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I am looking to set up a low impact home next year and want to be self-sufficient as far as power is concerned. Not wanting to rely on either solar or wind generation to charge a bank of batteries I was wondering what I would need to link the two. As an emergency back up or on the odd occasion when I would need to use a power tool (yuck) I was planning on getting a small generator which would also need to be linked into the system.

Can anyone give me some advice on this? Thanks

opps here's UK version. http://www.sma.de/en/products/off-grid- ... 4248u.html

Hi Sambanut,

Are you planning on going off grid? in which case you really will need batteries as you can't really use the power directly from a wind turbine unless you heat water which is in effect a kind of battery. whilst you could use some things directly off solar panels, lights, chargers etc, the lights aren't much use when the sun is shinning and chargers well they charge batteries. If your on the grid then a grid tie inverter is the answer but bear in mind when the grid fails so does your system. Here's my system http://lifeattheendoftheroad.wordpress. ... the-house/ I should really edit it to make more sense and put more pictures on it now I've got broadband. Basically I've two systems a 12v one that is charged by wind, solar and hydro and a large 2.5kw wind/hydro/diesel genny system.

Hope it makes sense, Paul

If you just want to feed both to a battery pack, then all you need is two diodes (one in each of the positive leads). Hook the anode of one diode to the solar, the anode of the other to your wind generator. Tie the two cathode sides together and attach to the battery positive. It isolates the two power sources from each other. Both will be able to charge the batteries at the same time. The diodes need to be rated for the voltage and current they will be handling(they may also need a heat sink), of course. Cost should be under $20, even for some high-current diodes.

camillitech wrote:Here's my system

I presume those batteries are 'deep cycle' batteries? I wonder if you happen to know the answer to these questions...

Is there any value in second-hand deep cycle batteries if you can get hold of them?
Do they last 'forever' with proper care?
If you happen to have bought a car battery instead, what is a safe minimum charge before recharging it so that the metal in the battery doesn't disintegrate?

Cheers!

Sambanut, have you thought of incorporating 'dance power' into your system? Shame to waste all that energy.

Hi Rod,

In answer to your first question yes they are deep cycle batteries as in a fork lift truck. As regards 2nd hand it's always a risk though I know a few people who've been lucky. Firstly if you are going to look for 2nd hand take a hydrometer and volt meter with you, make sure the batteries have been lying idle for a couple of days then check the voltage and SG. If they're out of the same bank and they should be as you shouldn't mix batteries of different ages/types/sizes then they should all read the same voltage and specific gravity. You will need a good meter because a fully charged cell is 2.12v and a 50% charged cell is 2.01v as for hydrometer readings it's more a case of making sure they're all the same around the 1.24 to 1.28 as I've got 4 hydrometers and they all read different Regarding car or even leisure batteries, forget it unless you have an endless supply, a good contact for disposing of the old ones or can keep your Depth of discharge to no more than 10% 12.5v, trust me on this one I have a 'lead mountain'

Good Luck, Paul

Thanks for the comprehensive reply Paul.

Reason I ask is that I bought a pedal generator to go under my desk so that I can pedal while I work. I already bought a car battery without thinking too carefully. Then I bought a multimeter. At the moment, I'm using my car battery to recharge my shaver and mobile phone via an inverter. I'm thinking that I may actually be able to maintain the charge cycle within a safe range since the amounts in/out aren't that great.

So if I discharge down to 12.5 V you reckon the battery should be OK?

Rod in Japan wrote:Thanks for the comprehensive reply Paul.

Reason I ask is that I bought a pedal generator to go under my desk so that I can pedal while I work. I already bought a car battery without thinking too carefully. Then I bought a multimeter. At the moment, I'm using my car battery to recharge my shaver and mobile phone via an inverter. I'm thinking that I may actually be able to maintain the charge cycle within a safe range since the amounts in/out aren't that great.

So if I discharge down to 12.5 V you reckon the battery should be OK?

Morning Rod,

I think in that kind of application and by keeping an eye on the voltage your battery will last for years and you'll get very strong legs!

Keep up the good work, Paul

sambanut,

To charge batteries with solar, wind or both you will need a charge controller. This regulates the voltage entering the batteries.

Marlec produce a controller that handles both wind and solar - http://www.marlec.co.uk/products/windch ... ontroller/

I assume you are going to buy all the hardware so the wind turbine will have a rectifier to convert the three-phase sinusoidal current into a smooth DC current for your battery. Any panels you buy should have blocking diodes in them to prevent battery drainage into the panel when the Sun goes down. However, most charge controllers do the blocking for you.

If you cut down your electricity to the barest minimum then you will be surprised at how solar (even on cloudy days) does everything you need. If you are in town then a wind turbine is a waste of time. If you are on a very windy site then you could be buying a new turbine every year.

I have put my battery in the back of the car and hooked it up to the cigarette lighter via a charger and inverter. On a drive to the shops the car generator is as good as any.

I have both a wind turbine (small Marlec) and solar panels. I originally used a Marlec charge-controller which had inputs for both wind and solar. It was IMHO a complete waste of time.... it was simple and crude. It shoved both power inputs into the battery until the voltage reached x (forgotten exactly what) and then switched it into the dump-load - an internal heater.

It spent most of its time wasting energy into the heater.

Then I acquired a BP-Solar "smart" controller for the solar panels.. This was a lot different. As the battery voltage rises with continued solar energy input, it eventually starts "pulsing" - cutting the current to the battery (by shorting out the panels with its power-FETs) for a small fraction of a second.... this allows the battery to recover a little and take more charge.... as the voltage rises further it changes the ratio of on to off pulses until eventually (with continued sunshine and no load drawing power from the batteries) it is more off than on, then mostly off with occasional pulses. This protects the battery from overcharging and drying out from "gassing" - unrestricted high-voltage charging splits the water into hydrogen and oxygen (dangerous - both due to the explosive mixture, and by reducing the water level it can ruin your batteries). It controls this by its pulse control.

However the smart little charge controller also keeps track of how long it was since it last had a good belt of a charge - coz short bursts of high-voltage charging are good for the batteries - the gas bubbles stir up all the electrolyte and move the gunk off the plates so it can hold more charge. This is the "equalisation" charge.

All this is great if you have a constant solar input, but in this country we don't, so this grand theory can get torpedoed by the sun going behind a cloud for a random amount of time.... How does the charge controller handle it? no idea... there is no information.

Suffice it to say that ANY amount of pulsing is wasting energy - it isn't going into a dump load, but it is still being wasted (not going into any battery). When I happen to see this occurring (the meter flickers like crazy) I try and USE some battery energy!

Now - on to the wind input... I guessed that the control method of shorting the panels would not be a good idea for a wind turbine. But I tried it anyway. In a reasonable wind, and with crocodile clips, I removed them from the battery terminals directly and connected them to the charge controller input. As I disconnected from the battery you could hear the turbine accelerate like an aircraft on take off.. as I connected to the charge controller.. it was like the brakes came on. Then i waited for the pulsing to start... It was like brake/accelerate/brake/accelerate multiple times a second... it was rattling the turbine around like mad and shaking the whole pole+structure. So I connected it back to the battery directly. Don't use a solar charge controller for a wind turbine.

Then I did some calculations and observation - the solar side of things needed at least 10 amps to drive it into gassing mode, and the wind turbine rarely got above 3... so very little risk of overcharging from wind (in fact the WT is pretty useless really - as further revealed and confirmed by the Warwick Wind Trials).

A further factor is the SIZE of the battery bank. Mine is 4 x 110Ah deep-cycle leisure batteries. If I added more capacity - say to 10 times the size, the relative power input of my solar panels would NEVER give it enough oomph for the periodic equalisation charge. So if your battery capacity is too big relative to your likely power input, it will never overcharge, but your batteries will not be kept in peak condition (without an external equalisation device, like a generator or a mains charger. ) If your battery capacity is too small it will either overcharge without a controller or just waste energy via the charge controller, unless your dump-load does smth actually useful. So its a skilled job getting it just right.

Just a comment about connecting solar and wind simply via diodes - there are probably already diodes inside your panels and maybe the WT too. Every diode loses voltage (around 0.7v I think) and wastes energy as heat. You can get low-loss Schottky diodes that minimise this if you have to use them, and you may need to heat-sink them to avoid fire risk. On a 20-amp system for instance a normal diode would generate 0.7v x 20A = 14watts heat, the same as a soldering iron !

Fascinating topic.

FWIW I ruined 2 x 110Ah batteries whilst learning all this stuff! 100 years ago the ruined batteries would have been repairable. not now. Progress eh?

Somewhere on the internet there is a scan of a 100-year old book on lead-acid battery maintenance - awesome!

I will look through my accumulation of wind information, but I'm fairly certain the wind turbine needs it's own controller and it may even need a controller specific to the turbine. I may not get back for a few days though.

Hi Hary and welcome to Ish.

You've posted on a very old thread here, although a subject relevant to your signature, as are your other two posts. It's breaking our rules to advertise on your signature until you've been an active member for a while so I've removed it, but I'd like to invite you to go to the Welcome section and tell us a little about you.

Join in a bit and you can then re-instate your signature.