August 2012 - Small Solar System on a budget

DSinORDSinOR Registered Users Posts: 18
I wanted a small solar backup power system that didn't break the bank. Goals: enable me to briefly operate my water well, a computer, and a few small-battery chargers during power outages. When the grid is on, I intend to use the power either to run the pump to water my garden and lawn, or perhaps run my office (2 computers, printer, two phones, and modem/router).

After reading many threads on this board, I'm starting with the components described below.

This board is full of critiques and varying opinions on pretty much everything, but it's also full of good information. Perhaps other small system builders may benefit from some of my findings.

All prices are "delivered".

I started with 4 Costco 6v golf batteries, in series for 24v - about $400.

Next - four DMSolar 145w 12v panels (18vmp) - $640 on Amazon.

Next - charge controller. MPPT is attractive because it efficiently uses any incoming voltage, but it's expensive. PWM is just peachy as long as panel voltage is reasonably matched to battery voltage. In winter, panel voltage increases. For users who materially deplete their batteries each day, the increased panel wattage in winter is "lost" because of the material difference between panel voltage and battery voltage. This lost power can be "regained" using money. Either spend more for an mppt charger, or spend more on panels to buy more wattage generation. Rather than pay a $500 premium for an mppt controller, I spent an additional $320 for two more panels.

So - two more panels for $320. That brought my panel total up to six (870 watts).

Then, $205 for a Morningstar TS-60 PWM charge controller on Amazon. This controller is flexible: it can be used for 12, 24, or 48 volt systems, up to 60 amps.

Then, I bought a 2000w Samlex pure sine wave inverter for $682 on Amazon. That's a pretty good price for a decent 2kw inverter.

I found almost 300' of 6awg aluminum drop cable, salvaged from a power run out to an old barn. The cable is in very good condition. Aluminum cable is peachy, under the following conditions:

1 - use one or two awg sizes larger than copper. According to the cable charts provided by our host, for 24 amps at 24v, I can span 26' with 8awg copper, so that will be my limit on a short run of 6awg aluminum.

2 - The user should understand that bare aluminum oxidizes almost immediately when exposed to air, resulting in an ultrathin surface layer of insulating oxidation. The solution is to coat the aluminum in an airtight film of appropriate conductive grease or paste, and then abrade the surface of the aluminum with a greasy steel wire brush to debride the layer of oxidation, then crimp the connections into air-tight, grease-filled crimp connectors. The compaouns most often used for this work are known as de-ox, penetrox, noalox, contax, etc. Aluminum crimp connections (splices or termionals) can be bought at any electric supply, either dry or pre-filled with compound. Some of the compounds contain a gritty conduction metal powder that is intended to perform the abrasion process during the crimp operation. The 66150 Harbor Freight crimping tool with dies will do the job up to 6awg, and can handle larger cables with slight grinding modifications to the nearly useless small-cable dies that come with the tool. At $58 delivered, this is by far the best crimping tool for the dollar. It makes a crimp you can loop over a hook and hang your body weight on.

3 - The user should undertsand that any electrical connection that experiences heat cycles will require maintenance. As things expand and contract, fasteners come loose and need occasional attention. Aluminum has greater expansion and contraction than copper, and therefore may require more frequent inspection and tightening of connections. Regardless of metal, a loose connection is a resistive connection is a hot connection. This contributes to power loss and risk of fire.

4 - Aluminum cable will work harden faster than copper. If your PV array is mobile, take care to avoid excessive movement of cables.

5 - Bimetallic connections invite electrolysis problems. Don't pay up for copper connectors for aluminum cable. use aluminum connectors.

Okay, so aluminum can be good, and bought new, it is a third the price of copper, even using heavier gauge.

Check your local electrical surplus or construction recycler for bargains on aluminum drop cable.

Back to my list, I spent $58 on the HF crimper.

I bought a Grundfos 15SQ10-220 soft start well pump that operates on 7.4amps at full duty. No start up surge. $693 delivered with an underwater splice kit. Central Pump and Supply, Modesto, CA.

I bought a 5000VA autotransformer for $215 from Mastech Power Supply. At 230v, it's rated for ~22 amps, more than enough to power my soft-start 7.4amp well pump.

So, my current tally is $3213. The panels, CC, and inverter were from Amazon; I signed up for their credit card and got 1 year with no interest, so that $1847 chunk will be paid interest free at $154 per month. That leaves $1366 of up front costs so far.

Side note: I have a 6kw gas generator that will run my pump and many househld items, but I wanted some solar action anyway, so now I have that too. I read a Hoover Institute white paper on immenent power grid problems caused by a collision between a weakening economy and increasing demand for energy. The paper described rolling scheduled blackouts, with rural coops getting the short end of the stick. I live on a rural electric coop.

Next items on my list:

Panel mounts (I'll probably use aluminum angle iron as described by ywhic at http://forum.solar-electric.com/showthread.php?16038-21-adjustable-angled-mounts-DIY/page2&highlight=aluminum)

Aluminum cable splices and terminals and various connections

Battery box with vents

Sub-panel in the house

Pull my old pump and install the Grundfos. I may or may not need new drop pipe and cable.

That's it for now. I'll update this from time to time if anyone is interested. Also, if you know of a supplier of reasonably priced aluminum crimp connections, let me know.

Also, my system is not perfect. But it is relatively inexpensive and potentially quite functional. If you don't like my choice of PWM controller or some other aspect of the stuff I bought, I'm okay with that. I don't need critiques explaining why I should have spent thousands more. This thread isn't for you anyway. It's for people who are looking for a decent amount of reliable backup power for less than $2500 (excluding the pump and autotransformer).

DS

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,497 admin
    Re: August 2012 - Small Solar System on a budget

    Sounds like a nice system... One suggestion (if you have not already done it), try to have that 5kVA transformer "switched" by the well pump switch (probably use an isolating relay) so that you don't power the transformer when the well is not pumping. you could have a fair amount of losses with that (if you can measure the transformer's idle power consumption with a kill-a-watt meter--I would be interested to hear--I have read to expect upwards of 5% of rated power as losses--that would be 250 watts for a 5kVA transformer--sound scary high).

    Regarding PWM vs MPPT--Agree that if you get a good match with Vmp to battery bank voltage (Vmp~35-38 volts for a 24 volt battery bank) and you do not have long cable runs between the array and the charge controller/battery shed--I would never suggest MPPT just for that extra ~10-15% extra power in the winter (in sub freezing climates) you may pick up. The extra panels are usually a more cost effective solution.

    There are a few people with cold climates and reflections from snow/lake ice that do really well in the winter with MPPT, but that is more the exception than the rule for most folks.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: August 2012 - Small Solar System on a budget

    Hi DS,

    One point; MorningStar makes some nice products, and the TS-60 is a good PWM CC. You may know that, essentially MS likes to make everything an option. The TS-60 DOES come with a manual, but, the Remote Temp Sensor to compensate the charge voltage from the measured battery temp.

    You may have also ordered the RTS -- it is $25-30, and very well worth the price. But looks likea nice system. AND, hope that you have comfirmed that the Samlex Inverter can actually start your pump, but that is another topic. good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • CDN_VTCDN_VT Solar Expert Posts: 492 ✭✭✭
    Re: August 2012 - Small Solar System on a budget

    DS , I would NOT look for crimpable Aluminum fittings, They are normal tinned copper ones for crimping , but for straight Aluminum , they would be aluminum LUGs that have a setting screw that clamps the AL wire strands . Attachment not found.

    Also Make Sure the transfer from Aluminum wire to copper connections you have the used correct lugs and fittings.
    Nothing wrong with the aluminum If you know how to work & deal with "It's" characteristic's..


    REMEMBER that paste is conductive !!! (I say that , BeeeCuz ;) )

    VT

    Sorry forgot to add, Good Post & luck on the work.
  • ywhicywhic Solar Expert Posts: 612 ✭✭
    Re: August 2012 - Small Solar System on a budget

    Any thoughts on a combiner box for the panels to come into and then HOME RUN to the controller??

    Since you got a PWM you have to do 3 parallel strings of 2 panels each.. and need fusing/breakers on that..

    I did a write up using a Square D QO one.. buy since you have some cash the Midnite combiners are nice and you can get 150vDC rated breakers for their combiner.. (mine is limited to 48 vdc with certain QO breakers..)

    Keep in mind depending on the model of Samlex their special PIN terminals use upto 2 AWG (and maybe 0 AWG).. at 2000 watts though if its a 24V model than that is almost a moot point.. HD sells 2 and 0 AWG wire for a nice low price FWIW..

    I too was at 870 and then decided I wanted year round MAX numbers from the panels so I sold my MS TS45 (pwm) and meter front and got the Midnite Classic 150 MPPT..

    Suggest the battery temp sensor and meter front for the MS TS...
  • PhotowhitPhotowhit Solar Expert Posts: 4,994 ✭✭✭✭
    Re: August 2012 - Small Solar System on a budget

    Removed previous post due to erronious internet information, first specs that came up on Google search...

    I read around a bit more, still think you ight be pushing things with the inverter, but 'Coot replied on an earlier post about the same pump that it would just run slowwer if it didn't have enough current. Between the pump (other places state 7.1 amps at 200 volts or 6.4 at 230V) the wire, even at 220 you may have 400+ feet out for a well and the auto transformer I think your cutting it close for full performance from a 2000 watt inverter.

    I guess you've already figured your run time, I'm not sure about watering your garden as this will draw you down pretty quick. I think 'coot or someone mentioned a large storage tank for longer cycles... at close to 2000 watts, call it 2000 watts with the 85% inverter eff, at 24 volts your looking at 83 amps (actually much higher, look at Peukert Effect)from your 220 amp hour battery bank in an hour.

    I'll PM you a link for some electrical stuff off site that you may find useful.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • DSinORDSinOR Registered Users Posts: 18
    Re: August 2012 - Small Solar System on a budget

    Thanks to everyone for the great replies!

    I'm excited to implement the system, but boy is this not a small job! There's a lot to be said for gaining immense wealth and then vacationing in Patagonia while a contractor installs your 50kw gridtie with 10000ah battery backup.

    RE pump: It's a 1HP pump. All my specs say 7.4amp "full load current" and 11amp "overload current". The total cable run between indoor pump controller and submersible pump is 240'.

    BB - thanks. During research, I rarely encountered mention of isolation of the transformer to prevent idle losses. It's included in my grand plan, but it's so infrequently discussed online that I still need to flesh out a design for it. My pressure tank and controller are in a basement closet. In the present curcuit, the 240v supply runs through a Square D pressure switch on the tank to the 1973-model Franklin controller box that contains a relay, start-up cap, and OL protector. In the new system, the electronics are on the Grundfos pump. The Square D pressure switch says it will work on 32v, 120v, or 240v. One option would be to change the well supply circuit to 120v, remove the pump control box, and replace it with the autotransformer to send 240v to the pump. The 120v would pass through the pressure switch and only power the transformer when water pressure called for it. This would be easy, but it would call for a lot of current through that pressure switch. Another option would be to change the pressure switch circuit to 120v as previously described, and also install a new dedicated 120v line to a new large relay in the closet. The 120v pressure switch circuit would power the new relay, and the relay would provide switched power to the transformer and on to the pump. I then include those two 120v lines in a solar sub-panel. Thoughts?

    RE AL connections: I'm a noob with these, but my research indicates that a proper crimp is preferable to an open clamp lug? To be clear: strip the wire, apply the de-ox compound, then abrade the wire with a steel brush that is also coated with de-ox, then use a hydraulic crimper to apply an airtight de-ox-filled aluminum crimp lug. More input welcome...

    I'm narrowing my PV location options. It seems I have enough of the free aluminum cable to "double-up" between the PV and CC. I've read that two combined 6awg roughly equals one 3awg. Any comments on doing this?

    Thanks!
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: August 2012 - Small Solar System on a budget
    DSinOR wrote: »
    RE AL connections: I'm a noob with these, but my research indicates that a proper crimp is preferable to an open clamp lug? To be clear: strip the wire, apply the de-ox compound, then abrade the wire with a steel brush that is also coated with de-ox, then use a hydraulic crimper to apply an airtight de-ox-filled aluminum crimp lug. More input welcome...

    The safest thing to do is to use terminations (lugs, ring terminals, or whatever) which are rated for AL and follow the manufacturers instructions. This will minimize chances of galvanic corrosion as well as oxidization. If you cannot find appropriate terminals, look for a Cu/AL rated splice instead and use a short piece of Cu for the termination part.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 29,497 admin
    Re: August 2012 - Small Solar System on a budget

    The relay(s) would only be powered when the pump is on--so you would not have much in the way of "extra losses".

    Part of it depends on how easy it is to get parts and replace them. If the pressure switch is easy and cheap to replace--It would seem adding another relay next to it would be silly.

    However--If the the pressure switch is relatively expensive, or you want to remote the relay vs the pump switch--Then the cheaper signal wiring probably would make it worth while if you have any distances involved.

    Also--You might want to run the signal level wiring through some sort of timer/secondary water flow detector--If pipe breaks, leaks in pump house, pump stays on for hours instead of 10 typical 10 minute cycle--Then having an alarm, extra "off switch", time limit timer (to prevent your batteries being taken "dead") etc., may make the "extra" relay worth its weight in recycled batteries.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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