Just getting started

Discussions about Renewable Energy, including photovoltaics, wind, and small scale hydro.
Creating power for your home, off grid.
Emphasis on nuts-n-bolts, hands-on projects.

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AccordGuy
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Post by AccordGuy »

Been away for a while but there's been no shortage of tinkering and upgrades here.

Shortly after I got those 80W panels, I discovered that the new Morningstar MPPT controllers had hit the UK (finally) and so it was time for a major upgrade...

I went the whole 9 yards and ordered the Tristar MPPT-60 and its optional meter. This meant I could dispense with the multimeters blu-tacked to the wall and talk to the thing over Ethernet rather than just a serial port.

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Mmmmm Shiny.

Got it all installed on the wall and only demolished one bit of plasterboard corner than will need some plaster patching (ahem...).

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I was pootling around in the local HW store looking for rubber grommets to go in the HUGE knockouts (wot don't knock out without a 50lb lump hammer >:() and saw some neat two slot consumer unit-type-things and next to 'em... 100A dual pole two slot MCBs! I'd been wondering how to upgrade the existing disconnect switches that I had (puny 20A automotive ones) and had toyed with the idea of 45A cooker switches. But 45A still isn't enough for a 60A charge controller. These 100A MCBs are ideal though (assuming they'll actually work at 24V-46V DC).

I'd never got round to putting disconnects on the PV inputs to the charge controllers before but as there were two sets of these things in the shop, I went for it. So I used one double pole MCB to break the two PV inputs to the two controllers and the other one to break the outputs of the controllers to their fused battery connections. Of course, normally both breakers will be closed and I'd try not to go opening them when under heavy load (that's how one old 16A switch burned out). I'd looked at "proper" solar DC disconnects but they are very expensive and I don't actually need switches rated for switching 400V DC.

I uprated all the battery wiring to the controllers (10mmsq all round for the old 15A SunSaver and 20/25mmsq for the new TriStar)... Pity that the feeder from the junction box outside was only 6mmsq... More on that later.

And with a bit of the magic yellow thing in the sky...

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THAR SHE BLOWS!!!!

Shame about the cheap yellow rubber buttons wot you have to stab quite hard to make work properly. And the charge status LEDs that don't come anywhere near the window in the front plate so you can't see them properly from anywhere other than straight-on in front of the thing... Might have to fettle that when the thing's been "run-in".

Stay tuned for more catch-up news (this was just February!).
AccordGuy
Posts: 144
Joined: Tue Jul 01, 2008 11:47 am
Location: West Sussex, UK
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Post by AccordGuy »

I've just started a "proper" blog site for my diary entitled "Solar Power - A Bodger's Guide". You can check it out at:

http://solarbodge.blogspot.com/

Meanwhile, back in February I'd got lucky with some cheap BP solar panels. They spent some time in the patio door windows while the weather was bad but finally made it outside to replace the last of the 12W amorphous panels.

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Other improvements included getting rid of the over head cables to the garage. These were causing a line shadow across the panels below and now that they were all crystalline types rather than amorphous, they were much more sensitive to partial shading.

So I buried the cables in some push-fit drain pipe under the lawn. I had to cut out the turf and save it so that I could re-lay it and in one day I managed to finish the job.

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I ran fatter cable than I needed over to the garage as that would allow for some expansion in the future...

Lucky really, as that "future" came quite quickly :D.

I got a deal on some new BP 380J panels. A guy was selling them at £165 each for multiples of 10 but I managed to talk him into selling me just five at that rate.

So I'm replacing all the plastic framed 15W panels with the new BP ones and will sell off the old ones at a car boot sale. As our planned trip to Japan got cancelled due to the volcano ash cloud over Europe in April, I had some spare time to make up a new mounting for four of the new panels, using the stainless steel bits I got free with the second hand BP panels I bought in February.

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I designed the frame to have a slightly lower angle so that the front row of panels wouldn't cast a shadow on the bottom of the Sharp panels behind them in winter. Although you can't see it in this picture, the thing is secured down to the roof with a ratchet strap and cinder block weights at the back and the heavy stainless steel frame at the front. Hopefully it won't go anywhere when the autumn storms come.

I also won a second hand BP 350J panel on eBay for £108 and luckily this was a 12/24V reconfigurable panel so I didn't need to find another one to match it. It was also just about the same width as the 160W panel over the patio door so it doesn't look too out of place next to it.

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All this expansion and replacement has taken my system up to 1.8kWp.

Time to get busy with an automated dump load manager... Stay tuned for more or if you can't wait, check out my blog site :wink:.
AccordGuy
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Re: Just getting started

Post by AccordGuy »

Getting the Lead Out

After a long time of running my solar system on cheap caravan batteries and then second hand industrial gel and AGM batteries, I embarked upon a new and exciting adventure this year.

The problem has been that even good gel lead acid solar batteries, like the Deka ones, only last for around 800-1000 discharge cycles if used significantly (50% discharge depth). And they don't like being discharged and then only partially recharged the next day. Worse still is the typical M.O. of solar systems where they get discharged and partially recharged for days and weeks at a time in the winter.

My lead acid batteries have lasted about 750 cycles (about 30 months), which is pretty good but not ideal.

So I took the decision to try out some emerging battery technology... Lithium ion cells. Specifically, Lithium Iron Yttrium Phosphate (LiFeYPO4).

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Now, lithium ion cells have been in use for many years. We all have them... in our phones, laptops, power tools. But that's little tiny 2Ah or 3Ah cells. I'm talking about a bank I've built using 400Ah cells to make a "24V nominal" 10kWh pack that can run my house for about a day and a half with the solar charger turned off. The resting full charge Voltage is actually about 26.6V but that's well within the normal operating range of existing kit designed for working from 24V lead acid battery banks.

You can check out all the build and charging details on my main blog, including a YouTube video diary.

http://solarbodge.blogspot.co.uk/2012/0 ... hange.html

These things are now actually safer than lead acid batteries, especially AGM ones that have a now recognised high potential for thermal run-away and fire when they get old. But most charger and inverter kit is designed around the discharge curves for lead acid batteries. That's not to say you can't use your old solar charger and inverter with them (I have). But they do need a bit of additional monitoring kit and some minor adjustments / modifications to make them work properly with lithium cells. The main thing is more robust protection from over discharge at the cell level (not just the whole battery pack, as is the case with all lead acid kit).

That's what the little box of tricks in this photo does.

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The cells are of course quite a bit more expensive than lead acid cells, but they do have several huge advantages. First on the list is that if you keep the discharge cycles to under 70% depth of discharge, they last for 8,000 cycles. TEN times longer than any lead acid battery when they are cycled to only 50% of capacity. Second, they don't mind (and actually prefer) to be partially charged and not kept fully charged all the time. The exact opposite of what lead acid batteries want. They fit the M.O. of solar charge and discharge usage patterns PERFECTLY.

They also put out HUGE power. Lead acid batteries have to be sized to not deliver more than 20% of their Ah rating either in charge or discharge (C/5). Lithium cells can happily be charged at 100% of their Ah rating without issue. Lead acid batteries lose a huge amount of their effective capacity if you try to discharge them too fast. That's why they have to usually be specified at the C/20 rate. A 400Ah lead acid battery will only be 400Ah for loads of 20A. A 400Ah lithium battery can deliver 400Ah at a discharge rate of 400A.

The down side? You can't get away with over discharging them. Lead acid batteries get damaged by running them flat. You can recharge them and they will recover with reduced capacity and you'll go on. If you over discharge lithium cells below their absolute minimum Voltage just ONCE, they will be totally and immediately destroyed with no reprieve. That's why you need the extra cell level monitoring on them. But design the system with that in mind and there's little risk of them being damaged in normal use.

You also can't get away with over charging them either - they swell up and the safety vents blow and then they're useless. But it's easier than you think to stop this happening. And you can enjoy super fast charging. I've now got 2.8kWp of solar panels and can make much more use of brief sunny spells on an otherwise cloudy day to charge my battery.
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stuartcnz
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Re: Just getting started

Post by stuartcnz »

Welcome back, from a long absence!

It's good to read about your experience with these batteries. Is this the same technology as they are using in modern electric cars? If it is, I believe they can also be configured to fit into different shapes, which would be handy in house buses.
AccordGuy
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Re: Just getting started

Post by AccordGuy »

Thanks,

Yes, they are Winston Battery Company cells that have been used in a lot of EV conversions although the cells I'm using are much bigger than the typical 100-200Ah cells used in cars. They come in various (mostly brick shaped) sizes and can be used upright or on their sides as they are sealed but the recommended position is upright, in case they vent in a fault condition. Being much smaller and lighter than lead acid batteries also makes them easier to find a home for and they produce absolutely no gas in use (unlike even AGM lead acid so called "sealed" cells that actually do vent small quantities of gas when charged hard).

If you move your house bus, the weight saving over a lead bank improves your gas mileage.

The Winston cells come in sizes up to 1,000Ah so it would be possible to make a single string battery pack of up to 52.8kWh on a 48V nominal PV system.

There are a couple of other makers of similar cells (CALB, Sinopoly) that I know of, both also Chinese makers.

A123 are supposedly an American maker of small (20Ah) cells but A123 sub-contracted all the manufacturing to a factory in Korea and the Koreans stamp "Made in USA" on them!

You can buy them from Jack Rickard's EVTV web site. He buys them from a Chinese trader for half the price that A123 sell them to US auto companies for. Rare for an auto company to be taken for a ride... :D
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stuartcnz
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Re: Just getting started

Post by stuartcnz »

How much lighter than lead-acid are they?
AccordGuy
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Re: Just getting started

Post by AccordGuy »

A 400Ah 3.2V cell is 13.7kg. You need 4 cells for a 12V nominal battery and that weighs 54.8kg.

My 180Ah 6V gel lead acid batteries were about 31kg each, so 62kg for 12V at 180Ah. Scaled up to 400Ah, that's about 137kg.
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Headache
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Re: Just getting started

Post by Headache »

I love this! Please keep us updated. I'll check out your website too.
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