Advice on Batteries etc

cokebbehcokebbeh Registered Users Posts: 8
Hello All,
I purchased two 205 Watt panels - specifications below. I want to use this in Africa to run a few bulbs, a fan and possibly a color TV. Any advice on what other things, brands, specification I need. Battery (12V or 24V), Inverter (what size), charge controller ( what brand) anything else I need to buy to make my system work.

SUN-A-205-fa2, 205 Watt Solar Panel

205 watts
11.15 Imp
18.4 Vp


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice on Batteries etc

    You're sort of going about it backwards, as it were. :p

    You need to get a handle on your loads or potential loads first. That will tell you what you need in terms of inverter capacity and battery bank size which in turn will determine what you need for panels and a charge controller.

    However, going about it the other way says you've got 410 Watts (peak) of panels. So if you can determine how much sun you can get (hours of direct/ 'direct equivalent') you can make a rough estimate of how much power you'll have available which will determine what you can run.

    Most systems have an over-all efficiency rating of about 80%, although some would say it's closer to 50% (depending on location). Let's assume you can pull an average of 70% of the panels' rating over five hours: that's 410 * 70% = 287 Watts for 5 hours = 1435 Watt/hours per day. How you use that is a function of how long you leave what on drawing how much power.

    To do the same kind of 'backwards figuring' we can get a rough estimate of how much battery bank those panels can keep charged: 287 Watts/12 V = probably 24 Amps of charge current, which is 5% (min) of 480 Amp/hrs of battery. Keeping the Depth Of Discharge to 25% (you don't want to draw down below 50% maximum - it shortens battery life considerably) you have 120 Amp/hrs * 12 V = 1440 Watt/hrs. Just about the same figure from the panel calculation.

    As far as choosing an inverter, it has to be capable of handling the highest total wattage you expect. Given the specs on the panels and the rough calculations, I'd say you're looking at a 12 V, 2000 Watt inverter as being practical.

    Please note that these are rough, rule-of-thumb calculations that don't include efficiency losses, wire sizing, fuse numbers, and all the other details that go into a well-planned system. But you have to start somewhere.

    I suggest you try to get a handle on your load potential, and come up with some idea of how much sun you're likely to get.
  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Advice on Batteries etc

    If you could power everything you need with 12V DC you could avoid using an inverter. You can get 12V compact fluorescent lights, 12V fan and even small 12V TV. If you are ok with that, you can get TriStar TS-45 charge controller, but you don't get MPPT feature.

    If you only need 120V AC or 220V AC for small loads, you can get SunSaver 15A MPPT controller and wire your panels in series for 24V DC system. This will allow you to use both of your panels with that controller. At 12V it will only let you use one of your panels. Then you need good sine wave inverter. What voltage and frequency do you use in your country?

    If you don't mind spending $500 on charge controller, then get Outback Power FM60 MPPT 60 Amp unit. It will allow you to easily add more panels later.
  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Advice on Batteries etc
    You're sort of going about it backwards, as it were. :p

    I did the same thing. I could only afford to get 2 panels first, then I added loads based on my production. Kinda backwards, but it works for me (177KWh since March).

    Batteries will be second most expensive item. You will need at least 200Ah for 12V (100Ah for 24V), or 2400Wh of battery capacity. That will work, but it's a bare minimum, and you will want to increase capacity within a month of using your system. I recommend getting two FullRiver DC240-12 240Ah 12V batteries. You can wire them in parallel for 12V 480Ah or in series for 24V 240Ah. These are Chinese-made batteries, but they are good quality and cheapest. I have used their 100Ah batteries for 2 years until I upgraded to 850Ah (12V) of used Lifeline AGMs. You can use regular flooded batteries, but you will lose 20 - 30% of your solar energy harvest into these batteries because of their lower efficiency (haven't tested that myself, I always used AGM type)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice on Batteries etc

    I think you'll find that the maximum current potential on those two panels into 12 V would be ~35 Amps so the Sunsaver 15 won't work. If you've got good solar exposure, a PWM type controller will work fine. Something like this:

    Don't discount the value or power of flooded-cell batteries. The main drawback with them is a need to keep an eye on the electrolyte levels, especially in a hot climate like Africa.

    One of the most significant factors in choosing any component is; what can you get, and for how much?
  • BB.BB. Super Moderators, Administrators Posts: 32,212 admin
    Re: Advice on Batteries etc

    The SunSaver MPPT from Morning Star will work just fine with 1x 205 Watt panels at 24 VDC battery bus (under 15 amps at 24 VDC).

    The SunSaver MPPT especially needs the Remote Battery Temperature Sensor option, and many other controllers too--you should make sure which ever controller you purchase---that you get a RBTS.

    I personally like efficient AC powered devices over 12/24 VDC devices--but in the end, you need to support what is most often used in your installed location and will be understood and taken care of by the end users...

    Choosing 12 volt vs 24 volt is an issue--once you choose, it will affect everything else. Inverters, Charge controllers (charge output is in amps, a 24 volt battery system can take 2x the amount of wattage vs a 12 volt battery system from the same controller).

    The best small 12 volt input True Sine Wave inverter is the MorningStar SureSine 300 watt (600 watt peak) unit--but you may have problems finding a 230 VAC 50 Hz unit in the US -- and it may be too expensive to justify if purchased overseas.

    Other good quality inverters are here (recommending True Sine Wave--not Modified Square Wave if at all within your budget). There are a couple Inverter FAQ's near the bottom of the page.

    Depending on the batteries you purchase--Flooded Cell vs AGM--your local supplier will probably limit your choices (you can fly/ship AGMs filled, or dry charged flooded cell batteries--but expensive).

    Maintenance wise, the AGM's are very nice but sensitive to overcharging. The Flooded Cells are nice--1/2 the price and can be refilled with distilled water (or filtered rain water) and are good "training batteries" because most users will kill their first bank.

    Monitoring... The MorningStar MPPT 15 controller does not have any LCD panel meter--so you will want something to measure its ouput (somebody can talk about usefulness of remote MS LCD display vs having no display?).

    Flooded cells, you will want/need a hydrometer. And you can look at getting special battery caps that can reduce the amount of "water used" (and acid mist that gets out and corroids your wiring).

    AGMs (and really for flooded cell) -- you should get a Battery Monitor. Will give you a XX% state of charge reading of how much power you have in the battery and tell you how fast you are charging or discharging your battery bank. The end user will have a very easy rule--if <50% state of charge; turn off the loads and/or start the generator.

    Tristar is a good lower cost meter. The Xantrex models are good higher end meters. They are not cheap--but will save you from killing your battery bank in months, instead of getting 5-8+ year life from your battery bank.

    In the end, defining your power needs and setting up your system so that it is not "deficit charging" (never getting back over >75% state of charge for days to weeks at a time) is important. Between deficit charging (running battery near dead) and running them dry (overcharging / not keeping electrolyte up with distilled water) are probably #1&2 battery killers.

    I am a big believer in locally sourcing components where reasonable. If you will be able to get parts/support from the US to Africa in a timely fashion... The lower prices here are nice.

    Depending on the sun available for your area--you will probably get 5-6+ hours of sun in the summer. Using Flooded Cell batteries with an AC Inverter--assume ~52% overall efficiency (will be higher when the batteries are new, can drop to near 52% when the batteries are old):

    2x 205 Watts * 5 hours of sun * 0.52 = 1,066 Watt*Hours per day (long term average)

    If you have a few lights, a small TV, etc... You add up the average watts used and the number of hours each will be on per day... Say you want to use 200 watts average:

    1,066 Watt*Hours from system / (200 Watts AC load) = 5.33 hour per day

    Conservation is obviously important with any Solar RE system. As is having a backup generator + good battery charger (if power during winter/bad weather is a requirement).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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