August 2012 - Small Solar System on a budget

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