Bit of a slog under the log today, brace yourself. On our community energy page under Green Design we talked about energy storage and smart metering. We mentioned the existence of various energy storage techniques but left it there. Today we’re going to talk about some of these techniques, the types of storage media, and how they’ll shift in effectiveness as the energy generators on the grid shift toward renewables.
First, we should distinguish between thermal and electrical energy storage. The latter is convenient because electricity is versatile and therefore valuable. However, systems that store electricity are typically quite expensive. Whereas thermal energy storage is relatively inexpensive, but its potential uses are far fewer. Both types have their place and can be used to buffer some of the peaks and troughs in energy production and consumption.
When we’re talking about thermal energy storage, anything that has a high thermal mass that you can easily input and extract energy from can be used. Large tanks of hot water are a great option because many conventional heating technologies are already adapted to using hot water and there are many choices for heating the water. Space heating systems that employ the use of thermal storage have a broad range of options for how that stored thermal energy is used.
For example, lets imagine a district energy system with a thermal storage lagoon that is tied to a ground source heat pump system. The buildings tap into the thermal storage system with individual heat pumps that lift the temperature to domestic needs. The community employs solar PV, wind turbines, as well as tying into the grid for electrical energy. So, the factors we need to consider are grid energy price, solar insolation, wind, air and ground temperature, as well as the behaviour of those occupying the buildings. We want to be able to charge the lagoon with the ground source heat pumps when we have solar or wind energy or when the grid electricity is relatively cheap. However, we should also be mindful of when the energy will be needed by looking at community usage behaviours and weather forecasting.
You also need to decide what sort of temperature range you want the lagoon to achieve. A warm lagoon with temperatures between 20 and 50 degrees Celsius will require precautions against legionella, a separation between the system and domestic water would likely be needed. If the temperature range is higher, above 60 degrees, it should be safe from bacteria, but will be difficult to insulate adequately and will likely result in higher losses. You may also strive for a shifting temperature range throughout the year to account for shifting community demand. If the thermal storage’s main use is space heating, then it would make sense to lower the temperature range moving into the summer to account for increased cooling demand. Doing so would also help recharge the geo-field with heat.
As you can see, there are many factors to consider when deciding how to employ thermal energy storage. Your control algorithm might have a hierarchy that prioritizes maintaining the desired temperature band and then charging when surplus wind or solar is available. When grid electricity is cheap, it can be used to charge the lagoon if bad weather is forecasted. However, when the electricity on the grid is expensive and the forecasted weather is temperate, you might choose to sell surplus solar and wind energy to the grid rather than charging the lagoon. Depending on how complex you want to get, there are some interesting control schemes that integrate the different system potentials being employed.
The case is almost completely different when it comes to electrical storage. For one, you aren’t dealing with temperature, at least not directly, and so all this concern about temperature bands is completely irrelevant. Here, all we really need to worry about is how electricity is coming in, how the storage system is going to keep it there, and where it’s going once it’s gone. Obviously, when we’re talking about electricity the source is going to be electrical, but what’s the voltage and current? Is it alternating current or direct current? Is the signal regular? Depending on the generator and how it’s being transported, an electrical signal can behave in a wide variety of ways, some of which can’t be used by energy storage devices. For the sake of simplicity, lets assume our signal is like that we see on the grid. This just means that any renewables we’re talking about are linked to some sort of inverter technology that produces the same sine wave it sees on the grid.
Once you have a regular electrical signal coming into the energy storage device, it can be designed to work with that signal. Different energy storage technologies work better in different usage conditions. Energy storage devices vary in their desired charge and discharge rates, the amount of energy they can store, how far they like to be charged or discharged, and how efficiently they store energy, to name a few. Something like an ultracapacitor can’t hold as much energy as a battery or pumped hydro, but it can dispatch its energy very quickly. Furthermore, they can remain charged without constantly losing a lot of energy. This makes a charged bank of capacitors good at responding to momentary dips in the grid that only last a few seconds but require near instantaneous responses. Something like pumped hydro is quite different. The efficiencies of energy input and extraction (pumping water and running a turbine) are significantly lower than charging a capacitor. However, you can keep a reservoir of water elevated for extended periods of time virtually without storage losses. This makes pumped hydro storage better at taking surplus renewable energy generation and storing it for days, weeks, or even months until it’s needed.
Depending on the desired use for the electricity being stored and how that electricity is coming in, the choice of electrical energy storage will vary. If you’re in Canada, trying to take the surplus of solar energy in the Summer and use it in the Winter, obviously you want something with low storage losses. However, if you’re main renewable energy is coming from wind in an area with relatively consistent winds throughout the year, your storage system might be doing more hour to hour or day to day work and so a high transfer efficiency may be more important. Perhaps all the system is doing is buying grid energy when it’s cheap and selling it when it’s expensive. Then you’re going to want a high rate of charge and discharge so you can buy and sell plenty of energy during the troughs and peaks. Energy storage devices are highly site specific, like many renewables. However, their site constraints are generally the nature of the generators and loads that are tied to them. That said, pumped hydro usually only makes economic sense when the landscape lends itself to the creation of an elevated reservoir.
As the grid changes from central and dispatchable generators to distributed and renewable generators, the energy storage requirements will change in kind. Right now, operators don’t really have much need for energy storage. What capacity exists is typically used to ride out times when generated energy is relatively expensive. However, once the grid is populated with more renewables, it will likely be necessary for grid operators to set up strategically located energy storage banks to buffer the intermittent generation of solar and wind.
If this hasn’t been confusing enough, let me conclude by saying that thermal and electrical energy storage are far from our only options. Finding ways of preserving the summer harvest to be eaten throughout the winter was one of the first ways we started storing energy. The plants act as our energy input devices, taking in solar energy and storing it in fruits, veggies, roots, stalks, and the like. Our methods of preserving the food increase the storage efficiency and our bodies act as tools for extracting the chemical energy.
Continuing the trend from our thermal bridging post, today’s post will be covering another energy efficiency topic, solar gains. Some may peg love or compassion as the most important things in our corner of the universe, but they’d have to do some strong arguing to beat the Sun. The Earth literally revolves around it, despite what recent pop pseudoscientists might have you believe.
At Carbon Busters, we like our homes to revolve around the Sun in kind. As such, several features of our homes are designed with our solar overlord in mind. One of the biggest considerations is the home’s windows. We use high-performance windows with special glazing that is tuned to each window’s orientation toward the Sun. Most of the windows are placed on the South facing sides, maximising the natural light and solar heat gains within the rooms. However, in the summertime when you’re trying to keep the house cool, isn’t that a bad thing? Very true, that’s why we design overhangs into our buildings so that the high summer Sun can’t pour in directly. We also landscape our homes with deciduous trees sheltering these windows, shading them in the summer. In the winter, the leaves fall off and allow the Sun to passively heat the home.
Windows aren’t the only thing affected by the Sun, though. We also like to put our roofs to use by placing arrays of solar PV. So, we make sure that the building has enough roof space oriented in a South direction to place an array that can offset the building’s annual energy use. Of course, if the site allows for other forms of renewable energy generation, the roof design has more freedom. That said, the vast majority of sites in Canada have enough Sun to make the falling costs of solar PV the most economic option. Designing solar PV into a building’s façade can also be a great option for offsetting annual energy. By replacing conventional siding choices with sections of PV you offset its cost making it even more fiscally prudent.
Another component of buildings that can provide substantial passive heating and cooling is the thermal mass of the building itself. An object’s thermal mass is its ability to retain heat. Some materials like stone, concrete, water, and many more can store thermal energy and then release it over time. By designing certain walls and floors that receive a lot of sunlight, they can then store that solar energy as heat and release it after the Sun goes down. In turn, when the morning comes and the Sun is starting to heat your home, the large thermal mass has cooled down again, absorbing the excess heat that would trigger the cooling system.
We can’t talk about solar design without mentioning the photosynthetic basis of virtually all our food chains. At Carbon Busters, we believe that if our society is to make the shift toward a sustainable future, it’s imperative that homeowners can grow at least a portion of their own food. On a site where we’re building a single detached home this task is relatively simple. We work with landscape architects who practice permaculture techniques to ensure the best possible soil health that helps grow the pristinely fresh produce logistically absent from supermarkets. However, even in our multifamily designs we strive to allow each unit some space to grow. We do this by ensuring each unit has balcony space that gets adequate sunlight during the summer or designating pieces of the courtyard for private garden plots.
Although we have a quick blurb about thermal bridging on our Energy Efficiency page under Green Design, thermal bridging can be a tricky topic to grasp. So, this post will try to elucidate some of the nuances that might have been overlooked.
First, let’s think about the components that you’ll typically find in the wall of a Canadian house. Obviously, you’ve got structural components called framing; most Canadian homes are framed with dimensional lumber but sometimes you’ll see steel components in place of wood. The other major component is insulation, of which there are many kinds: fibreglass, cellulose, and foam are just a few. There’s also a vapour barrier, mechanical, electrical, and plumbing runs, but for our purposes the framing and insulation are the two important components.
The second concept we need to talk about is thermal conductivity. Any material out there has some quantifiable thermal conductivity, measured in Watts per meter * degree Kelvin (temperature). Looking at the units we can see that thermal conductivity is the material's capacity to allow thermal energy to move through it from an area of high temperature to one of low temperature. Obviously, this quantity is going to be important when choosing what material to use to insulate a home. You want something with a low thermal conductivity so that any heat trying to leave your home in the winter has a harder time getting out. However, considering the thermal conductivity of framing is also important. Steel has a very high thermal conductivity. Wood’s is lower, but not nearly as low as fibreglass, cellulose, or foam.
So, what does that mean? You aren’t trying to insulate your home with the framing, so why should you care? Although you aren’t trying to insulate with wood or steel, they still occupy space within the wall. Space that can no longer be insulated. Many conventional homes are built with a 2” by 6” wall where the structural joists run from the inside of the wall to the exterior sheeting. This leaves a “bridge" for thermal energy to pass from warm to cold unimpeded by insulation. So, the wall in the areas where the studs exist is essentially uninsulated. Some conventional buildings have gotten slightly better by adding an exterior layer of insulation or offsetting joists to allow for thin layers of insulation between framing and wall. However, these measures still only allow for a thin layer, essentially a speed bump before the bridge.
At Carbon Busters, we design our walls so that instances of thermal bridging are reduced to a minimum. The framing around windows and doors has been clearly thought out to provide insulation between the inner and outer studs to sink the conventional bridging. Our proactive efforts against thermal bridging is just one of the ways a Carbon Busters’ Home provides maximum thermal comfort.
Come on down to Cafe Linnea next Monday night to meet some of the people bringing Edmonton's net-zero community to life.
From 7-9 pm, Emily Dirk and Erin Hettle are hosting an informal meet and greet with the Carbon Busters team. Here's your chance to learn the ins and outs of sustainable living and net-zero buildings, how Blatchford is planning on building a sustainable community for 30,000 people, and how you can become a part of it!
At the end of the day, who doesn't like to learn something new and have some free food while doing it?
The term efficiency gets thrown around a lot these days, but it can mean a lot of different things depending on the context. A lot of the time it's being uttered by some high-rise dwelling business executive who wants those expense reports done by Friday, but its use becomes more constrained in the technical field.
Technically, the efficiency of a piece of equipment is defined by the useful energy produced divided by the energy needed to operate that equipment. So, for your standard natural gas boiler, we typically look at how much heating energy we get out of it, compared to the embodied energy of the gas burnt. The case is basically the same for any fossil fuel burning contraption.
However, in the age of renewable energy the question becomes significantly more complex. Take heat pumps for example. If we measured their efficiency, it probably wouldn't be great because you're taking thermal energy from some source and using pumps and compressors to upgrade it and move it to a desired location. However, do we pay for the source of thermal energy? Does it slowly run out? No. The entire pool can be considered a component of operation rather than strictly a fuel source.
So, the performance of heat pumps is generally measured with the coefficient of performance (COP). This is a ratio between the number of units of thermal energy pumped from the heat pump compared to the units of electrical energy needed to run it. Essentially, it's an efficiency figure that negates energy being moved to or from a borefield or the atmosphere.
What about other renewable energy technologies? Do they use efficiency? Yes, but the case is changed slightly from fossil fuel applications. For wind turbines, solar PV, or hydro installations, the input energy considered isn't some depletable resource that you're paying for, but the rising Sun, gusting wind, or gushing river. Fossil fuel advocates like to point to high-efficiency furnaces that are 96% efficient and compare the figure to a solar PV module that might have an efficiency of 18%, concluding that it would be silly to go with solar. The fallacy being that this would only be an adequate comparison if one, they were paying for Sunlight, two, they pay the same rate per unit solar energy as they do for gas, three, using the Sunlight contributes to greenhouse gas emissions, and four, their continued use of the Sunlight would somehow diminish its source. Obvious malarkey.
If this post was getting a little bit technical for you, check out our green design tab for more information about renewable energy.
Last Friday, the Carbon Busters Homes team went down to the construction site at the old municipal airport for the soon to be commissioned Energy Centre One (EC-1). This being the first location of the central energy centres that will provide Blatchford residents with comfortable and sustainable heating and cooling.
The community takes an innovative approach at district heating, combining geo-exchange, heat-exchange with sewer mains, and heat pump technology. Over 500 boreholes have been drilled under the storm-water collection pond that feed thermal energy back to EC-1. In addition to this huge pool of energy, the warm municipal sewer mains from Northwest and West Edmonton run under the site. A heat exchanger allows EC-1 to pump back much of the heat.
Currently inside the centre is a massive 1 MW heat pump that can operate with a mind-blowing coefficient of performance of 10! That's 10 units of heating or cooling energy to every 1 unit of electrical energy expended, or in other words, absolutely bonkers. The heat pump conditions water to be sent through a network of pipes laid underground throughout the district. Homes will then use this conditioned water with the help of heat pumps to keep their homes comfy.
The centre itself has been built
with efficiency in mind, boasting
thick walls, high performance windows,
and is topped with solar PV. Not to
mention the beautifully designed
building itself. It will be an excellent
centrepiece for one of Blatchford's