Almost completed 24V upgrade

[Webchat]

I had fun pulling all the lighting wires from the distribution panel into a new one next to it which I fed from a 12V battery array and 1Kw of solar panels. Using mini-fluorescents the house has been solar lit for some months.

I have now reconfigured the batteries so that I have 20 T105s set up in 5 rows of 4 to get 24 Volts and have increased my solar panels capacity to 6Kw. I have three charge controllers which fill the batteries nice and quickly.

What I want to do now is try to get fully off the grid. If I have 6Kw generating capacity and up to 8 hours a day on sunlight in South Texas then I could generate 48Kw/hr on a good day? Am I right that each T105 is 1.35Kw/hrs so I would need a minimum of 36 batteries to handle full sunlit days?

Evening power consumption is low and the house will probably pull 1Kw between 5pm and 9am - so that's about 16Kw/hrs?

During the day with cooking and washing etc I would expect to pull 3-4Kw between 9am and 5pm - so that's 24-36Kw/hr.

So my 1st question is - how many T105 (225Amp/hrs) do I need to run efficiently, and take account of several couldy days in a row etc?

And secondly - is there a good cheap inverter that I can connect to these batteries and wire stright into the distribution panel without plugging into AC outlets on the inverter - so that I can pull the full 5Kw or so through one set of wires?

Thanks for any advice you may have!

- Webchat

[Nando]

With so much power and the number of batteries forming your bank a much better solution you could have.

The Battery Bank can be converted to 120 volts and the 6 KW panel rewired for 120 volts

Direct 115 volts 10 KW MSW generation with a low cost design that you could build.

In a past message, I described how to build a 5 to 10 KW MSW for around 200-300 US

$ dollars that may be a good solution for your site if the conversion to 120 volts is done.

Nando

[Nando]

>During the day with cooking and washing etc I would expect to pull 3-4Kw between 9am and 5pm - so that's 24-36KW / hr.

You meant 24-36 KW-hour/day

So if you want 2 days backup then 36 * 3 = 108 Kw/hr

108,000 / 24 = 4500 ampe-hour battery bank BUT the battery bank should not be discharged less than 50 % so the bank will requires 4500 * 2 = 9000 amp-hour.

No allocation for inefficiency due to the low 24 volts battery bank which could add up another 20 % or 1800 am-hour for a total of 10800 amp-hour

A huge battery bank.

BUT if you go for a 120 volts you save for practical purposes 1800 amp-hour bank ( the reduction to 100* 24/(120 + 24) = 16.7 % of 1800 );

Most all equipment could be 115 VAC, and for practical purposes as AC driven house.

Regards

Nando

[Webchat]

Thanks Nando, I am very interested in the 120V option - it would be easy to rewire the solar panels - but I couldn't find the article you referred to about the 10KW converter - could you please point me to the URL?

Many thanks!

- Webchat

[oztules]

Now that is some serious solar set up.

A few things. If you are currently on the grid, check your power bill and find out just what you have been previously using....saves guessing. the only diff will be your light...probably insignificant.

At 24v you will be trying to charge them at 250 amps for your 6000w input. I dont think their life expectancy will be too flash at that rate. ie 6000/24=250A although at that rate your batt volts will be much higher and current may drop off to maybe 180amps...still over the top for these little batteries they'd be boiling madly.

I think that Nando has the  right idea here. 120 volt system

In fact 40 batteries will be in a better position to accept the coulombs you are developing, and bring your current back to a more reasonable 40-50 amps (20-25amps per 120v string).

Nando's version of a msw converter will offer you very good efficiency  with the  dc/ac conversion (because no stepup is required), and if self built, will give you a good degree of self sufficiency.

120v x 550ah= 66kwh  (two strings of 20 series connected t105's in parallel)  at your guess, thats enough for only a day or two.... However I think I would not expand further until this limit is tested, as even on cloudy days, a fair bit of power will still be generated from this setup.., and you may well find that you have overestimated what you can get by adequately with.

My vision is still somewhat clouded by my incessant drooling over your 6000 watt solar collectors.

..........oztules

[Webchat]

Also,

what would I do about controlling battery charging at 120V? I guess it's not a huge concern in that rarelyt will the batteries be 100% full - but... I need a way to prevent overcharging too if I go this route?

- Webchat.

[Webchat]

That's good too on saving batteries at 120V.

So, if I have 20 6V T105s at 225Amp/hr each - I already have 4500 amp/hrs? So, have I got that correct and if so do you think my battery bank would be sufficient already at 120V?

Thanks again - this is the most useful info I have read in many weeks.

- Webchat.

[Webchat]

Hi oztules!

Well, the first year in this house we were using 9,000 Kw/h per month in winter. It's a 6,000 sqft house and has four central AC units with electric heaters. Having learned about this and seeing as we have some land we switched to mostly wood burning and using fans to circulate the heat. The winter gone we were down to 5,000kw/h per month. By February I had this down to 4,000Kw/h. I'm going to have to investigate Trombe walls and things for the winter.

In our first summer we used 6,000Kw/h per month. I soon had all our thermostats changed to programmable ones and set the temperatures higher and made use of ceiling fans so that last summer we just slipped under 3,000Kw/hr per month  - our lowest ever.

I think this will drop a lot too now that I have solar water heating for the pool so that electricity won't be used any more either.

But any way you look at it, with bills that could be upto $1,000 per month I just had to start buying cheap solar panels on the web!

I am pretty certain that if I discount AC & heating I can run the house now on 6KW - I also have a wind generator ready to add as well so I will have additional backup.

My only problem is getting all this power into the batteries - and out again!

Once I have the 110V side of the house off the grid then I will start thinking again at how to replace the 220V appliances. Right now I am thinking about evaporative coolers in each roomfor summer and geothermal heating for winter - but I guess I'll get to those projects in another year

- Webchat.

[zap]

My $.02... Webchat with that much power you might want to look into ground source heat pumps for both your heat and ac.  I know of a house using it in the coastal bend area and might be able to get some figures for you.

I believe this is the story to which Nando was referring. http://www.fieldlines.com/story/2006/2/27/183513/106

[oztules]

WOW  and wow again. I live on an island, our grid system is diesel powered. We are charged at 40 cents kwh... when you were burning up 9000kwh/month, it would have cost me $3600/month......on those figures, I guess I would start buying cells at a prodidgious rate as well.

It would appear that the power system you will end up with will by necessity be very big, and high voltage.

As I see it, when yoy have to move current in and out of a battery, the less the better.

As a watt=VxA, then it is nice to push the voltage up, and keep the current the same to achieve a higher wattage.

You batting above my league, so I'll leave you to the thoughts of others who are experienced in the power levels you desire.

.........oztules..........9,000,000 watt hours per month...yeow.....

[Webchat]

Thanks Zap!

Yes if you do come across the figures you mentioned as I am in Kingsville, pretty close to the Coastal Bend so they would likely apply pretty closely here.

However, I read the story you linked to but I am not experienced in electronics. I understand basic electrics well enough to do house wiring with the correct types of wires and breakers and also well enough to wire a solar array, charge controllers,  power inverters and batteries correctly - but no way could I build anything electronic - even with full diagrams

So, I wonder if anyone knows where I could get a 120vAC/12vDC 10Kw transformerless inverter ready made?

[Webchat]

Ooops typo:

Should have been...

... 120vDC/120vAC ...

[Nando]

Can you do mechanical work ?.

The electrical is too simple, just to follow a few simple wiring lines.

The place a bit difficult is the wiring of the Power MosFets or IGBTs, which for those interested a small kit can be done.

I am trying to find some time available to do the drawing for any to make it.

I can not find the original design, too many years and lost interest when just 3 were built by many people asking for it -- I got a list of about 150 people and at the end 3 builders because people initially think that can do it then procrastinate until forgetting the idea and buy a already made.

One in my native country, that I know is still alive and well 115/ 220 @ 5/10 KW .

Another in Center America -- 10 KW

One in USA, the owner died a couple years ago and the wife sold the place.

Nando

[wdyasq]

Webchat,

I think you are under-guessing the amount of batteries you need.  If one has a 225AH @ 6V battery it is 1350WH - full discharge - something that does not want to happen.  if you figured them at half a kW it would still be a deep draw on them if done often.

You state you want several days of backup.  This is a huge amount of batteries.  As you live in the Coastal Bend area I would recommend a large wind turbine as suppliment.

I would also recommend you fine a less energy intensive method of washing an cooking.  A propane stove - if it doesn't have a 'glow bar' for the oven uses little electricity. The 'Equator' brand clothes processor uses a lot less than what you claim but is not like a 'regular clothes-dryer'.

Possibly your first step SHOULD be to determine exactly how much energy you use. A 'Kill-A-Watt' or similar, I have a 'Watts up Pro', will allow you to get those numbers. Then figure out how much you can eliminate and still live in the method you desire. The most efficient appliances are about 5 times cheaper for purchase + run on PV than just the PV panels to supply inefficient stuff.

Good luck,

Ron

[Webchat]

Well, Nando, if it's truly that simple I would certainly build one. Seems to me there is a huge business opportunity here for someone prepared to make a small garage/factory. The way electricity is going up in price many people will want to get completely off the grid and It now appears that the 120V solution is going to be the cheapest/most efficient.

If you can get me the diagrams I won't procrastinate - I have 6Kw of panels on the roof waiting to be used! I would also be very grateful indeed!

- Webchat.

[Webchat]

Thanks Ron,

I also thought I must be underestimating. That's why I asked. But by rescheduling most things I hope to pull power directly by day so that I would only drain the batteries minimally at night. My only problem would be a week overcast.

But then, I plan to remain connected to the grid even if not using it and have a switch to switch back to mains power in emergencies - at least until I have installed the 1.5Kw home-made wind generator I purchased from a small company in Arizona which I will add to the mix later.

This should help quite a bit. I already replaced the clothes drier with washing lines - that was a big saving. I am also investigating replacing the range with inductive burners. They are much more efficient.

I have a clamp meter now attached to the wiring but that only gives me spot readings of Ampage so your idea of an actual meter is a good one I will follow up on.

Thanks again for your comments!

- Webchat.

[Nando]

Not difficult, there are several ways, one simpler is a power diode and a shunt regulator for a ballast load.

There are others that we can work, so keep my email address for future reference.

I prefer to analyze the complete system to define the necessary pieces of equipment to have the optimum system.

All depends on power control in a simple manner.

I see that you live near the coast, a good idea is to have a wind mill, capable of supplying enough energy for days that the SUN goes to bed because it caught FLU.

If you cannot build one, try to twist the arm of some in this group that have a MASOCHIST hobby of building wind mills like the WINCHESTER widow that had to build, build and build. !!!!!!!!!!!!! and may build one for you like DanB.

Nando