﻿Unstable power grids, planned shutdown of electrical power, or even blackouts:
How can we prepare our homes and home automation systems against such
events? Today we will cover these topics with the eyes of an engineer, and I will show how I protect
our home against short and longer outages. In part one we protected our homes against
short outages. Today, we will protect them against longer outages. I will focus on my PV,
but also show how you could use a ordinary emergency generator
Grüezi YouTubers. Here is the guy with the Swiss accent. With a new
episode and fresh ideas around sensors and microcontrollers. Remember: If you subscribe,
you will always sit in the first row. According to my definition, long outages
last longer than a few minutes. For short outages we used a UPS.
Frequent viewers know that I built a 9kW peak PV on our roof and a Huawei SUN2000 inverter,
including a LUNA2000 10kWh battery, in the basement. When we ordered, the battery was
financially not attractive because of the low electricity prices. After February 24th, things
changed, and I did something I never thought I would do: I ordered a so-called backup box. Why?
As shown in video #438, a typical PV has to stop producing power when the grid is off. So,
your house is without power even if your battery is fully charged and the sun shines. This is
also the case with my SUN2000 inverter. Not what we want in these times, right?
To solve this problem, you can buy specialized inverters that automatically
disconnect the grid and start to supply the home in off-grid mode on all phases.
Or you buy a so-called “AC battery.” Often, you need a “backup box” that switches the
grid off and starts the off-grid mode of the battery. Both solutions are expensive
and sometimes even complicated because they include devices from different suppliers.
If you watched my last video, you know that I hate complicatedness. And like most of us,
I want to spend my money to create a quality of life. This is why I went with the inexpensive
and simple Huawei inverter. In addition to its regular “inverter” job on three phases,
it manages the battery to maximize our profit. And it offers off-grid supply for one phase.
It also needs a “backup box” to interrupt the grid and switch the inverter to off-grid.
As we will later see, this is the cheapest possibility I found to fulfill my wishes.
But, it needs some “hacking.” No problem, we are makers, right?
The backup box provides three main functions: 1- As soon as the grid is off, it interrupts
the connection from the grid to the inverter. The inverter automatically
switches off because it senses “no grid.” The backup box has two breakers in series,
to be sure. This is what utility companies want 2- As soon as this interruption is confirmed,
it starts the inverter in off-grid mode 3- And finally, it connects phase one of
the inverter to a “Backup Load” outlet. This outlet is intended
to supply all critical loads like the freezers
Function one and two are fine with me. Function three is not acceptable
because of the following reasons: 1. One freezer is built-in in the
kitchen. I would have to run a cable to the backup load outlet in the basement
2. As shown before, not only a cooled beer is essential. Also,
a working internet is a must. That would be the next cable from my lab to the backup load outlet
3. Our heating works with wood. But it needs electricity for the brain and the pump. A
third cable would be needed for this system 4. And finally, having light in all rooms,
and maybe even a working TV would get me many points from my wife. Which can
be exchanged in situations where I “forget” to do my household duties. With the single-phase outlet
of the SUN2000, this is impossible because consumers are equally distributed across all
three phases. And some high-power devices are connected to all three phases in parallel.
Major problems. But, as usual on this channel, we want more!
Fortunately, my son Julian knows a lot about electrical installations. When we sat together,
he proposed a simple solution: During off-grid operation, we short-circuit phases 2 and 3
to phase 1. Sounds like a horrible idea, right? Let me explain why it could work:
Most of the loads are only connected to one phase and ground. They do not care about which phase
they are connected to. Only our stove and the oven are connected to all three phases.
Is this a problem? Such utilities can be connected in star or delta configuration.
Star is similar to the single-phase constellation and will work for all
resistive loads. It will not work for old motors because they need a rotating field.
Delta is different. Because the loads are connected between the phases,
they will not be powered because all phases are connected and have the same potential. So
the loads should not be harmed. All in all: All loads except the
stove and the oven should work, and no device should be destroyed. Excellent!
Now we have to find the correct wiring diagram. This is relatively simple because,
during off-grid operation, the inverter is disconnected from the grid. In this state,
it can be compared to an emergency generator running on fuel. So we can install such an
automatic transfer switch to switch the load from the grid to the “emergency generator” and back.
The rest of the installation stays the same. This is the diagram: The transfer switch is
connected to the load, the grid, and the backup power outlet. Phase 1 of
the backup power outlet is connected to all three phases of the transfer switch.
We could manually switch the load from the grid to the backup power outlet. But we want more.
For an automatic failover, we connected source A to phase one of the grid and source B to the
backup-load outlet. Position A is chosen if source A or both sources are powered. Here, the load is
powered by the grid. Only if the grid is off and the inverter supplies backup power it switches
to position B, where the house gets the energy from the backup-load outlet. Exactly as planned.
The installation of the backup box was done by professionals because DIY is not allowed
in fuse boxes. Because it was already late, the electricians went away before the test. So it is
up to me. Here I can switch the grid entirely off. What do you think will happen? Did we
consider everything? Is the wiring correct? I am pretty confident with low voltages. But here, I am
nervous. Also, because I know that we will not get a new inverter for a long time if I destroy it.
But there is no other possibility, I have to take responsibility.
Test
What happened? I disconnect the grid with this switch. All lights went off because the house
had no power. Except the devices powered by the UPS, of course. Immediately afterward,
the backup box insulated the inverter and sent its off-grid start signal. The yellow LEDs
started to blink while it powered on. The backup power outlet got power, and with it, source B.
Now the automatic transfer switch disconnected the load from the grid and connected it to the
backup-load outlet. The lights went on, and the entire house had power again. The stove and the
oven survived, and the Eaton UPS protected the network and the PC during this short time! Cool.
So the battery backup works. But what about the solar panels? As we see here, they still worked
and supplied the home. And, other than Huawei communicates, the battery is charged with the
excess power from the roof. How cool is that? Compare it with other solutions offered to you!
You know now what questions you have to ask! And what was the price of the inverter,
the battery, and the backup box? - The 8kW inverter was 1267.-
- The 10kWh battery was 4501.- - And the backup box was 685.-
A total of 6003 Swiss francs or $6500 or Euros. Of course, this does not include the smaller
parts and the work. Not bad, I think. Keep in mind, I live in Switzerland, where everything
is expensive. The UPS was less than 150.-, BTW This project was not simple because it involved
unknowns and some “head-scratching.” - To protect my network and the PC
against short outages, I installed a UPS - For the longtime backup using my PV and
its battery, I had to buy a backup box and hire professionals to mount
it between the fuse box and the inverter - The SUN2000 inverter is only capable of
providing power on one phase, and the backup box only offers
an independent “backup-load outlet” - This is not what I wanted. I wanted
to power as much of the house as possible - With the help of my son, we found a simple
solution: A transfer switch switches the load between the grid and the backup box.
By connecting all three phases to the backup-load outlet, we can get most of the consumers in our
house powered from the inverter. Only the oven and the stove do not work because they use three
phases. But they are also not harmed. And I purchased a small gas cooker for emergencies
- The SUN2000 inverter can deliver up to 3.3k VA in off-grid mode.
The house without cooking and washing consumes less than 2kW. So plenty of power
- As the cherry on top of the cake, the SUN2000 inverter uses the available sun to power the
home and even charges the battery while in off-grid mode. More than Huawei promised.
For a price of $6500 for the parts alone I am happy with my solution. And now,
after my prototype is running, my neighbor will get the same.
One last thing: The Shelly sensors got a new place: Here, they measure
only the power going to the consumers. If you remember, the inverter has no way to measure
this value and has to calculate its value. These calculations sometimes contain artificial peaks.
With the new position of the Shelly current transfprmers, these peaks are gone.
This was all for today. As always, you find all the relevant links in the description.
I hope this video was useful or at least interesting for you. If true,
please consider supporting the channel to secure its future existence. Thank you! Bye