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Solar energy as part of the renewable energy sources is a good alternative to fossil fuels. The sun's energy reaches a daily average intensity of around 165 W/m² on the earth's surface. This can be used directly with photovoltaic systems. In Germany, the annual radiation output (GHI = Global Horizontal Irradiation) is about 1,056kWh/m² and in my adopted country of Thailand it is around 1,800kWh/m² per year. This data can be found in GLOBAL SOLAR ATLAS.
In addition to the fact that there is enough solar energy here in Thailand for use, the reliability of the local power supply (grid) leaves a lot to be desired. The electricity is often cut off for a few hours in heavy rain or when repair work is being carried out. Stupid because our water pump also needs electricity. The greatest possible independence from the grid would be a clear gain in convenience. There is (so far) no reimbursement system like in Germany here in Thailand. The roofing of the carport was the third argument. After all, it rains heavily here or in the blazing sun the (black) car roof reaches a temperature of over 80°C.
What are the key points for the new solar system:
An important parameter is the required power that the new solar system should provide. To estimate one should roughly know the consumption values of your own household. In PowerMeter I have already described how to record the power consumption. Here is an example of the daily consumption in our house:
In addition to the air conditioning, the main consumers are of course thecirculation pump of the pool. The total consumption of this sample day was 18.8kWh. Typically, our daily consumption is between 15kWh and 25kWh. Almost half (45%) of this amount is at night (6:00 a.m. to 6:00 p.m.). The current maximum power requirement is around 5kW. In the worst case, however, this can go up to over 10kW if all 4 air conditioning systems, the pool and dwell pump, washing machine, water heater, etc. are in operation at the same time. However, 14.5kW is the maximum anyway, since the house is only connected to the grid with single phase and maximum of 63A.
For electrical autonomy, the planned PV system should therefore be able to deliver around 25kWh and the battery at least 11.25kWh.
The calculated consumption results in monthly costs of:
15kWh...25kWh/day * 30 days * 0.19€/kWh = 86,-€...143,-€ per month (1kWh = 7Baht -> ~ 0.19€)
In fact, the costs are around €95. If the investment in the PV system should have amortized after 5…10 years, the system should not cost more than €5,700…€11,400. Let's see if that's too challenging…
In recent years, the efficiency of solar panels has increased from 15% to over 20%. The efficiency mainly depends on the cell design as well as on the cell layout. Here is an overview of the most common versions:
My choice, also in terms of price and availability, felt on Half-cut mono PERC MBB
, i.e. a monocrystaline module with Multi Bar Bus which, according to the manufacturer, achieves an efficiency of 21.2%.
Since the panels are also intended to serve as carport roof, the geometry and area (approx. 25m) are given.
I was able to achieve the best coverage with the VERTEX series from TRINA SOLAR. The panel measures 228.4cm x 109.6cm with an output power of 545W (product number: TSM-DE19-545W). Despite its size, it can be easily assembled by two people with a weight of 28.6 kg. In 2021 this version was available directly from the Thai wholesaler GODUNGFAIFAA for around €150.
The carport is oriented a little more to the west with a south azimuth of +15°. This value results in any hardly measurable losses in yield. The best angle of inclination for the panels depends on the location of the installation and depends on the southern high point of the sun. The data for this can be calculated with the help of Sun Earth Tools. Here the elevation for Dusseldorf (GER):
In Germany, the angle of inclination is between 30° and 40°. Here in Thailand, the midday sun is much more vertical and you get a maximum of 82° elevation. Incidentally, for the self-cleaning of the panels, you should take into account a tilt of at least 5°. Our carport roof has been given an incline of 6°, again due to the optics.
The substructure for the panels, i.e. the basis of the carport roof, must meet a number of conditions. The weight of the panels is still manageable with a total of almost 300kg.
With the help of the local steel construction company, we then came up with the following substructure:
The aluminum rails are mounted on the upper cross braces using the L-Feeds:
The panels should be mounted with a distance (in our case 2.8cm) to avoid mechanical stress caused by temperature fluctuations between the panels. There are still two challenges:
To seal the gaps, we need an UV-resistant EPDM sealing material. That turned out to be more difficult than expected. After a long research I found the company https://www.rinengsolar.com in Taiwan via Alibaba, who produced 30m for me. The EPDM Gasket looks like this in cross section:
and is simply clamped between the panels. There is also a suitable EPDM adhesive tape for sealing the crossing points.
Typically, the panels are attached to the aluminum rails with mid and end clamps.
However, in order not to come into conflict with the EPDM seal, I used the existing mounting holes on the underside of the ALU frame of the panels. To do this, I take the lower part of the standard end clamps, mount the fastening screw from below and push the part into the aluminum rail. The panel can then be mounted on the protruding screws and fixed with a self-locking nut (see also the upper picture with the aluminum rail).
Important: Don't forget the grounding clips during assembly. Anodized aluminum is not conductive on the surface, otherwise the necessary grounding will not succeed later.
Once assembled, the carport already looks very appealing:
After the panels have been mounted, it is now time for the electrical installation. To simplify the connection, the 5 panels of the second row are rotated by 180°. This means that the existing connection cables with plug/socket (MC4) can be directly serially connected. With the 10 panels we get a maximum power voltage VMPP of 31.4V * 10 = 314 V, which then travels to the inverter.
A first selection point is that we are not planning any power feedback to the grid. Therefore the inverter is an off-grid variant. That does not mean that it is not connected to the grid, but only for the direction of consumption.
My choice felt on the SPF5000ES from the Chinese company GROWATT. Among other things, it offers:
In Thailand I was able to get this variant for around €920.
There are two main battery technologies that can be used for storage:
I left out the classic lead-acid batteries because of the danger of oxyhydrogen and the higher maintenance effort. The same applies to the classic lithium-ion batteries. Overcharging can easily lead to dangerous overheating.
The lead-gel compound prevents outgassing and is extremely low-maintenance. This type of battery is significantly cheaper than the lithium-ion battery but has two disadvantages. For one, the weight is very high. A 12V/200Ah block weighs around 60kg. We need at least 8 blocks and we're already at almost half a ton (480kg). The second major disadvantage is that the lifespan depends very much on the depth of discharge. At only 50% discharge, the typical number of charge cycles doubles. By the way, this is around 1000 cycles. Or to put it another way: after 1000 cycles, the lead-gel battery still has 60% residual capacity. Typically, lead-gel batteries are only used with a maximum discharge of 50%.
The LiFePO4 batteries combine a number of advantages:
On the other hand, the price is almost twice as high (€512 for 4 modules with 3.2V/310Ah in 2021). However, the additional costs are compensated by the longer service life and higher usable capacity. Therefore, the choice felt on the LiFePO4 batteries. We installed 16 LiFePO4 modules with 3.2V/310Ah from CATL, all together results in a maximum storage capacity of 15.8KWh. This is well above the typical night-time consumption of 11.25KWh mentioned above and should therefore be sufficient. In terms of costs, this is the largest single item at €2.048, more expensive than the 10 solar panels. The source of supply was again ALIBABA.
The picture above already indicates that we also need a battery management system (BMS). The battery modules are built in series to get the nominal 51.2V for the inverter. However, the individual modules do not behave in exactly the same way during the charging and discharging process. This BMS is required to balance fluctuations and to keep each individual module within the permitted voltage range (2.5V - 3.65V). The Chinese company JKBMS has made a name for itself online. From their product portfolio, the B2A245-20P fitted quite well, although it is a bit oversized afterwards. The BMS has a Bluetooth interface and connects to a clear app on Android/Apple phones. And with approx. €165 procurement costs, it's still within reasonable limits.
Integrated in HomeAssistant, for example, parameters such as charging status, cell voltage and temperature can be clearly displayed.