SWH prototype project part 6 - prototype conclusions

Here's a bit of a belated update to where we're up to with the prototype panel. For the last few weeks it's been sitting out in the orchard soaking up the rays, and using the energy from said rays to warm up its little tank of water. We set it up on some legs, cunningly constructed from a pair of old doorframes nailed together. It's now sitting at an angle of about 50° to the horizontal*.



















(*For the best all-year-round collection, we would set the panels at an angle equal to our latitude - here it's 34.26°. Setting it up a bit higher favours winter collection (by facing the lower winter sun better), and slightly reduces the chances of the panels overheating in summer. I did lots of complicated calculations to try and figure out the best angle, but these remained somewhat inconclusive - so I reverted to a rule of thumb suggested by some people who seemed to know what they were doing...)

At present there's no pipework in place to enable one to actually make use of this warm water, but that doesn't mean this setup isn't useful. Running a closed system like this allows us to calculate, to a ball-park figure at least, how well it's performing. By measuring the tank temperatures at the start and end of the day we can calculate fairly accurately how much useful energy we're collecting (obviously we have no way of measuring the energy losses, but we can estimate efficiency by comparing our daily energy collection figures with solar insolation data collected over a couple of decades at a weather station not far away).

























Here are some numbers. If you have some objection to numbers, feel free to skip to the pictures and chatty bits lower down!

Some simple thermodynamics also tells us that the hotter the system is running, the higher the heat losses, and therefore the lower its efficiency. Which just means that a record temperature in our tank doesn't necessarily equate to the greatest amount of energy being harvested.

The greatest daily (useful) energy collection we've witnessed so far was 10.6MJ, with our 59l tank rising from 17°C in the morning to 61°C in the late afternoon. Comparing to our insolation figures for January, (9.4MJ/m² per day x 1.79m² = 16.8MJ per day), this suggests an efficiency value in the region of 63%**.

The highest tank temperature we've recorded, after it had been sitting out for a few successive clear days, was a mighty 75°C (with the panel sitting at 81.5°C, and water entering the tank at 78°C). But since the water was already sitting at nearly 50°C from the previous day, this equates to a much less impressive 5.3MJ, and 32% efficiency.


















(**All these calculations contain hefty doses of approximation and a little guesswork. We take several measurements in the tank, as the water tends to stratify in layers of different temperature. You can stick your hand in and feel the temperature lower significantly as you move it downwards in the tank. Also, the weather station's figures are averages over the whole month, for many years. If we happened to get an above average clear sunny day, then this would tend to push our efficiency figure upwards. So we might surmise that we're operating somewhere in the range of 50% - 65%.

Also, the system in it's current state could be improved significantly by the simple expedient of insulating the connecting tubes, by insulating the tank better, and by not opening it up every hour to stick a thermometer in!)

Bear in mind that these measurements are all for the middle of winter - in midsummer we would expect to gather at least twice as much energy.

In case all that maths really wasn't your thing, here's a few of the conclusions I've been coming to about this, and therefore what I would keep or change for the design of the large system:

• The basic design seems to be working well, and we have suitable solar resource and a suitable location and use for it in the hospital.
• The 1.2mm aluminium is seriously hard to work with. Find some thinner stuff.

• Get someone who knows what they're doing to do the copper soldering. Q'bad's finest looks pretty, but I wouldn't want to guarantee its quality.

• Two layers of glass is really heavy, not to mention prone to breakage. Try to get hold of some of that polycarbonate stuff they use for greenhouses.
• Don't let the panels sit outside in the sun with no water in them - it hit 103°C the other day - I suspect the polystyrene insulation in the back of the panel melted a bit. Find some insulation that has a higher melting point. Work out how to shade the panels in the event that they're sitting out empty.
• Don't use whatever this material is for lining a tank with!

It appears to degrade over a few days in the hot water, leaving this interesting greenish flaky stuff:

• Don't drop the thermometer into the tank!

Photo post: Thandiani

This weekend we had a lovely time with our friends Jimmy & Erin (who we met at the orientation conference) who came up to visit us. They had access to a car belonging to another family who are home for a few months, so we grabbed the opportunity to take a little trip up into the hills in search of some snow. We had an early start, leaving at 7am, then after picking up our wheels stopped at a roadside eatery for naan, omelettes and chai.

On the road out of the valley, each new twist brought a better view. This is looking back towards Abbottabad (the hazy bit in the centre of this pic - click to see full size version):










The steep valleys are amazingly populous, with plenty of houses like these built into the hillside:



















Getting the materials up there in the first place must be a mammoth task!

After a while the road became a bit more like this:



















Most of the traffic consists of little Suzukis like this one:



















We'd already had two attempts at getting up this particularly icy corner when this guy came charging down. Downhill is easier than up, and 4WD doesn't necessarily help much when all 4 W's are on patches of ice!



















Pakistani roadsigns don't always tell you what you need to know. We deciphered the Urdu sign at this junction that said Thandiani 3.5km, but couldn't tell from it which direction it lay in. So we carried on for a bit straight on (behind the photographer) until we found some more troublesome patches of ice and snow. After a few tense slippery minutes we decided to turn around and try the other fork up the hill, which had obviously been cleared. A few minutes along that road the direction didn't feel right, so we decided to come back again, park the beast just before the snow started in earnest, and start our hike from there. (The cleared road turned out to be the main road to Muzaffarabad, a place where we're not supposed to go without a special permit, so just as well...)

It was lovely and quiet up here, thoroughly vindicating the early start to the day. A couple of cars (and even a motorbike!) braved the snow, the locals obviously being more determined drivers than we.

The daily commute:





































Balancing on top of the world:





































The view from the top - around 2700m (click for full size version):






We were told we could see Nanga Parbat from here, but we have no idea which bit of the distant mountain range it might have been.

A beach hut? Here?



















Thandiani town centre:



















Thandiani (literally 'cold place') is one of the old hill stations from colonial times, where people would retreat to escape the high summer heat lower down. In winter it's pretty much closed down, with few people around. All their water is brought up in tanks from a kilometre or so down the road. We stopped for some chai in this little eating place:



















Having brought his gaiters all this way, there was no stopping Jimmy wearing them. When they're all the rage next year, remember you saw them here first!





























































Crazy road-building skills once again in evidence:



















Looking back up one of the valleys on the way down:

What You See Is What You Get...

...but isn't necessarily what you wanted.

This week I and my 'boss', Mr P, at the workshop went down to Pindi on another shopping trip - mainly for supplies for the hospital, but also to try and reconnoitre the availabilities and prices of various materials for the solar project.

So after many deals and many cups of tea at various shops (including spending £500 on lightbulbs), we parked the van and hopped into a more nimble rickshaw to head into the narrower, busier streets of the metalworkers' bazaar.



















Riding in this thing feels very much like driving a fairground dodgem - the handling is pretty much identical - only it's more in your interest to avoid the other vehicles rather than take them on. And he can get through some minuscule gaps when he wants to. The bazaar is a bit different from your average one - the stalls/shops are much bigger and generally have piles of interesting things, and various guys making things out of other things.

Anyway, to come to the point of this blog post, here's a representative sample of one of the dual-language, triple-participant conversations in one of the shops. To give a little context, I'm trying to track down some plastic tubing for use as a heat exchanger. It'll need to stand up to nearly 100°C, and there aren't many kinds that'll do that.

(opening pleasantries)

Me: "Do you have any PEX pipe?"

(discussion back and forward between Mr P and shopkeeper in Urdu/Punjabi)

Shopkeeper: "What about this one?" (hands me a bit of tube - a yellow one, 1/2" diameter, no markings)

Me (thinks): "It's a yellow one, 1/2" diameter, no markings..."
Me (out loud): "Umm... what's it made of? It has to not melt at 100°C."

(more Urdu/Punjabi discussion)

Mr P: "Okay, how about this one?" (points out a different one - black, 1" dia, again no markings)

Me (internally): "It's black, 1" dia, again no markings..."
Me (out loud): "Do you know what it's made of? I really need to know the material it's made of before I can tell whether it's suitable or not..."

(more Urdu/Punjabi discussion)

Shopkeeper: "Also, I have this one over here..."

Me (in the privacy of my own head): "But what the @£%$!!ing $£^^@ is it made of???!!!!! Aaaargh!!"

What You See Is What You Get...
...but that doesn't necessarily mean you know what it is, and neither does the shopkeeper.











Random addendum: for ages I've been trying to get a picture of one of the painted trucks at night, because in many cases all that amazing decoration is done in reflective paint. But, not wanting to blind oncoming drivers with my camera flash (road travel here being quite dangerous enough already!), I had to take a short movie and grab a frame from it - not the full glory, but you get the idea:

SWH prototype project part 5 - temperature logging

A quick foray into some electronics, just for a change. The plan is to build a little data logger which will record the temperatures at various points in the panels and tank over the course of the day (or week, or month for that matter) - and thus save me having to take the lid off the tank and check a glass thermometer every hour!

This nifty little screen will eventually give an up-to-the-minute temperature display.



















For my fellow geeks, the red board is a Seeeduino Stalker microcontroller - an Arduino variant with onboard real-time clock and microSD slot for data logging purposes. I'll be connecting up a few MCP9700A thermistors in the next couple of days. In it's current state I have 6 inputs to play with - possibly expandable with a multiplexer at some later stage if I feel like it.

Time and part-availability* permitting I might think about adding a light sensor of some sort, and an alarm for if/when the panels get too hot in summer (so that someone can take some sort of action - probably just shading the panels. It'd be sweet to have some sort of canopy unfurl automatically, but I think that's probably a bit over-ambitious!)

(*a big problem - trade embargoes at the UK end mean RS orders take 6-8 weeks to arrive, after they've obtained an export certificate - I had to get our recent visitors to bring out the thermistors for me. On the other hand, the circuit boards arrived from Singapore without too much hassle...)



















The absence of breadboards means a whole lot of trying to solder ends of wires to each other - a bit messier than I'd like.

I think this soldering iron is designed for somewhat larger applications...

Logging

Coming back from Abbottabad the other day there were some guys doing some logging - apparently part of the latest stretch of road-widening works scattered along the KKH. This is more exciting than it first sounds, when you take into account the fact that they’re doing it right next to the main road. Combine this with the general behaviour of Pakistani traffic, and you get a interesting ten minutes of pleasing chaos.

Given my abject failure to gain any photographic evidence of this fantastic piece of theatre, I shall relate it in the form of scrappily-drawn diagrams.

1. Choose a suitable looking tree.



















2. Create a roadblock with a few branches and sticks. Some drivers take notice and stop.



















3. TIMBERRR!!! (Or the Urdu/Pashto/Hindko equivalent). Given the proximity to all the waiting cars, now 2 or 3 rows abreast, this takes some confidence in your felling angle.



















4. Well done, you’ve successfully avoided hitting any vehicles, and have beautifully blocked the entire road with your tree. Meanwhile, Pakistani drivers not being the epitome of patience, they have continued to fill up any available space. We’re now up to 3 or 4 rows of traffic, leaving only the narrowest possible lane free for any traffic that might want to come the other way.



















5. Chainsaw man begins removing the side branches of his tree. Some of the front row of drivers hop out and move the original road block of sticks.



















6. Chainsaw man finally gets round to cutting the trunk in a couple of places. His helpers start to manoeuvre a section out of the way. In the meantime, having run out of road to fill up, vehicles are now extending the traffic jam sideways out on to the dirt at the side of the road. As I may have already mentioned, patience is for other people.



















7. One particularly impatient driver five or so cars back decides to chance it and races round the very outside, bounces over the remains of the stick-block and charges for the narrow gap where the section of trunk used to be. Unfortunately the gap is a few inches narrower than his car - he just about manages to screech to a halt in time.



















8. The gap is widened enough for a car or two to pass: cue manic free-for-all scramble for the gap. At this point the drivers will be forced to take notice of that glaring flaw in Pakistani traffic self-discipline, that our esteemed readers will have spotted ages ago: namely that making the traffic jam fill the entire width of the road on both sides of the obstacle doesn’t really leave much room for any oncoming traffic to pass.

Many small horn-honking and finger-waving negotiations ensue, with general precedence going to whoever managed to stick their vehicle in the gap first. Looking back, the traffic jam extends as far as we can see. The whole thing only took about ten minutes.