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Solar System


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.

 GHI Worldwide

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:

  • the PV panels should span the carport as best as possible and be rainwater-proof
  • A battery unit is required to bridge the night and cover power supply in the event of grid failures
  • the inverter can be off-grid (without feedback) and should automatically switch between the energy sources (solar, battery, grid) as needed.
  • the solution should support DIY, to be able to be integrated in Home Assistant and remain affordable.


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:

Daily Consumption (ex.)

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…

Solar Panels

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.

Carport with frame and solar panels

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.

  • The stability and load capacity should be dimensioned sufficiently. Here in Thailand we don't have to deal with snow loads (75kg/m² or 125kg/m²) but with gusty wind speeds of up to 100km/h. Data on wind strength can be found in Global Wind Atlas.
  • The panels are mounted on aluminum rails so that assembly and alignment (we want the roof to be waterproof) is easy. The substructure must support the easy installation of these rails.
  • The whole thing should also look visually appealing enough. Ugly examples can be found enough here on the island of Koh Samui.

With the help of the local steel construction company, we then came up with the following substructure:

  • Eight galvanized post stands 10x10cm (2mm wall thickness) with concrete anchoring on the existing outside wall
  • Galvanized steel beams 10x10cm (2mm wall thickness) for lower cross braces
  • Galvanized steel beams 5x10cm (2mm wall thickness) for upper cross braces

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 in Taiwan via Alibaba, who produced 30m for me. The EPDM Gasket looks like this in cross section:

EPDM gasket

and is simply clamped between the panels. There is also a suitable EPDM adhesive tape for sealing the crossing points.

Mounting without brackets

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:

Electrical topic

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:

  • Integrated MPPT charge controller (MPPT = Maximum Power Point Tracking → more efficient)
  • Maximum PV input voltage up to 450VDC
  • Configurable grid or solar priority
  • Wifi remote monitoring as well as integrability in Home Assistant
  • Compatible with lithium batteries
  • Maximum 5KW power
  • Scalability up to 30kW in parallel operation

System overview

In Thailand I was able to get this variant for around €920.


There are two main battery technologies that can be used for storage:

  1. Lead gel battery (maintenance free)
  2. Lithium-ion battery (LiFePO4)

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.

Lead gel battery

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%.

Lithium Ion Battery (LiFePO4)

The LiFePO4 batteries combine a number of advantages:

  1. significantly lighter (at 12.8V/310Ah with four blocks only 22kg)
  2. High number of charging cycles (typ. 4000)
  3. high usable capacity (up to approx. 95% discharge)
  4. high discharge currents and fast charging (1C).

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.

Ready LiFePO4> battery block


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.


After we have selected all the important components, it is now about to wire. To protect the system and the individual components, we still need some safety equipment and the right choice of cables.

Our finished connection cabinet looks like this from the inside:

Solar breaker board

It might seem overwhelming at first, but let's go through it in order:

Solar Panels

The solar panel voltage (typically 314V DC) is first routed via a 32A DC fuse. Any overvoltages are then counteracted by overvoltage protection. The panel voltage then goes on to the inverter via a 63A DC circuit breaker.


Since the input voltage from the grid can also have overvoltages (here in Thailand the supply cables are mostly above ground), the inverter is also protected with overvoltage protection at the input. In between is again a 32A AC circuit breaker.


The output of the inverter on the way to the house supply goes through a reversible over/undervoltage protection and another 32A AC circuit breaker.


There is a 100A DC circuit breaker between the battery block/BMS and the inverter.

Here is the entire system overview with the associated cable thicknesses. The 2AWG battery cable and the 12AWG solar panel cable are flexible variants.

Solar system overview

:!: Should the inverter have a total failure, you would quickly be left in the dark. It is therefore very clever if you also install a transfer switch in the house supply, which switches the house completely back to the grid if necessary.

Automatic transfer switch

MC4 connector and cable lugs

Since we are dealing with considerable voltages and currents here, we have to take a closer look at the different types of connections. Let's start with the panels. The solar panels are fitted with MC4 plugs and sockets as standard. The mounted cables of the panels are so long that they can be connected directly to the neighboring module. We only have to lend a hand for the series connection at the end and the connection to the inverter. It is best to buy a set with MC4 plugs/sockets, crimping tool (2.5/4/6mm²) and MC4 keys for little money (12.00 €).

MC4 set

The assembly is described in detail on the Internet (e.g. here ) and is very easy.

Another important connector is the good old tubular cable lug (ring terminal), which we need in different diameters and for different cable thicknesses.

The battery blocks are connected to each other with metal rails and nuts, which are included in the scope of delivery. The battery connection on my CATL LiFePo4 has an M6 thread. To connect the 16 balancer cables of the BMS to each cell we need a cable lug 18AWG(1mm²) to M6. For the connection between the two battery rows, the BMS, the 100A fuse and the inverter it is a 2AWG(35mm²) on M6 and M8. The right crimping tool for the 18AWG cable is again inexpensive everywhere. For the 2AWG you need a hydraulically supported variant to apply the mandatory force:

Crimp tool 4-70mm2

You could even get it here in Thailand in a well-stocked DIY store for around €40.

The remaining cable lugs depend on the screw connection used in the fuse box. I used 8AWG(10mm²) on M6.

Image Cable Diameter Hole Diameter
18AWG(1mm²) M6
8AWG(10mm²) M6
2AWG(35mm²) M6
2AWG(35mm²) M8


Before we can go into operation, we still have to setup the BMS and the inverter.


The basic setting can be easily made via the app and at first the battery type LiFePo4 is selected. The other parameters should then be adjusted to the characteristics of the battery. For me, the most important parameters look like this:

Balance starting voltage               3.00 V
Balance trigger voltage                0.01 V
Cell count                             16
Cell voltage overvoltage protection    3.60 V
Cell voltage overvoltage recovery      3.45 V
Cell voltage undervoltage protection   2.60 V
Cell voltage undervoltage recovery.    3.00 V
Max balance current                    2.00 A
Max charge current                     62.0 A
Max discharge current                  100 A
Power off voltage                      2.50 V
Total battery capacity                 310Ah


The inverter can be set directly at the device via the control panel or via the Growatt server. I have listed the most important parameters below:

Program	Setting Option	      Description
1	SBU (SBU priority).   Output source priority: To configure load power source priority
2	62A	              Maximum charging current: set total charging current for solar and utility chargers. 
3	APL (Appliance)	      AC input voltage range
4	DIS (disabled)	      Power saving mode enable/disable
5	US2 (user-defined 2)  Battery type
6	DIS (disabled)	      Auto restart when overload occurs
7	DIS (disabled)	      Auto restart when over temperature occurs
8	230V	              Output voltage
9	50Hz	              Output frequency
10	16	              Number of series batteries connected
11	30A	              Maximum utility charging current
12	48.0V (3.0V x 16).    Setting voltage point back to utility source when selecting “SBU priority” or “Solar first” in program 01
13	54.4V (3.4V x 16).    Setting voltage point back to battery mode when selecting “SBU priority” or “Solar first” in program 01
14	CSO (solar first).    Charger source priority: To configure charger source priority
15	ON	              Alarm control
16	ON	              Backlight control
17	ON	              Beeps while primary source is interrupted
18	ENA (enabled)	      Overload bypass
19	56.8V (3.55V x 16).   C.V. charging voltage.
20	54.0V (3.375V x 16)   Floating charging voltage. If self-defined is selected in program 5, this program can be set up
21	44.0V	              Low DC cut-off voltage.

Integration in Home Assistant

As mentioned above, there is a handy app for the BMS for live data and settings. It runs via Bluetooth on iOS and Android. But in order to access it via Home Assistant, we needed a Bluetooth gateway.

:!: Warning: It must support Bluetooth 4.2 to be able to use frame lengths of more than 20 bytes. The 300 bytes of live data are sent in three notification frames.

A simple solution can again be achieved with an ESP32 module and ESPHome. You can find the software description here. My setup can be found in the attachment for reference.


The GROWATT Inverter can be integrated directly into Home Assistant via Integration.

Operation and Costs

The plant has been in operation since March 2022 and generates between 430KW and 500KW per month depending on the weather. The best day so far was in March with 24KW and the worst with 1.2KW in November. However, October and November are also the months with the most precipitation (see rain sensor).

Solar production 2022

The specified values are not the really achievable ones, since the inverter regulates down when the batteries are full and the house demand is below the current production capacity. What should he do with the energy if nobody can take it. We have observed this effect a few times. Nevertheless, the solar panels are only completely self-sufficient in sunny weather. On average, we draw additional energy of approx. 100..200KW/month from the grid because our AirBnB guests keep the air conditioning in the guest room running almost continuously, which means that consumption is higher than forecasted above.

With an approximate average of 450KW/month, this results in an annual production output of 5,400KW. One kilowatt hour costs us 7 baht/19 ct (1€ = ~37 baht), so we save approx. €1,021 (€85 per month). The entire solar system without the service line and roof substructure cost us 206,000 Bath, which is €5,567**. The work output was my own that kept me meaningfully engaged during the pandemic, so I'm not counting it. I don't count the steel substructure for the carport either, since it was necessary anyway to cover our fleet (motor scooters and car). Incidentally, the local offers for a comparable system were more than twice as high (but then with wages).

From today's point of view, the system will pay for itself after about 5 ½ years, assuming there are no maintenance or repair costs. The goal envisaged above has thus been easily achieved. The first thing to do is to replace the batteries. With around 4000 cycles, that would be after 10 years and the solar panels would be down to 85% performance after 25 years. The future will show how and whether the values will really be achieved.

Not to be forgotten, however, is the increase in comfort in the event of a grid failure when the neighbors have to fiddle with torches and candles, as well as the really good feeling of using solar energy when you turn on the air conditioning…

Finally, the charging and discharging chart over three days. The batteries are charged from around 7:00 a.m. to around 6:00 p.m., after which the discharge begins. If the charge falls well below 20%, the grid will charge. Shown by the linear increase on the first and last night.

Solar battery charge/discharge


If you want to support my work, you can donate me a cappuccino or something like this…

en/tech/solarvilla.txt · Last modified: 2024/06/27 01:27 by bullar