Throughout the course of human civilization
we've enjoyed what we believe to be effectively unlimited energy and resources in our global
playground enabling us to do more or less whatever we wanted wherever and whenever it suited
us without any concern for the consequences. And when there were only a few hundred
million of us scattered around the earth that philosophy was probably quite valid. But
there's nearly 8 billion of us now, and we'll be more than 10 billion by mid-century, so the old
mindset of 'nature's infinite bounty' doesn't hold true anymore and we've reached a point where our
earth systems are really creaking at the seams to cope with our rapacious demands. Most
rationally minded people have at least recognized that the major causes of our current predicament
are over consumption and of course the burning of fossil fuels. Our policy makers all know very
well that we need to very rapidly move to low carbon sources of power like wind and solar in
what will become a much more electrified future, but that paradigm shift will ask an awful lot
of our electricity grids in the coming years. By 2030 most people who own a car will be driving
models powered by batteries not hydrocarbons. Millions of homes around the world will be running
electric heat pumps instead of gas boilers. Significant additional strain will be put on our
grids by more and more data centres to feed our insatiable addiction to social media and digital
information, and all of that will be exacerbated by things like cryptocurrency mining facilities
and the rapid increase in air conditioning systems. So I think it's probably fair to say we
no longer have the luxury of being profligate in the way we use the energy and resources available
to us on our little blue galactic spaceship. In fact what we need to do is find really smart
ways of optimizing the energy we generate so that virtually none of it is wasted and therefore the
amount we need to generate in the first place is minimized. Solar panels are a great example. The
best technology available on the market today has a sunlight to electricity conversion factor
of about 18 to 20 percent. That means more than 80 percent of the energy hitting the panel
is simply wasted as heat. And actually, because of physics stuff that we won't go
into here, as the heat builds up on the panel it reduces the panel's ability to produce free
electrons to make electricity. So ironically on a nice hot sunny day in summer a solar panel rated
at 20% efficiency may only be achieving about 12%. So here's an idea straight out of the
Edward de Bono school of lateral thinking... why not find a way of capturing that excess
heat, drawing it away from the solar panel, and doing something useful with it? That way
you kill two birds with one stone - you get more efficient solar panels and you use
less energy producing heat somewhere else because you can just use the energy the sun has
already provided. Sounds a bit obvious when you say it out loud doesn't it, but it's only very
recently that people have been developing it into a marketable proposition. It's called photovoltaic
thermal or PVT, and it could increase the amount of energy your solar panels can harvest by
as much as three times. So let's take a look. Hello and welcome to Just Have a Think.
Now you might be thinking 'hang on Dave, surely rooftop solar heating has been around
for decades?' And you would of course be quite correct. Jimmy Carter had solar heating panels
installed on the roof of the White House while he was president in the late 1970s, before Ronald
Reagan had them removed during his administration. Rooftop solar hot water heaters can achieve
sunlight to water heat conversion efficiencies as high as 50% or more, but they have very low
capacity factors. So what does that mean? Well, a typical system is designed to meet water heating
demand even in the depths of winter but in those colder months it can take most of a day to meet
the heat demand of the household water system. On a sunny summer day the water can
get piping hot within an hour or so, and that means all the solar energy for the entire
rest of the day is completely wasted. By contrast solar photovoltaic panels generate electricity
that can either be used immediately or stored in batteries for later use by the householder.
But unless you've got a roof the size of a small warehouse you're only likely to have one
or the other installed for your domestic needs. And because in most parts of the western world
natural gas for home heating has, at least until recently, been so cheap and gas boilers have
become so efficient, solar thermal panels have largely lost out to solar photovoltaic panels in
a battle for that limited rooftop real estate. But what about that Solar PV
panel inefficiency factor? According to this 2017 analysis paper by the
Swiss federal funding programme Energie Schweitz, "approximately 10% of the solar irradiation on
a crystalline photovoltaic cell is reflected and cannot be utilized. Around 17% of the remaining
90% of the irradiation that is absorbed by the cell can be converted into electricity
and 73% is converted into thermal energy. In a photovoltaic module the thermal output
remains unused. It raises the temperature of the cell and can thus have a negative effect on the
electrical efficiency of the module". And here's that again in layman's terms... a typical solar
panel is rated for optimal efficiency at a cell temperature of about 25 degrees Celsius. That's
not ambient surrounding air temperature, that's the solar cell temperature. For every 10 degrees
Celsius the solar cell heats up above that level, the panel loses something like 5
percent of its rated performance. So a panel at 75 degrees Celsius would have lost
a quarter of its ability to generate electricity, and on a sunny day in somewhere like Australia,
which by the way has the largest proportion of solar PV panels per household in the world,
it's not uncommon for panel temperatures to hit 100 degrees Celsius. It's almost the
definition of irony isn't it really - a device that relies on the sun but actually
gets less efficient as the sun heats it up. And the really harmful enemy of solar panels
is sustained heat. According to Professor Martin Green of New South Wales University, who's
affectionately known as the godfather of solar PV, a decrease of 10 degrees Celsius in operating
temperature could double the lifespan of solar panels and boost their performance every day.
Now you could stand on your roof with a hose pipe in your hand spraying all your panels
with water during the hottest part of the day. That would certainly cool the panels down
and immediately improve their efficiency. But you'd probably get bored and eventually
you'd get heat stroke and fall off the roof. Plus you'd be using a bunch of water, which is another
precious resource you don't really want to waste. And natural gas isn't quite as cheap as
it once was is it? Over here in Europe, where bad things are happening, our home heating
bills are about to go off the scale. Plus policy makers in most countries are now looking for ways
to urgently reduce the carbon dioxide emissions from their national energy sector, not to mention
reduce their reliance on fossil fuel supplies from less than reputable sources. So if there was a
safe and reliable way to cool down solar PV panels to optimize their electrical performance and
divert that recovered heat to do some useful work then you'd be on to a winner right? And that's
where PVT technology comes in. It's actually been in development for a few years. Early designs
attempted to combine the design of a solar thermal panel with solar photovoltaic technology by
essentially adding liquids in an energy reservoir heat exchanger box bolted to the bottom of the
solar PV panel. The liquid was plumbed up to the box from the house and a pump was used to control
the flow and outlet temperature. But these early designs came with a few drawbacks. Firstly, the
heat exchanger typically had an inlet at one end and an outlet at the other. That meant the cells
closest to the inlet were always cooler than the cells closest to the outlet. The difference could
be quite significant across the panel, and because of the interdependent way that cells work on a
solar panel that temperature variation meant the performance of the whole panel was only really as
good as the hottest cell. And the liquid needed to be in constant contact with the back of the panel
to allow the heat to be dissipated away. Industry research showed that even with a small air gap the
heat transfer dropped exponentially with gap size. And in colder climates an antifreeze like glycol
had to be used to prevent the heat exchange liquid from freezing. Leakage from joints was also an
issue, and you don't really want liquid escaping into a confined space with high voltage DC current
flowing through it. Add to that the complexity of all that plumbing during installation, and the
extra difficulty of repairing or removing the plumbed in panels, and you've got yourself a bit
of a cumbersome solution that could be a difficult sell to the average punter. The alternative is
a PVT system using air or gas like this one from an Australian startup company called Sunovate.
In a recent web chat that I had with Sunovate's co-founder and technical director Glenn Ryan,
he explained how the system works. An airtight cassette is created using the same inexpensive
stamping machines that make car body panels. The air box is designed to be simple enough that
it can either be factory fitted to the underside of the solar panel or retrofitted to existing
panels on a rooftop in such a way that it doesn't affect the warranty of the existing panels. At
each end of the box is a fan that pushes ambient air in, which then gets heated by the excess
panel heat and sent back out of an exit point. So you're constantly removing heat energy from
the underside of the solar panel which means its electrical generation capacity is being improved
and you're harvesting the heat energy to do some useful work. Sunovate's research showed that on
a typical 25 degree Celsius day you can easily get 40 degrees Celsius of heat energy from the
cassette system, which effectively increases the amount of solar energy being utilized by the panel
from 17% right up to about 50% and increasing the operational life span of the panel from about
20 years to something more like 50 years. And of course once you've captured the heat
energy there's a whole bunch of options for what you can do with it. It can be fed directly into
a ducted system to provide direct space heating inside the house, or it can go through a heat
exchanger to supplement your home's hot water system. There's even a company called Stiebel
in Germany that makes an interior air source heat pump which could take the excess heat
energy directly from the Sunovate system and use it to provide all of the homes heating and
hot water, even on colder days. In hotter regions like Australia and the southern states of America,
where your house may not need any heating, these systems could dump heat somewhere
else like into the pool in the garden, which I'm told are a popular choice in those
parts of the world. If I had one in my garden here in England it'd probably be more useful as
an ice rink to be honest, but the point is you're still removing heat from a PV system to allow it
to operate far more efficiently and sending that heat into something that would otherwise be using
electricity to keep it warm. And as an added bonus the exact same cassette system can harvest
cool air at night time when the surface of a solar panel is typically about eight degrees
Celsius cooler than the surrounding ambient air. That air can then be circulated around the home to
provide a more comfortable night time temperature in those hotter countries. But these PVT
systems also have a great potential in larger applications. In a commercial setting they could
be used for all sorts of services like wood drying or supplemental heat for industrial processes. And
perhaps one of the most promising opportunities is in district heating systems. Sunovate's plan is
to integrate their solar PV heat recovery system with glass house type structures to
create multi-megawatt installations. District heat can supply residential homes and
public buildings as well as commercial greenhouses and industrial processes. They can also be
connected to large seasonal storage facilities where heat energy can be squirreled away for
winter and high demand periods. In Denmark for example they've got systems that collect heat
during the summer and dump it into huge pit storage systems with insulating foam toppers. And
in the Netherlands there are facilities that force hot air into subterranean aquifers for long-term
storage. All of these existing systems could be greatly enhanced using harvested energy from PVT
technology. It's certainly an ambitious goal, but if it can be achieved then we'd have something
that would be making a really tangible difference to our global decarbonisation challenge. Sunovate
themselves have a couple of big scaling steps to go through before they can provide commercial
scale data for their levelized cost of heat production, but in our web chat Glenn Ryan told
me he's confident that once they reach mass production levels they'll be at least competitive
with natural gas with an applied carbon price. My YouTube buddy Rosie Barnes visited Sunovate's
prototype site out in Perth, Australia recently and she's produced a fascinating video over at
the Engineering with Rosie channel looking at how solar thermal is likely to fit in with the overall
renewable energy matrix. And I'll leave a link to that one in the description section below. You
may well have direct knowledge of these systems or perhaps you're already working in the industry and
you can share a few nuggets of insight. If you do, or if you just have views on the subject one way
or another, then jump down to the comments section below and leave your thoughts there. That's it for
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