The climate and biodiversity crises are accelerating, and people are beginning to see the effects right outside their own front door. This has prompted many people to try and improve the sustainability of their own homes. But what are the options for renewable heating?
Your options for heating your home with renewable energy include heat pumps, solar thermal panels, and biomass burning. These are only three of the most popular choices, but any electric heating is renewable if the electricity grid in your country is sufficiently clean.
Now we know that there are a few different options for heating your home using renewable energy. In this article, we will be going through all these options in detail to find out how they compare when it comes to price, ease, and sustainability. Let us get started!
What Makes Something ‘Renewable’?
The term ‘renewable’ means that the ultimate energy source is not finite or can be replaced. For example, solar energy is renewable because we are not going to run out of sunlight. Something like biomass burning is a less clear-cut case, as we will discuss in a later section. Non-renewable energy comes from things like fossil fuels, which are finite in nature and will eventually run out if we keep using them at the current rate.
While fossil fuels would technically be ‘renewed’ eventually, this would take millennia to occur, so they are not considered functionally renewable. If an energy source is non-renewable, it is also not sustainable. In particular, fossil fuels are unsustainable since, in addition to being finite, they are causing untold damage to the planet in the form of Greenhouse Gases (GHGs), which are the mechanism through which climate change is occurring.
It is good to distinguish between renewable and low-carbon energy. For example, nuclear energy requires a finite fuel for its operation, which means it is not renewable. However, it is one of the lowest carbon options available, which means that the quantities of GHGs it releases per kilowatt-hour of electricity are lower than those of other energy forms. In fact, the only carbon emissions from a nuclear plant come from constructing the actual building.
Our first option for renewable heating is a controversial one. Biomass burning is the oldest form of renewable energy by a long shot. When the first caveman realized they could heat themselves by setting fire to a log, they were burning biomass. It simply refers to any energy or heat obtained by burning organic materials, typically wood. The steps in this process have become much more sophisticated since the time of The Flintstones.
Is Biomass Burning Sustainable?
The reason biomass is so controversial is that it is arguable whether it is genuinely renewable. There is an even weaker case for it being sustainable. The idea is that biomass burning is renewable because you can simply grow more trees to replace the ones you burn. The problem is that trees take quite a while to grow. When you burn wood, you release carbon that has been stored over the course of tens to hundreds of years of tree growth.
It is technically true that if you planted a tree for every tree you burned, the process would be carbon neutral. Unfortunately, we are cutting down trees at a much faster rate than we are planting them, and even then, it will take decades before we start to see the carbon sequestration benefits of that growth. With the climate crisis accelerating, you could argue that we do not have the time to spare to let the new trees grow, and we should protect the old ones.
There is still some sort of argument for biomass burning. For example, if you use agricultural waste instead of trees, you can get pretty environmentally friendly energy for pretty cheap. If you are one of the people who think biomass burning is a good idea, here is some info on how it works and how you can install a biomass burner in your home:
Biomass Burning in Practice
These days, home biomass burning usually consists of a wood stove connected to a ‘back boiler.’ That means that as well as heating the room containing the wood stove, you can also heat your water using the fire’s energy. A wood boiler is likely to be a fair bit bigger than a gas or oil burner, so make sure you have space for all the components before committing to biomass burning.
In addition to the sustainability issues, biomass boilers could actually cost you more per year than a typical gas boiler. That is quite unusual for renewable energy. Usually, there is a high upfront cost, then a much lower yearly cost afterward. For these reasons, it is my opinion that biomass burning is the worst option available for renewable home heating. However, they are still better than fossil fuels.
Ok, now we are getting into the good stuff. Heat pumps absorb heat from a few different sources, which is then distributed into your home. There are a few different options. The heat source can come from either the air, the ground, or a body of water. Heat pumps are truly renewable since they require no source of fuel whatsoever to run. Admittedly, some electricity is required for air compression, but heat pumps are still extremely low-carbon.
Are Heat Pumps Sustainable?
The simple answer to this question is yes. If everyone heated their home with heat pumps instead of gas and oil, we would be in a significantly better position to reach global climate goals. The same cannot be said of biomass burning; if everyone heated their homes by burning trees, soon there would be no trees left, with dire consequences for the climate and biodiversity.
When it comes to ground source heat pumps, which use geothermal energy to generate heat, how sustainable they are depends partly on whether they are open-loop or closed-loop. In an open-loop system, the fluid used to transfer the heat from the ground to the home (usually water) does not stay within the system. In a closed-loop system, the fluid (refrigerants) remain within the pipes and are recycled. These systems are much more sustainable.
If you would like to learn a bit more about sustainability in ground source heat pumps, check our post “Is Geothermal Heating Bad for the Environment?“.
Heat Pumps in Practice
As we mentioned above, heat pumps can get their energy from the air, ground, or water. All three share a major benefit: they are not dependent on the weather outside to function properly, unlike wind and solar energy. We will now go through each of these options individually and compare the pros and cons of each:
Ground Source Heat Pumps
Ground source heat pumps are costly to install initially but then become extremely cheap to run afterward. You can choose to either run the pipes down vertically, which requires expensive drilling equipment, or you can run them horizontally, which requires you to own quite a lot of land. Vertical pipes are the more expensive option, but in either case, the installation will end up costing quite a bit.
Installing a ground source heat pump can cost up to $18,000, depending on the type of pump you get and how much space you have to heat. Depending on the type of heater you replace, you can end up saving around $2,000 per year. Considering heat pumps last around 25 years, you should make your money back and then some.
Air Source Heat Pumps
Air source heat pumps work by gathering the latent heat in the air, then compressing it into a usable heat energy form. This is the same process that occurs in ground source heat pumps. The only real difference is the source of the heat. Since there is almost always some latent heat present in the air, these pumps can generate heat even when the outside temperature is as low as -15℃ (5°F). That is very impressive, given they take their heat from the air.
Air source heat pumps are significantly cheaper to install than ground source since you do not have to bore deep holes or lay huge amounts of underground piping. In fact, it can be around half the cost of a ground source. You will need to install a pretty large piece of machinery on the outside wall of your house, so make sure you have space for that before committing to an air source heat pump.
Water Source Heat Pumps
Water source heat pumps consist of a series of pipes containing heat transfer fluid, submerged in a body of water. The heat from the water is then compressed and converted into a form in which it can be used for water and space heating. While water source pumps can often be more efficient than the other two options, they will not be discussed in as much detail here, since they require quite a large body of water to work, and not many people have access to this.
Solar Thermal Panels
The use of the sun’s energy to heat water for domestic use goes all the way back to 1897! These days, solar thermal systems can have up to 70% efficiency, meaning that 70% of the total solar energy that hits the panels will be transferred to your water tank or space heater. The way it works is that the sun heats a transfer fluid contained within the panels, which is then transported to the boiler, where it heats your water.
Is Solar Thermal Sustainable?
Broadly speaking, yes, it is! However, just how sustainable it is will depend to an extent on where you are in the world. In the UK, for example, where the sun is almost always behind a cloud, solar thermal systems have to be backed up by gas boilers, making them less sustainable.
Solar energy is truly renewable. Every day, enough solar radiation hits the earth to fulfill the entire world’s energy needs 10,000 times over. Unfortunately, that would require every square foot of the earth to be covered with 100% efficient solar panels.
However, the point is that there is plenty of solar radiation to go around, and we are not going to run out of it any time soon. The main environmental impact comes from the materials required to build and install the systems.
Solar Thermal in Practice
With relatively low installation costs (compared to other renewable options), solar thermal is actually a pretty viable way to generate clean, renewable heat. In fact, 1.3% of US households have already installed a solar water heater. That is 1.5 million homes! Installation is relatively straightforward and costs significantly less than a ground source heat pump. The initial cost of solar thermal in the US is about $7,700 for a full system.
The life cycle cost of solar thermal panels can vary quite a bit. In the US, it can take anywhere from 4 to 13 years to make your money back, depending on how much sun you get each day, what kind of system you are replacing, the size of the system you are installing, and many other factors. The huge number of factors makes it very difficult to be more specific than that. Given that they last 25 to 40 years, however, you will definitely make your money back.
Two Types of Solar Thermal Water Heaters
At the moment, there are two main contenders in the world of solar water heaters: Evacuated Tube Collectors (ETCs) and Flat Plate Collectors (FPCs). Although they function in very similar ways, there are quite a few differences that you should take note of before committing to one or the other. Let us also go through a few of the pros and cons of each:
Evacuated Tube Solar Thermal
ETCs are the more sophisticated of the two options, which means they are also a bit more expensive. ETCs consist of a series of highly insulated tubes containing a heat transfer fluid and a copper pipe. The transfer fluid is heated by the sun, then pumped to the water boiler, where the heat is deposited. A big difference between the two is that in ETCs, there is a vacuum surrounding the tubes for much better insulation, hence the name ‘evacuated.’
- Achieves higher temperatures – ETCs can heat water to over 250℉ (121°C). That is significantly higher than FPCs, which can reach 170-180℉ (77-82°C).
- Lightweight – ETCs are lighter than FPCs, which can be a big plus for ease of installation. It also makes ETC the better option if you have fragile rafters.
- Extremely efficient – Thanks to the vacuum’s amazing insulation around the glass tubes, these systems are highly efficient.
- Expensive – As mentioned above, ETCs are a more sophisticated device and can cost significantly more than FPCs.
- Overheating – Since ETCs get too much higher temperatures, it is much more likely that they will break from overheating, especially in a hot climate.
- Less Efficient In Hot Temperatures – Although they get more efficient than FPCs in cold weather, they do not perform hugely well in the heat.
Flat Plate Solar Thermal
The other for solar thermal water heating is Flat Plate Collectors (FPCs). The main difference is that instead of exposed tubes, the front of the panel is a single flat plate. This increases the panel’s surface area, increasing the total amount of energy it can absorb from the sun. FPCs are not only cheaper but also more durable and less likely to overheat. Unfortunately, they are also heavier and more difficult to install.
- Cheaper – These are simpler systems that will cost about 10-15% less than the alternative, although it must be said that ETCs are getting cheaper by the day.
- No Overheating – Due to the lower operating temperatures, FPCs are extremely unlikely to overheat, meaning they are likely the better option in a scorching climate.
- Warranty – FPCs generally have a much longer warranty due to the lower likelihood of overheating. They can be in warranty for 20 years instead of just 10 for ETCs.
- Less Efficient – Although they can often work better in very hot temperatures, FPCs are on average less efficient than ETCs.
- More Wind Damage – FPCs can more easily be damaged by wind due to the large surface area, and this means you have to mount them at a less efficient angle.
- Harder to Install – Due to the extra weight, it is more difficult to install FPCs. They also might not be suitable for roofs with fragile rafters.
There are loads of great options when it comes to heating your home with clean energy. Each option has its pros and cons, and, unfortunately, all are still pretty expensive up front. However, you will make your money back in a few years using any of the above options.
Given how serious the climate crisis is becoming and how little governments are doing to combat it, installing one of these sustainable systems is worth it for the environmental benefits alone. If you can also end up saving money on your bills in the long run, what is stopping you?
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