Tuesday, November 30, 2010

Slightly Niffy Battery...

What's that nasty niff?

Oh...  That's the unmistakeble smell of battery gas.  Not good when you're running a bunch of "sealed for life" gel and AGM batteries.

Closer inspection revealed two of the AGM Marathon batteries were way out of balance under charge.  I'd been cutting back on usage to get the bank fully charged (as you never know when it will be able to charge again in these gloomy and now snowy days).  The pair in question have some kind of lost capacity problem. One is getting full or has a higher internal resistance than the other and so the two 12V batteries are out of whack, with one sitting at 14.4V; boiling up and gurgling (never a good sound from an AGM pack), and the other is languishing at 13.2V; not even making the float Voltage...  When operating at partial charge, they bumble along without one gassing, but the partial charge will soon destroy all the batteries in the bank; not just these misbehaving twins.

Probably the only thing for it is to take them out of service (dropping my bank capacity from 495Ah to 395Ah), and use them as spares for a 12V system, where they can run in parallel (and not suffer the series Voltage imbalance stress), or be used just one at a time.  I took them out of service for one afternoon to load test and,  individually, they seem ok.  They just can't "get along" as a series pair.

The only other alternative would be to invent some kind of active pack balancing electronics to bypass some of the current on one or t'other battery when charging; a-la lithium ion packs that have individual cell balancing.  Lead acid batteries (especially sealed ones) would last a lot longer if the makers introduced similar Battery Management Systems (BMS) that makers of more flamable cells are forced to.

Heaven only knows how you manage to keep a 48V AGM pack from self-destructing from imbalance.  Most fork lift packs suvive because the passive balancing they employ is exactly allowing some cells to overcharge and "blow off a little steam", so to speak.

On the upside, I've just started making enquiries about a new 24V 160Ah lithium iron phosphate battery module from an American outfit that makes large format lithium cells.  Other makers put together packs using small (3-10Ah) cylindrical cells in big blocks, with a BMS to keep them in check.  International Battery make these new HUGE 160Ah-200Ah cells, so the BMS is simpler and the construction is simpler (and cheaper), as it only has 8 cells connected in series to give a 24V pack.  A lithium pack should offer much more usable power, as you can run it in partial charge mode all the time, and it won't die like a lead acid pack.  In fact, lithium chemistry prefers not to be kept fully charged for long periods.  Ideal for opportunist solar charging. Operating in partial charge mode also means not wasting solar power when your battery has gotten full and can't accept any more charge.  If your battery gets full every day, it's too small for the array.  But lead acid chemistry demands that you keep the battery as close to fully charged as possible all the time.

The specs for the pack look promising.  Min working Voltage is 20.0V (the inverter cuts out at 21.0V).  Max working Voltage during charge is 29.0V and the inverter can work up to 30.5V before cutting out.

I'm hoping they'll say that I can use my existing Morningstar charge controllers as they can be programmed to provide Voltage phases (as in bulk, absorption and float phases with different Voltage limits) or even a single Voltage limited output (float only) with a current limit.  Over-current shouldn't be an issue though as the cells are rated for 1C discharge (160A) and C/2 charge (80A).  The inverter load at 3kW tops out at 125A and the most I've ever seen from my solar array was 73A charge.

Check it out here:

Wednesday, November 10, 2010

Insulating Our Walls

Our house is a 1950's build.  It has a cavity wall but no insulation in it.  Something like 30% of all the heat your home loses is through the walls, so insulating them is a easy and cheap (compared to double glazing) way to make your home warmer and cheaper to run.

The government is offering grants to people to get their homes insulated to save energy.  So we took advantage of this and got a company round to survey the house.  They can also do the loft insulation, but we'd already done some and you have to take up the loft floor to do it properly and ours is full of boxes.

They measured the walls and depending on the total area, you pay a contribution to the total cost and the company claims the rest from the grant scheme.  They do this directly, so you don't have to fill out any forms or apply for it.  In our case, we had to pay £199 for the job.

A few days later, the van turned up with the gear to inject the mineral wool insulation into the wall.

There are other types of insulation that were used in the past.  Our previous apartment was a 1985 build and did have insulation in the form of polystyrene beads.  There were some early horror stories about using chemical expanding foam as the insulation where the curing fumes from the foam solvent made people ill, so now most installers use this rock wool with no glue or solvent or anything.

They have to drill lots of holes at regular spaces in the mortar (between the bricks) to get the tube in and then just pump the stuff in (well it's actually blown in with compressed air). 

Before injecting the stuff they fit a long brush thingy in the whole height of the front and back walls of the house to keep the insulation from spilling over into the next door house wall (we live in a semi-detached house).

They also check any holes in the wall for air bricks and the central heating boiler vent to make sure they are sleeved with tubes so that the insulation stays out of those holes.

All the preparation work took about a couple of hours and made a lot of drilling noise outside (they don't need to do anything indoors).

After pumping the insulation into the various holes, they made up some new mortar, matching the colour of the old stuff fairly well and plugged all the holes in the walls.
Once dried, it's very hard to tell where the holes were.  A good match.  You can see one hole circled in the photo and one of the air bricks they had to check for sleeving.

Hopefully, we'll save quite a bit on gas this winter.  We got this installed just in time!

Thursday, October 21, 2010


Trees.  Good for the environment but no good for your solar power.

In the winter, my panels used to get shaded by a bunch of trees near by, as the Sun made its low 15 degree arc above the horizon.

Well, now a big gap has opened up in the horizon!  For years, there has been this nearly dead fir tree in someone's garden, on the other side of the courtyard, blotting out the late morning sun in our garden.  But yesterday, unannounced, a van turned up with some tree surgeons and a massive shredder.

It took about a day and half, but the dead tree was gradually chopped up and shredded, leaving a big new window on the horizon - and no doubt a few extra welcome Watt-hours on the clock this winter.

Time lapse over two days

Sunday, October 3, 2010

Dodgy Plastic Panels...

Hmmm... I'm glad I sold off most of the plastic framed amorphous panels.  One of the two remaining ones broke the other day.  It suddenly went open circuit.  Rather than bin it, I decided to take it to bits to see how they were put together.

The black caps on the back hide a load of small screws that hold the thing together.  Luckily, the sealant that was under the cover wasn't glue so I could easily take the back off of the panel.  Under the silicone sealant on the positive lead, the end contact on the glass had broken off and the red wire came away with the sealant it was embedded in.  This was possibly from thermal stress as I remember hearing the frames creaking in the sun and shade. 

There was a thin stub of copper poking out from under the laminate. The panel seems to be made from a sandwich of two plates of glass (presumably with one having the amorphous cells evaporated on to it). I just about managed to solder a thin wire on to this and then joined it to a new thicker wire and potted the whole thing in silicone sealant again before screwing the back on.  How long will it last?  Who knows...

To save propping up the thing on a garden chair, I made up a rear leg, just fixed on with the usual brass hinge.

Now that it's getting darker in the days, it's actually better to have the amorphous panels at a shallow angle as they produce more power from just "seeing" more diffuse light from a bigger proportion of the sky than if you aim them at the non-existent Sun. 

Friday, September 17, 2010

A Nice Solar Powered Office

Coming back home from work out in Green Park on the edge of Reading, I noticed one of the new office buildings that they have recently completed.  No one has moved in yet but it seems finished.

The outside wall has a bunch of solar panels integrated into the design.  Looks good but in mid-summer when the sun is directly overhead, it won't make much power using these polysilicon modules.  Amorphous would have been better.  Or forego the "look at me!" architects design and put the panels unobtrusively (and more efficiently) on the roof.

Still, they meant well.
You can see my Honda Insight parked outside the "Eco-Office" for added effect... Now all I need is a plug-in hybrid and somewhere to plug it into that free electricity the building is making...

Tuesday, September 14, 2010

Save Fuel, Drive Smart

One of the biggest consumers of energy is our cars.

The best thing would be to not have one but that isn't practical in my line of work, having to visit clients and far flung offices at odd hours of the day and night.

Still, I try not to use my car if possible.  I spend quite a lot of time working at home. No fuel used for days at a time.  But I do often have to go to an office in Reading, some 65 miles away.

I'd normally go there by car but recently I had cause to go there by public transport (as some low life crashed into my car at the Reading M4 junction and ran off without stopping - GRRR!!!!). Two trains and a bus and over 2 hours each way weren't ideal (especially when I discovered the Reading night bus doesn't accept the return leg of your train "Plus Bus" ticket and you have to buy another ticket).
Any way, I digress...
I normally drive a Honda Insight, a cheaper cousin to the Toyota Prius, in that it is a hybrid petrol/electric car. This car has a driver feedback system that teaches you to drive more efficiently by showing you a colour change from green to blue in different shades as you waste more fuel by "lead-footing". But the lessons learned by driving the Insight are applicable to any car.

While my car was in the workshop, the dealer loaned me a little Honda Jazz. To my surprise, I found that it could get very good mileage by careful driving. It's a smaller car than the Insight and has a smaller 1.2L engine, which helped in traffic jams (less fuel wasted when idling). I could get it up to about 62mpg on the run to Reading. This is diesel territory normally and excellent for a petrol car. The Insight can do 72mpg on the same run.

The main lessons that need to be applied to get these sorts of returns are:

Don't overload the car - remove all junk from the boot, travel light. It costs fuel to accelerate a mass. The heavier the mass the more fuel. So ditch the weight to save the fuel. If your favourite petrol station is on your route, consider filling up only half a tank twice a week rather than a full tank once a week. Carrying a full tank of fuel around weighs a lot and wastes fuel.

Look ahead MUCH furter than you're used to and try to drive without using the accelerator or brake. An odd suggestion, but one that saves fuel and makes you a safer driver.

Don't accelerate agressively - use a light touch and change speed gradually. Don't accelerate to a fast speed if you can see that you'll have to stop or slow down seconds later.

Don't brake unnecessarily - stopping wastes your stored kinetic energy in the moving car and then you have to waste fuel to speed up again. If you can see far enough ahead, let the car slow naturally and with luck the lights will change before you get there. Accelerating from a rolling start uses less fuel than starting from a stop.

When driving a hybrid, the last point is a big factor as the electric motor acts as a generator when slowing down or braking. It recovers some of the kinetic energy that would have been lost in the brakes and stores it in the battery for use when speeding up again. In a non-hybrid car it still makes sense to preserve the kinetic energy you have, rather than waste it in heating the brakes.

Drive slowly - no, really... I mean it. Unless you are in a hurry, drive at the most efficient speed for the engine and gear box. If you are always in a hurry, leave earlier! Change up gear as soon as possible, keeping the RPM counter below 2500. The Jazz had a shift light for the manual gears to prompt you to change up and it's earlier than you'd think. The Jazz did well for such a small engined car - 53mph at 2300 RPM. The Insight has "long legs" with the CVT only making 1600 RPM at 53mph.

Air resistance is much lower at slower speeds too - An average car only needs 10hp to drive at 50mph but at 100mph it requires 80hp just to overcome the air resistance. I've noticed that Tesco lorries have reduced their regulated speed from the usual 56mph to 52mph. This must be to save the company fuel costs as the frontal area of a truck is huge and the aerodymanics are bad so the air resistance is very high.

Consider the trip average speed. It's meaningless to drive round the M25 in the morning at 70mph between traffic jams where you travel at 15mph. You'll just get to the next traffic jam faster. For instance, I know there's no point in driving at 70mph until I get past the M3 going round the M25 so I drive at 53mph max until then (and sit in the traffic jams 5 cars behind the guy who sped past me earlier). Once past the jams I'll drive at up to 70mph, as I know it will actually make a difference to my arrival time.

If you get through the jams more quickly than usual, drive more slowly afterwards. A sat nav will tell you your estimated time of arrival and "range to target". Use that information to adjust your speed accordingly!

Drive up steep hills more slowly than when on the flat or going down hill (especially on motorways)... Stressing the engine to maintain high speed on a hill wastes a lot of fuel with little saving in time.

Chose a motorway route if available. Motorways allow for constant speed driving, increasing efficiency. Use the cruise control if you have one. It maintains your speed with much greater accuracy than your right foot can and saves fuel. You can't use cruise control on a twisting A road and you have to stop for round abouts and so on. Plus motorways allow other faster traffic to go harmlessly around you. A roads suffer from "caravan syndrome". Even if a motorway route is slightly longer it may be actually more fuel efficient.

Don't put anything on the roof! Roof bars, boxes and so on increase air resistance significantly.

Inflate your tyres properly. Under inflated tyres waste energy as the rubber side walls flex and generate heat and can be dangerous at motorway speeds, increasing the risk of a blow-out.

Have your car serviced - make sure fuel and air filters are replaced to avoid wasting fuel from poor air-fuel mixture ratio. Use the thinnest grade of engine oil suitable to the climate you live in (the manual usually suggests a range of different oils for different climates). Thinner oil increases engine efficiency. Change the oil regularly - old oil gets thick with goo and doesn't protect the engine well.

Where's the solar power relevence of this post then?  The Insight is big enough to ferry my panels from their various original homes to their new one... using the least fuel possible.

Sunday, August 15, 2010

Updated Monitoring Network

I finally got round to completing the Morningstar monitoring network.  The problems with the Toshiba laptop and Vista and the clunkiness of having to start up the machine and configure the logger and so on each day (to save wasting too much power at night) got to me.  Below is an example of the type of connection that can be made between Morningstar products.  I don't have a Relay Driver but it shows that you can connect a bunch of things to the EIA485 data bus.
The Morningstar SunSaver MPPT charge controller can talk to the TriStar controller if it has the right adapters.  I already had a RS232 adapter to connect the SunSaver to the laptop but you need an EIA485 converter to connect it to the same port on the TriStar. 

Although EIA485 isn't common in day to day PC networking, it is common in industrial telemetry as it can work over a four wire bus and transmit up to 1.2km without repeaters.  RS232 is only good for a few meters and even Ethernet runs out of steam at 100m.  It's a bit of a pfaff when you only want to connect two things together by a 30cm bit of string though...

The instructions suggest using Cat 5 Ethernet cable for the 4 wire bus.  Two are used for +12V and Ground power lines and the other two are the A and B serial data lines.  They suggested using Ethernet cables because they have twisted pairs to eliminate interference.  But I ignored that and just used 4 core flat telephone wire as it was such a short cable I was making.  They also say that you're supposed to terminate the A and B wires at each end of the bus with a 100 Ohm resistor between them.  I sort of did this by putting a 100 Ohm resistor at one end (inside the Tristar wiring box where it would be safe from being knocked).  I didn't have two 100 Ohm resistors in my spares box so I didn't bother with the one at the other end...  Seems to work ok without it.  I've been receiving data from the SunSaver without problem so again it's probably only important for long wire runs. 

With the SunSaver connected to the TriStar, you can use the MSView software to talk to any device on the EIA485 bus (up to 128 devices) using IP.  The TriStar can be set to bridge the Ethernet and EIA485 networks (it just forwards the MODBUS packets to the devices on the EIA485 network).  It's especially handy because with the exception of the TriStar MPPT-60, no other Morningstar products are IP enabled but now they can be.  It opens up the possibility of using cheap and commonly available networking products to move the data around.  For instance, I don't have Ethernet cable run around the house.  I have a wi-fi transmitter and the TriStar is actually connected to the computer upstairs via an Ethernet switch and a pair of Netgear Ethernet over AC power adapters.  This was more reliable than the wi-fi (which has a dead spot in that part of the house) and the CCTV data also travels over that switch and link.

So now my laptop upstairs can fetch performance data from the Tristar controller and also directly from the SunSaver controller.  The two controllers share the same IP address on the Ethernet but have different MODBUS IDs so each controller responds only to it's own commands.

You have to run the custom settings wizard for each controller to change the default MODBUS ID (all Morningstar devices are preset to "1").  So I changed the SunSaver controller to be ID "2" and left the TriStar on its default of "1".

The EIA485 network needs external power of 12V DC so I connected the two power pins on the EIA485 connector plug to the variable lab power supply that I use to run the AA battery charger and mobile phone chargers.  This converts the battery 24V to the needed 12V, although the EIA485 adapter isn't fussy and will work on any voltage between 8 and 16V, so you could just connect it to a 12V solar battery directly.  But I'm running a 24V system so I have to use a DC-DC converter.  The pair of adapters (RS232 and EIA485) together only consume about 20mA (or 0.5W power) so I can leave them running 24 hours (unlike the Toshiba laptop that consumed about 11W.

Tuesday, August 3, 2010

10:10 - Mission Accomplished

It's taken a while, but I've reached a milestone.  I signed up for the 10:10 challenge to reduce my electricity use by 10% in 2010.
June and July were bumper harvest months, with my solar system making a record 45% of my total demand for July.  The running total - the Lifetime Contribution (blue line) that my evolving solar system has made since I started this experiment is now just over 10% of total demand (and climbing fast now).  The green columns are daily solar kWh consumed, showing a good run of sunny days this summer with many days delivering 5-6 kWh.

Tuesday, July 20, 2010

Make Windows 98 See Vista / Win7 Shares

Sneaky Micro$oft...  In the move to Vista and Windows 7, they broke connectivity to Windows 98 clients without telling anyone.

When you install your file shares on a new Vista or Windows 7 machine you'll discover a weird error message on your Windows 98 machines when trying to connect to file shares on the new machines.  It just keeps saying that the password for a share called IPC$ is no good.

My charge controller data logger is a Windows 98SE Toshiba laptop that can't be upgraded to XP. Although I could use a newer machine, I like the Tosh because it only uses 11W of power to do its work and doesn't need a fan to keep cool so it will work quietly in the corner of the living room.

Fear not.  I've found out how to get around the problem.

The basic problem is that after XP, MS changed the logon authentication method to improve security.  Windows 98 uses LM authentication.  XP uses NTLM1 and LM authentication so it was backwards compatible.  Vista only uses NTLM2 authentication (but it was ok because XP machines got upgraded automatically to NTLM2 by automatic update).  Poor old Win98 got left behind.

However, what you need is the Directory Services Client package from the Windows 2000 Server (from a server or the server CD or as a download from Microsoft).  This allows Win98 machines to log on to Windows 2000 domains but also includes the updates to support NTLM2 authentication.  Download DSClient.exe and install the package by running it.  Make sure you get the Win9x version (there was a NT4 version with the same file name).

That's the first step.  After installing it you need to enable NTLM2 on the Win98 machine.  To do this you need to edit the registry to add a new value to a key.

Run regedit and navigate to:


Add a new value called LMCompatibility of type DWORD and value 3

Setting this value to 3 tells Windows to use NTLM2 authentication.  Reboot.

Now, Windows 98 can't log on to shares using a different user name (XP introduced the "connect using different user credentials" option) so you need to make sure your Win98 user and password is the same as a local account on the Vista machine that you've given permission to use the shared folder.  This is the same as normal share set-up.

On the Vista machine you also need to edit the registry to change the hashing of LM credentials.  Otherwise, you'll be able to see the share but not be able to access any file from the Win98 machine (if you try, you'll wait for a few minutes and Windows 98 will say something like "the network resource is no longer available").

Run regedit on the Vista machine and navigate to:


There should already be a value called nolmhash set to a value of 1.  Change it to 0.

This will make Vista file shares less secure but only to the same degree that XP was.

The final step is that on the Vista machine you have to reset the password for the local user account that you will be using on the Win98 machine to access the share.  You can set the new password to be the same as the old one but by going through the change process, it changes the way the new password is decoded by Vista (to the old method used by XP).  Now you should be able to browse the network neighbourhood to the Vista machine from the Win98 machine and access files on the share. 

I still had some weirdness after this in that I could write new files and rename existing files on the share but not open existing files for reading or copy a file from the share to my Win98 local disk.  Some kind of permissions problem on the Vista machine but in my case I only needed to write logged data to the share and rename yesterday's file (and I could do this) so I wasn't going to fret too much about not being able to read/copy files.

There were some bugs in the Win9x DSClient package originally and these did apparently get fixed in a Windows 2000 Server service pack but you can't download this updated DSClient package separately for some reason (unless you have a Windows 2000 Server and get it in the service pack).

So for now (at least), my Windows 98 laptop lives on to fight another day!

Monday, July 19, 2010

Saved From the Dustbin

In a move to reduce the power consumption of my "server" room upstairs, I replaced the XP desktop machine that was doing file serving, CCTV recording and mail filtering with a Vista laptop I picked up at a car boot sale for £20. It was a bit busted, the power supply was lost along with the battery, and the OS was trashed but as a server it doesn't need all the keys on the keyboard to work, doesn't need a battery as it will live exclusively on the mains and I found a matching power supply at the same car boot sale for £1. Best of all, the hidden recovery partition was still in tact on the hard disk so I could re-image the machine and now it works fine. It consumes a mere 25W of power compared to the 110W of the old desktop, greatly extending the time the server can run on solar power.

My wife's laptop recently expired from overheating - a design defect in the HP G60 series :( but the memory from it was compatible with the car boot machine so it now has the salvaged RAM from the dead HP.

The HP may yet live though. In the spirit of "make do and mend" to reduce the waste of throwing things away that can be fixed, I found a company that specialises in repairing the G60. It usually dies because the graphics processor had a poorly designed heat sink. It gets too hot and the the solder joints on the chip fail. The company resolders the chip on the motherboard and then fits a new customised copper heat sink and an upgraded BIOS that makes the fan run faster all the time to prevent the problem recurring.

The operation runs from a garage in Thatcham and I was shocked to be met at the door of an ordinary suburban house by a man in a white coat! He showed me the "lab" and the stack of machines awaiting repair along with a couple on soak test after being fixed. At £50, it will be an economic repair (if it works) and I'll have saved a machine from becoming unecessary land fill fodder. If it doesn't work, they only make a charge for return postage so I'll only have lost £10. I'll scavenge the hard disk for the new server (as the HP one is twice as big) and sell off the carcase to repairers who can use the LCD screen and plastic body parts to refurbish other G60's. There's a market for them on eBay...

"Waste not, want not..."

Tuesday, June 22, 2010

She Cannae Take the Power Cap'n!


Automotive blade fuses... PAH!

Don't use 'em.

I had my new batteries connected to the main bank with an in-line blade fuse holder and a 30A fuse.  Not a cheap-o rubbish fuse holder but an RS one.  It was the day after the longest day today and the sun was beating down after I'd more than half drained the batteries watching movies last night.  Pulled 6.4kWh from the system :D.

Today though, the secondary bank was very greedy and spent quite some time sat at about 25-30A charging.  The poor little blade fuses couldn't hack it.  Two of them melted (the plastic holders - not the fuse wire!).

So I replaced the in-line fuse holder with an old 32 Amp MCB breaker that I got at a car boot sale a while ago.  It's better that way any way as it can disconnect the battery if there's a fault and it also serves as an isolation switch.
The rest of the afternoon's sun was soaked up without further melting or burning of plastic / rubber / fingers...

Wednesday, June 16, 2010

More on Balancing Batteries

Googling around the last couple of days I discovered that Elecsol (well known maker of leisure batteries) has released a new range of sealed VRLA AGM batteries primarily aimed at solar storage.

They make some impressive claims like that these batteries can deliver 1,100 100% discharges and 1,400 80% discharges.  They offer a 7 year "unlimited" warranty on them.

You can read the blurb on them here:  http://www.elecsolbatteries.com/literature/

The tech book / brochure did have an interesting addition to the traditional star pattern series-parallel wiring scheme.  It had not occurred to me to put balancer cables between the mid-points of the series strings to allow internal equalisation of the bank.  I'd had a problem with one of the six new batteries in my bank being low (out of balance with the other one in series) but I cured it by taking that pair out of circuit and slow charging the weak one to bring it up and then put them back in circuit.  The whole bank appears to be behaving ok now but I periodically measure the volt differences on each block. 

I might put a star equaliser network in (connecting the mid points of all three pairs to a common point so they will equalise er... equally).

The red/black lines are the power lines I have on my bank and the green ones would be the equalisation network that would allow all the weak batteries in pairs to charge up more without over charging the stronger ones.  In my "bad" pair they showed 28.2V across the pair but one was 13.8 and the other was 14.4.  With the equaliser network added, the weak "bottom side" battery might continue to charge by "finding" another weak "top side" battery to pass current through (13.8 + 13.8 is only 27.6 so that pair would continue to charge without over charging the others sitting at 14.1V).  It wouldn't help in every scenario though - if all the bottom side batteries were weak and all the top side batteries were strong then the equaliser network wouldn't help. 

Maybe it's just as well to rotate batteries in strings (like tyres on a car)?

Meanwhile, it's been a great couple of days harvesting.  In those partial cloud surges that I mentioned before, I've seen surges up to 1.98kW from my 1.8kW array (over 109% of rated power). The Sharp ND170 340Wp string stole the show though, putting out 409W (120% of rated power).  They might have managed more but the charge controller capped the output at 15 Amps!  The other charge controller was also close to capping its output to the 60 Amp limit, as it surged to over 57 Amps - the pair pumping an eye-watering 72 Amps into the battery bank.

Friday, June 11, 2010

Balancing Batteries

When connecting batteries in parallel to get more capacity, you have to be careful to balance the individual strings of batteries so that they all do the same amount of work.  Otherwise, some will become more discharged than others and suffer damage from hard lead sulphate forming on the plates that cannot be dissolved by charging.

Having batteries of different sizes is also not a good idea as the small ones will discharge to a greater extent than the bigger ones and so suffer again.

So what did I do?  I bought a bunch of different sizes and types of battery and connected them all up together... Go figure.

So, how do we bodge this so that the batteries all stand a chance of surviving?
The main block of batteries are gel types and 180Ah in size.  They have a rating of 1,000 cycles at 50% depth of discharge (the deeper you discharge a battery, the fewer times you can do it).  The Marathon ones I've just bought are AGM types and 104Ah in size.  They are intended for computer uninterruptible power supplies (UPS) and as such are not expected to be discharged every day (if ever).  They probably have a rating of 250 cycles to 50% discharge.  But if discharged by only say 25%, they might last nearly 1,000 cycles.

So, to balance the different batteries lifespans, you have to try to balance the amount of work each does. To do this your main tools are size of battery and the wiring that connects them.  Thinner wires resist the flow of current and so large loads will drain batteries connected by fat wires faster than ones connected by thin ones.

In the diagram above you can see how I've wired the batteries together.  The big gel ones are directly connected to the solar chargers and the AC inverter by very heavy gauge 35mmsq cables.  This lets the gel bank do the bulk of the work when under high load. The weaker Marathon batteries are connected in 3 groups that use a star wiring pattern.  This means that each group is connected by wires that are individually quite thin (6mmsq).  But the wires are deliberately a bit long and are all the exact same length (hard to draw so take my word for it).  The other important fact is that they are all connected together at one point (I soldered them together after weaving the ends into a sort of knot. This means that, as far as possible, the wire resistance for each branch is the same and so each group of batteries will do the same work.

The whole group of six batteries is then connected to the main bank by a single pair of 6mmsq cables with a 30A fuse.  The fuse is important as 6mmsq cable can only carry about 50A and a fault could cause a few hundred Amps to flow.  If the main battery dried up or got a short circuit somewhere inside it, a very large current could flow and start a fire.  Actually, each of the groups should have a fuse but adding fuses in every leg makes it difficult to balance the resistances as the fuses and connectors introduce variances.

So, by having the Marathon battery bank 1.7 times the size of the gel one and using thin wires to connect it, I hope to keep the workload low enough on the Marathon bank to make it live for as many cycles as the gel ones.

When running loads, I've noticed that the gel bank does do more work (delivering about 2/3rds of the current).  But as the gel bank starts to run down the Marathons start to assist more.  This is because gel batteries are designed to resist deep discharge by being acid starved.  They don't have enough acid to fully convert all the lead in the plates.  As the acid runs out, the gel battery increases its internal resistance and so does less work until the output voltage falls to a point where the protection in inverters causes them to turn off.  

Because the resistance of the gel battery increases as it gets discharged, the balance of resistance between the gel bank and the Marathons will change.  At some point, the Marathons will have the lower resistance path and so assist the gel bank by doing more work.  So it's more important that before for me to stop discharging the bank before it gets much below 50% as beyond that point, the Marathons will start to be drained quite quickly.  But even then, that shouldn't be a big problem as they are 1.7 times bigger than the gel bank.

Tonight we're at 50% as the last couple of days has been very gloomy (it rained all day today).  Hopefully tomorrow will bring some sun.

I'll have to watch the charge in the morning as the reverse is true for charge balancing.  Because the gel bank is low and has high resistance, the Marathons will accept more charge current than the gel battery (at first).  The charger can deliver up to 73A and could cause the 30A fuse on the link wire to blow...

Thursday, June 10, 2010

Hello Darkness My Old Friend

Dark days have indeed returned.  The last couple of days have been a steady deterioration from the wall to wall sunshine of last weekend through the record breaking partial cloud of Monday (when I briefly saw the 1.8kW array spike to over 1.94kW) to today's wall to wall gloom.

Solar cells are temperature sensitive and when in full sun they get hot and lose some power.  But on partially cloudy and cold days, the cells get cold when there's a cloud but when the sun peeks out they put out more power for a short time before they heat up.  Also, as the sun peeks out from behind a cloud a sort of focusing effect happens to the light and for a few seconds it can be stronger than in a clear sky.  Under these circumstances it is not uncommon for solar panels to put out as much as 115% of their rated power for a few seconds.

The new larger battery bank is capable of absorbing a lot more power now and had no trouble lapping up the 73 Amps that the solar chargers blasted out.  Sadly, although these events produce very high rates of charge, they only last a few seconds so don't actually charge the batteries much.  So over the last couple of days the batteries have been slowly fighting a losing battle.

Having increased the capacity from 180Ah to 492Ah has made a big difference though, extending the time that we can survive without a decent sunny day from just one day to maybe two or three, depending on how reckless I am in the evenings.  But tonight after a particularly gloomy day where the PV output never crept above 375W and with the forecast for tomorrow to be non-stop heavy rain all day, the battery gauge is sitting at 69% tonight and likely to fall to below 50% tomorrow night.  We might have to switch the fridge freezer back to mains power at night until Saturday when the forecast is for sunny intervals again.

We'll see.

Tuesday, June 8, 2010

How to Bodge Ammeters

One of the big problems you have when putting together a battery based solar system is measuring where the juice is going.  You need to know whether it's going in the battery or to the inverter and how fast it's going.

For this you need low loss ammeters.  You need ammeters that can measure maybe 100-200A without causing much voltage loss.  You can buy shunts that you can connect in series with cables to read the current but this means more joins in the cable and each join adds resistance that causes loss.  Shunts are also mostly of the type that create a Voltage of 50mV per 500 Amps passing through them which is quite a small signal when most of the time you'll be measuring a few 10's of Amps.  They're also quite expensive...

Enter the In-Line Bodger's Shunt... :D

Solar battery systems by necessity need to be connected together by big fat cables to carry the heavy current without losing Volts ('coz we're working at maybe only 12V or 24V).  Any bit of copper cable (no matter how thick) will have a resistance and so make a voltage across it's length when a current flows.  Even the cheapest digital multimeter will read down to 0.1mV (they all have a 200mV range).  So all you need to do to measure the current in a cable is attach some sensor wires to the cable at a distance apart that causes some useful Voltage to be developed relative to the current.

I have two types of in line shunt in my system.  One uses a long spacing (about 50cm on a 10mmsq cable) to give a reading of 1mV per Amp.  On my big group of four 6V batteries, I made one of the huge 35mmsq link cables that join the blocks a bit longer than the others - just enough to make 0.1mV per Amp when I soldered the sensor wires at the lug ends. So that DMM reads 0.1 for 1A and 1.0 for 10A - you just have to ignore the decimal point on the display.
This one's a shorty as it's on a bit of 6mmsq cable.
It should go without saying (but I'll say it anyway) that you should only do this on low voltage DC power cables.  Don't try it on mains AC lines, as a) it won't work and b) you'll probably get electrocuted and die.

All you need to do is connect another DMM with a 10A current range in series with the cable in question and arrange for a few Amps to pass through it.  Then solder a sensor wire to the fat cable and using a pin, poke the cable at different places until you find the distance that gives you 0.1mV per Amp reading on the new meter.  Then you can either cut the insulation away at that point and solder the other sensor wire in there or sometimes on big 35mmsq cables you can just solder the sensor wire to the head of a drawing pin and just stick the pin into the cable at the spot.  Tape it up with electrical tape and run the sensor wires to where you want to see the meter.  It can be some distance away (like a couple of meters) as the sensor wires carry no current so won't lose any volts on the way (the DMM input is usually about 10MOhms so the fraction of one Ohm on the sensor wire makes no difference).

Here you can see my three bodged ammeters.  The top and left ones read net battery current in or out of the two main banks at 0.1mV per A (so showing 3A charge each) and the third one reads the current from the smaller Morningstar MPPT15 charge controller at 1mV per A (so showing 2.0A charge).  The big Morningstar TriStar has a built in meter so I didn't need to bodge a fourth meter. The meters are arranged so that positive readings mean charge current and negative readings means discharge current.
Ok, these shunts aren't going to be super accurate and the short (or fat) ones will only read to a resolution of 1A but mostly that's all you need to know - whether the battery is charging or discharging and by roughly how much (some Amps or lots of Amps).  

Maybe most importantly, it can tell you when there are no Amps flowing as that tells you two things: a) something is busted or b) the battery has finished absorbing power and is full.  In a system like mine with several batteries, it also tells me how well (or otherwise) the batteries are sharing the load or charge... More on this in the next post!

Monday, June 7, 2010

Attack of the Killer Bees

Woke up this morning and noticed that the end pair of panels on the patio were being partially shaded by new growth from a tall bush by the fence.
No problem, I thought.  I'll just get the loppers out and trim a bit off the top so that the morning light can reach the panel.  Snip... snip...snip.  Hmm quite a lot of bees on these flowers... You can see all the blue flowers all over the branches.  No worries, they'll just fly off.  Snip...snip...snip... what the..?  Hey! Ouch!  Wahhh!!!

Retired to a safe distance to see the top of the bush a mass of bees.  I thought one had "bumped" into my hand rather hard.  Then it started to come up in a red bump.  Oh oh...  

Luckily, we have some anti-histamine tablets in the house as I get hayfever and we had some sting neutralising liquid (ammonia solution).  If you put it on quickly after a sting the bump goes away completely and you're as good as new.

Back in the garden, I took a closer look at what I was cutting...  Hidden inside the thickest part of the bush was a bees (or is it a wasp?  Never quite sure...) nest.  Quite beautifully crafted from paper and always has a couple of "sentries" guarding the entrance at the bottom and others making the next layer of the shell from chewed up wood.
 It's an ideal spot for them as the bush has a lot of flowers and we grow roses and all sorts of flowers plus there's a pile of rotting wood next to the bush so no shortage of building materials for them.

Oh yeah... I managed to half clear the offending branches that were shading the last pair of panels on the array so I guess I bought a few more Watt hours in the morning but I doubt I'll be doing any more hacking and slashing this summer.

Sunday, June 6, 2010

Even More Batteries!

Well, the first two Marathon batteries I bought a couple of weeks ago worked out quite well.  And flush with the money from the car boot sale of my old solar bits and bobs, I went back to the same UPS battery guy and bought up four more of the same batteries for £50 a pop.

The first pair I bought certainly hold a decent charge (although I haven't measured them on a discharge cycle) and assist the gel battery bank quite well.

Here you can see my cinema...
And nestling under and behind the sofa...
492Ah of 24V batteries! 

Ought to be "enough" for now ;)

Friday, June 4, 2010

Sowing Some Seeds

With the upgrade of all my plastic 15W amorphous panels to "proper" high power BP and Sharp solar panels complete, there remained the question of what to do with all those spare panels gathering dust in the garage.

We decided to take part in a car boot sale.

We had a load of other unwanted things to unload as well (the usual bric-a-brac) so we saddled up and headed out for the fields of Sussex.

I had the original four wet batteries and eight of the 12 solar panels to sell.  I also had a bunch of little 7Ah AGM batteries that a Hungarian dude gave to me for free when I bought a 40W panel from him last year.

Business was a bit slow at first but by the middle of the afternoon the big batteries had all gone for like £8 each and even some of the 7Ah batteries had gone for £3 each.  

Once I got my solar demonstration working (a panel plugged straight into a 12V fan) people were drawn to our pitch and were curious to know more about solar power.  By the end of the afternoon, I'd sold all eight of the panels for between £15 and £20 each and even had someone come round to my house to collect another two that I'd not had time to unscrew from the wooden frame before the sale.  I'd also sold some of the LED lights that were part of the kits and two of the charge controllers.

Some kids were amazed by solar power, asking where the electricity was coming from and exclaiming "Cool!!" when I showed them that it was coming from the sun, making the fan go slower or faster by having them stand in front of the panel so that they cast a shadow on it.

Hopefully these kids will have been as impressed as I was as a kid when I was given a solar power electronic experiment kit from Tandy (remember those "10 in1" and "30 in 1" experiment kits?).

My other secret plan was to get adults hooked on solar power.  As I've discovered, collecting solar power is addictive.  You start off with one or two small panels and before you know it you've got loads of the things and are making serious amounts of power.  By selling off these seeds at a low price, I hope that some more people will experiment with solar power and eventually take the plunge and get a full blown system.

Wednesday, June 2, 2010

Made in Japan (part 3)

Back in November 2008, while out sightseeing at the dammed lake reservoir near Miharu, we stopped at a hotel spa place that has a very good tofu cafe that sells all sorts of yummy food entirely (almost) made from tofu or derivatives (even the donuts!).

Anyway, while walking about I noticed that somehow they had also built an observatory (it gets very dark up here in the mountains away from any town).  

Next to the observatory was what at first glance appeared to be a bus shelter (err.. because it had buses parked under it).  In fact it was a sizeable solar array!

It consists of 8 rows of 14 x 167W 48 cell (23.2V MPP) Kyocera panels (I could read the info plates on the undersides).  From the date stamps on the panels it seems to have been in operation since 2002.  The nominal output is 18.7kW - maybe enough to offset most of the power used by the small hotel, observatory and cafe.

The electronics were all in a sort of phone box shaped hut next to the back row.

Travelling from the remote town of Takayama through the mountains to Matsumoto I saw quite a few new looking home based PV systems but many more old looking solar hot water systems.  These types of evacuated tube or flat plate collectors have been popular for decades with the Japanese.

Monday, May 31, 2010

Made in Japan (part 2)

This time we're in Miharu in the prefecture of Fukushima to the NNE of Tokyo by some 200km.

If you keep hitting (+) on the map it will zoom in and show Miharu (eventually!).

My father-in-law's house has two arrays on the South and West facing roof slopes and luckily even though it is in a quite steep valley, the valley runs East to West and his house is on the North side so it gets a fair bit of sun even in the winter.

The panels are made by Hitachi and are their newest hybrid crystalline amorphous type that have layers that give excellent wide spectrum responsiveness on cloudy days but the high output of crystalline panels on sunny days. The Sharp ones used on the house in Tokyo were a common crystalline type. On the South roof there are 18 panels and another 13 on the West roof.
All the power conversion kit is made by Sanyo.

As the array is split into unequal strings of 18 and 13 panels, they work at two different DC voltages. So outside on the wall is a voltage converter / combiner that converts the two different DC supplies into one at a common voltage that then goes into the inverter indoors.
A single DC cable goes to the power conditioner in the house where it is converted to mains. It's a less elaborate unit than the Sharp one and just has a single display that toggles between current kW output and the lifetime kWh generated. The information plate says it is rated for 70-380V DC input and 5.5kW output at 200VAC with an efficiency of 95%.
Outside, the utility company has fitted two digital electric meters, again one for power used and another for surplus power sold to the grid.
The inverter appears to be putting out 200V rather than the house 100V, so either it's designed to be split phase (100-0-100) relative to earth or it actually doesn't feed the house directly but just the grid through the separate meter so that the household usage bill is offset by the generating credits.

My father-in-law said that in the summer and up until September it generates a net surplus to the household requirements but by November it doesn't quite make enough to completely offset their usage.  On the clear sunny day shown here, the inverter reported making 3.0kW for a short while around mid-day but 2.1 to 2.6kW for the bulk of the day. The sun was quite low in the sky even at noon and as it moved round to the West, the output declined a bit.  In summer it was probably ok with the sun much higher in the sky and on cloudy days it probably doesn't make much difference either having part of the array facing west.

Another novel feature of their house is a Sanyo air source heat pump (ASHP) that heats water by extracting heat from the outside air (usually hot and humid). Using a sort of reverse air conditioner it pumps the heat into an insulated hot water tank. 

It uses about 60-70% less electricity than a resistive heater. The Japanese call it an Eco-Cute. It doesn't mean "cute" though... "kyu" is a kanji in Japanese than means "to heat water". The difference between an ordinary air conditioner compressor and these water heaters is that the refrigerant is at a much higher pressure in this system to more efficiently extract heat and it's only in recent years that they've been made small enough and cheaply enough for home use.

Inside the house is the large hot water tank and compressor. A digital display shows the water temperature and how "full" the hot tank is as a bar graph.
The system also controls the heating of the bath to a constant temperature - very important for Japanese.  You take a shower and wash and then sit in the tub just to relax and get warm while the system cycles the water.  You could sit in it all evening.

He also had the kitchen refitted and they changed from a gas hob for cooking to electric induction.  This wastes a lot less energy (95% of the energy goes into heating the pan rather than the hob or the air) but did have the drawback that they had to replace most of their cookware.  Induction hobs only work on ferrous metal pans, so the typical aluminium or stainless steel with copper bottoms don't work well.  As they generate quite a large surplus of electricity, it made sense to change from gas to electric for cooking.

Saturday, May 29, 2010

Made in Japan (part 1)

It's not just me in my family that has solar power, no sireee.  It was actually my in-laws that started things off.

My wife is Japanese and her sister lives in the suburbs of Tokyo.  Back in 2008 they installed a grid tied 3.07kWp Sun Vista system by Sharp.  

Sharp call the inverter a "power conditioner" and it has a control and info panel near the utility breaker panel indoors.  It lights up different colours during the day to indicate the power level.  Blue means the system is generating a surplus and is selling electricity to the grid and yellow means it is generating but grid power is being used as well.

The panels are mounted on both sides of the roof but the slopes face sort of east and west so one half of the array is always sub-optimal. The sun doesn't make such a low angle in winter in Tokyo when compared to the south of the UK so the variation of day hours are less extreme and Japanese Autumns and Winters are characterised by clear sunny days (very unlike the UK). In the summer the sun goes mostly directly overhead so it's not such a problem.

Their house is the one at the back of the white one - you can just see the panels on the roof.  The houses are terraced back to back.

The installers mounted the inverter on the outside wall and then ran a wire to the remote control panel inside.
The mains is fed to two meters outside that the utility company installed.  The digital one on the left measures grid power drawn and the old school mechanical one on the right measures solar power sold to the grid.

The remote panel in the house displays an estimate of power being generated as well as the proportion being used or sold and the lifetime kWh. Flicking through the menus you can pull up generating history graphs for the last hour, day, week, or month.

It's about 11am in this shot and it's just started to make a surplus now that we are done with breakfast and have stopped using the kettle.  The sun is a bit hazy today. 

They tend to sell a lot of power during the weekdays when they are out at work but then buy it back at the weekends when they use the air conditioning and clothes dryer.

The whole system is a kit made by Sharp but a local installation company fitted it.

Wednesday, May 26, 2010

PV in Germany

I knew that solar was more popular in Germany than the UK but this set of pictures gives you some idea just how far ahead they are compared to us in the UK...

I wasn't intending to go on holiday in Germany but fate (or rather volcanic ash) interceded and we had our flights to Japan cancelled.  So, not wanting to spend the whole of the four weeks I'd booked off sitting in our back yard, we caught the ferry to France and drove across to Germany.  We went to Seiffen near the Czech border and up to Berlin and across to the Nurburgring (but I couldn't drive on it as my insurance excludes it by name!).

Along the way, we were amazed by how many houses had solar PV or thermal (sometimes both) and here is a sample of what we saw.  The biggest array by far was one in the "back yard" of Amazon's warehouse in the middle of nowhere in the middle of Germany.  Absolutely huge it was.... a whole field of trackers.

Some like this one are communal, shared somehow by the residents of a block of flats.  This one has 121 panels and at a typical 180Wp per panel that's about 21.7kWp

Many businesses install very big arrays on their warehouses or factories.

This was one pair we saw from the window of our castle hotel at Neuhausen near Seiffen that specialises in wooden toys and other intricate wooden decorations.  You can see the 88 panel array on the house but also a bigger one on the barn just peeking over the hills behind.  This house had in the region of 15.8kWp installed.  And this is quite common in Germany.
These two we saw in another castle town, Wernigerode, where we stayed at a ski hotel.  This house must get through a lot of hot water! It has a massive thermal solar panel.
This one not only has panels all over the roof but also on angles all over two garages / sheds to the left of the house.
Driving in the scenic valleys to the North of Kassel, we saw a solar showroom.  A big ex-supermarket type building with a large car park.  Could solar be so popular that they have something akin to a car showroom for selling installations?  A helpful woman enquired if I needed help.  I looked at a selection of example panels they had in different powers and styles (including black framed ones and big amorphous ones).  They stocked some brands but she pointed out that they also made their own brand too.

Driving on through that town we started to see more and more installed PV systems... Obviously, the showroom had been doing plenty of deals for the 'Burghers.

Driving along the 80 towards the fairytale town of Hameln (as in the Pied Piper of), we were stopped in our tracks by the sight of this village (Oedelsheim) with its numerous houses with big PV arrays.
The farmhouse on the far left having some 264 modules installed on the upper and lower roof! I did notice on my travels that mostly the Germans seem to go for poly panels rather than mono types.  Maybe they're a lot cheaper or perhaps the German made ones are predominantly poly types?
The neighbours were keen to keep up with the Johans in some arms race to see who could have the biggest array.
Hameln Banhof (train station) has this bus station with see-though panels specially made to make power and act as a sun shade. They are not so different to normal panels just the cells are spaced out a bit and a clear backing used instead of the usual white / blue EVA.

Treysa in Schwalmstadt to the SE of Kassel has a walled old town and from the ruin of the church you can see this school complex with a massive PV array on several buildings.
This office, visible from the old town wall has 198 panels (~35.6kWp) installed.  By now this looks "average" as installations go.
Even some of the old timbered houses in the town have been kitted out.  Not sure massive solar arrays on quaint English Tudor houses would sit well with the parish council but the Germans don't seem to mind.
Just outside the nearby castle village of Ziegenhain (supposedly the town of Red Riding Hood) some nutter has put a 5x5 module tracker on his shed...
Ferienhof Todenhausen wins the award for the most solar systems installed in one village though...  It's not that big a place but it has a crazy amount of PV installed.
I counted 14 PV / thermal installations on different houses in this close-up shot alone.
And someone went mad on the far right of this shot where they installed PV all over the two enormous grey sheds with specially designed sloping roofs!
All the excitement went to me head and I bought the used 50W panel and 5x new 80W panels off of eBay for me home brew setup when we came back home.

On the way to Yorkshire to pick up the 80W panels, I noticed plenty of large buildings (offices, warehouses, farm buildings, homes) that were all ideal candidates for massive PV arrays that would almost certainly had one if they were in Germany... Not a sausage here.  Pitiful.