Work in progress which control charger, inverter ?

SystemSystem Posts: 2,511 admin
Hello to all that use this forum and to compliment the forum for all the useful information. My plans are to build a system that will ultimately allow me to cut my monthly electric bill as much as I can. Im hoping I can call on the knowledge of those that have gone thru the trials and errors to help me save a few $$ in setting up my system. I would preffer to buy the right items the first time instead of buying lesser quality items several times. I just recently purchased my first two panels Suntech STP175_24Ab-1 so I will start off with 350 watts of power ( plans are to purchase 4 more of these in the near future to end up with a total of 1050 watts ). What I need is some insight as to what control charger would you suggest to handle 6 or 12 volt deep cycle batteries near 200ah either gel or AGM configured to produce 24v and next what pure sine wave inverter would you suggest in the 2500 watt range?
Im a newbie at this so any guidance or information would be greatly appreciated,

thanks
Cody's

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,022 admin
    Re: Work in progress which control charger, inverter ?

    Welcome Cody's!

    For larger controllers, look at the Outback and Xantrex family (80 amp max, or 60 amp max respectively). Midnite Solar is also supposed to be coming out with a new MPPT solar charge controller this summer--may be a very interesting unit.

    You mentioned saving money... Just as an FYI--Off grid solar power (involving batteries) will never save money over the cost of grid power...

    Roughly (all numbers are very rough guesses based on US pricing--your system costs and available solar will vary), you are paying around $0.10 to $0.30 per kWhr. A full off-grid system (battery--Off Grid)--you will probably pay around $1.00 to $2.00 per kWhr... Assuming 20 year system life, battery replacement every 7-10 years, cost of system components, etc.).

    While, an off-grid capable system is very nice if your power is not reliable (storms, ice, etc.)--a Grid Tied system (with government rebates/tax credits) will produce power much more cheaply... In fact, in some states (like Northern California with Tiered Power Rates that are $0.38-$0.58 per kWhr at the peak power usages) Grid Tied can save money because it is so efficient and does not have the costs associated with batteries (~$0.14-$0.30 per kWhr or even less--depending on your local sun conditions, tax credits, etc.).

    Otherwise, if you have been lurking for awhile--the answer is to spend your time and money on conservation first. Almost always, adding (lots of) ceiling and wall insulation, double pane windows, CFL lighting, new high efficiency A/C, secondary hot water from A/C heat pump, etc.--will pay off much better than just throwing solar panels at the problem (it is cheaper to conserve power than to generate it).

    For home use--a Kill-A-Watt meter is well worth the time and money to check your existing 120 VAC 15 amp max appliances.

    Normally, we do not recommend adding to systems (starting small and adding panels and batteries)... Batteries age and adding more batteries in parallel may end up with the newer batteries not lasting much longer than the original set.

    Also, small systems require different controllers and, usually, different battery bank voltages (small systems tend towards 12-24 volts, large systems tend towards 48 volts)... So you end up needing to reconfigure the solar panels and battery banks 1/2 way through.

    Now--many people do start with a small system to learn--but realize that you may use little of the old system when building out your new/large system. Even solar panels are a bit of a pain to mix--the Vmp and Imp ratings of the panels change over time--and it can be difficult to mix the old array with panels of new design/manufacture (need to match Vmp and/or Imp for proper operation).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Work in progress which control charger, inverter ?

    i'm a bit confused on what battery voltage you are planning for and is the bank to be about 200ah or the batteries you plan on using? how were your planning to wire the pvs, parallel or series and parallel? what you are hoping to generally do and run with it can possibly have some bearing on what we might say.
  • System2System2 Posts: 6,290 admin
    Re: Work in progress which control charger, inverter ?

    I plan to run the 2 panels I have now in series ( suntech STP175s-24, Vmp 35.2V, Imp 4.92Amp ) ( in the near future I plan on purchasing 4 additional panels giving me a total of 1050 watts) wanting to run battery bank at 24v using either [email protected] or [email protected] for a total of 1200-1400ah which ever battery offers the better setup for the $$, also wanting to drive a 2500 watt pure sine wave inverter. Maybe my setup ( thoughts ) are all wrong and someone could advise on a better way ??
    What charge controller and inverter can you suggest for a project like this, that surely will expand in the future.

    My intention is just like everyone else here to cut down on what I am paying to the gridmaster each month.

    hope this clears things up a bit

    thanx
    Cody's
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Work in progress which control charger, inverter ?

    whoa, that's a big battery bank. the bank would need a 5% charge rate minimally to sustain it. that gives a range of 60-70 amps as a minimum for the ah range of 1200-1400ah at 24v. with all 6 pvs you will be somewhere in the range of about 30 amps tops. if you can't cut back on the battery bank ah ratings then you better figure on getting at least double the number of pvs you are proposing. odds are the ah can be reduced and conservation used to keep the usage in check so as to allow the proposed 6 pvs to be used. that would be cutting in half what you thought you would need in ah capacity though and i don't know if you can conserve that much.
    maybe you can explain the need of the ah capacity you listed? although, i state 5% for a charge rate, keep in mind that that is a minimum and something like 10% might be a better goal. this affords a quicker charging of the battery bank and would represent roughly a 10hr rate to recharge as oposed to the 5% being roughly a 20hr rate to recharge. if you get 5hrs of full sun per day a 10hr rate needs 2 days to recharge the batteries with the 20hr rate needing 4 days to recharge the batteries. but that would be from 0 soc and we don't recommend lower than 50% so the number of hours needed would be halved. what's worse is that does not account for seasonal solar intensity lows or cloudy periods that would hamper the solar power harvested. you have to plan on being able to put back what you use and thensome for other losses.
  • BB.BB. Super Moderators, Administrators Posts: 32,022 admin
    Re: Work in progress which control charger, inverter ?

    What you are planning--from what I can see... For every $1.00 you reduce in grid costs, you will gain $10.00 in costs operating an off-grid system... It does not save money...

    If you want to save money, then you should look at a Grid Tied system (solar panels, Grid Tied / Utility Interactive Inverter)... Much more energy efficient (from solar panels to useful power) and saves the whole cost of a battery bank and battery chargers.

    If you want a solar powered backup system, you should look at a Hybrid GT/Off-Grid system--It can do off-grid (and solar/generator) backup if your power fails--and you can save some money on batteries by sizing a smaller battery bank and the fact that the batteries are no cycled during normal operation (when the utility grid is up and running). Take a look at the Xantrex XW system... Still not "cheap" but may be closer to your goal of reducing energy (or at least stabilizing) costs--and providing some emergency power backup.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Work in progress which control charger, inverter ?

    I was a little aggressive on the battery bank ,what would it look like cutting it in half say to 600ah.. what controller for the system ? what about the inverter ? guess what Im looking for is name or model number to look at and evaluate.....
  • StorminNStorminN Registered Users Posts: 12
    Re: Work in progress which control charger, inverter ?

    Cody, how much power do you use now? How many kWh per month on your bill?

    -N.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Work in progress which control charger, inverter ?

    did you buy this battery bank yet? if not then a smaller system would most likely be in order, but do you need battery backup or not is the real question? more efficient and less cost would be realized with straight grid tie and no controllers will be needed in this system. if you need some battery backup this can be done too as a grid tied system with battery backup and supplemented with the solar pvs. also note that controllers generally handle more watts at higher battery output voltage levels because the current capability of the controllers stay the same. this means 2x the voltage x the current = 2x the wattage.
    again, before i ramble on here too far, did you buy these batteries yet and do you need a battery backup system because of power reliability issues?
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