Professional Off-Grid Power supply for microwave Radio Stations

Fuel cell as the cheapest and cleanest off-grid power supply!

Today, off-grid electricity is usually understood to mean photovoltaic, wind
and diesel generators or, under extreme operating conditions, thermoelectric generators (TEG). In this regard, photovoltaic and wind turbines are the most cost-effective power generators, as they require no additional fuel and little maintenance during operation. However, their major shortcoming in many cases is the volatility of solar radiation and wind supply, which necessitates the use of additional generators. In addition, depending on the available solar energy of the area (Arizona and northern Canada have dramatically different levels of solar irradiance), power loads greater than 100 W can require a significant footprint for solar panel installation, not to mention snow and dust cover which can be an additional challenge in some areas. Larger power requirements are therefore often met by diesel generators. These, in turn, are inexpensive to purchase but require frequent maintenance due to oil and filter changes and regular refueling. Generators are often oversized for the load demand, resulting in an "underloaded" operating condition that can stress the generator over the long term and reduce its efficiency to less than 20%. Legally mandated emission limits will make it more difficult to operate these units in the future. Thermoelectric generators, another alternative with an efficiency of about 3% and the associated high emissions, are only used in special applications and especially at particularly low ambient temperatures. Generators are often oversized for the load requirement, resulting in an "underloaded" operating condition that can stress the generator over the long term and reduce its efficiency to less than 20%. Legally mandated emission limits will make it more difficult to operate these units in the future. Thermoelectric generators, another alternative with an efficiency of about 3% and the associated high emissions, are only used in special applications and especially at particularly low ambient temperatures. Generators are often oversized for the load requirement, resulting in an "underloaded" operating condition that can stress the generator over the long term and reduce its efficiency to less than 20%. Legally mandated emission limits will make it more difficult to operate these units in the future. Thermoelectric generators, another alternative with an efficiency of about 3% and the associated high emissions, are only used in special applications and especially at particularly low ambient temperatures. Another alternative with an efficiency of approx. 3% and the associated high emissions, are only used in special applications and especially at particularly low ambient temperatures.

Fuel cells are the sustainable alternative. Classic low-temperature hydrogen fuel cells based on PEM technology or methanol fuel cells are ideal for backup applications with a short runtime of a few thousand operating hours. They start up relatively quickly, can bridge short grid outages, or can recharge batteries in photovoltaic hybrid systems, provided the insufficient irradiation times are not too long. However, the service life of the stack, the core system of the fuel cell generator, of typically 3,000 to 7,000 operating hours significantly limits their applicability in continuous operation. In addition, the volumetric power density of hydrogen, even when stored and transported in pressure vessels, is very low compared to liquid or liquefied fuels such as diesel, methanol, propane or ammonia.

Solid oxide fuel cells (SOFCs) with ceramic electrolytes have proven themselves in stationary continuous operation for several years. These are based on the principle that many ceramics become conductive to oxygen ions at temperatures above 650 °C. These are therefore high-temperature fuel cells, which are usually operated in the 700 °C to 850 °C range. Unlike the aforementioned technologies, these fuel cells require little maintenance. Intervals of up to 10,000 operating hours are possible. The core of the SOFC fuel cells can achieve a service life of 20,000 to 30,000 operating hours in continuous operation. Sunfire Fuel Cells GmbH has been manufacturing and selling such fuel cell generators since 2014, and they are currently available for operation with natural gas or propane gas as fuel. With the expanded availability of renewable ammonia or hydrogen, corresponding product variants will also be available in time. So there is nothing standing in the way of switching to a highly efficient, clean and sustainable solution.

Netzunabhängige Mikrowellen-Funkstation mit SOFC-PV-Hybridkonfiguration in Alaska – Sunfire-Remote 400 installiert 2019

Fig. 1: Off-grid Microwave Radio Station with SOFC-PV Hybrid Configuration in Alaska – Sunfire-Remote 400 installed 2019

The question is: How do the different power generation technologies rank for off-grid power supply? For this purpose, the total cost of acquisition, operation and maintenance of different off-grid generators was determined and compared as the total cost of ownership (TCO) for a directional station with an average power consumption of 220 W. Further, the carbon dioxide emissions were calculated assuming fuel from fossil sources compared to fuel from non-fossil sources. The temperate climate zone of the northern hemisphere was chosen as the region.

The following technical solutions were considered:

1. SOFC Fuel Cell Stand Alone
The fuel cell, in this case a Sunfire Remote 400, is combined with a small to medium-sized battery bank. This supplies energy to start the fuel cell and can cover short-term load peaks during continuous operation of the fuel cell.

2. SOFC fuel cell in a PV hybrid system.
Depending on the energy needs of the consumer, a photovoltaic generator and a fairly large battery bank with several days of power reserve are combined to meet the energy needs of the application during the months with good irradiation availability (typically April to October in the northern hemisphere). When the days get shorter and the weather gets worse, the Sunfire Remote 400 fuel cell is activated and provides energy during the low-radiation winter season.

3. Diesel generator with battery storage
Diesel generators can also supply a load directly, but then they usually operate in an inefficient underload state and quickly reach a high number of operating hours. For this reason, these generators are often hybridized with batteries in off-grid applications in order to run in full-load mode for as few operating hours as possible.

4. Methanol fuel cell stand alone
Equivalent to 1. the same case is considered for comparison with a 500 W methanol fuel cell.

5. Thermoelectric generator
Thermoelectric generators produce electrical energy from combustion heat and are usually combined with batteries in off-grid applications.

Vergleich der 10-Jahres-TCO und CO2-Emissionen der verschiedenen Lösungen

Fig. 2: Comparison of 10-year TCO and CO2 -emissions of the different solutions

The investigations carried out give the following picture: In terms of costs and CO2-emissions when using fossil fuels, the combination of SOFC fuel cell in winter operation and photovoltaics in the summer half-year is unbeatable. If there is not enough space for a PV generator with corresponding battery storage, the Sunfire remote fuel cell can also be used in stand-alone operation. A further reduction in CO2emissions by up to 90 % is already possible today with BioLPG from bioresidues available in Central Europe or, in the future, also electricity-based e-propane. Diesel generators have low efficiencies in this power range. Fuel costs and maintenance costs eat up the comparatively low investment costs. Methanol fuel cells, on the other hand, have the greatest impact on total costs. The relatively high price of methanol is associated with shorter fuel cell stack life. Finally, thermoelectric generators hold the negative emissions record due to their low efficiency.

In summary, the SOFC fuel cell, like the Sunfire-Remote 400 considered here in this real-world example from Alaska, offers the optimal solution in terms of security of supply, total cost, and emissions. Ultimately, however, it is recommended that a project-specific cost estimate be made. External factors such as available space, access frequency, and seasonal inaccessibility may also be additional factors in choosing a low-maintenance, robust, and proven solution.

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