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Discussions about Renewable Energy, including photovoltaics, wind, and small scale hydro.
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AccordGuy
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Just getting started

Post by AccordGuy »

I'm just playin' around with some cheap PV panels...

I've got 6 panels so far (2x 12w 17.5v and 4x 15w 17.5). The 12w ones have blocking diodes built in and the 15w ones don't. If wiring them all in parallel, do I need to add blocking diodes to the ones that don't have them?

I'm running them through a charge controller that possibly includes night discharge protection but was wondering if the panels should have diodes as well to stop charge leaking through a panel that has a shadow on it (for example)... The 12w panels are on my garden wall but the 15w ones are on a ground frame that I can move to catch morning / afternoon power from different angles so there will be times when I've forgotten to move part of the array and it gets shaded.


Image
Last edited by AccordGuy on Thu Jul 24, 2008 9:06 am, edited 1 time in total.
Sharkey
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Post by Sharkey »

"Blocking diodes" are now known as "Dinosaur diodes". If it's not too much effort to remove/bypass them, do so, you'll get more output from your panels.

Back in the old days, the idea was to prevent the panel(s) from consuming a small amount of power overnight by blocking the reverse flow of power from the batteries. Multi-crystal panels were more prone to consume power than single-crystal panels.

Fact is, the small voltage drop across ~any~ diode will result in a significant total power loss when calculated over the number of sun-hours in a day.

Back when I was running panels without a charge controller, I calculated the loss during the day with diodes, then calculated the loss overnight without them. Bottom line was that I lost less overnight without the diodes than I did during the day with them, so I removed them from my power center.

Any halfway modern charge controller is going to have backfeed pevention built in for dark hours. Get rid of the blockers.

Bypass diodes, on the other hand are installed on nearly every PV module, and are not detremental. In fact, if you have a large series array, you want them to prevent panel damage and system losses during partial shading. Be sure you remove/bypass blockers, not bypass diodes.
AccordGuy
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Post by AccordGuy »

Thanks Sharkey.

Although an electronic engineer (in the past) I'd never played with PV cells beyond some little toy kits. Incidentally, for anyone else who wants a good primer on PV technology and theory you can look through this on-line study guide.

http://www.udel.edu/igert/pvcdrom/index.html

It's a bit mathematical but there is some interesting stuff on how efficiency gains have been made over the years by improving the way light is trapped in the silicon layer plus an explanation of all the common performance characteristics of cells. It also explains with animations what happens in shaded cell banks and why bypass diodes are needed for protection.

I'll have to measure the leakage current of these panels (when I get them back..). I had it all set up in the garden and then on the first test run on a brilliantly sunny Saturday afternoon something must have gone pop in the No.3 panel as on Sunday I noticed lower charge rates and discovered that one of the new panels had died (<2v Voc in full sun and zip Amps).

Worse still, the retailer I bought the set from doesn't keep spares and wouldn't break a set to create spares... So I had to pack the *whole* thing up (about an hours work!) and arrange for them to collect it and replace the whole set (rather than just the one panel that went bad... how stupid is that?).

They are amorphous panels and the bad one is a bit conspicuous as it appears a much darker shade of brown than the other three that look red-ish.

As for the other two original panels, I can't remove the blocking diodes as they are built into the sealed weatherproof frames... They were being sold singly as low-rate charger / maintainers for RVs without the need for a controller. The 60w kit came with a 10A controller.

BTW... loved the history of your solar power endeavours! My wife reckons I'm a bit of a closet mad scientist. In a couple of years our house roof will need replacing as it's getting on for 60 years old and I'm considering getting a full grid connected array - the UK government now gives grants to householders who want to do this kind of thing. Our roof faces south and there are no pesky tall trees near the house to shade the roof so it's ideal.
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Post by Sharkey »

Thanks for registering. Through the magic of database manipulation, I've attributed your original post to your new user name...

The good thing about PV's is that they are adaptable to changes in the system, within the limits of things like the charge controller and inverter. I've ripped my system apart and rewired it several times, and the parts and pieces are like building blocks that can fit together multiple ways.

These days, I'd be hard pressed to fool around with solar power at all. If I was investing from scratch, I'd be putting my money into microhydro. I have a spring on the new property that is 160 feet in head, and about 120 gallons per minute in the winter. Rough estimates of available power come in around 36 kWh per day. If I had any money these days, I'd be running a 3" polyethylene pipe up the ravine and getting something like a 1.5 kW Harris Hydro installed.

Can't say that I'd choose to put PV's on the roof if given a choice. Most of my array is ground mounted, and I appreciated that this last winter with al the snow we had. The panels out in the yard were fun to clear of snow, but the panels on the carport roof were a pain. No joy standing on top of a ladder with a 12 foot extension pole squeegee scraping solid H20 off the 12 volt array so I could charge the batteries that run the lights in the housetruck.
AccordGuy
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Post by AccordGuy »

Was there a reason for using 6v batteries rather than 12v ones in your set-ups? - other than the problem of lifting such massive 350Ah batteries?

My wife was mentioning my experiments to her family on a web cam the other day and my father-in-law piped up "Oh we're getting solar power installed too!". Only he and his son have remodelled the whole house and decided to get what must be a pretty big grid connected system as it cost 7 million Japanese Yen (about $65k)!

We're going to Japan this Autumn so hopefully I'll get a chance to see it in action.

I'll have to ask him about how he's going to clear the snow from the solar roof! We don't get any snow in the South of England (well, none that lasts more than a day) but in his part of Japan, they routinely get 2 meters of snow in the Winter. The up side is that Japan is nearer the Equator than the UK (he lives at the same latitude as Las Vegas) and so has more even length daylight hours than the UK which can get down to 5 useful hours a day in December.

Hopefully, my little 60w array is coming back today as the retailer tested the duff panel and has shipped out a replacement whole kit... I should be cheeky and ask them if I can buy back the incomplete set for a discount :wink:
AccordGuy
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Post by AccordGuy »

Nice and sunny the last few days and I finally got my system back together. Unbelievably, the replacement set of four panels they sent me was more broken than the one I sent back! They didn't send me a new set at all but scavenged a new panel from another returned set but this was shattered (they claim in transit) and even part of the frame was now broken.

Some stern words to their service desk ensued and the lady this time gave in and rather than insisting the whole thing be sent back again agreed to send out spare parts.

In fact, the broken panel isn't completely useless as it is formed by two panes of tempered glass with a plastic backing. Luckily, the backing and the frame held the glass together and I managed to patch up the front plate with weather proof clear tape and clear silicone window sealant so that water can't get into the cracks and rot the silicon of the active layer. The panel still puts out about 72% of it's rated power and I keep it as a booster panel that I can move around to catch the best sun (propped up on a garden chair mostly). It won't last forever but it's another 11-ish Watts of juice that I didn't have to pay for 8)

While I was waiting for that saga to play out, I spotted a couple more of the cheap 12W panels in the same chain store in London. Their web site said everywhere was out of stock but I just found these two boxed panels propped up in a corner of the store by a clearance bin - result! Well, it would have been if it were not for the fact that one of those turned out to be cracked as well when I got it home GRRR!!! Luckily, when I took it back to a nearer branch of the store, they also had a spare panel still sitting in their shop window so I got the broken one replaced. This store's stock control is lousy...

Anyway, here you can see the whole array up and running this morning.

Image

At peak, I can make about 7.2A now and it certainly seems to keep the two batteries topped up provided I don't hammer the big AV system at night watching TV... That lot draws about 230W of mains. The cable TV box is the worst! It has a on/standby button but it actually consumes almost the same power as when fully on (28W on / 27W "standby"). I'd had this thing plugged into the mains permanently at a cost of 245kWh per year!!!

Indoors, I modified the charge controller a bit so that I now have a switch that I can select either "normal" charge cut-off of 14.4V or an "equalise" set-point of 15.0V. This latter setting has been useful on days when I've drained the batteries a lot and want to push them quickly up to 100%. The controller isn't so intelligent and the battery voltage quite quickly gets to 14.4V and so the charger starts cutting out and charging some more and cutting out. It's ok on an extended charge run over a couple of days with only light loading (if I'm not working at home, visiting clients or at an office) as it slowly does the last 10% charge and the battery ends up sort of hovering around the 13.8V float range but if it's partly cloudy and I've only got a couple of hours good daylight before the next nights onslaught of drainage, I can set it to boost for an afternoon until the packs have stabilised at about 14.7V and then switch it back to "normal".

As mentioned in another thread, I got a new 1kW pure sine invertor as the 600W modified sine one I bought a few weeks ago wasn't at all suitable for running my AV gear that buzzed like mad (mechanically and through the speakers). This, plus the extra loads I now run means I'm on the lookout for more power again... I've got my eye on a MorningStar SunSaver MPPT charge controller. It's a new much cheaper low power (15A) MPPT charge controller that can put 30% more Amps into a 12V battery than a normal charger. It costs about 150 Pounds whereas the Outback ones cost 480 Pounds (but are rated at 60A - far too much for my setup).

To save the solar juice used by my main AV setup when just watching the breakfast news, I found a little 10" portable LCD DVD player at a car boot sale for just 15 Pounds. It was an in-car one and was cheap because the guy had lost the car mounting brackets for it but it stands up just fine by itself on our dining table. All I had to do to turn it into a proper TV was buy a cheap digital TV tuner from the local supermarket for another 15 Pounds and use one of my spare 12V power supplies from an old portable hard disk drive. Actually, I could run the thing off of 12V battery power directly but a) the TV tuner is mains only and b) I couldn't be bothered to run another wire round the edge of the living room and risk antagonising my wife further :roll:
AccordGuy
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Post by AccordGuy »

Hahaha... I'm on a roll! I scored two more 12W panels this week.

I took back the no-good modified sine inverter but the store would only give me a credit note as a refund. Happily, they were also selling some solar lighting kits at half price and I had a discount voucher if I bought two of them (and annoyingly a resistor to take the total order over 100 Pounds).

Although 6.50 more than the panels I bought before, these kits included a better panel (aluminium framed with junction boxes rather than the ABS plastic ones) and a whole kit consisting of a 7Ah battery, 4A charge controller and a pair of LED bulbs with E27 bulb holders.

If I sell off the bits and bobs of the kit I might even be able to get the panels almost for "free". I've seen the LED bulbs selling for about 10 Pounds each and the battery for 15 Pounds and the charge controller for another 10 Pounds. I'll probably keep the LED bulbs as they are pretty good... I'll get some nicer mains wall lamps instead of the nasty bulb holders and just cut off the plugs to use them with 12V DC.

This now brings my array up to 132Wp (or 143Wp if you count the partly broken panel)...

I've got a roof ladder on order as well... I'm thinking of mounting some of the array on the roof as it catches more morning / late afternoon sun than the south wall of the house.
AccordGuy
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Post by AccordGuy »

I've got even more of those panels now! I signed up for a newsletter from the store and they send me more discount vouchers by e-mail every month. So I could get another two panels with a 7 Pound discount and what with selling the spare bits of the kits it's pretty economic. I've now got 4 of them (making a total of 13 panels putting out 167Wp) and they work pretty well. Had to re-wire the outdoor junction box with bigger 30A terminal blocks to get all the wires in.

I'm tempted to buy even more as they are so cheap but I've reached the limit of this charge controller. Today was the first sunny day after re-wiring it all and the array was kicking out 10.6A and it's only a 10A rated controller. If I'm not careful the 10A fuse in it might blow but it seemed to be holding this afternoon. Even when it was overcast cloudy the array was mustering about 0.7A. If I bought the Morningstar MPPT controller next, I'd get another 3A for "free" into the battery on a sunny day due to the power conversion. If I buy more panels, I'd probably overload the Morningstar (as it's rated for 15A) and then have to buy a much more expensive controller...

Plus my garden is starting to resemble an actual solar power farm... :D

My ladder came and I fixed some gutters on the roof and started to look at how I might mount some of these panels on the roof rather than having them all over the lawn.
Last edited by AccordGuy on Sat Aug 16, 2008 6:28 am, edited 2 times in total.
AccordGuy
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Post by AccordGuy »

This "free" energy is getting to be quite an expensive hobby!

Another set of discount vouchers came in the post the other day from this store (they seem to be keen on giving money away at the moment) and I noticed that my repaired 15W panel was starting to give out (despite my attempts with weather tape and silicone sealant to fix it). The cracks are getting worse and it had dropped from 72% capacity to more like 50%, so I bought another 12W panel to replace it. I might still be able to use the broken panel a bit but not outdoors. Every time I move it, the broken glass flexes and cracks more and so it gets worse.

Here's the current photo of the garden. I've taken the broken panel indoors.

Image

I also decided to order the Morningstar Sunsaver MPPT controller. As well as my present controller only being able to handle 10A, it's a very crude charger with just the one set-point for 14.4V (that I'd frigged to be switchable to 15V). The Morningstar is a proper PWM 4-stage programmable charger and I can even experiment with wiring up the modules in series up to 36V nominal (or 75V absolute max. Voc) as the controller will convert this down to either 15 or 30V automatically for 12V or 24V batteries. This may be useful when I mount the panels on the roof and have to extend the feed wires. At the moment there's quite a lot of copper in the feed as panels are either wired individually or at least in no more than pairs via 16 gauge extensions to the junction box and then by a single, fatter 10 gauge cable to the controller indoors (it had to go through a hole in the wooden patio door frame).

When I put them up on the roof, I'd like to have just one wire coming down to the junction box and on to the controller so a 24V or 36V system would mean I could get away with longer wires. It might also improve the cloudy day performance of the system as there would be a 3x lower light threshold at which 12V charging could start compared to the current straight 12V nominal panel parallel array. The only problem would be numbers of matching panels... If I bought one more same 12W panel, I could easily make a string of 7x 24V pairs or 4x 36V triplets but I'd have to give up one 15W panel as I've only got 4 of those.

The new controller should arrive on Sat morning so I'll have something to play with this weekend (although more torrential rain is forecast - it's been more like Autumn / early Winter storms here this week than August Summer).
AccordGuy
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Post by AccordGuy »

The Morningstar MPPT controller arrived yesterday and it was pretty easy to swap over from my old controller as it has good chunky screw terminals for fat wires. It's smaller than I imagined and is fairly unobtrusive, screwed to the wall near the shelf where the old controller is.

Image

I decided to keep the old one as a voltmeter and to provide load sockets. The Morningstar has just a pair of load screw terminals but the old controller had a car 12V socket, a couple of 12V jack sockets for some LED lights I got in the other 12W kits, a 9V, 6V & 3V jack socket and even a 5V USB socket. The Morningstar has a three LED battery gauge (red, yellow, green) but I liked the big LED voltmeter on the old one, despite it sucking up a bit of battery power. It has a separate switch to turn off the meter but 50mA on a 140Ah battery bank isn't going to kill me.

The green LED on the battery gauge doubles to show what final charge stage the controller is in. If it's solid it means "bulk", if it flashes 1/second it is in "absorption", 2/second is "equalise" and 1 in 2 seconds is "float".

The max power point tracking seems to do what it says on the tin. I measured the solar input current and compared it with the battery charge current while in bulk mode. The controller managed to boost the current by up to 35% when it was sunny and the battery was low (I'd hammered it the night before watching the big TV). That's the good thing about the MPPT controller, the lower the battery is the more the controller can boost the amps into it (unlike before when the low battery voltage forced the panels to work far outside their optimum power range). Even when the battery was getting full it still managed to boost the current by 15%.

The only thing I've noticed that isn't so good is that in order to monitor the battery voltage without a separate sense wire, the controller periodically (once in two minutes or so) disconnects the charge current (and loads) for a small fraction of a second in order to take a battery voltage reading with no current (and hence volt drop) in the charge leads. It makes a very short, quiet blip of a beep sound at the same time. While this means it can track the battery voltage without using an extra pair of wires, it does mean any sensitive 12V load connected to the Morningstar load terminals might get a drop-out that causes it to flicker or maybe worse for digital gadgets. Of course, the big invertor is plumbed directly into the battery so isn't affected but I'll have to see how my phone behaves when running off the car charger plug. It might start beeping as it does so when it is connected or disconnected from a charge source.

They made this controller with a big finned heat sink and warned about ventilation and so on but today it was running at between 9 and 10.7A for lots of the time and barely got warm at all... Not sure why they over-rated the heat sink so much but at least it should be reliable at it's claimed 15A maximum.

The cloudy performance is also very good. I'd looked at the much bigger Outback controller but being designed for much bigger solar arrays it said that unless there was more than 1.25A of input current, it wouldn't bother turning on! This controller works on much smaller arrays (like mine) and so is quite happy to charge with anything over 0.2A coming in. The controller takes about 65mA for itself - quite a lot compared to traditional controllers (my first 6A one took just 3mA) but considering the current boost in most conditions, it's worth the losses.

You can see the charge current meter reading -00.0 as the controller and voltmeter are draining the battery a bit at night. I measured a 1mV/A length of charge lead (about 31cm with this cable) and soldered multimeter taps on it to give me an ammeter reading without plugging the meter in-line. The meters built-in shunt is about 0.1 Ohms and so had too much of a voltage drop and it isn't rated for continuous duty at above 10A reading. With the 200mV range you get 0.1mV resolution, so conveniently this meter now reads up to 200A with 0.1A resolution.

In case you're wondering about the figure on the controller, it's Stimpy from Ren & Stimpy, posing with the caption "Ask Dr. Stupid". My loving sister gave it to me years ago.
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Post by Sharkey »

So is this MPPT controller a buck-converter? That is, can it take higher voltage panel configurations and charge your 12 volt batteries? With as many panels as you have accumulated, you would have no probelm running higher voltage arrays.

The Outback MX60 on my 24 volt system can take input voltages up to 100+ volts and charge batteries from 12 volts up. The advice I got was to use a higher nominal voltage at the input than the output, so I configured my panels for 36 volts, bucked down to 24+ for the system. My only other choice was 72 volts, given 18 panels. I ended up with three panels in series, paralleled with another three in series. There are three of these series/parallel arrays total. I usually see 38-42 amperes at 27.7 volts when the system is in float mode. The current is being inverted by the Outback GTFX and backfed into the mains, which is my charge controller regieme. If the utility fails, then the MX60 regulates at 27.9V.

I'm rather envious of your ability to purchase discounted PV's. My 12 volt system will be growing in storage (the NiCd cells I scored), but I still have only 100 watts or so of PV to charge with on that system. Thinking of hauling out that toy microhydro project from a few years back and putting it to use using the house water supply from the spring up on the hill. In the middle of winter, even an extra 24 ampere-hours a day would be welcome. In the darkest days, the 12 volt system ends up being charged with mains power, so I could use some additional juice.
AccordGuy
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Post by AccordGuy »

Yep, this one can charge 12 or 24v batteries from PV strings of up to 36v nominal (75v max).

I've just bought another 12w panel to get me to a even number of panels so I can make up 7 pairs of panels and run the input side of the charger at 24v nominal to charge the 12v batteries.

It will regulate to a max of 15v for equalise charges and 14.4v for absorption charge. The rated conversion efficiency is about 1% lower for 24v to 12v operation but I guess you save at least that on line losses for the solar feeds working at half the current of 12v operation and it might improve low light charging on cloudy days. These amorphous panels can make 10v even in twilight at dusk (granted at only 20mA) but 10v into a 12v battery doesn't work... Put in series pairs though, 20v at 20mA x7 is still useful-ish.

Hopefully with the current boost nature of the controller, even with 5A flowing into the controller at 35v (2x the 17.5Vmpp of these panels) on a sunny day, I'll still see 10A into the battery but with better low light performance as well.
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Post by AccordGuy »

After having spent all this time playing with a solar system and built an array that can push out 180W of electricity, it became clear that my 8 year old (and heavily abused) 70Ah leisure battery and it's new-ish (but rapidly being ruined by deep discharging) 70Ah car battery were due for replacement with something more suitable.

A couple of weeks ago we were driving home from my parents house and spotted a caravan showroom. We stopped to look at some stuff in their shop (12v gadgets basically). I noticed that they had cheap leisure batteries but was still toying with the idea of getting a pair of Elecsol carbon fibre batteries as they are supposed to last up to 1000 deep cycles and resist sulphation if left flat. But they are expensive.

I worked out that for my largest load of some 230W inverter mains I'd actually need four 110Ah batteries as they are only rated at 110Ah for their C/20 discharge rate. The inverter draws about 10A per 100W of 230VAC mains used so at my load it would draw about 23A. For the battery pack to comfortably deliver it's rated capacity run-time I'd need to keep the discharge below C/20 or 5.5A for each 110Ah battery. So four batteries was close enough, delivering a C/20 rate of 22A.

In theory, I should be able to run this load for 20 hours but that would run the pack flat and quickly damage it (as they are regular flooded cells). The most I've used the AV kit that generates this load is about 4 hours in an evening and that completely killed the two old batteries - a) because they had to deliver more than three times their C/20 rate and b) because they weren't in great shape to begin with.

With 440Ah on tap, the four batteries should be able to deliver four hours of the load and not be discharged by more than 20%. Even if I have a couple of cloudy days with not much charging, this pack should hold out for at least three days before getting 60% discharged (still not too dangerously low).

The clincher was haggling with the store owner... He wanted 70 Pounds per battery and 9 Pounds for the snap-on terminals but as I wanted four of everything he let me have the batteries at 65 Pounds each and the terminals at 7.75 each, saving 25 Pounds. The Elecsol batteries are about 110 Pounds each...

In selecting the batteries from the pile, I made sure they were all exactly the same age as they have date of manufacture stamped into the plastic on their tops. Some in the pile were a couple of months older. I'm not sure it makes a huge difference but I'd read somewhere that it's best to get batteries that are no more than a few months different in age and to use them and cycle them together from the beginning or else they can get unbalanced if you put a new battery in an old group.

Image

The silvery things are the carry handles that neatly snap flush into the tops of the batteries. Behind the pack you can see the 1kW pure sine inverter.

These snap-on terminals are pretty good - a Swedish make. They have big screw down pressure plates for the wires and I could easily get the 2AWG inverter cables plus other pack link wires in there - unlike the regular car battery terminals that really were a pain to get even just the inverter cables into the holes and then the screws chewed up the copper. The snap-ons also have built-in colour coded insulator tops.

For the pack links I used my 1mV/A shunts on the positives so I can measure the individual battery loads and on the negatives I used shorter lengths to keep losses down. Ideally, I should have wired them all in a star formation so that all the batteries have the same resistance path to the main load (the inverter) but I compromised by putting the load on the no.3 battery and the solar charge leads on the no.2 battery (it wouldn't fit on the no.3 terminals that were too full of wires with the inverter leads and link wires and the inverter DC isolator relay feeds). If I get bored of monitoring the currents between batteries and they start to get out of balance a lot due to the different resistances, I may try putting a fat loop between the no.1 and no.4 batteries as these are the ones furthest from the charge / load points on the busses. The end battery terminals have plenty of space left in the clamps so it won't be hard to get the extra wires in there.

The pack fits quite well behind the armchair by the patio door but I wonder if they will gas too much and risk an explosion... The old leisure battery used to draw more current when fully charged than the car battery and used to gas so much that it was always gurgling (like my stomach after a heavy meal) but I've read that old batteries are like that. We'll see tomorrow - the forecast is for sunny weather so hopefully the full 180W of PV will be brought to bear on the pack.

The patio door has a vent strip above it that can be opened and closed and lately I've kept it open to let a little draft in just above the batteries. Not sure what I'll do in winter when it's too cold to leave it open.
AccordGuy
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Post by AccordGuy »

After having all these panels propped up on our garden chairs, it was time to build a couple of frames to put the new ones on more permanently.

Being as recycle-friendly as we are, all the wood came from a car boot sale where a guy was selling broken up picket fences and fence posts. Handy, as they are already treated for outdoor use. I painted them with waterproof wood stain as well to make them look better and while I was at it, painted the patio door frame that was also in need of protection before the winter.

Image

The frame on the right is just propped up against the kitchen window sill. The left one is on the lawn with the top bolted to a pair of fence posts driven into the ground.

I'd also bought two more of the 12W panels in the last push of the store sale before they sold out, bringing my total generating capacity up to 204Wp, the limit of the MorningStar controller. Well actually they say 200W for 12V batteries (or 400W for 24V batteries) as the controller caps the battery current at 15A but with the weather we get here, it's only going to be at maximum output for a few minutes at a time. August was officially the darkest and wettest on record for the UK... Even sunny days aren't fully sunny here as there is usually some wispy high cloud or just haziness that means you don't get the full power... Not like Spain or the south of France that gets crystal clear sunny days.

As well as putting all eight new panels on these frames, I decided to re-wire the array for 24V operation. The controller can handle up to 36V nominal arrays. I paired adjacent panels in series at the panel end of the feeds and joined the 24V feeds at the junction box on the wall. This meant that I could reduce some of the now quite messy parallel 12V feeds back to the main junction box without incurring any more resistive power losses (as the currents have all been halved while doubling the voltage). Of course, now I have to be a bit more circumspect about playing with the wiring on a sunny day as there's 35V at 5-6A flowing in the system (and more like 50V when off-load), maybe not lethal but certainly not friendly. I picked up some cheap waterproof little junction boxes that I'll put the panel connections into next weekend (if it's not raining). For now the joins are just protected with tape and heat shrink tubing.

Sure enough, the low light performance is better now. The additional voltage meaning the charge light comes on much earlier (even if it's only putting 100mA into the battery pack). It also consistently puts more Amps into the battery during the day, even when black clouds threaten overhead. We had a big thunder storm this morning. That reminds me... Must look at getting some lightning arrestors and a lightning rod to earth the array ground side. The MorningStar has surge arrestors built in for the array input, battery output and load outputs but it does recommend separate earthing and lightning arrestors for the array and battery pack.

The original four 12W panels on the wall have non-removable blocking diodes built into them but I'm wondering about the others now that the system is running at 24V. If part of the array gets shaded, it could put stress on it as there's much more back-emf available and each panel has only a quite low reverse breakdown diode voltage... although now there are two such diode packs in series, so it shouldn't leak current more than it did before. At these low powers (12-15W per panel) I doubt it's worth considering bypass diodes (common on high power crystalline arrays), especially as each cell is spread out over the entire length of the panel, making it hard for just one cell to be shaded completely.
AccordGuy
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Location: West Sussex, UK
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Post by AccordGuy »

This week I decided to get rid of the 180A DC relay for the inverter. It was taking up 220mA of juice when the inverter was on (even if sleeping) and it seemed to be causing some surge capacity issues with running / starting big loads (like my cinema kit, especially the projector). Despite the contacts being rated to 180A it got warm when running a sustained 30A inverter load. So I ordered the dedicated remote control panel for the inverter and cut out the relay, connecting the fat inverter positive lead directly to the battery pack via the fuses.

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This is a neat unit that allows the inverter to be started and stopped and also provides a bunch of information, such as the battery voltage, load %, whether the inverter in on-line or sleeping and any error conditions. It had a long enough telephone type wire for me to install it near the living room door light switch, for easier access. That then gave me another idea...

I decided to convert my house lights to solar!

Up until now I'd started with some table lamps plugged into extensions from the inverter but decided to plug the inverter into the house lights proper. I wanted to be able to use the solar power on the house lights but be able to choose easily between grid and solar as I'm not sure there will be enough sunlight in winter to do the whole house. So some kind of change-over switch was in order.

There's a safety issue with this though... You have to be very careful that the grid mains and the inverter mains never see each other... They are at different voltages (grid here is 240V and solar is at 230V) and the phases aren't aligned (it's not a grid-tie inverter) so if they met on the same wire bad things would happen.

You can't get double pole change-over switches in normal mains fittings (at least not at the local DIY stores), so I opted for a completely manual change-over arrangement.

Luckily, a guy came round from the power company last week and changed our power meter for a much smaller digital one. This left a bit of space on the board so I put two 13A sockets in the utility cupboard, one taking it's feed from the original grid lights breaker and the other from the solar inverter. I spliced a bit of 3 core flex with a 13A plug on the two house lights ring feeds and ran that out of the fuse panel to the sockets I installed. So now I can choose between solar (left) and grid (right) power for all the house lights by swapping the 13A plug from one socket to the other - the two power supplies are kept safely apart. The only thing they share is the earth connection.

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The whole house doesn't take that much power for it's lights as they are all low energy types. My solar energy meter showed about 95W for all the lights in the house turned on together.

The only problem now is that if I turn the inverter off at night, I have to go downstairs (in the dark or by the bedside light, which is on the grid wall socket ring) to turn it on... I'll have to look into a wireless remote for the inverter's remote. I could just leave the inverter in it's power save mode but it still draws 250mA when sleeping so would waste about 3.5Ah of battery overnight. Given that I've now got 440Ah available I might live with it for a while and see how things go.
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