea. yes by non feedback i mean not feeding back into the grid from the ups, most grid tie inverters feed excess power back to the grid but in many cases there are laws that stop you from doing this.

    as far as the load controller (which you can find part of most cheap solar charge controllers) it allows you to set a voltage you want the load to come on at and a voltage to turn off your load, this stops you from discharging your batteries completely. in my case my load turns on at 13.1v and turns off at 11.5v this means my batteries have time to fully recharge from my solar panels