Wednesday, May 25, 2011

Measuring Dirt

A friend asked me if I could quantify the dirt on my solar panels from the previous post... o_O

I'd never tried to measure the effect of dirt before, but the conditions were right today to give it a go.  Not completely scientific (I am a bodger after all), but here's what I did:

Firstly, there was the pair of panels from the pictures in the previous post.  Now, they were very dirty, and I'd cleaned half of them to show the dirt.  These modules are easy to measure, as they have a chocblock in the link between the pair.  So, I crawled under them (taking the opportunity to clear out the weeds growing under them!), and inserted an Ammeter in the circuit.

I manually recorded some values for the current at 15 second intervals; before cleaning, whilst cleaning, and post cleaning.  Obviously, while cleaning the things, I didn't actually record any data in my scrap of paper, so missing values are just the last known value repeated (to fill the gap - Excel wouldn't draw a line unless every cell had a number in it...). The modules were still wired into the array, and the battery was at bulk mode, so was drawing all the current it could.

Afterwards, I took a copy of the logger file that had the time and other solar system data (like the solar sensor data that tells you how strong the sun was as a percentage of the maximum it could be), and input the manual data against the same time records.  A bit of fiddling in Excel chart maker and...

If you click on the graph, it will open up bigger.
You can see that when I washed the pair of modules (half of which had been washed yesterday for the photos), the output current jumped up.  The solar input power remained within 1% of flat the whole time, so it was definitely the effect of the dirt on the module that made the difference.  I've noted on the chart where the modules were wet, and I dried them with a cloth, and then you can see the panels output drop off a bit, as they warm up again in the sun.  PV cell power drops off a bit, as they get hot.  I used warm water to wash them, so as to prevent any thermal shock to the glass, and not cool them down too much.

Then I thought, that seeing as I'd got all set up for washing these panels, I might as well do some of the others too.  The trace below shows the power output of the TriStar array controller while I cleaned most of the panels attached to it.  This time, I just let the modules dry in the sun.

I excluded the power figures from the SunSaver array, as those panels are completely separate, and I didn't clean them.  I also ran out of water before being able to clean the bunch of panels at the front of the garage.  In truth, I couldn't be bothered to do them, and I was supposed to be doing some work anyway :D.

Again, you can see a marked improvement in output from not having a load of grunge on the array...

Tuesday, May 24, 2011

Muddy Solar Panels

One problem that solar panels face in such long dry spells of weather as we're having now is the accumulation of dust, pollen and other bird grunge on their surface.

It doesn't help that we've had some very light rain over the last day that has, in itself, contained a lot of mud.

This can degrade the output of the array until a really good downpour washes the panels, or you get a telescopic window cleaner out...


Monday, May 23, 2011

Some Fav Quotes by Thomas Edison

"To invent, you need a good imagination and a pile of junk."

Amen to that.  Bodgineering is at the heart of invention.  Once you've bodged something together from bits of this and that, you can see how to do it "properly".

"We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy; sun, wind, and tide.... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that."

That was his hope in 1903.  He'd be shocked that we're still "working on it" over 100 years later...

"Hell, there are no rules here - we're trying to accomplish something."

OFGEM, take note.

Thursday, May 19, 2011

1 MWh on the Clock

A bit of a milestone today.  Since fitting the "proper" OFGEM generation meter back in March last year, the AC power generated (consumed) from my solar panels has been ticking up.

Today, it passed the 1000 kWh (1 MWh) mark.  But amazingly, a full 153kWh of that total was generated just last month!  May is shaping up pretty well too, having made 114kWh this May, compared to only 92kWh last May.

Wednesday, May 11, 2011

Big Capacitors!

Get a load of these babies!
Giant 1 Farad capacitors.  Used originally on super loud car audio systems.

I found them at a car boot sale, going for a tenner for the pair.  They'd cost about £30 each when new.

They have these so called protection circuits on the top.  I thought that it was an anti-surge device for when they have power applied.  They have extremely low internal resistance (maybe as low as 0.002 Ohms) so can draw a huge surge current when connected to a source of current.   But no, the circuit turned out to be just a buzzer that sounds when they are reverse connected by accident, or when subjected to over-Voltage.  They have a quite small maximum working Voltage of 16V.  Given the near explosion that occurred when I over-charged the baby capacitor on the bike generator, these would pose quite a risk, if mal-treated.
The display reads Volts and the two other LEDs are really just for show (they're for car audio "enthusiasts" after all)...  Although, they do serve a useful purpose as discharge loads, to make the capacitors safe in a short time after the power is removed.

Luckily, the tops just unbolt, and you can remove the circuit board.  It's just held on the capacitor terminals with press contacts.  Then the bolts can screw back into the terminals directly.
The Voltmeter circuits are possibly useful later for something.  On their own, they're worth £5 each, so the capacitors were actually "free".
I thought that as I had a pair, I could wire them in series to allow them to be charged from one of the left-over small amorphous solar panels.  Wiring them in series increases the Voltage they can handle, but reduces the capacitance, so you get a 0.5F capacitor that is safe up to 32V.  If you wire them in parallel, you get a 16V 2F capacitor, and mind bending amounts of current (the internal resistance is halved again to 0.001 Ohms, giving a short circuit current of up to 16,000 Amps!).

The panel puts out about 23V, open circuit, in the sun, but you can't use that Voltage, as the current is so low.  But you can charge a 0.5F capacitor from that current, over a minute or so.  The capacitor, unlike a battery, does not seek to limit the Voltage it charges to.  So, eventually, it will store a unit of energy at the highest Voltage attached to it, and can later deliver that energy with massive current.

I disconnected the charge source, and started measuring the Voltage across the capacitors, thinking the charge would leak away in a few minutes.  To my surprise, only about 10% of the energy had leaked away after 24 hours!  The energy level of a capacitor is exactly proportional to the Voltage it reads, unlike batteries that can read 12V, but be completely flat.

But what use are giant capacitors..? I'll let you know when I think of something :D  They're just cool toys right now.  A bit dangerous though.  I shorted the wires of the pair when charging it from the small solar panel, and the entire lug at the end of one wire completely disappeared in a green flash of copper vapour discharge light.

Monday, May 2, 2011

Recycling Grey Water for the Garden

The other thing the Met Office said about April was that it was also the driest April for many years, with some parts of the UK receiving only 2mm of rain.

Despite having bought a second water butt for the garden last year to collect rain water, it still wasn't enough this month.

We've previously filled the water butt using saved bath water, but it was a troublesome process, and the cheap drill powered pump I had wasn't very good.  In short, it was a... pain in the butt :D.

With more dry weather forecast, it was time to do some bodging...

First of all, you have to collect your grey water.  This is water that isn't full of bits (mud, rocks, etc) or full of chemicals or organic matter.  So water from the kitchen is no good (contains fats and food bits and so on).  Washing machine water can be ok, but often has too much soap, fabric conditioner or even bleach in it.  Used bath water is fine.  Just don't use any bubble bath, bath salt, or go mad with the shower gel and shampoo or conditioner.  The plants don't mind a little bit of soap.

Then you need to catch all the hair and bits of fluff in the water, as the pump won't like it (even with an inlet filter) and you don't want to clog the water butt or hoses either. 

The missus had this handy tool, just for the job.
Dunno if you can get them here, as she bought this one at a 100 Yen shop in Japan, where they are very common bathroom accessories.  You can easily make one with a coat hanger and a bit of old net curtain though.

Incidentally, in Japan, it's actually quite common to recycle bath water into the washing machine for the wash cycle, as the soap powder will suspend the dirt in the water anyway.  Clean water is only needed for the rinse cycle.

Next, you need a water pump.  I'd been looking around for something better than the drill pump (a water pump you attach to a cordless electric drill).  I found this new one by the garden hose makers, Hozelock.
It's designed to be used in a water butt to power hose pipes and sprinklers and so on.  It also says you can use it for emptying small paddling pools, and recycling bath water.  It seems to retail for £70, but with a bit of shopping around, I managed to pick it up for £52.
Water is sucked up from the bottom of the unit through a removable foam in-let filter that catches medium sized (1mm) particles and hair. In the screw-on hose adaptor at the top, it has a finer mesh outlet filter to catch particles as small as maybe 0.2mm in size.  You need to use the fine filter if you're using the company's miniature irrigation system that drip feeds plants, or a hose fitting that has small spray holes that could get clogged.  If you're using ordinary hose pipe fittings then you can take the fine filter out to get more flow.

The water in our water butt has bits in it anyway, and is only used with a watering can tap or jet hose, so I took the fine filter out.

I rigged up the hose outside, cable tying it to some big electrical cable clips I hammered into the wall.  I then used a bit of string to hang the coiled up end loop outside the bathroom window, for when we're not using the hose.

The other end is just coiled up under one of the solar panels at the base of the wall.

When we need to pump water, I just un-roll the bottom end and stick it in the water butt, securing the pipe with a brick... useful things bricks. :D

Then I pull up the other end (using the string from inside), un-roll, and plug it into the pump, which sits in the bath.  The pump uses normal Hozelock click-fit connectors, so you can use any normal hose.

The pump is designed to be completely or partially submerged, with the 10m water proof rubber cable going off to the mains remotely.

Make sure you use a RCD breaker on the socket!  Don't sit in the bath (or pool) while using the pump, just in case... O_o
Then it's just a case of remotely turning the power on.  It draws about 300W, so I ran it from the solar power in the computer room.

The pump proved to be very efficient, quiet and fast.  It emptied the bath of about 100 litres of water in 2-3 minutes, and it had enough pressure (1.1 bar / 16 psi) to ensure that the old hose, that has some kinks in it, opened up and worked beautifully.

The only thing that was a bit annoying was that the pump has a small hole on the side of the body, which sprays a jet of water out sideways, while working.  This is normal as it's a "vent" to allow air to escape from the pump (part of its self-priming function).  That's ok, when it's in a water butt, but it splashed water around the top of the bath tub when the water level got below the height of the hole.  Some fettling may be required...  A small cowl, or summat, to tame the (quite violent) jet that squirts out.

The pump has 2mm high "feet", and this allows it to suck up water right to the last couple of millimetres of water in the tub, especially if you position it over the bath plug.  Very good.  They make another pump which is intended for clearing floods, but it can't work in less than about 75mm of water... No good for draining a bath tub!

This water butt pump doesn't have an automatic float cut-off, so you need to watch it, and turn it off as soon as the water has run out, as running the pump dry will damage it.  Ideally, you should turn it off just as it is about to start "gurgling" at the bottom of the bath.

If using it in a water butt, they recommend standing the pump on a couple of bricks at the bottom of the tank, so that it is clear of the worst of the sediment that collects at the bottom.

Given that we have grey water available every day, and the pump only cost a few Pounds more than buying yet another 150 litre water butt, it seemed good value.  And we get the most out of our metered water.

Sunday, May 1, 2011

April 2011 - The Warmest (Sunniest) on Record?

The Met Office were reporting yesterday that this April may have been the warmest and driest in the UK on record.  Judging by the record amount of electricity I harvested, it may also have been the sunniest.

Now this time last year I'd admit that I had less PV installed.  The last lot of BP panels were installed in May and I had about 1.50kWp installed in total.  But the fact that I have just over 2kWp installed this April doesn't account for the power harvest being 2.9 times higher than the previous year.
The upshot has been that my solar system has offset just over 53% of my total electricity demand for the month, and up to 66% of weekly demand in the best week of the month (the last week).  On a daily basis, the best day was the 28th, with over 85% of electrical demand served by solar power.

Quite astonishing, given that I didn't install the upgraded capacity from the recent haul of solar panels until the middle of he month.

The newly upgraded immersion heater controller is also maybe having an impact, as it can more effectively use the spare power available in the system.