How Much Energy Can A Home Biogas System Generate?

“Hey there! I’ve just started experimenting with a home biogas system here in a small town in Wales, and I’m trying to figure out how much energy I can really expect to generate as I’m looking to offset some of our energy costs. We’re a family of four with a small garden and a fair amount of organic waste from our kitchen and some backyard chicken manure. Is a biogas system powerful enough to make a big dent in our bills? I also wonder how much daily organic input I would need and if seasonality or temperature are going to be major issues. Thanks for your help!” Cheers, Andrew, Swansea, UK.

How Much Energy Can A Home Biogas System Generate?

First of all, Andrew, kudos for making the leap into biogas! If you’re looking to offset some of your energy costs, especially in a family of four, a home biogas system can absolutely help – but there are a few variables to keep in mind. In this article, we’ll explore just how much energy you can generate, what factors can affect that output, and the types of organic waste you’ll want to feed your system. Let’s break it down and provide a clear idea of what to expect from your biogas efforts.

Understanding Biogas and Its Energy Potential

Biogas is a renewable source of energy commonly made from the decomposition of organic matter in an anaerobic (oxygen-free) environment. When bacteria break down this waste, they produce gases – mainly methane (CH4) but also carbon dioxide (CO2). The methane is the star here because it can be used as fuel for various purposes, like powering a gas stove or generating electricity.

A liter of biogas typically contains around 50-65% methane, with the rest being largely CO2 and trace gases. The amount of energy in biogas varies, but on average, 1 cubic meter of biogas has a calorific value of around 6 kWh (kilowatt-hours). To give you an idea, 1 kWh is roughly equivalent to running a single 1,000-watt appliance for an hour, like a toaster or window air-conditioning unit.

How Much Organic Waste You’ll Need to Produce Energy

Your biogas production is directly proportional to the volume of organic waste you feed into the system. For a rough estimate, 1 kilogram of organic kitchen waste can generate around 0.3 to 0.5 cubic meters of biogas. Meanwhile, animal manure tends to be slightly less productive, with 1 kg of fresh cow manure generating about 0.2 to 0.3 cubic meters of biogas.

Since you’re based in Swansea and have kitchen waste and chicken manure as inputs – let’s break this down. Assuming you can provide around 5 kg of mixed organic waste (let’s say a combination of kitchen scraps and chicken manure) per day, you might produce 1.5 to 2 cubic meters of biogas daily. Based on an average energy value of 6 kWh per cubic meter, this will give you about 9 to 12 kWh of energy daily.

Energy Applications: What Can You Do with 9-12 kWh of Energy?

So, what does 9 to 12 kWh look like in practical terms? Well, it’s enough gas to cover:

• Running a gas stove for approximately 3 to 4 hours.
• Powering a gas-powered refrigerator for about a full day.
• Heating hot water for showers for a family of 4 for a day (assuming an energy-efficient water heater).

However, if you’re considering converting this biogas into electricity using a small gas generator, bear in mind that you’ll lose efficiency in conversion. A typical household-size combined heat and power (CHP) generator has an efficiency of around 30-40%, meaning 9-12 kWh of raw energy would produce around 3 to 5 kWh of usable electricity – enough to power a few basic appliances, but not entirely offset your grid use.

Factors That Influence Biogas Production

Andrew, the amount of biogas your system generates depends on several factors, including the type of system you have, the temperature and season, the kind of organic material you feed it, and the size of the digester.

Types of Feedstock

Not all organic matter is equal when it comes to biogas production. High-energy waste like food scraps (vegetable peels, fruit scraps, etc.) tends to produce more gas than low-energy waste like animal manure. Chicken manure has a decent biogas yield, but if you can supplement with high-energy kitchen scraps, you could maximize your production.

Temperature and Climate

In a location like Wales, your biogas system’s performance can fluctuate with the seasons. Biogas production is temperature dependent since the microbes breaking down your waste are most active in warmer conditions (around 30-40°C). Lower temperatures will slow down gas production considerably.

If your system isn’t insulated or heated, you’ll likely notice a drop in biogas output during the colder months. Some people in cooler regions install a heat source or insulation to keep their systems operational year-round, but this obviously adds to the upfront cost (and energy use). You might want to consider seasonality when planning your biogas use.

Retention Time

Retention time refers to how long the organic material stays in the anaerobic digester. The longer the retention, the more thoroughly it gets broken down, increasing gas output. In colder weather, you may need to extend retention time to compensate for slower bacterial activity.

Troubleshooting Lower-Than-Expected Energy Output

The amount of biogas you generate depends on maintaining the right conditions in your digester. If things aren’t going as well as expected, or you generate less gas than expected, here are a few common issues to check:

• Temperature: As we discussed, a drop in temperature can prevent microbes from efficiently digesting organic matter. Installing a heat-retention system or locating your digester in a sunny spot could help.
• pH imbalance: The microbes in your digester thrive in a slightly neutral or alkaline pH (around 7 to 8). If the pH is too high or low, gas production could drop. A simple pH test can help you monitor that.
• Clogging or poor mixing: If the organic waste isn’t broken down evenly or gets stuck in the system, gas output may drop. Proper pre-processing (chopping food waste into small pieces) or occasional stirring might help here.

Optimal Use of Biogas: Heating vs. Cooking vs. Electricity

Once you’ve got a steady supply of biogas, it’s natural to ask what the best way is to use it. Historically, the most efficient way to utilize biogas is through cooking or heating. That’s because converting biogas into electricity incurs efficiency losses, as mentioned earlier.

If your goal is to offset natural gas usage in your kitchen, you’re in luck! Biogas works perfectly with standard gas stoves for cooking. It’s direct and efficient, allowing you to make the most of every cubic meter of gas without major energy losses in conversion.

How Much of Your Energy Needs Can Biogas Really Cover?

I get it, Andrew, you’re asking the million-dollar question: can this lower your energy bills?

The answer depends on a couple of things: the size of your biogas unit, the organic waste you consistently have access to, and of course, how efficiently you use the gas you produce. A typical home biogas system can generally replace around 30-50% of a household’s gas cooking needs or contribute meaningfully to space or water heating. If you’re producing biogas consistently every day, there’s a good chance you’ll notice the impact, especially if you focus on cooking.

Larger systems, combined with access to a consistent supply of high-methane-content organic waste (like food scraps and oils), can provide even more power, potentially up to 100% of your cooking needs and some space heating if you’re already energy conscious. But, if you’re relying on electricity or other fuels for heating, the impact may be more modest but still noticeable.

Final Thoughts…

Andrew, thanks again for sending in your question. Based on what you’ve described with your family size, organic waste sources, and location in Swansea, a home biogas system can make a satisfying contribution to your household’s energy demands, particularly when it comes to cooking or hot water heating.

Remaining mindful of your inputs, seasonality, and long-term care for the system will all play a part in the energy you generate. While it may not replace all your energy needs, it’s an exciting and sustainable way to supplement what you’re currently using, cut down on energy bills, and reduce waste. Stick with it; I’m sure you’ll see significant benefits in the long run!