There are several different types of technology that can be used to provide power for remote, off-grid applications. This section will provide a high level overview of these technologies and summarize the pro's and con's of each technology.
TEG technology has been around for 40+ years and has proven to be a reliable, low maintenance, long-life power generation system. These solid state devices operate on the Seebeck effect where the heat differential across a thermocouple produces a small direct current. Utilizing a series of these thermocouples (to comprise a thermopile) a TEG can produce low levels of power. As the heat from the burner (using propane or natural gas) is applied to one side of the thermopile, the other side is kept cool by heat sinks. The resulting temperature difference across the thermopile creates DC electricity. TEGs are available with outputs ranging from 21 watts to 550 watts but can be paralleled to service higher loads. TEGs are intended for continuous operation. TEGs typically take about 60 minutes to start up before producing electricity.
No moving parts and solid state design results in low maintenance and high reliability
Thermopile life can approach 20 years when run in a continuous mode
Can operate in extreme environmental conditions
TEG output varies with ambient temperature and voltage chosen. The output rating could be derated as a result
Remote monitoring or control is not available
Because TEGs use combustion and have low efficiency they emit harmful greenhouse gas emissions
Ratings over 500 watt consume significant footprint area to allow for the heat exchange apparatus
Due to their high fuel consumption, for sites that do not have an indigenous source of natural gas (such as on liquid pipelines), TEGs can be extremely expensive to operate
For more details see Atrex Energy's Technical White Paper "SOFC Power Generators vs TEG - Technical Comparison"
Internal Combustion Engines (ICE) Generators (Gensets) are a popular power generation technology. Having been around for years the ICE Genset technology is field proven in providing backup and continuous power.
ICE Gensets Advantages
ICE Gensets' acquisition cost is very competitive compared to the other technologies
They can run on a variety of fuels
ICE Gensets are ideal for back-up power applications and can be started up almost instantaneously
ICE Gensets are available in a wide range of power output and voltages
ICE Gensets Disadvantages
These devices, when operated in the 500 watt to 1500 watt range, operate at 10% to 15% efficiency in turning fuel into electricity. In continuous run applications, this inefficiency results in frequent refueling and increases Operating Expenses (OPEX)
Most require frequent maintenance for oil/coolant relacement, fuel and filter changes, typically between 250 hours and 500 hours depending on the lubrication oil scheme. For some models complete overhauls are required after 10,000 hours of operation
Typically Gensets arefuel rated 6kW and above. When used on remote applications with loads under 2.5kW the Gensets are overrated, run at a small fraction of their optimum output and are not efficient. Typically they are used intermittently to recharge a bank of batteries and the batteries provide the steady power (“cycle charge mode")
Because they use combustion to create electricity they emit harmful greenhouse gas emissions
Diesel models run the risk of an environmental hazard should their seals break and diesel fuel leaks into the ground.
Gensets are extremely noisy and uncomfortable to be around for extended periods of time
Photovoltaic (PV) or solar panels have become more mainstream as the cost of this technology has dropped over the past 10 years. Solar has proven to be a viable source of DC power by converting the sun's energy into electricity. A battery storage system is required to allow the system to provide power 24/7/365. The main advantage of using PV technology is the systems operate on sunlight and do not require any additional fuel. Solar is appropriate for use in remote areas providing unattended power output. If designed properly, with adequate solar resource and no shading, the PV system can be a reliable power generation system.
No emissions or harmful byproducts
No fuel required
The solar panels can be arranged in a parallel or a series configuration to provide a range of voltages and power ratings
Minimal maintenance required - typically cleaning of the panels, checking connections and checking the battery system
The solar panels themselves are designed to perform for 15+ years
In some areas government subsidies are helping to keep solar affordable
Solar works well in areas with extended periods of sunlight.The fewer hours of solar resource available the less cost effective solar systems become
Depending on the solar resource indigenous to the site, a solar stand-alone system could require arrays that are 10X to 15X the size of the load to be serviced (e.g. a 200 watt load might require a 2,000 watt PV array with great solar resources or 3,000 watt PV array with marginal solar resources). This is necessary because the panels are at a fixed angle and only achieve peak output when the sun is directly perpendicular to them. Cloudy days also reduce the output. To ensure proper power output large solar arrays may be required and result in high Capital Expense (CAPEX), high installation costs and consume a large footprint
There are many design aspects to be considered in order to provide the most efficient solar array that provides the necessary power and reliability. Inexperienced designers or cost cutting moves often result in inferior designs or too few PV panels that don't provide the power required
The achilles heel of PV systems is the battery system. The larger the load or the less solar resource there is the larger the battery bank must be. The batteries require maintenance and can often degrade quickly. Battery cost and labor to change out the batteries can increase OPEX significantly
Any external object that blocks the panels such as dust, bird droppings and incidental shading has a negative impact on the output of the array. In areas where there is frequent snow, some panels may need to be manually cleaned after a snowstorm. Just 5% shading could result in a loss of efficiency approaching 70%
Vandalism and theft (of panels and/or batteries) continues to be an issue
For more details see Atrex Energy's Technical White Paper "SOFC Power Generators vs Solar - Technical Comparison"
These are also referred to as Organic Rankine Cycle engines and have been in use for over 40 years. A burner uses various hydrocarbons to heat the fluid in the vapor generator. The fluid vaporizes and expands through a turbine wheel thereby producing shaft power to drive an alternator. The vapor then passes through a condenser where it is cooled and condensed back into a liquid state. The liquid returns to the vapor generator where the cycle begins again. The unit is hermetically sealed and as long as fuel is fed to the burner to heat the fluid the unit produces electricity. The AC power produced is rectified to DC current. Ratings range from 600 watts to 5kW.
Can operate at extreme environmental conditions (as low as -60oC)
CCVTs are inefficient in converting natural gas or propane into electricity. The average efficiency is 6% which translates into high fuel consumption and high operating costs
Principally, these are offered by Ormat Turbines with manufacturing and service located in Israel
The acquisition costs are very high - nearly 2X to 3X the cost of most of the technology discussed here
CCVTs are considered specialty equipment that requires specially trained technicians and unique tools and replacement parts to maintain the operation
Because CCVTs use combustion they emit harmful greenhouse gas emissions
CCVTs consume a large footprint and have a height exceeding 19 feet (nearly 6 meters)
For more details see Atrex Energy's Technical White Paper "SOFC Power Generators vs CCVT - Technical Comparison"