Many people compost their horse’s manure, or apply it to their land. But what if you have insufficient land or space, or are dealing with progressively stringent regulations surrounding the use and disposal of manure? One alternative being increasingly implemented around the world is using manure to make renewable energy.
While the idea of using manure for energy isn’t exactly new (sundried manure has been used for heat since the days of ancient Persia and Egypt), the technologies needed to turn horse manure into renewable energy, in an efficient, economical, and environmentally-friendly manner, are a lot more recent.
Biomass boilers and gasifiers
There are two main types of technology to choose from: biomass boilers and gasifiers. Biomass boilers are similar to the conventional gas boilers most readers will be familiar with; the key difference is that instead of burning natural gas or oil, biomass boilers burn biomass, such as wood chips, to produce heat. Biomass boilers are also much larger than their conventional counterparts, and require a mechanism to feed the biomass into the boiler.
Gasification involves the partial combustion of biomass in small amounts of oxygen at high temperatures of 900°C to 1,400°C. Instead of burning biomass, gasifiers convert the chemical energy in biomass into a fuel gas known as “syngas”. Syngas is commonly made up of a mixture of hydrogen, methane, carbon monoxide and carbon dioxide, and can be utilised in a range of applications to produce renewable heat, electricity or liquid fuels.
While biomass boilers and gasifiers are fundamentally the same (the conversion of biomass to renewable energy), the cost, flexibility and energy output of each are very different. In general, biomass boilers are cheaper, smaller and better known than gasifiers, making the technology a more economical and less risky option. Gasifiers, on the other hand, are cleaner (requiring much less emission control), and have greater biomass and energy flexibility, enabling the use of more “undesirable” biomass and the ability to make heat, electricity or liquid fuels. Deciding if these technologies are right for you will depend on a number of variables, including the type and volume of horse manure you have, your onsite energy needs, and local regulatory requirements.
Manure type and volume
The cornerstone of any successful biomass renewable energy project is feedstock — in this case, horse manure. Understanding the characteristics and volume of horse manure is essential to determining the economic feasibility of using it to produce renewable energy. Stall bedding material, housing climate and management practices can vary between equine facilities. Understanding how these can impact the composition, moisture content and volume of horse manure is essential.
Horse manure that consists primarily of wheat, oat, rye, straw, hay or dried pasture clippings can be difficult to use for renewable energy production due to its high ash content and low ash-melting temperature (the temperature at which ash becomes sticky, adheres to surfaces and causes corrosion). While not insurmountable, these difficulties require more expensive equipment, making economic feasibility very challenging. Sand-based horse bedding is also undesirable as the energy content is extremely low.
Horse manure that consists primarily of shavings, pellets, sawdust, other woody materials, or peat moss, is much more conducive for renewable energy production. This type of manure has a lower ash content, a higher ash-melting temperature and higher energy content, making renewable energy production easier, cheaper and therefore more economically feasible.
The moisture content of the manure is important, as wet manure will likely require some form of drying before it can used in a biomass boiler or gasifier. The amount of drying required will depend upon the type of boiler or gasifier used. While heat from biomass boilers and gasifiers can be used to pre-dry horse manure, any heat used for this purpose reduces the amount of renewable energy that can be used onsite or sold, negatively impacting project economics.
Manure volume is also key. Generally speaking, biomass boilers and gasifiers that are twice the size of regular ones, and produce twice the amount of renewable energy, are less than twice the cost. Therefore, larger volumes of horse manure generally lead to improved economic feasibility thanks to economies of scale. If you don’t have enough horse manure from your own equine facility, consider working with a close neighbor to combine your manure. Bigger is almost always better.
Onsite energy needs
If feedstock is the cornerstone of a successful biomass renewable energy project, an equally essential criteria for economic feasibility is onsite energy needs. As mentioned previously, biomass boilers produce heat. If there is no demand for heat onsite or within the vicinity of a biomass boiler, there is little value to be gained from producing it. Furthermore, if the cost of heat is low, even if demand exists, the economics will likely not add up. To overcome this problem, manure could be transported and converted to heat at a site with a high heat demand. However, transportation costs can quickly eat into project economics.
Unlike biomass boilers, gasifiers produce syngas that can be utilised in a range of applications to produce renewable heat, electricity or liquid fuels. Electricity can be injected into the local grid for sale to a utility, while liquid fuels can be transported for offsite use. However, while gasification might overcome limited onsite energy needs, conversion of syngas into electricity or liquid fuels requires additional, sometimes expensive, technology.
One size doesn’t fit all
Using horse manure for renewable energy production offers a number of advantages to equine facilities. Renewable energy can be cheaper than propane, electricity or natural gas, while using the manure this way can minimize disposal costs. It can also have a number of environmental and social benefits. These include minimizing the odor caused by land application, reducing runoff from storage, and replacing the use of fossil fuels.
While horse manure for renewable energy production can be a good idea, it should be noted that one size doesn’t fit all. What might work/make sense for one equine facility might not work for another seemingly similar facility. What type and volume of manure do you have? What are your onsite energy needs? What are the local regulatory requirements? All these factors must be carefully considered before deciding if this project is right for you.
 Pyrolysis isn’t considered here as most systems are designed for the production of biochar (a product similar to charcoal) and not renewable energy.