Please check my assumptions and logic

Re: Please check my assumptions and logic

dan,
i'm not sure that'll quite work the way you think it will. you may need to go over the loads you will use and for how long to come up with the watthours of power needed to be used in say the weekend or 2 days. the usable power from the batteries over that 2 day period will be 105x12=1,260 watthours. over 2 days that will be an average hourly draw of 1,260/48=26.25 watts. is that enough for your needs? the battery capacity would be enough to run your inverter at 600w for 2 hours!
also note that you may need more pv to charge those 2 batteries as a good rule of thumb is to have between 5% and 13% rates of charge to the batteries. 210ah x .05 = 10.5 amps minimumly from pv and could go as high as 27.3 amps at 13%. seeing as how it will have the opportunity to charge over several weeks then you could stay on the low side of the charge rates and you may even get away with that 1 pv as we also say 3% as an absolute minimum with no loads on and given enough time to charge the batteries. 7.39a/210ah=3.5%. for more batteries employed, more current to charge them must also be employed.
also note that if you think you'll get 478 watthours (not watts) a day from that pv the weekly figure at best would be 7x that or 3,346wh and let's face it it will be cloudy or rainy on some of those days further reducing the net wh you will reap from the pv.

Re: Please check my assumptions and logic

A quick look, and the first thing I can think of is your loading. With judicious use of cfls for lighting, especially for the motion lights you could reduce your lighting load a bit.

Second, there are some 12vdc ceiling fans that draw between .5 and 1.2 amps which would reduce your fan loads a bit as well.

I don't know it you are pumping from the lake or a well, or what head (pressure) you are pumping to, but you could possibly reduce your water pumping load a bit. ( I use a shurflow 12/24vdc submersible that pumps to 60 psi (more in fact) and draws ~3.5 amps/12vdc to pump 1 gal/min into 60 psi.

I guess my point is, as in all RE, the cheapest energy investment is in conservation (Reducing the load) Then building a Pv system becomes much cheaper and fulfills more of the load(s)

Icarus

Re: Please check my assumptions and logic

dan,
you are right that i would be reluctant to say 1 130w pv will suffice as it would be close for the 2 batteries you initially propose. if you up the amount of battery capacity to 3 of those batteries the charge needed from the pvs will also need to be increased so that could mean 2 130w pvs. with your current requirement of 1700wh that means the batteries have to hold double that so that you don't exceed 50% depth of discharge or 3400w total capacity. 3400w/12v=283.3 amphours of battery capacity.
as was brought up by icarus, that if you can conserve and use less power that it will make a big difference and if you manage to conserve enough it could make the system you initially proposed work.
the batteries will be in parallel as you stated you won't be there for several weeks at a time to switch the individual batteries for charging. also know that you could add to the 130w pv if the initial pv system isn't enough for you, but when it comes to the batteries you should get the capacity you need now as adding later isn't advisable unless you'll know quickly. if you wish to learn more of the why not add a year later, there are threads on it in the forum as it comes under mixing different batteries or capacities of which you shouldn't do. you don't have to add another of the same pv to add to the pv system as a 90w pv could be added to a 120w pv when operating in parallel as long as the vmp is similar. cross that bridge if and when we get to it.

Re: Please check my assumptions and logic

Danny,

A couple of observations.

Before you buy or install anything. (If it isn't too late!)
spend a bit of time reading and learning about the detail of PV systems. To do so would avoid a lot of Ready, Fire, Aim, and thereby reinventing the wheel. Many of us here have made a lot of expensive mistakes over the years and perhaps you can avoid some, (probably not all!) of them.

My initial observation is that loads increase over time, once you realize how nice it is to have power 24/7. As Neil suggests, adding panels later is an easy option, but if your controller is too small you will end up buying twice. Same for inverters. Batteries can be added later but there are significant consiquences to doing so. (See related posts.)

If I was starting over, I would spend the extra for a MPPT controller upfront, and then buy and oversized battery bank, and then add panels as needed.

I would also buy a good charger depending on how you are going to power it. For a small system like this using a small generator the Xantrex TrueCharge 20/40 series works great.

I know that there is considerable discussion on these boards regarding the ratio between panel capacity versus battery capacity. I personally feel the debate is a bit over blown. In a system like yours that will have days to charge between discharge cycles I think having more battery and less panel is a good way to start. (Of course there is really no such thing as too much panel! I always want more!)

You will need a fuse between the panel(s) and the controller, between the battery and the load(s) In a simple system, you wouldn't need a breaker box, but it might be nice to start our with one, instead of auto type fuses.

As to grounding. I live on a lake in the Canadian shield where we have little or no soil. Grounding anything electrical is a challenge. What I have done, and it has worked for years with several lightning strikes over the years to proof it, is run a ground wire at every proper ground location to the lake, and then a dozen feet or so under water. The generator neutrals, the fuse/breaker ground lugs, the panel frames etc.

Enjoy the process, and learn along the way,

Icarus

Re: Please check my assumptions and logic

i concur to go bigger if you can. i did indicate that reducing your loads would make the 2 batteries with a 130w pv more workable and you can always add to the numbers of pvs if it isn't so. this also comes in handy for a reserve capacity, just in case, and your lighter loads will allow a longer lifespan on the batteries.
go with a controller that not only will have expandability for more pvs, but will have a float voltage setting along with having it capable of a battery temperature sensor as we always recommend using the battery temp sensor. in the case of mppt controllers it is advisable for you to read up on them before deciding to get one of them as they are usually for larger pv systems than you are going for, but in some cases it is feasable if you wish the extra costs involved and they do help recoup some losses for an average of about 10%.
as to the capacity of the inverter it doesn't hurt to have that extra 300w from the 600w model that gives you the room for future expansion with a slight increase in cost now and not having to sell the smaller one at a cheaper cost to recoup later.

Re: Please check my assumptions and logic

Dannyo
I'm curious about your boat lift, you say that it uses 1452 watts and your proposed inverter is a Samlex 600, it seems to me that you might have a problem using the boat lift with that size inverter. Just a thought. Maybe I misread your posts. Anyway the rest of your system will probably work just as you have proposed, with just a few tweeks along the way.
Larry

Re: Please check my assumptions and logic

My previous post overlapped yours. You'll never regret having "too much" panel capacity!

Icarus