Biomass has its origin in grown material. We get the energy from biomass by combusting it. Carbon dioxide is emitted into the air and again taken from the air by living plants and trees. It is a short carbon cycle and therefor called CO2- neutral.
There is biomass in very different forms, e.g.: Residual from sewage treatment plants; Manure from livestock farming; Organic waste from agriculture and food industry; Vegetable and garden waste from consumers; Algae and seaweed (experimental); Wood from trees, pruning and other woody waste; Grown energy crops like rapeseed corn and palm oil.
Different Forms of Biomass
Different Forms of Biomass
All these forms of biomass have their advantages and disadvantages and can be converted in various kinds of fuels. We can convert energy crops into liquid motor fuels, but maybe it is better to use them as food as long as people die from hunger. Furthermore does cultivation require a large land use and often valuable nature areas are destroyed. More liquid biomass such as manure and residues can be converted into biogas and processed into pure methane gas. Wood and woody waste is incinerated and can bring harmful emissions and particulate matter into the outside air, especially when there is an incomplete combustion. And of course it is important to plant new trees when they are harvested so they can absorb the carbon dioxide that is emitted during combustion.
Till now we discussed sustainable energy sources like solar but at this moment wood and woody waste is the largest renewable energy source in the world as you can see in this graph. Private households’ cooking and heating with wood fuels represents one third of the global renewable energy consumption. In the European Union 45% of the renewable energy origins from wood fuels, which is 6% of the total energy consumption.
Biomass seems to be a serious renewable energy source and has its advantages against wind and solar energy because it is energy and energy storage at the same time: You combust it when you need it. Wind and solar are fluctuating sources that are not always available when there is a demand and therefor they need storage which makes it more complex and expensive.
There is a case sudy in the Dutch city of Maastricht. In this project, we have quite a lot of sunshine here during spring, summer and autumn. they collect this solar heat with 10 square meter of solar collector on the roof and store it for a few days in a 900 litre vessel to use it for space heating and domestic hot water. But now it is winter and they do not have much solar heat.
In summer they only need domestic hot water and there is more than enough sunshine to provide all the heat that is needed. During spring and autumn they also need heat for space heating and most of it can be provided by the solar collectors from the storage vessel. The vessel provides domestic hot water and is connected to the radiators and floor heating system in the house. In winter there is almost no solar heat for heating. they have a heat storage for a few days but not for a whole season; So now biomass comes in.
This piece of dry wood of approximately 2,5 kg contains the heat of 1 litre of oil or 1 m3 of natural gas; a quite compact form of stored energy. In cold weather, so they will put it in the woodstove. The heat from combustion is emitted into the room through the glass and heats our living room completely. they have a special woodstove, with a heat exchanger inside that is connected to the heat storage vessel and pumps part of the heat produced.
There is enough heat from the solar collector or wood stove stored in the vessel to provide domestic hot water and to heat other rooms with radiators, beside heating the living room. Then there is still enough heat stored in the vessel to heat the living room in the morning with the floor heating system, so they do not have to wake up early in the morning to fill the woodstove. And even when they are too lazy to fill the stove, there is a gas heater that heats the vessel. But of course natural gas is not CO2-neutral.
Wood Stove
Scheme of the heating system at home
Now, we can see what you can do at home on a small scale but it is also possible on a larger scale like they do it on the Danish energy neutral island of Samso. Here they have a large field of solar collectors, standing in a meadow.
The solar heat is stored in a large vessel and when there isn’t enough sunshine, it is heated with biomass in the boiler house, behind the large vessel. This large solar-biomass plant is connected to a heat grid that provides a small village with heat for room heating and domestic hot water.
There are a few of these local district heating plants on the island of Samso. At The biomass origins from wood or straw from the island itself.
In fact straw is also a kind of energy storage and takes some space as you can see in picture below. After harvesting the corn (in August), the straw is dried and stored so that it can be used for heating during the winter season.
Each straw block weighs about 600 kilos [1,300 pounds], which is the equivalent to 200 litres [53 gallons] of oil. The ash of the incinerated straw is scattered over the fields as a fertilizer.
High Tempreture Heat Storage connected to a Heat Grid (Samso)
Boiler House with Straw Incinerator and Storage of Straw
Seasonal Energy Storage with Straw for District Heating (Samso)
In fact biomass is stored solar energy but the efficiency of converting solar radiation into biomass is poor: In this photosynthesis process, less than 1% of the solar irradiation is converted into biofuel. For solar collectors, the efficiency is about 40% and for Photo-Voltaic panels about 20%. So the land use for biofuels is high and for that reason it is better to use biomass from waste-flows and maintenance of nature protection areas.
In the Dutch city Sittard there is a biomass energy plant that runs on wood and prunings from maintenance and management of green spaces in the city. This biomass energy plant produces electricity and heat at the same time. The electricity is supplied to the grid and the heat is distributed through a district heating network. In the summer when less heat is needed, cold for cooling is generated with heat from the biomass plant by absorbtion cooling.
Biogas from Manure
Energy From Biomass
