Situational System

Congratulations!


I agree completely.  The grid is old, dependent on subsidies, and increasingly unreliable.  And in the event of economic and/or social collapse, it'll be completely useless.  However, perhaps you should reconsider the grid-tie portion.  If it's off-grid capable, why maintain a grid connection at all?  The grid is like training wheels.  If you still think you need it, your system is not truly off-grid capable.


It sounds like you need to establish your actual requirements.  Sure you can start with 1kW and expand it, but it will be cheaper and easier to start with the minimum of what you actually need.  In my experience, you're going to need *at least* 1-2kW of solar and 1kW of something counter-cyclical to solar -- wind is good, though water is great if you have it.  If you only use solar, you'll need *at least* 3kW and a bigger battery bank.  These figures are dependent upon you having high-efficiency appliances and lighting and NO electrically-powered heat (incl. hot water, dryer, oven, etc.).


Distances can be solved with two methods -- up-sizing your wiring or up-converting your voltage, or both.  My system is 24V.  That's what my wind turbine puts out and what I designed my battery bank for.  The solar accomodates that too, by down-converting from 48V at the charge controller.  I like 24V because many things natively operate at that voltage, including a wide selection of down-converters to 12V.  I have no problems getting 24V some 150' to the opposite side of my house with virtually no voltage drop.  The wire isn't terribly expensive, but it's not cheap.  I don't recall what guage I used, but it's whatever was recommended by the wire guage charts.  If you want to use a cheaper guage wire, design your system to be 48V.  However, understand that some of your other components may be more expensive.


That's typical.  It's cheaper and easier for them to install grid-tie-only systems.  And because of tax rebates, they have plenty of business doing only those.  I personally think it's insane to do a grid-tie system, as there is no benefit from the expense.  You're still dependent on the grid, but now a very expensive producer.

You'll be better off doing it yourself.  I wouldn't trust most of them to touch my system anyway.  I started off using a contractor because the wind turbine was only available through a dealer-installer.  They screwed everything up.  Reversed polarity, no disconnects, no fuses or lightning protection, inappropriate grounding, etc.  I had to redo everything.  It's best just to do it yourself from the beginning -- as long as you do plenty of research and ensure you're being safe.

Personally, I would only go with batteries designed and warrantied for long life in the intended role.  Golf cart batteries may work well, but what if, as you fear, we have a global currency crisis and you cannot find replacements in 3-5 years?  I'd rather have something I know will last at least 10 years and have been known to last 20+ years, which the Rolls-Surrette deep cycle batteries are known for.  I've also just recently added two redundant parallel banks in case one or more of the batteries fail.  If you only have a single string of batteries, e.g. 6x4V=24V or 8x6V=48V, then the loss of only one of them results in the entire string being worthless since you cannot maintain your system voltage without it.  I have two strings of 6x4V in parallel (or I will just as soon as the new ones are delivered anyway), preventing a single point of failure.  Therefore, I'm confident my batteries will see me through the current economically/politically/socially volatile times.

How about this system built from parts available on AltE:

• $13,770.00 = 27 x ES-A-210-fa2 solar panels (5.67kW total)
• $ 2,606.16 = 6 x IronRidge 180" adjustable mounts
• $ 2,002.50 = 3 x Outback Flexmax 80 charge controllers
• $ 6,624.60 = 12 x 4-CS-17PS Rolls-Surrette batteries
• $ 3,637.70 = 2 x Outback 3500W grid-capable off-grid inverter
• $ 3,000.00 = assorted accessories, wires, fuses, panels, breakers, etc.
• ---------------------------------------------------
• $31,640.96 = total

Plus shipping of course, but you can probably get free shipping for an order of that size (plus some 5-10% discount probably).

That's also tax-deductible... I think it's a 30% federal rebate, so you'll get $10k back.  In fact, if you buy this or anything similar, stop paying taxes for the rest of the year if your normal tax liability is less than $10k.

That gets you almost the 6kW you were looking for, plus redundant strings of deep-cycle batteries, and redundant grid-capable inverters, for barely more than you were willing to shell out for only 4kW.  Granted, you have to install it yourself, but that's the only way you'll know it's done right, plus you'll be intimately familiar with it so that you can troubleshoot in the future. 

BTW, that list assumes that you have 30' available across your roof -- 3 strings of 9 panels; each string connected in series for 108V to one of the charge controllers.

I would build the battery boxes out of plywood.  I used 3/4" so that I could screw them on-edge.  Insert a 2" PVC pipe for a vent.

For best results, add a wind turbine or water turbine to this system.  I would recommend the Bergey XL.1 1kW turbine on an 80-100' tower.  Cost should be around $8k, tower & accessories included.  If that's too much, I would eliminate one of the strings of PV panels (plus 2 mounts and 1 charge controller) to get the wind turbine.  It's counter-cyclical to the solar, so you'll greatly improve your average production.  I have direct experience with this.

As far as being debt-free, that is a noble goal, but directly at odds with your recognition that the central bank is inflating our currency to nothing.  The most rational course right now is to take a home equity loan at 3-4% interest to purchase capital improvements such as this.  Leave your liquid assets in inflation-protected investments such as precious metals, commodities, and mining company equities.  So long as you have assets that can be liquidated to pay the debt in full at will, you are essentially debt-free.  But the leverage of cheap credit at a time when the real inflation rate is far greater than your interest rate is too good to rationally pass up!

Here's a diagram I created when I was spec'ing out a system for my father.  Thought it might be helpful to visualize.


In this case, he already had a main utility-connected breaker panel and would be adding the off-grid stuff, transferring some of his circuits to the uninterruptible panel.  My preferred design would be to remove that panel altogether and move all of the loads to the FlexWare panel, perhaps with subpanels.  The utility grid would be directly connected to the Outback panel then.

I also prefer moving as many circuits to DC as possible.  E.g. replace the well pump, refrigerator, lighting, etc., so as to have the improved efficiency and fault-tolerance of not needing the inverters for those loads.  DC-direct also eliminates power factor losses on pumps, motors, CFL & LED lighting, etc.

I think the system design here is overkill for any residential purpose, but he wanted to do this for tax reasons without having to change any loads to make them more efficient.  With proper care to make the loads as efficient as possible, anyone should be able to eliminate 1/2 to 3/4 of the solar and 1/2 of the wind and be just fine.  This system ought to be able to power a small community, which I guess it very well might if/when the SHTF.

I would recommend bringing a DC line back to the house if you can, for the reasons given previously, in addition to your AC.  According to the method recommended by AltE, if you wanted to run 450 Watts of loads on DC (more than enough for most lights and small appliances), could find a 6% voltage drop sufferable, and you had a nominal system voltage of 24V, then your Voltage Drop Index would be: VDI = (19*150)/(6*24) = 19.79, which is #4 AWG wire.  If your batteries were at 25V, then a 6% drop would give you 23.5V at your load when drawing 19A (456W).  You can get 150ft of #4 THWN (direct burial) wire for about $175.  If you wanted to upgrade to #2 THWN, it'd be about $350 for 150', and you would only get 4% voltage drop over 150' for a 19A load.  Or you could up your load to 30A (720W) at 6% voltage drop.  You could of course likewise keep increasing the gauge (and price) to achieve less voltage drop at higher amperages.  You have to define your likely loads and budget to figure out which is best.  But at least some capacity to run DC loads directly off the batteries is a good idea for fault tolerance, redundancy, efficiency, etc.