by guest blogger Ben Whittle
Some might say my claim of authority to write on this
subject is sketchy at best: I’ve only lived with and monitored a solar thermal
system for less than 6 months, and I have only seen data from a few
installations ever. But maybe that is exactly why it is a subject that needs
discussing in the solar thermal industry… because I have been installing and
designing solar thermal systems for around 10 years and I can count the number
of installations I’ve seen that have monitoring on them on one hand, (and one
of those installations is my own). And when I say we need more data-logging, I
don’t mean turning on the heat quantity measurement function, I mean proper
data-logging: measuring temperatures at the top, middle and bottom of the
store, pump on and off times, boiler trigger times, heat measurement, the lot.
Over all the years I have worked in this industry I have
seen a lot of mistakes made in designing and installing systems (and some of
them were my own mistakes). How do I know they were bad designs and mistakes?
Because I had to go and fix them. How can we possibly move on as an industry if
we can’t try and make some sense of what mistakes were made in the past, and
learn from them? Of course we have made leaps and bounds in some areas: the
quality of the panels, plumbing, tools and fittings we are using (thank the
lord for press fit pneumatic tools and filling pumps!), the MCS standards, the
list goes on. OK, great, we can install stuff quickly and efficiently and it
doesn’t leak… what’s the next step? Actually measuring how the systems are
performing. Because I can tell you in the UK we have a long way to go in terms
of getting our solar thermal systems to perform as well as can be achieved as
seen across mainland Europe and America , and keeping track of performance is
the only tool that can help us do it.
Now of course there are all sorts of reasons as to why we
don’t normally achieve performance levels of a high quality Austrian
installation… predominantly that is because the average UK house doesn’t have
space for a 500-1000litre hot water store in the 700mm wide airing cupboard.
But let’s put aside the things we can’t tackle and talk about the things we
can.
To my knowledge there are only 2 or 3 solar thermal trials
of any significance that have been published in the UK on solar thermal, and
probably the best of these was conducted by the Energy Savings Trust three
years ago. For those that are interested it’s called “Here Comes the Sun – A
field trial of solar hot water systems”. It’s a great document, short (24
pages) and to the point. It tells you what you need to know – the biggest
impact on solar thermal performance has nothing to do with evacuated tubes or
concave reflector plates or low emissivity glass. But how did they reach those
conclusions? By measuring things and writing it down – and, you know, analysing
it and stuff.
And that is where we need to be going as an industry –
looking at data, working out how to improve things, and changing our behaviour
to suit. Not only will measuring performance allow us to understand the
mistakes we make, it can inform our design decisions and help us to improve
everything we do… and of course there are other benefits to consider as well.
1: Data logging is another chance to “add value” to your
installation work. It’s a slightly more expensive controller, or an additional
bit of kit to be sold, and a chance for your geekier clients to play with a
spreadsheet or two. Now if you haven’t had a great experience installing solar
thermal and the thought crossing your mind right now is “yeah right, and the
customer is going to use this data to beat me with like a stick when it all
goes wrong,” then I really am talking specifically to you. Because there are
thousands of systems out there in the world that do perform absolutely
perfectly, and as an installer you need to understand how they work.
2: It’s a chance to fault find, and take the correct action
if things do go wrong, instead of guessing.
3: It will help you understand how people interact with
their solar systems.
4: It can help get you out of trouble if the cause wasn’t
your fault. One of the few logged systems I have seen was a school pool system
that was constantly stagnating and losing pressure after being installed. When
the data card was posted back to the company I worked for, it didn’t take long
to diagnose the fault. The college maintenance man had been turning the system
off at the main switch on a regular basis (even though it had a sign on it
saying “Solar – do not switch off”). We were even able to re-program some of
the settings using the data card and send it back to them in the post to plug
back in. That’s quite an unusual feature specific only to the controllers made
by Watts industries as far as I know, but a pretty handy one for commercial
systems.
Just imagine what could be possible if we all took this a
bit more seriously – imagine coming in to your office on a hot summer day in a
few years from now after installing a 1000 systems across your local area, to
find a couple of automatically generated emails where your data server had
logged some de-pressurisation warnings at a couple of properties. You could
then log on to watch some live system data to check them, and dispatch a
maintenance team to fix them before your client was even fully aware there was
a problem. All part of the regular maintenance contract you sold them at the
time of installation…. There is no reason why this fantasy couldn’t come true,
and it’s up to us to make it happen. It is already happening in the world of
heat pumps.
As an aside, maintenance contracts are another area I think
we need to explore further as an industry. I recently saw a report suggesting a
very significant proportion of people who buy solar thermal systems would be
happy to pay more than £100 for regular servicing, another possible revenue
stream for any installation business.
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Red=panel, Yellow = top tank,
Blue = mid tank, Grey = low tank
R1 = solar pump on, Rs = boiler on
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I should probably qualify that performance figure by
pointing out that I do not have an “average” UK system, so I’m comparing apples
with pears… but I hope to explore that issue in a further blog post, looking
into hot water storage, and how we might start improving solar thermal
performance in the UK.
