For the avoidance of doubt, I’m the dummy in this scenario. My partner and I struck out to renovate a pair of barns on our property, and it was important to me to pursue sustainability wherever possible, remain efficient, and be economically viable. We do not have endless resources, and balancing budget with sustainability has certainly been a driving force in my desire to understand the long-term consequences and benefits of various energy options.
But, I have no knowledge or understanding of engineering or electricity and very limited knowledge of renewable energy technologies – other than what turns up in a google or youtube search. So, I knew the hill I’d have to climb would be to understand the detail behind how renewable energy systems work together to optimize output and minimize cost.
So, I thought I’d share what I learned – my own little playbook for the layperson. It works for this very singular scenario, and every scenario will be different, but perhaps the thought process and learnings that we went through could be beneficial to others (or to me). As a friend rightly said, “write it down because if you ever decide to do another project like this, trust me….you won’t remember it.” Ah, the joys of middle-age.
Sidenote: I’m going to use phrases like “more sustainable” or “striving” or “trying” throughout the description of my sustainability journey. I do this out of acute awareness that no project is completely sustainable. There are compromises everywhere. Naysayers love to pick up on the hypocrisies imbedded in any pragmatic project and leverage them to assert superiority: they say the project was sustainability focused, but did you see how much concrete went into the foundation? Hmmph – judgey mcjudgeface….#I’dratherdonothing. This is a pet peeve of mine.
When people are trying to do something good, it is counterproductive for others to judge that good act and drag it down by pointing out all of its flaws – but, let’s face it: that is human nature. If it makes a person feel better about his lack of action to drag down others that are trying (and often failing!), that is something for said person to work through in therapy. For my purposes, I’m going to applaud the attempt, and try to not judge the compromises. Instead, I’ll just try to share knowledge so future compromises are informed.
The first and biggest question I had when looking at a more sustainable home was how to keep it warm. I started researching ground source and air source heat pumps as an alternative to gas boilers. For more on that, have a look at our An Idiot’s Guide to Heat Pumps.
One of my major conclusions in carrying out this research was the discovery that heat pumps can be much more expensive to run when electricity and gas prices are at historic levels, because electricity prices per kWh are so much higher than gas. I also recognize that if thousands of homes in the UK are converting or planning to convert to electricity based heating and hot water generation, and millions of people are going to switch to electric cars, we are going to need a lot more electricity. In fact, according to the the Sixth Carbon Budget it is estimated that the UK’s electricity demand will increase by 50% between now and 2035, and will nearly double between now and 2050.
In our strive to achieve a more sustainable home, we explored options to offset our electricity needs, and to support the drive to more renewable electricity generation. Solar panels certainly seem to be the most straightforward option for this. As part of the build, rather than putting a traditional roof on our property (the existing roof is derelict and has asbestos material in it), we are hoping to install a set of frames that can hold solar panels in place of traditional roof materials over the majority of the roof. This achieves two things: 1) it does not impact the footprint of the house. Traditional solar panels are mounted on top of the roof, and stick out; 2) it saves us paying for a roof that we will then cover up with solar panels.
The first thing we had to understand was our power supply. We have single phase power to the barns today – meaning we could return a maximum of 3.68kW to the grid. That means that without a battery in place to store the power we don’t use, there wasn’t much point putting more than 16 solar panels on the roof.
So, after much googling and youtube searching, I cobbled together a meager understanding of electricity supply and distribution, and applied to our electricity provider (Northern Powergrid) for a quotation to install three phase power to the property. It estimated that an investment of roughly £8,000 to upgrade from single to dual phase electricity, and £15-20,000 to upgrade our power supply to three phase power would be required if we wanted to return more power to the grid.
Three phase power would give us up to 75kVA on 100 amps per phase (55kVA on 80amp per phase), and allow us to return up to 11kWh to the grid in return for payment. If we install an inverter larger than 3.68kW on a single phase supply or 11kW on a 3 phase supply, we will need to submit a G99 application to return that amount of power to the grid.
We will likely get paid 5p per kWh for any electricity we return to the grid, so this is not the motivating factor. In fact, it is much more logical to invest in battery storage alongside the solar panels so that we can use the electricity we generate ourselves to offset the cost of electricity, rather than maximizing the amount of power we can return to the grid.
Overall, the up front cost of purchase and installation of the panels and batteries is significant. That being said, it is the best way to maximize the benefit we get from the solar panel installation. Without battery storage, energy we generate above what we are currently using is sold back to the grid for 5p or lost.
With battery storage, any electricity we are generating above what we are currently using gets stored (assuming we get the right size battery). And, we need a big enough battery to store what we aren’t using, because if we overload the system with more electricity than we can store or return to the grid, we are likely to experience faults in the system.
With stored electricity in batteries, we can use the excess generated energy from earlier in the day overnight when we aren’t generating electricity from the solar panels. Using the electricity we generated earlier in the day, rather than selling it back to the grid helps us avoid paying 35p per kWh to our energy company for that electricity (because we are using the energy we stored earlier in the day). So, instead of getting 5p for each kWh we generated during the day above what we used, we are saving a net 30p on avoided cost overnight.
Smart systems can help batteries pay for themselves even more efficiently when flexible electricity tariffs are available. For example, if I have a cheaper tariff overnight with my energy company, I can program the batteries to recharge themselves from the grid overnight, and then I can use that energy during the day, avoiding peak electricity rates.
Our expectation, based on estimates from experts, is that we could fit a maximum of 32 solar panels on the two roofs – powering the ASHPs and hot water plus electric vehicle charge points. We estimate we will require 14,700kWh per year to power the buildings. Our estimate is that we can fit 32 solar panels on the roof and that would generate about 60% of the required energy to power the residences over the course of the year. The remaining power required to power the buildings will come from the grid.
Naturally, the amount of energy generated and our energy needs will fluctuate wildly throughout the day and the year. We will be able to sell electricity back to the grid at some times, and buy electricity from the grid at times. The aim is to more than offset the additional electricity needs of the ASHP, and achieve very low utility requirements (and therefore bills).
In speaking to other families with solar panel installations, the advice has resoundingly been in favor of investing in battery storage alongside a solar installation for two reasons. The first is that it provides you electricity provision in he case of an outage from the grid. While outages are not common at this point, there is some speculation they could become more frequent as demand increases (but this has yet to be validated or proven).
The second reason is that the payment you receive in return for energy you provide to the grid averages around 5p per kWh – quite a discount off the 35p per kWh that you will be paying for electricity. So, overall, it is overwhelmingly attractive to generate power and store it for your own consumption, rather than selling it back to your energy company.
I recognize that battery storage is expensive, so not all households will be able to invest in solar panels and batteries up front. That being said, battery investment should pay off in the long run. For a battery that requires £5,000 to purchase and install, it will pay for itself in the storage and use of between 16,000 and 17,000 kWh. That is a little more than the estimated annual usage per household for a 4 bedroom house.
That is not to say that your battery will pay for itself in a year – it is more complicated than that, because battery storage will only kick in when you are generating more electricity than you are using. So, the time span over which the battery investment pays for itself will depend on the size of your installation, the weather, and your usage.
The cost of this additional investment is estimated to be about £20,000 for the panels themselves. It is estimated the solar panels will pay for themselves over an 8-10 year time horizon. But, given that we have an electric car (the solar system includes an inverter to charge the car directly), and we are generating hot water for bathrooms, washing up, and all the electronics that will be running on the property, we expect that our electricity needs will be higher than average, and the panels will pay for themselves slightly faster than that.
Throughout this journey, I have been helped immensely by our partners, Pure Renewables, in understanding the science, mechanics, and engineering required to make renewable energy in our home a reality.