Solar panel on the balcony: using grid-tie inverter

Hi geektimes. The previous part was about testing the charge controller. During the day the battery is charging, in the evening or at night the accumulated charge can be used. That system can be considered complete, something fundamentally new to add to it is already difficult. Everything works, the current battery capacity of 12 hours is enough for evening lighting of the room with LED tape and charging various gadgets. Everything works, however there are drawbacks:

- Rechargeable batteries are a rather expensive and not very durable component.
- Accumulated energy has no place to go. For all the time I have never discharged the battery by more than 50%.
- On a sunny day in the morning by 9-10 am the battery is fully charged, respectively, the solar panels are idle for nothing.

As a result, it was the turn to test the next, more modern and widely used approach - the return of electricity directly to the power grid. The technology is very relevant, since eliminates all the above disadvantages - electricity is given to the home power grid and consumed by other devices.

How it works, details under the cut. Those interested can also watch a brief video version on youtube .

Grid tie inverter

The scheme of connecting the inverter to the mains is very simple:

In fact, the grid tie is not much different from the conventional 12-220V converter, although there are several significant differences:

- grid tie is synchronized with periods of mains voltage,
- grid tie automatically stops production if the network is turned off (for security reasons, for example, if the network is de-energized for repair),
- grid tie can use MPPT (maximum power point tracking) technology and find the maximum power output point for solar panels.

How do you end up using grid tie?
- Reduced electricity bills: home consumption from the urban network is reduced by an amount corresponding to the output of the inverter.
- Reduces the load on the urban grid.
- The system is easy to connect and operate.

There are 2 types of inverters on the market:

- “Standard” (conditionally), which are placed in the house, and they are energized from the panels. Power can vary from 250W to several kilowatts, the issue price from $ 60 to $ 6000.

- Microinverters. They are placed directly on the panel, so the mains voltage of 220V is obtained directly from the panel. The method is convenient because you do not need to pull the thick wires of low voltage, well, and the reliability of the system as a whole is higher.

The system will easily parallel and expand, like this:

In general, all this is interesting enough to test.


Before testing the "balcony" system, one problem emerged - they simply do not produce inverters for such a small scale. Inverter grid tie typical parameters are power from 250W and voltage of panels 22-65 or 45-90V. I have 2 parallel-connected solar panels of 50W were given 12-21V. Finally, after searching on ebay, almost the only model with a long name 500W MPPT Micro Grid Tie Inverter 10.5-28V was found. The word “micro” is obviously marketing here, because the possibility of mounting on the panel is not provided. Inverter looks like this (photo from the seller's page).

And actually, testing. It's simple, the inverter connects to the outlet through the wattmeter, which is convenient for evaluating the readings. Solar panels overlook the east side, and already at 9 am, in sunny weather, the output was 30W.

Everything is good, I only have time to rejoice "to which the equipment has reached," as I hear a very loud noise - the cooler turned on in the inverter. The Chinese have saved on the dimensions of the inverter, and the high-speed 40mm cooler gives such noise and whistling of air that it can be heard in the next room. Of course, ideally, the speed of the cooler would have to be adjusted depending on the temperature of the inverter, but in my case it did not work. Since I do not plan to use an inverter at full power of 500W, I just ordered another, less noisy cooler, which should be enough for 100-200W.

By the way, the inside of the inverter looks like this:

This is how its parts heat up during operation, the temperature of the components is up to 40 degrees:

This is basically a bit, on the other hand, and the power is only 1/10 of the maximum. It would be interesting to check its heating at full 500W, but there is no such possibility.

Another drawback manifested itself in the evening when the solar panels give little energy - the inverter tries to turn on, the LED lights up, but the voltage of the panels from the load sags and it turns off, then the process repeats again. It is unlikely that such on-off is useful for electronic components, on the other hand, there’s nothing really terrible here. Developers could provide a more intelligent way to turn off the inverter, on the other hand, this is the cheapest model on the market, and the work from 100W panels for a 500-watt inverter is not standard.

The result : judging by the wattmeter, 0.25 kWh * h was transmitted to the network entirely from a 100-watt panel on a sunny day. In the prices of electricity, anyone can recount themselves, as well as the payback period of the inverter (its price is about $ 80). The peak power recorded by the wattmeter is 65W, and the average power in the morning (panels are directed to the east) is 30-40W. (Theoretically, from a 100-watt panel you can get 80-90W of power, if you expand it in a more correct way and use thicker wires).

The next day was overcast with rain, and the inverter is quite expected, did not start at all. He tried to turn on in the morning every 5 seconds while starting up the cooler, and “explode” was heard throughout the room. In general, with such an inverter, an alarm clock is definitely not needed in the morning. Although this is not a problem with the inverter itself - firstly, the 500-watt inverter is simply not designed to use a 100-watt panel, and secondly, it is not intended to be installed in a room.
When the rain ended and the sky became relatively clear, the inverter started up, the power delivered to the network was about 12W.


Grid tie technology works, almost as expected, even with small balcony-sized panels. "Almost" because the power of the panels is not enough to operate the inverter at full capacity. At the same time, even in this form, the inverter works, giving power to the network already at 10-20 W output. For my balcony panels, the peak power recorded by the wattmeter was 65W, and the average in the morning and sunny time of the day was about 30-40W.

On a clear sunny day, 0.25KW * h was transmitted to the network from a 100-watt panel. By the way, is 0.25 kWh much or little? This is enough for 15 minutes of operation of the microwave, 30 minutes of operation of the computer, 24 hours of operation of the LED lamp, or 2-3 uses of a small electric kettle.

However, I cannot recommend the inverter shown above for a balcony installation - it is better to take a micro-inverter that does not contain coolers, and the power of the panels should be at least 200W at a voltage of 20-40V.

PS: With the return of electricity to the network there is another interesting question - what will happen if the total output of the panels is greater than the power consumption?

The answer is not as simple as it seems, there are 2 options.

If a conventional meter is installed, it simply counts the energy “by module”, so that the surplus energy goes to the house network to the neighbors, and the meter will sum it up as consumed - you also have to pay for the energy given to the neighbors (which of course is insulting).

Modern meters can count “export” and “import” of electricity, these items of indications are separately in the menu. Ideally, this should be taken into account when making payments and settlements. Alas, the ability to export energy to the network in the Russian Federation is not yet officially available. In Europe, of course, there is such an opportunity. From the CIS countries, electricity sales are available in Armenia, Ukraine, Kazakhstan and Belarus. Therefore, when installing a grid tie inverter, you must either calculate the power so that it is all consumed by home devices, or install an additional module (grid tie limiter) that prevents return to the network if it is more consumed. In Russia, the issue of exporting electricity was promised to be resolved in 2018, as it will be, is still unknown. Obviously, of all the problems, this is not the most urgent in the country, so a quick solution of the issue is not expected. So far, as Google suggests, in Russia there is only one house , the owner of which privately registered the possibility of exporting energy to the network, but this is rather the exception. In the case of a balcony, of course, there is no talk about selling surplus, but even 50-100 watts of energy may well be useful for compensating the work of a WiFi router or a mini-server, not to mention a refrigerator.

The next in line for testing is the battery of ionistors, which is planned to be used for the accumulation of electricity. What comes out of it, I do not know myself. It is also planned to post on the youtube video demonstrations of the system, but it takes more time than planned.

To be continued.


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