1428-1857: High Reliability Biomass Home and Grid Power Generator


ARPA-E Contact: None.
Technical Subcategory: 1.2 Thermal-Mechanical
Funding Request: $500,000 Funding Request.
Project Duration: 12 Month Project Duration.
Project Abstract: This project is to design and create a prototype 5 KW rate high reliability biomass pellet burning home turbine steam generator for grid power production. A generator with 30% thermal efficiency gives 10 KW waste heat rate to heat water which can be used for hot water, close drying, and home heating for effective energy use.


All energy sources cannot be guaranteed. Energy disruptions and shortages can cause economic quakes that can disrupt the economy. A majority of the current US energy used, is from CO2 polluting fossil fuels that may be damaging our world. Switching to electric cars does not solve this since the additional electric grid energy used is often supplied from using more ground based fuels to run the generators. The electric grid has the potential of instability due to limited number of power sources and has high losses in transporting electric power long distances. The need for new localized sources of usable stored energy generation is needed.

The success of using low cost, high energy biomass-fuels, such as wood pellets, in a low cost and efficient manner such as direct burning of pellets to provide energy in the form of both heat and electricity will have a significant impact in the US economy and energy security in the following ARPA-E Mission areas: (i) Reduction of imports of energy from foreign sources, since new local power and heating can offset heating oil needs. (ii) Reduction of energy-related emissions of greenhouse gases, since most imports are fossil fuels that permanently adds CO2, while CO2 is removed from air while growing plants and only released when used, making the full process carbon neutral. (iii) Improvement of energy efficiency, 1) For home usage needs by utilizing heat that would be lost in central power generation. 2) Localized electric power transport is more efficient since long distance losses are lower due to lower currents across those paths.


Fuels represent stored energy which can be stored over a period of time and be used at selected times and this focus is on fuels that do not result in permanent green house gas increases for the full process, nor are huge investment fuels, such as nuclear fuel. The competing biomass fuel is liquid or gas based fuels that can be used in an internal combustion engine.

The current technologies are insufficient and undesirable because most are based on converting the biomass natural state of plant cells to a different form, such as liquid or gas. This takes additional energy to convert and reduces the amount of energy that is available. In addition, most of these have other issues: Exotic methods, non-stable, dangerous/poisonous, have low volume, high risk, restricted bio-types, cost conversion and/or use additional ground sourced fuels to produce. In the end much less energy is available as compared to manufacture into pellet forms.


The new idea is a small homeowner owned biomass power generator, that can be used to establish a local power generation economy that can work now and logically fits into a probable future energy market, which could last indefinitely. There is no incumbent for home owner biomass electric power generators outside of fossil fuels. However, wood pellet fuel is often used for home heating making this a natural transition from heat only to both electricity and heat.

The primary innovation is a new local power economy method based on the biomass fuel power generator. The power generation is strait forward. Wood and related biomass pellets burn in a power generator that produces both electricity and heat as the end product. Basically, the heat from the pellet burning produces heat which is converted to steam which runs a simple highly reliable steam turbine engine, that drives a generator and inverter to generate electricity for the home owner and for putting excess power on the local grid, where the home owner receives some cost and heating economic advantages.

An example scenario, is of a hypothetical town located in an area that creation of pullets for energy production makes sense, has a managed forest area that can be used for pellet production which supports local jobs and pellet production industry. This town might also be located somewhat close to a major freeway, but probably outside of the large metropolitan areas.

This power system is a community project that all people of the community benefit from. A large portion of the population of this town owns these pellet power plants and is part of a local energy production cooperative. When their home needs heat for hot water or heating the house, or needing electricity and the local electric grid computer indicates that power for the grid is needed, it starts the power plant which produces heat and produces electricity. When heat can be used for cooling the house, the generator can also be used. If the owner has an electric car, charging is also done at this time. Since a turbine engine tends to only run well in a small power range around the designed power range, the house management computer tells the local electric power grid computer how much excess power is available for use. Once the heating and electric needs of the household has been met, the pellet power plant shuts down. The owner can also program the local home management computer to generate electricity when not needing heat and the price of the electricity power is high enough to justify running the power plant independent of heating needs, and may have additional water tanks to store the extra heat generated. The home owner might also have a solar power generation system for additional power generation.

The local electric power grid computer determines the current local power usage and amount of power available in excess of the current needs. 1): Excess power is fed into the local power storage batteries which act as a power transition control and for supplying local power for times when heating needs are low and not much power is needed; (like in the middle of the night and external temperature is 70F). 2): The Excess power is then used to charge Long Distance Auto Travel Batteries. These high energy batteries slide into travel battery slots of electric cars and are exchanged as needed during long distance travel along major routes and is essentially rented where user pays a daily rent fee and for power used out of the battery. 3): When power grid prices are favorable, some power maybe sold on the distributed power grid. 4): Any remaining power is used to generate hydrogen, which is sold to local hydrogen auto users and remaining hydrogen is shipped in large tanks to areas of hydrogen users.

Home energy generation using solar power panels is currently used, but other types of low home electric power generation is rare. Wind and solar power performance are subject to the changing weather and solar conditions making their power generation unstable to a power grid. This power generation is fuel based allowing for time and use of energy generation to be adapted to the changing environment and can be used to stabilize a local power grid. Adding computer controlled coordinated management of operation and generation across the local grid, can create a much more stable and reliable local power grid. Since more energy can be stored in a water heater by having a higher water heater temperature, as needed, and having additional household hot water storage, and learning the patterns of hot water usage, it gives some flexibility to schedule better operation times across the local grid while still adjusting for dynamic changes of wind and solar input, as well as daily and seasonal changes of grid use. The higher temperature water heater can still put out the users selected output target temperature by mixing the hotter water with cold water to adjust the output temperature.

This advance of state of the art is really about a new low cost energy generation system to eliminate the requirement of needing any CO2 environment adding fuels to do the required work. Although a home use scenario was presented in this discussion, a high reliably generator of this nature can be used and scaled for other work. A major downside is that even though the biomass fuel maybe carbon neutral, considerable greenhouse generated fuels are currently used for planting, harvesting, processing and distribution. Until we can effectively utilize the carbon neutral fuels in small enough units, but large enough power level to effectively get localized work done such as in planting, harvesting, processing and distribution without using additional fossil fuels, we are still generating tremendous amounts of earth damaging CO2 pollution. There are many ways biomass can be used to generate power and heat.

Biofuel/Biomass Efficiency Equip cost Distrib Heat Net Green house Comments
Home Power plants 60% Low Yes No Pre-Processed pellets
Large Power Plants 20%-27% High No No  
Combined Heat Power (CHP) 80% High No No Targeted heat use
Cofiring 40% High No No Greenhouse fuel mixed
gasification/chemical To Fuel High   No Lost potential energy
Bio-chemical Conversion To Fuel High   No costly or unreliable
Bioethonal To Fuel High   No Food used, Fossil fuels
Non-Biomass chemical fuels A Fuel Low   Yes Greenhouse fuel

As we can see, there are multiple of ways that biomass can produce power. Most of these require huge costs well outside what a normal person or even a small business can withstand.

Batteries have come a long way to around 256 Wh/Kg but with wood at 14.9MJ/kg = 4138 Wh/kg, with 30% efficiency is still 1241 effective Wh/kg, 5 times higher usable power density. Wood at 14.9MJ/kg = (((14.9MJ/kg)*(Ws/J))/(3600s/h))*0.45359kg/lb*2000lb/ton = 3.755 MWh/ton energy = 3755 KWh/ton. Pellets @ $200/ton, costs $0.05327 per KWh of energy.


The most complex challenge is correctly designing a steam generator heat exchanger and steam turbine engine to have high efficiency at the target power output. It is known that steam turbine engines only run well within a narrow operating range and the design engineering is difficult work, with most current turbine designs focused is on very large power plants. May need to do multiple designs and prototypes to get a good matched design at such small power levels. By using water bearings and good designing, the durability and reliability will allow for low maintenance and long term use.

The innovation is in the configuration, sizing, and engineering of components to allow targeted home owner sized power generation from pellet biomass fuel. The innovation is also from choosing the right operating environment that allows the waste heat to provide value and that operation can be done when needed, including seasonally, as in running in the winter time and does not needed to run continuously. For a joint community cooperative, the innovation is in a multitude of small generators running at random times to heat the needed hot water that will produce a stable economical local power grid that provides economical value to the owners of these generators. Computer controlled starting, stopping, and precision controlled burning of biomass fuel pellets will probably take some minor innovative work. However, all components in themselves, are well understood and do not have high technical risk.

The primary techno-economic challenge is having an economically priced pellet power generator, hot water heating, house heating system that can be easily installed, connected to the power grid, and connected to a home energy management computer; (it can be installed at same time, but needs internet connection). Easily connected to a hot water heater tank and hot water to connected to home heating system. For living room installation, hoses can be routed to hot water heater and water radiator with fan can be placed next to the generator. Installation economics will depend on the particular house design. Initial use will be self-contained operation, but later can be hooked-up to a home energy management computer that can talk over the internet to the power grid service computer, if and when community coordination comes into play.


The object is to design and build a prototype 5,500 watt turbine steam engine that uses wood pellets to heat the steam generator heat exchanger. This turbine drives a 280V multiphase generator and inverter for connecting to a home and to a 240V power grid with each approximately 0.95% efficiency for a net power output of 5000 Watts. The target thermal efficiency target is >= 30% , which will use about a 18.3KJ pellet burn rate. With wood having 14.9 MJ/Kg, this power level will have an average 0.00128 Kg/sec burn rate. The generator will be able to be started, and warm up, run for a moderate period to bring up the temperature in the water heater, larger than current standard sizes, to the target level and shutdown as needed.

Design and prototype work will include computer controlled pellet burner, steam generator heat exchanger, turbine steam engine, generator, power inverter, monitoring and control components, and a control computer system. Software to design steam turbine and steam generator, will be needed or created. Controller software and control algorithms will be created. The primary product will be a system to design more, high reliable generators, at other target power levels.


The project will be managed and developed by Mike Polehn, BS of Computer and Electrical Engineering, OSU (Oregon). Education included mechanical engineering statics, dynamics, strengths, thermal dynamics , etc. I grew up on a large orchard, know many issues of farming. Spent time working on and fixing equipment, modifying engines with gear head friends, resulting in practical experience that would apply to creating components and building the system. We will hire ME collage students locally from WSU, Vancouver part time and/or paid interns to enhance their education experience.