Building a system piecemeal?

2twisty2twisty Solar Expert Posts: 182 ✭✭✭
I know that it's not "optimal," and from what I've read in other posts, building a system piecemeal requires careful planning. However, those threads didn't really go into the "careful planning" process.

I will be going off-grid in the next 2-5 years when my wife and I move to Texas. I am starting this early because my budget is very limited, so building a system piecemeal is about the only way I can go. I have time for "careful planning," so I want to carefully plan for a system that will meet our eventual goals, and require a minimum of discarded technology.

I have not yet defined what that goal is. I know, I know... Get out the Kill-A-Watt (I *do* have one of those, lol) and start collecting data. I will be starting that soon.

My initial plan is to have a genset that can supply our power at about 80% of our "preferred goal." I want to then build out a system to transition off the genset so that it becomes a backup only, or for when we need to greatly exceed our nominal use, such as for construction projects, etc.

We have already pared down our power use a lot here, but there is a LOT more that we need to do to be able to fit into ANY reasonable off-grid scenario. Last month, we consumed 1114KwH. This is with electric water heat, electric stove, electric clothes dryer, refrigerator, 2 upright freezers and several computrers, in addition to the more "usual" loads such as lights and using the microwave and charging our phones.

When we move out there, those huge loads will be either gone or greatly reduced. We won't be using electricity to heat ANYTHING (clothes, food or water) and those are probably our biggest consumers right now, even though their loads are transitory. We will probably drop one of our freezers and look to replace the refrig with a smaller, more efficient unit. I've read about converting an upright freezer to refrigeration by using a thermostatically controlled 110v outlet.

At any rate, I'm thinking of buying my genset to match my final goal, as well as the inverter and solar charge controller (MPPT, of course) to match my final goal, and add battery and PV through time. What cautions and pitfalls are there in this approach?

I still have a lot to learn about PV. I'm sure I could spend weeks reading every thread here and gain a lot of that knowledge, but can any of you recommend a good, consise resource? Perhaps a book? THere are so many options out there, I don't want to waste money buying a crappy book. I figure you guys would know which ones are good.

Thanks!

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building a system piecemeal?

    "Piecemeal" is not the way to go unless you like having headaches and spending too much money. If you buy what you can when you can you inevitably end up with a lot of components that don't necessarily work well together or fit your eventual power needs. Used equipment does not fetch much on the market, so recouping on losses is not something you want to count on.

    Save up your money, and do the thing in stages.

    There's a couple of different approaches to this, depending on which best suits your particular situation. Which you use is a decision only you can make. Both rely on one important factor: knowing what your minimal power needs are now and what they will be "then". The other difference is with/without panels.

    For instance you can put together a 1 kW hour system now with panels that will just run lights, or you can put together a 3 kW hour system now without panels but with a generator that will run most everything. Almost always you will need a generator anyway, so buying a good one to begin with is a wise investment. And if you have that plan for "later" you can buy the right size gen now and avoid buying it twice.

    What you've done right so far: no electric heating of anything, getting the right size gen to start with, buying the MPPT charge controller that will meet your end needs now. I know this works because I did it.

    The most wrong thing you can attempt: adding battery over time. Mixing new batteries with old is throwing away money as the new ones get "sucked down" right away from trying to bring the old ones up. The more time, the more cycles, the deeper the DOD the faster batteries age. Plus, you always need to add charging capacity if you add battery capacity (assuming the balance was right to begin with). Since batteries should last for years, you don't want to plan a major bank capacity upgrade too often.

    I'd advise skipping on a 12 Volt system. In general they are only a choice where 12 VDC is vital for some reason (as in mobile applications). This means picking between 24 and 48. 24 Volt systems will run most anything, but as you go up in power (either Watt load or Watt hour storage) 48 becomes more attractive.

    This is all pretty vague and generalized I know. It can't be helped: solar installs are highly site & usage specific. Until you know how much power you need to supply it's difficult to figure out how to supply it.

    I know of no book that contains as much information as this forum. Okay, we're a bit disorganized and go off on tangents now and then, but you can't beat the input of dozens of "authors" vs. one for supplying a wide-range of practical experience.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Building a system piecemeal?
    For instance you can put together a 1 kW hour system now with panels that will just run lights, or you can put together a 3 kW hour system now without panels but with a generator that will run most everything. Almost always you will need a generator anyway, so buying a good one to begin with is a wise investment.

    Buying a generator-inverter-battery system with the intention to buy panels later is not a good idea in the US. If you buy the panels and controller at the same time you buy the inverter and batteries, you will receive 30% federal tax credits. The credit on the battery, inverter, wiring, fuses, conduit, meters, etc may be enough to buy the panels and controller. The generator is never eligible for tax credits.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Building a system piecemeal?

    Remember the two cardinal rule of off grid PV. The first is, loads ALWAYS grow with time, it is just the nature of realtiy. The second is, people almost ALWAYS under estimate thier loads, while at the same time they OVER ESTIMATE thier solar potential, in the net.

    A simple rule of thumb is that an off grid PV system will deliver this kind of power, net/net out the inverter: take the name plate rating of the PV, divide that number by two to account for all cumulative system loses, then tke that number and multiply it by 4 to account for the AVERAGE number of hours of good sun one might expect per day, over the course of the year. Ycan adjust that number up and down depending on local conditions, but see also rule #2 above!

    So, 1000 watts of PV is likely to look like this, per day: 1000/2=500*4=2000 WH/day. I can state from long time real world experince that this is a pretty good rule of thumb.

    The final rule, call it the Icarus Rule,,is,, the biggest single cost in an off grid system is the temptation to "Ready, fire, aim!". Unless you start with real life, realistic load calculations, all else is guesswork. Buying anything (or everything) this way, ends up with square pegs and round holes.

    God luck, welcome to the forum and keep in touch,

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building a system piecemeal?
    vtmaps wrote: »
    Buying a generator-inverter-battery system with the intention to buy panels later is not a good idea in the US. If you buy the panels and controller at the same time you buy the inverter and batteries, you will receive 30% federal tax credits. The credit on the battery, inverter, wiring, fuses, conduit, meters, etc may be enough to buy the panels and controller. The generator is never eligible for tax credits.

    --vtMaps

    "Tax credits" assumes you have a certain amount of income on which you will pay a certain amount of tax. The credits reduce that tax. If you just plain cannot afford the PV in the first place the tax credit issue is irrelevant. Since he's trying to do it on the cheap as can be afforded the tax credits probably are not a major factor here.
  • 2twisty2twisty Solar Expert Posts: 182 ✭✭✭
    Re: Building a system piecemeal?

    I wish I had the ability to have all the cash I need to set up the final system at the get-go. So, if I'm willing to sacrifice the tax credit (bad idea) it sounds as though the only thing I can do in any way piecemeal is the PV part of the system, since I need to buy the right gen, right size batteries (or plan to replace them later) and the right size charge controller.

    I've seen many threads about getting hold of used forklift batteries, identifying the damaged cells and putting them back together as a string.

    How feasable is this, and although Ive seen some stories of incredible deals on these things, what's a realistic expectation of price and longevity of these batteries after they're "reconfigured" or "reconditioned?"
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building a system piecemeal?

    If you buy the PV now you may take advantage of the tax credit, but you won't have a functioning system. The good news is the PV's won't deteriorate the way a set of batteries will from just sitting around. The bad news is you better get all you need now, because next year those panels you bought may no longer be available and what is may not be compatible. So again you have to plan in advance and set priorities that suit your needs which only you can determine.

    We'll see if any of the guys who use forklift batteries notice this thread and contribute their experiences with them.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Building a system piecemeal?

    Find threads started by user "adas" -- He has setup a large metal fabrication shop in Hawaii using "recycled" forklift batteries.

    A good forklift battery can last 20 years or more if reasonably well taken care of... And may batteries are "scrapped" when just one or two cells go bad or if the overall battery capacity is reduced by 20% (end of life definition by battery manufacturers) and there is still good life left in the old cells (call that capacity that new "100%" for you and if your system only uses 50% of battery capacity before starting a genset--you should have many years of life left in the used batteries).

    So--you can get good quality less expensive batteries that last 5-8 years (or less if you have an "oops" that takes a bank dead)--Or you can get low cost recycled/reconditioned/tested forklift batteries that may last as long or longer.

    One thing to remember with forklift batteries (in general) is that they have higher self discharge than other batteries (and AGM have very low self discharge). An old forklift battery may have 1-2% self discharge per day--And you will need a larger solar array to replace that amount of lost energy (more solar array, some more fuel for backup genset, etc.).

    I am not a battery engineer and do not have much experience in this area--So I am just giving you my limited experiences and from what I have read here and elsewhere.

    Hopefully, some others here can chime in and add to the discussion.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 2twisty2twisty Solar Expert Posts: 182 ✭✭✭
    Re: Building a system piecemeal?
    The bad news is you better get all you need now, because next year those panels you bought may no longer be available and what is may not be compatible.

    Waitaminnit: I thought you could mix panels with an MPPT controller. I must've missed something critical. Please explain.
  • PhotowhitPhotowhit Solar Expert Posts: 4,253 ✭✭✭✭
    Re: Building a system piecemeal?

    It's used fork lift are doable, but take a good bit of work if you want to reconfigure a battery. I have a moderate sized forklift/traction battery and each of the 12 cells weighs close to 100lbs and is tightly installed in a steel case. "rebuilt" batteries might serve from a distributer and at 1/2 the price of new might be servbicable for a while, but my understanding is they take more liquids as they age and might be more work than they' are worth. I'll PM you a distibuter who sells this type of battery.

    I do think the tax credit is worth understanding an considering. I do think you have the right approach and may be the only way to avoid replacing lots of equipment, but figuring your loads should come first, then a generator of a reasonable size for those loads and a battery and inverter so you don't have to run it all the time.

    Since the battery (even a used battery in my modest size used would run $1300 delivered and an inverter 4K Magnum $1700-$2000, so $3000 so even adding 3 panels of @200watt size at @$1 a watt and a Midnite Classiclite at $500 would be free after tax credit if you have any tax liability at all (OK $1000 of liability over then next couple years) Thats a small number unless you have other deductions. If you have a wealthy friend that would front you the difference and you willing to sign an agreement...

    Right now there is no problem to this from what I've read, only solar water heaters are required to replace 50% of your water heating...
    ...I'm no professional tax person...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building a system piecemeal?
    2twisty wrote: »
    Waitaminnit: I thought you could mix panels with an MPPT controller. I must've missed something critical. Please explain.

    Nope.
    You can use all kinds of different panels on an MPPT controller and get them to work with various system Voltages.
    But an MPPt controller will not allow you to mix panels with widely different electrical specs. There is nothing that can do that.

    When it comes to mixing panels, so long as the right specifications are close enough it works with minimal power loss, regardless of controller type.
    For instance when connecting panels in parallel it is most important that the Vmp be close. Less than 10% difference maximum, less than 5% difference is better. The second check is that the Imp's are not vastly different either, otherwise the higher current panel could cause trouble for the lower one should something go wrong with that.
    With series connections the most important thing is that the Imp be very close. In a series string the current will be held to the lowest rating, so if you put a panel with Imp 8 in line with one with Imp 4 you will lose about half the current from the higher rated panel.

    I am well familiar with this because Sharp no longer makes the 175 Watt panels I have. Even though I can add more Watts to the controller, it becomes a mathematical exercise in finding panels with specs that can be arranged in some mode compatible with the original's 35 Vmp & 5 Imp rating (arranged as a "48 Volt" array; 2S x 2P). One option for me is to parallel the existing panels with a string of four KD140's with a 17.7 Vmp and 7.9 Imp to make a string with a Vmp of 70.8 which is close enough to the two in series Sharps' Vmp 70. The Imp 7.9 would not "overwhelm" one of the other strings' Imp 5 if shorted, although all strings would then have fusing on them.

    See what I mean?
Sign In or Register to comment.