Cutting my teeth on renewable energy

[tomfassett]

Hello All!  I found your little corner of the globe while surfing the web looking for "home made" energy answers.

First some quick background information.

For some time I have been mulling over the idea of adding some kind of limited solar powered system to my home.  As I live in the central deserts of Arizona, there is ample sunlight for such a venture (300 plus cloudless days a year).  I am not looking to replace the grid supplied system or even take the plunge into a hybrid system (I can't afford it).  I am just looking to get my feet wet and use some of that energy that constantly beats down on my property.

In another related area, I work for a company that sells and installs computer/POS systems (POS = "Point of Sale," the things a waiter uses to enter in your order in a restaurant or pub).  As a consequence of doing business, we regularly replace dead UPS units.  Most of these end up in the recycling bin (or the garbage, when I am not keeping a close watch on my co-workers).  Many of the units that come back in to the shop are fairly expensive and in the 1000-3000 watt (output) range.  The vast majority just need a new battery but servicing them is more expensive than selling the customer a new one.  I have a few dozen of the really good (and more powerful) units stashed away in the back shop.

Now to the point--I would like to figure out a way to combine solar panels with these units to power non essential AC devices in my house.  One of my ultimate goals would be to run a small air conditioner (something in the 600-800 watt range) to reduce the load on my main cooling units when it is 110+ degrees outside (like today).  As the cooling is generally needed at the time of year when the sun is at it brightest (the middle of Summer), the highest potential energy would be available to recharge the UPS units.  They could also be used for lighting or running things like TVs and computers which are generally used only at night (I work during the day and someone else pays for my energy needs).

I have a working knowledge of electronics (I was an electronics bench technician for 10 years), but higher power has always left me a bit leery.  I don't like things like fires or exploding batteries so I need a bit of help pursuing my solar power dreams.  I looked around the forum but did not find any information specific enough to put this thing in motion.  Any suggestions of where to begin would be very welcome.

Thanks,

Tom Fassett

[DamonHD]

Well, though my cloudless days in London are rather fewer than yours, I'm doing a pilot project to 'get a feel' for what's involved as you say.

Here's my general solar PV pilot:

http://www.earth.org.uk/solar-PV-pilot-summer-2007.html

And here's the extension project where I'm trying to move all my 'always on' Internet servers at home onto solar power at least some of the time:

http://www.earth.org.uk/low-power-laptop.html

The price/numbers will be much better for you given that you have more sunlight, and that solar panels are about half the cost per Watt as here in the UK from what I can see.

I started with an idea of a specific task (replacing my home-office lighting with solar, which I've done) and bought a small 'kit' with the battery, solar panel, and solar controller.  It works, and gives confidence and that sense of how things might go...

...And now the addiction is really kicking in after only a couple of months, I have an extra much larger solar panel too, plans for a small wind turbine, moving all my servers (currently 670W) onto on laptop (<30W) which I hope to finish this week.  That is already going to be saving me the equivalent of ~$2000/year in electricity, which I can then spend on more panels, batteries, etc.

...though I can give up any time I want, of course.  B^>

Rgds

Damon

[DamonHD]

And on your comment on exploding batteries, etc...

I'm right with you there, so I sticking with proper pedigree (but cheap) commercial solar power controllers to protect the battery, and I'm sticking with sealed lead-acid so as never to have to start mucking around with acid or distilled water, etc.

This is as clean and unexplodable as I can make it.

Rgds

Damon

[kurt]

i can answer one of your questions. you would have to invest thousands of dollars in solar panels and batteries in order to run even a small a/c unit it is a basic rule that off grid homes do not have a/c units they use passive cooling and other techniques  to stay cool or they run a generator 24/7 any time cooling is needed.

[DanB]

Yes - AC is tough  (and evil they consume a ton of energy).  I expect in Arizona you'd do well with a swamp cooler and save a ton of electricity.

[RogerAS]

tomfassett,

Dozens? Would you consider selling one of the larger units? I am current looking for  backup inverter for my main unit right now. That main inverter is a 2500W Cobra. I worry that it could let out the magic smoke at any moment, and being over 2 years old now that possibility grows every day.

I live completely off grid and I too have isues with heat. However here in Arkansas we deal with humidity as well. I have 750+/- watts of PV and 1320 AH of deep cycle 12V~ flooded batteries. Unless I augment the PV's with my kubota/alternator I cannot run my 650W AC unit more than 3 hours after sunset. Another great feature of Arkansas summers is the heat sometimes lasts all night. A swamp cooler will not work well here, but very well might for you. Luckily it has been cooler here this summer than normal and we've had nice nights, but August has yet to come.

Has anyone tried using a swamp cooler and an eclosure for the hot side of a regular AC unit? I've heard of others using a drip/misting system for the hot side coils and wonder if cooling that side with a swamp cooler night be a workable alternative.

Anyway, good luck and please let me know if you could or would be willing to part with one of the larger units? I know some of these use a higher wattage units use a higher voltage battery base, but I would be willing to reconfigure battery voltage to use one of these. I'd like to keep the 12V setup, but....

Remove the antispam junk from my info to email me if you'd like, or respond to this message here. Or just ignore me. :-)

Thanks,

[tomfassett]

Good info for starters--exactly the kind of dialog I am looking for.

A few answers to comments:

I expect I will have to invest quite a bit to attain the air conditioner power.  Still, a small AC draws no more than two of my ISP servers and they run for hours (when power fails) from the UPS units I have on them now.  I know the UPSs suck current like a sinkhole when charging the batteries--I just need to figure out how to connect enough solar panels to replace most of their dependence on the grid power.  What I would like to do is start small while doing research for expansion.  Maybe a few lights or even some of the computer equipment.  What I have not researched is how much current is fed to the batteries while they are charging.  I guess what I am looking for is, "The Hackers Guide to Self Made Energy."  Something that gives me the ability to experiment with what I have to hand instead of plunking down a wad of cash and buying a ready made system.

Next, I have a swamp cooler and it works pretty well most of the year.  Right now it is not usable as we have entered the dreaded monsoon period.  That means humidity levels all the way up to the 50-60% range (OK, no comments from you guys in the UK, the Tropics or the Southeastern U.S.--50% is murder to us desert critters...  ;- )  The only problem I have with the evaporative cooler is it rusts my tools and the computers don't like the extra moisture in the air.

Also, in response to adding an evaporative cooler to the heat exchange side of an air conditioner, around here that is called a "piggy back" unit.  They are quite common.  Some people have problems with "freeze up" of the A/C coils, but only if they run their A/C constantly (and keep their house as cold as the Arctic--like my brothers).

So for starters, has anybody "reverse engineered" a UPS to get at the operation of the thing?  I know there are other variables when connecting such a beast to a solar array (like reverse current through the array and controlling the variable output of the panels), but first I have to deal with the charging requirements for the UPS units and modify them accordingly to do a bit more than they were designed for (like constant use).  I could probably figure it out myself in time, but I'd rather continue a dialog with others who have already taken most of the steps.

Tom Fassett

[RogerAS]

Tom,

Today (July17th) is the 105th anniversary of the invention of AC!

Being completely off grid this AC issue is a real problem.

I have seriously considered buying one of those units from a reefer semi trailer to provide AC. (No I'm NOT talking about THAT kind of reefer).

Since I often have to run my little Kubota anyway to fight off the heat why not one of those Thermo-King units? Those have automatic cycling, or they turn off and on as needed, and use very little fuel. The trouble is those things are WAY expensive and not that easy to come by. I've looked into it.

I've also thought of finding a larger automotive AC system and modifying that, driving it with a small IC engine. It wouldn't be that tough to build the system around an engine driven compressor. One could set the unit completely outside and duct the air transfer through a window. This idea might take a little more effort than I imagine. I'm not an expert on this in any way.

I've also considered using the same automotive compressor and drive it with a large DC motor. At least one could avoid the waste of converting the DC to AC and running a standard AC unit. Ducting the air the same as above.

I've considered putting a large canopy of some type over the entire house to keep it shaded and thereby reducing the suns' direct heating of the structure. The trouble with that idea is trying to keep it from sailing away when a thunderstorm rolls up. I do have extruded polystyrene window plugs that help, and remove them as fall comes along. (Come on October)!

Ground asisted stand AC, earth cooled air, and other ideas have been tossed around here on Fieldlines as well. Some make more sense than others. but all seem to have problems.

I feel the whole thing boils down to biting the bullet and just making the electricity needed to keep that cold air box running by whatever means at hand. It's hard to imagine how tough our forefathers were to be able to live without this luxury.

Take care Tom, and sorry but I was just too tired to get an email off to you last night. I had to mow the damned "yard" out in the heat yesterday. That sucked the life right outta me. (I live on a mountain side and not one sqaure foot is level and with my 20" pusher takes forever).

[wiredwrong]

I too used to work on POS equipment, If you get a chance to get a any of the old bigger security tag demagnitizers, there is a nice supply of magnet wire in them, tear them apart keep some wire for winding some coils, sell some wire to buy magnets and put up a genny, I once got one that had 15 pounds of good magnet wire in it, if you not interested in wind you could also use the money made from the wire to buy more solar.

[jonas302]

Roger great idea with the reefer unit  see them go quite cheap on ebay item 200129975804 $500 and not to far away think of the awsome air cond shop in the van trailer!!

[tomfassett]

I've tried a number of the "hacker" things mentioned (he, he).  At the time, this was not because I was trying to find a more "environmentally friendly" of efficient way to do things--I was just dirt poor and a scrounger...  ;- )  I actually had an automotive air conditioner in my wood shop 20 years ago.  I did find that it required one big monster of a motor--in the 5+ horsepower range or it would slow down considerably when the compressor was under heavy or continuous load (as it was most of the summer).  I hacked this thing together because I had an aftermarket A/C unit from my 1970 Ford 3/4 ton truck laying around and room air conditioners were darned expensive (and not very efficient) in those days.

As for alternate, and most efficient cooling systems (watt for watt and penny for penny), I got a crash course in "portable" non traditional cooling systems back in 2001.  First a little (OK, maybe a lot) of background.  I was a system technician and driver on a new car model tour for a major manufacturer.  They had this great idea of setting up the rollout for the dealers in big tents on things like abandoned airforce bases.  Our video engineering rack was part of one of the few portable virtual (green screen) systems in the world and was full of very expensive and sensitive equipment.  One of my jobs was to help keep it running during the show.  We soon discovered (to my horror) that highly sensitive studio equipment is not happy in a tent with evaporative cooling in the middle of the Summer.  Many of the critical components would overheat and go into thermal shutdown--often at the most critical time (like when the tent had a couple hundred people in it heating it up more--like during a show).  We also had a humidity issue with the evap coolers as well, compounding our problems.  To add to our misery, we were allotted only so much power as all power was supplied by portable generators and the A/V system was using about 95% of what we were allotted.  We could not just plug in a bunch of air conditioners as we had less than 3 amps left over when the system was running.  I aged about 10 years the first week praying that the system would not fail in the middle of the show.  Once it did and our bosses were not happy.  We were ordered to solve the problem no matter what.

The first thing we did was buy a bunch of high power UPS units.  These would charge during the between show times or rehearsals when most of the technical equipment was off.  We then had a "self taught" crash course in what would give us the most cooling for the least amount of energy.  We installed a small reefer unit on the back of the main rack.  This was wonderful but sucked energy like a black hole.  We then tried cooling units designed specifically for cooling sensitive equipment (like computers).  These drew a lot less energy but could not overcome the heat and humidity very well (they are not designed for outdoor use when it is 100 degrees).  We then tried the cheapest solution--small portable air conditioners.  These worked great, were quiet enough to use backstage and would run for about 2 hours on a fully charged 1500 watt UPS.  Not being one to let the most obvious solution rest, I started researching alternatives.  I noticed one day while waiting for a train to pass that the railroad block control cabinets have little air conditioners on them.  These things are metal, sit out on the full sun and are full of electronic circuits critical to the railroads operations (and safety).  I noticed a signal maintainer working on one a few days later and stopped to ask him how they kept the things cool inside.  They use a fairly standard "window" type air conditioner--the particular one he was working on had a 1200 watt Samsung A/C unit just like the hardware stores sell.  As I had a lot of free time in hotel rooms at night and a laptop computer, I started researching power draw versus BTU output for different cooling devices.  Even without considering cost, I found that those little window air conditioners beat almost everything for efficiency.  Adding the cost equation, I found nothing that could compete with them as you can get a unit that draws 575 watts and churns out 6000 BTUs for around $100 (I just bought another one last week).  Even after 6 years I still haven't found anything that beats the things for efficiency, maintainability and availability (and I have tried).  The units I bought back in 2001 made it through the tour (hauled--not gently--all over the U.S.) and are still working just fine chugging away day after day cooling my shops.  I hate it when a "two bit" technology beats out the high tech stuff--I love high tech stuff...  ;- )

Of course, the million dollar question pertaining to what I am looking for here is, what does it take to keep a UPS charged enough to run a small A/C unit?  I don't know (which is why I am pestering you good people... ;- )  The A/C units we were using on the car tour ran continuously--we set them on their highest cooling settings.  The units I use in my house cycle on and off.  I have found that at the hottest time of the year (right now), they run for about 30 minutes each hour.  Two 575 watt, 6000 BTU units keep a 500 square foot area quite comfortable.  In the Spring and Fall (still darned hot in Arizona--in the 80-95 degree range) they run for 10-20 minutes per hour.  This would allow a UPS unit to charge while the A/C is off.  My assumption (and please correct me if you think I am wrong) is if I had a solar panel that could provide enough energy to run a 400-500 watt A/C outright, there should be enough energy available on the off cycle of the A/C to recharge the UPS.  As the cooling requirements are relational to the heat (and here that means maximum sunlight), the load on the system should track with the increased solar energy available.  The only hitch I see is the highest demand for cooling comes right before sundown so you would be hard pressed to charge up the UPS to make it through the night.  I am not trying to achieve this level of independence from the power grid (right now), only to reduce my demand on it during the hottest parts of the day by supplementing the A/C units I have with one that provides some additional cooling without power that must come through my electrical meter.  That is the crux of my quest for now.  Far fetched or not?

Tom Fassett

[RogerAS]

Tom,

No your quest is not far fetched.

Here's my suggestion(s):

Replace the UPS battery pack with a much larger deep cycle setup. You'll have to use your own judgement as to size and type. I would start off with flooded batteries because they are much more forgiving than other types and are usually cheaper. Buy more storage than you think you'll need. It's always better to have too much than not enough, to me. Solder on much larger (gauge) DC cables to the UPS inverter section and bypass any clamping system for the battery cables. Lowering these resistance points will help the whole setup work better.

Hack the UPS charging circuit to switch on another charger-system or remove it and bypass that weak charger comletely. Or, use a charge controller and PV or wind or wahtever to recharge those batteries. Or keep an AC charger (wall) plugged in at all times, one that will provide some sort of controlled current to protect the batteries. or build a multi input control system, which isn't that tough. The bottom line is that built in UPS charger is a joke but nobody laughs.

I would use the highest AC wattage UPS you can/have. The surge of the compressor cycling on can really suck the amps for a few seconds. Keep the AC~ supply line(s) to the air cond unit as short as possible. I found that my "Portawattz" 1000 will run my little window unit if the feed AC~ line is very short and very thick.

Figure out a way to add more cooling air flow over the inverters heat sink area. A simple setup would be to use a thermistor and a op amp, with the thermistor intimately contacted to the heat sink(s). A real beefy op amp might be able to sink the load of a computer cooling fan or 2, but even a small mosFET would handle that easily.

The UPS may have a higher low battery shutoff point than a regular inverter. I have a small UPS (250 watts) and it will shut down a full volt and a half higher than my Cobra 2500. As far as I can tell this point is hard wired into the design, as I have not found a pot to adjust this in that little unit. That may not sound too important but it's something to keep in mind. This might be a good thing since the batteries will be protected from deeper discharge when the sun sets.

I've found that a small assisting fan, like a microwave squirrel cage fan, which helps move the air out of the AC unit make a big difference. I built a little hanger in front of the cool air port and use one of thise little fans to move the air out into the room with more force. I have no tested data to support this, but it seems to speed up the overall room cooling. The tiny fan doesn't draw much power either.

If you could figure out a way to reverse the UPS' main function you'd have something! If the UPS would stop using the batteries and switch over to grid power when the battery low voltage set point was reached it would be way cool (not a pun). Like this; The sun goes down, it's still hot out and the AC unit still working to cool the house/room. The batteries voltage starts to drop, they reach the cut off point, and then the UPS switches off completely and grid power is passed to the window units so the heat doesn't build. I sure this could be done with a contactor powered by the UPS itself. When the UPS can pull in the contactor, or was making AC~ power, the window unit runs from the UPS-battery pack. When the UPS drops out the contactor is released and the grid power is passed to the window unit.

Keep at it. This ain't rocket science. Above all keep some cool drinks on hand!:-)

AS always, hope this helps.

[tomfassett]

Helps a lot--this is what I am looking for.

A few points--if the UPS switches off the drain from the batteries when they reach a certain voltage (what I have found to be the case), one could build a simple external comparator circuit to switch back to grid power before the UPS kicks off by setting the comparator low voltage trigger a bit higher than the UPS low voltage trigger.  That way you bypass the UPS comparator circuit entirely.  If you also added a sense circuit to the solar array (or whatever alternate power device is being used), you could prevent the UPS from kicking back in until there is energy available from a non grid source.

As for the external fan on the room A/C, in my experience you are right on the mark.  I once tested the air flow at the front of a room A/C with smoke.  An awful lot of the cooled air is drawn right back into the input since the input and output are so close together.  Not only does this re-cool already cooled air, but it throws off the thermostat (which is right inside the air return) as it is sampling cooler air than is circulating in the rest of the room.  The things really should be built upside down from the way they are--cool air out the bottom, hot air in the top.  That way you could point the cool air vents down while the return sucks in hotter air from above.  That would create a better air flow out in the room by creating a circulating air flow.  I made "ducts" for one of the shop A/C units with foam board and a hot glue gun that forces the cold air away from the return vents.  The forced air now has to circulate out into the room before it encounters the lower pressure area of the air heading back to the return.  It may sound like splitting hairs, but it was a noticeable difference.  Your fan does something similar.

Lastly, it seems like there should be a way to overcome the surge from the compressor kicking in by using huge capacitors (similar to a fluorescent ballast).  The capacitors would only discharge when there is a load applied and recharge when the load is removed.    Some portable welders use a similar design.  If you used diodes to allow full charge to flow out but a "trickle" charge to flow in, you could reduce the drain on the charging circuit (by putting a resistor in line with the incoming diode) yet allow the output to draw whatever current it needed.  That way you would not have a reverse surge on the charging system when the A/C turned off.

Tom Fassett