Trying to design a system and have lots of questions

Kevinb · October 2008

Hi All,
This is my first post and it is going to be a long one with lots of questions, so I really appreciate anyone taking the time to read this and answer. I have to admit that I just learned of this forum and haven’t read a lot of threads yet, and have a lot to learn. I have never had a useful solar power setup but have messed around with small (Ametek 99 VDC) wind generators which charged some deep cycle batteries through a PWM charger, and used a small inverter in my garage to run the stereo and some lights a few years back. Since then I have built a 1200 square foot workshop in the back yard which I would like to run on a combination of solar and wind. I have a few saws, lathes, mill, etc. that run on 220VAC, and already have a 100 amp 220/110V breaker panel out there supplied from a 100A breaker in the main panel from the house. The solar/wind system is not needed but more of a hobby that I’m interested in. My ultimate goal is to have enough solar panels and wind generators to run the shop completely with batteries and inverter(s). Since we have a well for our water and the grid power goes out once in a while, I’d also like to be able to run some circuits in the house including the well pump by feeding power back into the house from the shop. It would also be nice to switch the house power over to the batteries when we don’t need to run things like the washer/dryer or stove/oven. I think that switching the house over to the batteries would also help us get into the habit of being more energy conscious by forcing us to use only the electricity that we need to. We don’t have or need A/C here in Flagstaff, and the water heater runs on Propane. Heat is either from the propane stove, wood stove, or both. There are also some electric floor strip heaters but we try not to use those. For solar panels and wind generators, I will be building my own. We live on an acre with few neighbors around so bothering them with wind generators and solar panel arrays is not an issue. I’ll start with about 500 watts of panels built from surplus cells that I purchased a long time ago on ebay, and mount them to track the sun. If they don’t last, I’ll buy good commercial ones. I have a small 3 phase wind generator that I built already, and will build a larger one with about a 9ft rotor. I was going to build the generator similar to the ones built with Hugh Piggott’s plans, but have found a much more efficient 1.5kW 3 phase alternator to base it on. We get a lot of wind in the area of Flagstaff where we live (outside of town in Fort Valley for those of you familiar with it.) I realize that the higher the voltage the better and would like to do a 48VDC system, but the wind generators I’m building are better suited for 24VDC battery charging. I’ll add more solar panels and generators as necessary in time.
Now for the first round of questions which I’ll break up into general categories-
1) SHOP LIGHTING/WIRING: I am still wiring the shop and have not done the overhead lighting circuits yet. I plan to continue to wire it so that it can run completely off of the grid A/C power and put in a manual transfer switch to switch the shop breaker panel between the grid supply and the inverter(s.) The inverter(s) will be located in the shop along with the batteries, charge controllers, etc. I was planning on using 4ft fluorescent fixtures for lighting, but now that I decided to try running it on solar/wind that’s not practical. I don’t want to use DC lights either. It seems to me that a bunch of individual light sockets would be best to use the spiral CFL’s. I looked on ebay and found that there are 120VAC LED cluster lights that use an E27 socket and use much less power than even the CFL’s. I can’t find any specs on the E27 socket. Would these work for shop lighting, and would they screw into a regular incandescent bulb socket? Any other ideas for low power consumption lighting that runs on 120V?
2) CHARGE CONTROLLER: For the solar panels I was going to get a Xantrex C60, but I see that the new XW accepts a much higher input voltage. Considering that my solar panels will only need 30-50 feet of wire to reach the controller, is it worth 3X the money to be able to wire them for higher voltage? With the MMPT would the XW work for a wind generator assuming it was rectified to DC and on a 60A circuit breaker, and voltage never exceeded 150VDC? I think I could program the aux output to control a relay to switch the wind generator to a dump load when battery voltage gets too high. Maybe that’s a question for a Xantrex engineer. Any other comments/suggestions?
3) INVERTER: I would like to get an XW4024 but they are pretty pricey. For what I want to do is pure sine wave necessary? I see DR3624’s on ebay all the time, and could probably get two of them and stack them for the 110/220 VAC that I need for half the price of an XW4024. For the extra efficiency and possibility of extending the life of my loads, maybe it makes more sense to put the money into the better inverter? Another consideration is that I’m also using VFD’s (variable frequency drives) to convert 220 single phase to three phase to run a couple of my machines, and I don’t know if a modified sine wave inverter would even drive them. Any opinions on inverters or other suggestions?
4) BATTERIES: This looks like it will be huge cost, and I really don’t know how many AH I will need. I think I’ll start with about 200AH, and add more as I grow the system. I know that all the batteries should be the same type and age, so how do you build a battery system that can grow in capacity?

I know that a solar/wind system is more expensive than grid power, but I really like the idea of being energy independent some day, maybe even run the whole house in addition to the shop full time. I’m doing the panels and generators myself because I'm an engineer and like to tinker. I also don’t want to waste money on more expensive parts than necessary in #’s 1-4, but also don’t want to find out later that I should have bought something better. Since I have grid power, I realize this may never pay for itself compared to paying APS, but like I said I think we'll be forced to think a lot more about how much power we use which will save moey initself. I’m a big fan of saving money by buying used or new old stock on ebay and surplus websites, but also realize that there’s a lot to be said for newer technology with a warranty. Any opinions and/or advice would be appreciated if anyone is still reading..

niel · October 2008

Re: Trying to design a system and have lots of questions

hi kevin,
i'm not going to talk specifics here and i'll say generally what you wish to power is very large. to do this purely from solar/wind involves great costs and it may be better with a grid-tie only arrangement (more efficient) unless you really feel the need is there to back it up with batteries. if grid-tie only then you won't be able to add batteries later unless you were to change out the inverter as in a future expansion option. in any case i doubt you'll produce enough to run everything without the need of the grid. odds are your best bet with battery backup is to have a small system that can run your household for up to 3 days with using only the necessary items(no air conditioning although some would consider that necessary). this type of system can sell some power back to the grid at a lesser efficiency and allow for the batteries to stay charged for outages. this can also double as your permanently off grid inverter (xw is good choice as are some others) if you ever achieve that much in power generation/conservation, it will probably be a circumstance that you grew into it alfter so many years and initial planning is important for proper expansion ability.
please do some reading, as there is plenty of it, so you can further acquaint yourself with more knowledge on what may be appropriate for you. and yes it can get real expensive so few get to have complete self contained power generation via renewables and tht usually involves a great deal of conservation that usually isn't the case using power tools. use the sinewave inverters as modsine does not tie to the grid and is not very clean power that can cause excessive heat buildup in electric motors and can blowout some things like battery chargers for tools. you will find this and much more in your readings and this keeps you from getting something you either wouldn't want or from making a big mistake.

Kevinb · October 2008

Re: Trying to design a system and have lots of questions

Thanks for your reply niel and I understand your points. I am willing to start relatively small and work up to running more and more things as I add to the system, that's why I want to start out with the right components so it is expandable like you said. I agree that I have a lot of reading to do. A grid-tie only system would save money on the power bill, but that's only part of what I'm after. Let's just assume for now that all I want to run are lights and a power tool once in a while. With a grid-tie only system I would miss out on the satisfaction of knowing that the lights burning at night are running on energy that I "made" instead of coming from the power company. People spend a lot of money on hobbies that don't make any money back, and the satisfaction comes from doing it and seeing the results. That's sort of how I look at this- I know it will cost money but I'll get the satisfaction of learning something new, and doing something that most other people don't. The other part is that I know I'll think a lot harder about using electricity when I know it is draining my batteries that I worked so hard to charge. When the sun is shining or the wind generator is spinning, I'll get the satisfaction of knowing that the batteries are charging for later because of something that I built. The power tools don't run that often or for that long at any one time, but if I can run my table saw for 5 minutes to cut up some wood for a project, I'll get a lot of satisfaction thinking that the power was "free" even though it actually cost me a lot of money and time to build the system. When I need to switch to grid power to finish the project that's fine, it will probably motivate me to expand the system capacity. So with that in mind, I'll simplify my questions using Xantrex for an example although I know there are other good equivalent products out there.
1) What would the most efficient 120VAC lights be for shop lighting?
2) In general, when is a Xantrex XW charge controller worth the extra money over a C60? Maybe I just need to do a lot of reading to find out this because there are so many variables.
3) I'll plan on a pure sine wave inverter and ask more questions down the road.
4) Would a battery bank of 200AH and an XW4024 have a problem starting and running a 3HP 220 VAC table saw for a few minutes assuming no other load and fully charged batteries? FLA on the motor is 15A, so if it draws 30 A when starting, that's 30X220=6.6kW, and the specs for the XW4024 say 8kW surge for 10 sec which seems fine. Is that a valid assumption? In real life it probably only draws 5A during normal cutting.

I need to read a lot on the different types of batteries and how the AH rating works in real life and how far they can be drawn down without significantly affecting battery life.

A great start for now would be suggestions for lighting because I want to finish wiring my shop.

Thanks again.

niel · October 2008

Re: Trying to design a system and have lots of questions

1> probably the 4ft flourescents that are typical for shops. you need lots of light for shop work.

2> you will need to read up on the differences between a standard pwm cc and an mppt cc. odds are you'll want an mppt cc even though they cost more and you'll see this in many posts, but i'll tell you here first that you should buy the battery temperature sensor for whatever mppt cc you get.

3> ok

4> in general you may need more than the 4kw from a single inverter even if the inverter could handle the saw because of the lights and anything else being on. there is an xw that has more capacity and inverters can often be stacked to add their capacities together. you can't stack different inverters either, but you'll get more info in this area as time goes on.
the batteries themselves can be problematic because it isn't advisable to add batteries as you go along. again, start reading. you need to size the batteries for the system you're shooting for or go with a bunch of el cheapos and upgrade later. you need to determine what all of your loads will be and not just at one time as it should be the total kilowatt hours or kwh for the whole day, plus you need to determine the kw capacity you'll need for the inverter(s). you can buy a meter called the kill-a-watt to measure the power draws for 120vac items, but the 240vac items may need to be guestimated if no other meter is obtained for it. the saws and such do have their specs like you read on your saw. don't count on it settling very low in watts even though it will dip some as they usually aren't at the stated plate specs. manufacturers cover their butts somewhat on the running power levels so it is not to ever be higher than what they state except of course for startup, which lasts for a few seconds. what could be done is to use a utility powered charger either from the inverter(built into some) or a seperate one to properly help charge the batteries when there's no or little pv power to do so.
this is what is refered to here as ready, fire, aim what it is you're currently doing. why worry if the 200ah batteries can handle the saw when you haven't even determined what you'll need for inverter power. that influences the battery capacity needed and those batteries will have to be charged at a rate within 5-13% of the battery bank's ah capacity and that helps to determine the necessary amount of pv power to be bought. it gets involved and you need to read.

BB. · October 2008

Re: Trying to design a system and have lots of questions

If you want to look at a "big" system... Read the posts/threads by "Adas"...

Find all posts by adas

He is in Hawaii and built out a large off-grid/battery system (using quite a bit of used/surplus batteries/inverters) to run his fabrication business...

-Bill

PS:I should add... That a "retail" system, installed using all new components, and accounting for battery replacement... Very roughly, you are looking at (these are very rough numbers) $0.25 per kWhr for a Grid Tie system and ~$1.00 per kWhr for an off grid system (assuming no rebates and no property taxes) based on a 20-25 year system life in a relatively sunny area.

Vs ~$0.12 per kWhr to $0.35 per kWhr for power here in Northern California (PG&E)...

crewzer · October 2008

Re: Trying to design a system and have lots of questions

Kevin,

1) What would the most efficient 120VAC lights be for shop lighting

Probably worth looking at standard 34 W 4’ florescent tube light fixtures. They're fairly efficient, and the lamps and fixtures are relatively inexpensive.

2) In general, when is a Xantrex XW charge controller worth the extra money over a C60?

“Big” MPPT controllers (i.e., Apollo, OutBack, Xantrex) offer several advantages over PWM-type controllers like the C60. One advantage is MPPT, which typically delivers anywhere from ~5% to 30% more charge current to the batteries, depending on array temperature and battery state of charge. A financial advantage of this feature is that you can use a smaller and therefore less costly PV array (fewer modules, less installation hardware, less installation hardware.)

For example, let’s say that an MPPT controller delivers an average of 10% more charge current than a PWM model. That would allow you to install a 910 W PV array instead of a 1,000 W array. At $4.50/W just for the PV module costs, buying the smaller array would realize a savings of 90 W x $4.50/W = $405. The MPPT controller has already paid for itself.

The big MPPT controller’s DC-DC step-down feature can allow for additional cost savings. Using a “high-voltage / low current” array, you can use smaller gauge (= cheaper) wire between the array and the controller.

3) I'll plan on a pure sine wave inverter and ask more questions down the road.

Good idea.

4) Would a battery bank of 200AH and an XW4024 have a problem starting and running a 3HP 220 VAC table saw for a few minutes assuming no other load and fully charged batteries? FLA on the motor is 15A, so if it draws 30 A when starting, that's 30X220=6.6kW, and the specs for the XW4024 say 8kW surge for 10 sec which seems fine.

This might be a problem. Assuming a 6.6 kW start-up load and 85% inverter efficiency, that’ll place a 7,765 W load on the battery bank. This load (~350 A) might/could/would cause the battery voltage to briefly drop below the “low voltage” threshold, which would cause the inverter to shut off. Even a 240 VAC x 5 A load won’t be trivial, as it will present a ~55 A load on the 24 V batteries.

Based on the specs and assumptions provided, I think you’ll need a 24 V battery bank rated for between ~700 Ah and 1,000 Ah to be able to reliably, regularly, and repeatedly start the big table saw.

HTH,
Jim / crewzer

mike95490 · October 2008

Re: Trying to design a system and have lots of questions

If you've bought nothng yet, I would really suggest a Grid Tie system. You get 95% efficiency, and you let the "grid" be your battery. No water to add, no cables to clean. And you have enough power to handle any surge. Daytimes, you watch your meter spin backwards, as you feed the grid. Evenings, you draw from the grid. Over the course of a year, it all averages out, depending on the size of PV array you install.

Wind - planned system voltage. Is there any chance at all of winding your alternator to be a 60V, to charge a 48V bank. It's already been explained how a 24V system will be hard pressed to start your saw. A 48V system (8, 6V batteries in series) will be easier to wire (no parallel connections) and have less losses. If you follow Hugh Piggott’s plans plans, you can change the wire size, (smaller) and place more turns, to get the higher voltages, as to the

found a much more efficient 1.5kW 3 phase alt

- I'd be interested in hearing more about that, as wind may become a factor in my plans. it's also possible to use a 3 phase transformer to boost the voltage (before the rectifier) to get higher voltage.

crewzer · October 2008

Re: Trying to design a system and have lots of questions

Another consideration is that I’m also using VFD’s (variable frequency drives) to convert 220 single phase to three phase to run a couple of my machines, and I don’t know if a modified sine wave inverter would even drive them. Any opinions on inverters or other suggestions?

OutBack's off-grid / back-up inverters (FX and VFX series) can be "stacked" for three-phase applications, with one inverter per phase. See page 14 in our on-line catalog.

HTH,
Jim Goodnight
"crewzer"
Eastern Regional Sales Manager
OutBack Power Systems

Kevinb · October 2008

Re: Trying to design a system and have lots of questions

Thanks for the replies guys. After looking into lights a little more I was surprised to find that LED lights that run on 120V are really not much more efficient than 4ft fluorescents for the amount of light that they produce. The fluorescents and are a lot cheaper also, and I agree with the 32 watt 4 footers being a good choice. For example, one 110 VAC, 120 LED bulb that I found is rated at 4.5 watts and 420 lumens, so about 93 lumens per watt. A 32-watt 4ft fluorescent was rated at 2800 lumens, so 87.5 lumens/watt. It would take about 6.7 of the LED bulbs to produce the same amount of light as one 4ft fluorescent tube. At about $15 each, that would be about $100 worth of LED bulbs compared to $2.5 for a fluorescent. No-brainer there.

For batteries, I went to the local Sam's Club to see what they have. There were 3 choices other than standard car batteries. I'll list all the info given- they are all 12V.

#1- Powerfast PF80. These are really big- 8D. They didn't say deep cycle though, and the only specs given were CCA of 1400, 400 min reserve. Price $129 each. Warranty 6 mo replacement, 36 mo pro-rate.

#2 Interstate Deep Cycle 29DGI. 675 CCA, 210 min reserve, 125AH. Price $71 each. Warranty 12-mo replacement, 30 mo pro-rate.

#3 Powerfast GC8 Deep Cycle. 90 min res, 170AH. Price $72 each. Warranty 6-mo replacement, pro-rate not listed.

Looking at the forum host's website, it appears that 200AH at 24VDC AGM would be about $500, and in seems doubtful that 200AH would be sufficient according to crewzer. According to the battery FAQ 8D batteries are 225-255AH, but #1 didn't say deep cycle or list AH, so I don't see how I can even consider that one.

If I choose approx. $500 for the battery budget to start with until I'm ready to spend big bucks on good ones, here's what it looks like the local choices would be:

6 of the #2,s giving me 750AH or
6 of the #3's giving me 1020AH, but a lot less reserve time.

Either scenario would be about $430 before tax, or I could add two more for another $140. Which would be better, or would it just be a waste of money to begin with? Is that correct for the AH with series/parallel connections to produce 24V or can that number even be compared to the AH rating of good solar batteries?

As far as the grid-tie system goes, that is still a consideration and I realize it's a lot more efficient and probably a smarter way to go. A backup generator for my well pump is no big deal, just not really the direction I wanted to go.

If I do build the wind generator alternator(s) myself 48 volt would be no problem. The reason I was thinking 24V would be better is because this is the generator I'm looking at using (If I shouldn't be posting this link I will delete it) http://www.ginlong.com/wind-turbine-pmg-pma-permanent-magnet-generator-alternator-GL-PMG-1500.htm

If you look at the voltage vs. RPM graph, it looks like it reaches 24V open-circuit at a little over 200 RPM, which I think is reasonable. 48V isn't reached until over 400 RPM, so I'm not sure if that would be good for lower wind conditions. Yes, I know it's made in China and I hate the idea of that over US or home-built, but it looks to be high quality and probably higher output than I could build for the size. I think a 10 ft rotor would work but not sure. The time saved by buying the alternator vs. building it may be more than eaten up by the time required to come up with the right blade design/size as opposed to following the Piggott plans. TLG wind power makes a turbine that I *think* is based on the smaller PMG-500 unit, which seems to have a decent output according to their website with a 5ft rotor. I guess the wind power section of this forum would be the place to discuss it, if it's even appropriate. They also make a higher voltage version that is suitable for grid-tie.

Back to the inverter topic, stacking for 3 phase makes sense if it's necessary, but the VFD's do pretty well converting 220 single phase to 3 phase, and with the ability to control the ramp-up (accel) time, I don't think starting current is even as high as using a contactor to start a 220V single phase motor. I can confirm that with a clamp-on amp meter.

crewzer · October 2008

Re: Trying to design a system and have lots of questions

#2 Interstate Deep Cycle 29DGI. 675 CCA, 210 min reserve, 125AH. Price $71 each. Warranty 12-mo replacement, 30 mo pro-rate.

#3 Powerfast GC8 Deep Cycle. 90 min res, 170AH. Price $72 each. Warranty 6-mo replacement, pro-rate not listed.

If I choose approx. $500 for the battery budget to start with until I'm ready to spend big bucks on good ones, here's what it looks like the local choices would be:

6 of the #2,s giving me 750AH or
6 of the #3's giving me 1020AH, but a lot less reserve time.

Kevin,

#2: I’m not familiar with this particular Interstate model number. It sounds a lot like the commonly available Interstate SRM-29 (Group Size 29, 12 V, 210 RC, 675 CCA). I suspect they're the same battery, but Sam's has it's own model number.

To create a 24 V battery bank, you’d have to configure the six “#2’s” (12 V batteries) in a 2 (in series) x 3 (strings in parallel) to create a battery bank rated at 24 V x 375 Ah.

Alternately, you could configure the six “#3’s” (8 V batteries, I believe, and not 12 V) in a 3 (in series) x 2 (strings in parallel) to create a battery bank rated at 24 V x 340 Ah.

These batteries are probably what are known as “hybrids”. They’re often labeled as deep cycle / marine / RV. They’re neither true starting batteries nor true deep cycle batteries. Accordingly, they’re not particularly good at starting a cold engine, and they don’t see much use in renewable energy applications.

However, compared to true deep-cycle batteries, these hybrid batteries can supply a fair amount of surge current without suffering as bad of an initial voltage drop. Accordingly, these might work for your application, but you shouldn’t expect years and years of service from them. One approach – not risk-free – might be to try one of the banks described above, and, if it has trouble starting the loads, then add another string or two of batteries right away.

Check this site for useful (though not the last word, in my opinion) information on wiring batteries (or battery strings) in parallel: http://www.smartgauge.co.uk/batt_con.html

HTH,
Jim / crewzer

niel · October 2008

Re: Trying to design a system and have lots of questions

kevin,
if you go with the 32w flourescents be sure the fixture is made for it as i have been told by some local store personnel that you just can't drop a 32w tube into a fixture made for 40w. not too sure why though as it's been some time since i was told that and i don't remember the explaination i was given at the time. i don't know the validity of what i was told to be true or not.

Kevinb · October 2008

Re: Trying to design a system and have lots of questions

Thanks again guys. Jim, I want to Sam's again and I'm sure you're right about the 8V batteries. They don't say 8V but have 4 caps for filling, so I assume 4 2V cells per battery. I also know enough about electricity to have realized that putting two batteries in series doubles the voltage but not the AH. I think I'll just get 8 of the #2's to get 500 AH for a total of about $650 with core charges and tax.

I'll probably wait to get them until I get the wind generator working. Then hopefully I'll be able to see how much wind it will take to charge them if wired for 48V compared to 24V using DC loads to draw then down for testing. After that I can pick the appropriate voltage for the inverter. I think I can just build the solar panels for the highest voltage that the MPPT charger can handle, and switch it according to the voltage I choose for the system, correct? Does anyone see a problem with this general strategy?

Niel, I'll check with my electrical supplier to make sure the fixtures work for 32W bulbs, I even saw 20W bulbs today that might be good enough.

crewzer · October 2008

Re: Trying to design a system and have lots of questions

Kevin,

I think I'll just get 8 of the #2's to get 500 AH for a total of about $650 with core charges and tax.

This may work rather nicely. It’ll at least give you the option of a 24 V x 500 Ah battery bank or 48 V x 250 Ah. Note that you’ll have 48 battery cells to maintain…

I think I can just build the solar panels for the highest voltage that the MPPT charger can handle, and switch it according to the voltage I choose for the system, correct? Does anyone see a problem with this general strategy?

This’ll work, but there may be one key problem to consider for a 48 V application.

In general, 150 V is the maximum input limit for most big MPPT charge controllers as well as typical DC circuit breakers. You’ll need to keep the temperature-corrected PV array Voc (based on your local ambient record low temp) below this 150 V limit to protect the controller and its warranty.

Note that these controllers’ operational limit is in the 140 VDC to 145 VDC range.

At the other end of the scale, the array will also need to be able to deliver at least 62 Vmp to 66 Vmp (measured at the array terminals) in the summer (hot array = low module voltage) to overcome voltage drop in the wiring and the controller (~4V total drop) and still be able to drive the battery bank to target absorb- and EQ voltages.

For example, string three "24 V" modules (typical Vmp = ~17.3 V, typical Voc = 21.6 V) is series (72 V nominal) will often exceed the controller's Voc limit in cold weather. And, string just two "24 V" modules in series (48 V nominal) typically has trouble charging a 48 V battery bank in the summer.

You can get local temp data from www.weather.com, and the NEC provides temperature correction instructions and guidelines (NEC 690-7). Your PV module data sheet should have specs for Voc and Voc temp coefficient. I strongly recommend that you address this issue before spec’ing/buying/installing PV modules, especially if your location is particularly cold and/or hot.

In sum, spec’ing a PV array for 48 V battery banks and one of the “big” MPPT charge controllers in a hot and/or cold environment can be a delicate balancing act. But, knowing all of the above, it’s quite doable. Let me know if you need any help with this issue.

Regards,
Jim / crewzer

Kevinb · October 2008

Re: Trying to design a system and have lots of questions

Got it, thanks for the help!

Trying to design a system and have lots of questions

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