A summary of Kaspar Bradshaw’s talk on 04.11.24
Kicking off our Green Open Homes 2024 season this week was Solar Thermal Engineer Kaspar Bradshaw, from Stoke Newington-based Next Step Heating.
With eight years of experience in renewable energy – learning in Scotland and working in both Germany and the UK – Kaspar admitted to being passionate about his subject. And it shone through his encyclopaedic, brilliantly thorough and engaging talk, explaining the mechanics, exploring the options and exploding the myths surrounding solar power and air source heat pumps, followed by a lively Q&A session with the audience.
Solar panels …
As Kaspar walked us through three solar energy options, unexpected take-homes included ensuring that bird mesh is fitted with “above roof” solar panels. They can cost up to £800 to fit retrospectively and birds nesting under panels is a major problem, which has been known to cause fires.
An alternative is a “flat roof” system where, despite the optimum angle for capturing sunlight being 35°, they are tilted at 10° to allow for water run-off, but mitigate against wind damage. Equally interesting, this results in less differentiation as the sun travels, thus spreading the power across the day.
And the third option is the “integrated” system, which sit on plastic trays flush with the roofline, but with the drawback of requiring flashing around the edge, which means that less panels are possible, and an inverter is needed, which also needs space; although Kaspar pointed out the option to then fit a battery to store excess energy in.
On the subject of batteries, we discovered that lithium-ion batteries were now being replaced by lithium iron phosphate, which are considered safer, last longer and are getting increasingly cheaper. Good news!
“Solar panels are very reliable” Kaspar summarised, “There are 50 year old panels in space that are still working!” It is the inverters that are more likely to need replacing over the solar panels, he added, because they repeatedly disconnect mechanically when the sun goes down. Most, however, come with a 5 – 10-year warranty.
Air Source Heat Pumps …
The typical perception of ASHPs is that they are noisy, expensive and take up lots of space. Not necessarily true, Kaspar explained.
Amongst many a “who knew”, we learned that they can be disguised in constructions similar to bike sheds or bin stores, but that the critical factor for ASHP efficiency is airflow, so louvred sides are imperative, with a specific 45° tilt for optimum airflow. Such a ‘disguise’, he added, can also deter thefts which can happen, although it was noted that it would require an engineer to do so.
Who also knew that they have a defrost programme, allowing them to work at -15C and that they can be sited up to 20 metres from a house, using underground, insulated pipework?
On the subject of airflow, ASHPs are generally sited at ground level – below ground will result in cold air blasting down and being trapped there, reducing efficiency. It is possible to install one on a roof, however, but at 150kg for the average heat pump, installation is more involved and a roof needs to be suitably robust to handle the weight.
Unlike combi boilers, ASHPs always need a cylinder, because they can’t produce a through flow of hot water, but heat the water in the cylinder up in stages. These cylinders need to be vertical, so somewhere with enough height is needed. The boiler upgrade scheme offers a £7,500 grant towards the cost of replacing your gas boiler with an ASHP, and this is likely to cover around half the cost, unless you also need to change radiators and do some further insulation. ASHP heating generally needs larger radiators than a gas boiler because the flow temperature is lower, but a proper heat loss calculation will be the first stage, and advice will follow from that.
And what about the infamous noise, an audience member asked? Kaspar explained that an ASHP typically emits 60 decibels from a meter away. For a neighbour, that is reduced to 42 decibels, which is akin to the hum of a fridge.
Mechanical Ventilation Heat Recovery systems …
And so, on to the gratifyingly abbreviated MVHRs: a very efficient way to keep a house well ventilated through the winter, when windows can’t be opened, an air-filtering boon for asthmatics, for example, and a great solution for basement rooms. But … expensive at between £6k -12k.
An MVHR system also needs space for a central unit and ducting running to each room. It expels stale air and draws in fresh air, recovering 85% or so of the heat as the air flows pass each other. They are often favoured in a whole house refurbishment and retrofit can be difficult, but it depends on the house.
And finally …
The three systems, Kaspar explained, are all separate, but can work together well when their positioning is coordinated, which requires a skilled installer. On how to choose said installer, his advice was to always look for MCS certification, which stands for Microcertification Scheme and oversees installers and enables redress. An evening of indispensable advice, then, and an encouraging one too – with a good turnout of engaged people, all armed with questions and looking for guidance in decarbonising their homes.
Huge thanks to Kaspar Bradshaw from Muswell Hill Sustainability Group and all who came to his talk.
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