Help Designing Backup Power System for Home Use in Africa

mocha
mocha Registered Users Posts: 3
I'm starting a new business installing backup systems electric power systems for homes in Africa connected to a grid system but with rolling blackouts. This is a situation where subscribers may receive grid power for just a portion of the day or every other day. Ideally, this same system would also be used as an off-grid solution where a solar array and/or a generator would be used to recharge the battery for home use or for telecom applications.

I need a reliable system as a solution, but must balance that with cost since for many people it will be a prohibitive cost. So any opportunity to purchase used or salvage, or purchase cheaper components from China or elsewhere would be welcome.

We can start with a 1500Watt and 6000Watt optional configurations for the charger inverter. I don't want to be concerned about incorporating a solar array at this point, but as an upgrade option. For the battery banks I want to consider one configuration of 200Ah at 24V which can be stacked in parallel to produce more capacity.

Things to consider are that the batteries will be used in an environment where the average temperatures can exceed 90 degrees F for three months of the year and gets hot and humid for other parts of the year. My concern is humidity and/or water evaporation in the batteries and the effect on battery life.

I'm asking for help in identifying the correct components and model numbers for the charger/inverter and batteries and where to find the best prices. I would also welcome your feedback and caveats based on your experience putting together similar systems.

Thank you.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help Designing Backup Power System for Home Use in Africa
    mocha wrote: »
    I need a reliable system as a solution, but must balance that with cost since for many people it will be a prohibitive cost. So any opportunity to purchase used or salvage, or purchase cheaper components from China or elsewhere would be welcome.

    Obviously, I cannot help you with sources in Africa--Sorry.

    But for batteries, do you have access to used forklift type batteries (near a port or warehousing district)? User "adas" has been pretty successful getting used/scrap forklift batteries, removing/bypassing failed cells and using the rest to run his off grid mfg. operation in Hawaii. Do a search on his name for threads he has started.
    We can start with a 1500Watt and 6000Watt optional configurations for the charger inverter. I don't want to be concerned about incorporating a solar array at this point, but as an upgrade option. For the battery banks I want to consider one configuration of 200Ah at 24V which can be stacked in parallel to produce more capacity.

    Those are pretty large inverters for relatively small battery banks. Nominally, we would be suggesting using 200 AH of 24 volt battery bank for every 1kW of inverter output capacity for a "reliable" system.

    To get an idea of the capabilities of such a system (200 AH @ 24 volts for a 1kW output inverter). Say they use an average of 500 watts of energy and the battery bank is only discharged by 50% (for longer life--and/or if you use salvage batteries with less than new capacity):

    200 AH * 24 volts * 0.50 max discharge * 1/500 watt average load = 4.8 hours of backup power usage per cycle

    Does that seem like a "balanced" system design for you?
    Things to consider are that the batteries will be used in an environment where the average temperatures can exceed 90 degrees F for three months of the year and gets hot and humid for other parts of the year. My concern is humidity and/or water evaporation in the batteries and the effect on battery life.

    Forklift batteries tend to use more water than other types--So, you could very easily have significant water usage costs (one gallon ore more per month for a "small" system?). The standard is to use distilled water, but using filtered rain water (after the roof has been first rinsed of dust/bird droppings/etc.) can be used as a source in regions with poor access to distilled water.

    Using well water (without distillation or de-ionizing filter) will probably give the batteries a pretty short life.
    I'm asking for help in identifying the correct components and model numbers for the charger/inverter and batteries and where to find the best prices. I would also welcome your feedback and caveats based on your experience putting together similar systems.

    Flooded forklift batteries are going to be the most rugged--But even those types are not going to like being discharged to "dead"--And other typically available batteries (truck batteries are used quite a bit in some places) are going to like being deep cycled even less. This gets into how to protect your investment in batteries from people that otherwise might not care if they leave the system on/drawing heavy power until the batteries are dead... Do that more than a few times, and you will have a dead battery bank.

    Adding a Battery Monitor (Victron is a good European brand) would be nice to let people see how much energy is in a battery bank--But they will probably still ignore its readings and still take the battery bank dead when needed.

    Some Battery monitors have alarm outputs that could be wired to an "inhibit/remote on-off circuit" for the inverter--You could setup your batteries to self protect. Downside is Battery Monitors are not cheap, and people will bypass the alarm circuit if they need power.

    You could use a simple electronic circuit to monitor battery voltage and cut the inverter if the bank voltage falls to ~21.0 volts (temperature and load dependent) for more than a few minutes...

    But, battery monitors and simple voltage controlled switches all have their accuracy issues.

    So--as you can see, my concern is the battery bank investment. If you "lease" the batteries to the end user, they have no reason to take proper care of battery bank and avoid over discharging (assuming you take care of the battery watering and maintenance).

    The normal solution would be to sell the batteries to the customer so if they miss-use the battery bank--It is money out of their own pocket.

    And if you are limited to "truck" batteries in your region--They are even less rugged regarding deep discharge and you may only get 1-2 years from such a battery bank (or weeks if a customer abuses the bank).

    What are your thoughts on the issue?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Help Designing Backup Power System for Home Use in Africa

    Tough problem, expensive solution.

    I'm glad you are able to include a Generator option. For 5 years, that is a good beginning, if someone will own the system longer, adding solar would be a good addition.

    If the local electrical utility allows grid tie, so that the solar can feed the grid while it is on, that is a grand bargain for the customer.

    You need to select the battery bank to either be large enough to endure through the entire rolling blackout, or just large enough to get the generator started. Then the generator can carry the load and recharge the batteries.

    A 24V system would be the lowest voltage, and I'd suggest a 48V system, if the parts are at hand.

    Keep the generator as small as possible, to carry the loads & recharge. Using too large of a generator just wastes fuel. The new Auto-throttle inverter generators match the engine RPM to the load demand and use the least fuel. There have been many discussions about generators, Power Factor, Chargers.

    Adding solar PV will be a major expense, which can be somewhat mitigated if the utility allows Grid Tie. But if the power goes off in the evening, you will still need the generator to run.

    For short blackouts, you can use an inverter with a built-in charger, so the grid can recharge the batteries.

    And each installation will need it's own engineering design ! Have fun.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mocha
    mocha Registered Users Posts: 3
    Re: Help Designing Backup Power System for Home Use in Africa

    Thank you for your response.

    To clarify some of the logistical questions raised, I live in the USA so the idea is to source all the components from here or elsewhere. So issues like access to used truck or forklift batteries should address the US market. In other words, where can I get used batteries here in the USA? I will definitely research posts by "Adas" and the work he has done with salvage parts.

    Regarding caring and maintenance of batteries, I will be selling them outright and provide a service for maintenance. Distilled water is also readily available. I don't plan to lease the batteries or systems to my customers.
    You could use a simple electronic circuit to monitor battery voltage and cut the inverter if the bank voltage falls to ~21.0 volts (temperature and load dependent) for more than a few minutes...

    I was hoping there was a built-in charger controller for the inverter that would handle battery charging without having to invest in a separate circuit. For example, set it to a 50% discharge depth then shut off when the threshhold is exeeded. So when the inverter specs say it has a built-in solar charger controller this does not control the inverter output?

    Does a solar charger controller provide overcharging limits on AC charging of the batteries? I like the idea of employing a circuit for self protection of the batteries, but I would have thought this would be integrated with the inverter.
    200 AH * 24 volts * 0.50 max discharge * 1/500 watt average load = 4.8 hours of backup power usage per cycle

    Does that seem like a "balanced" system design for you?

    This is a very helpful equation. So in my case does that mean a 4-way battery bank (200Ah @24V each string) could only power a sole 1.5 KW refrigerator or deep freezer for only 6.4 hours? Somehow that does not seem to be a very economical solution. We would need additional battery power just to be able to turn on some lights. So I must say it doesn't seem to be a very balanced system.

    Your thoughts?
  • mocha
    mocha Registered Users Posts: 3
    Re: Help Designing Backup Power System for Home Use in Africa
    If the local electrical utility allows grid tie, so that the solar can feed the grid while it is on, that is a grand bargain for the customer.

    Unfortunately, tie-in to the grid is not an option.

    You raise an interesting point about using a generator to charge the battery bank when there is no grid power available. My question is what is the trade-off between using the generator as the backup source versus the inverter, especially when there is no solar option available? Which is more efficient? has anyone done this analysis based on the prevailing cost of fuel and the inherent efficiency of batteries versus generators?
    A 24V system would be the lowest voltage, and I'd suggest a 48V system, if the parts are at hand.

    What is the advantage of a 48V system over a 24V one? Is it more efficient because if the lower current required?
    And each installation will need it's own engineering design ! Have fun.

    It now seems to me that a hybrid system consisting of BBU, AC charging and generator would offer the best trade-off for situations where the blackouts last for more than a couple of hours. The battery backup would kick in first. When the battery reaches 50% then an auto-throttle generator would take over to support the load AND charge the battery until AC power returns, while adjusting to the load demand. Would this be considered to be a good balanced design? My confusion is that if a generator is required anyway then why have a battery there at all? What is the benefit of having both?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help Designing Backup Power System for Home Use in Africa
    mocha wrote: »
    Thank you for your response.

    To clarify some of the logistical questions raised, I live in the USA so the idea is to source all the components from here or elsewhere. So issues like access to used truck or forklift batteries should address the US market. In other words, where can I get used batteries here in the USA? I will definitely research posts by "Adas" and the work he has done with salvage parts.

    Shipping batteries is going to be difficult (heavy, filled with acid, and for used batteries, if they are in shipment for over 1 month or so, they will start to sulfate (flooded cell/fork lift batteries should not sit for more than a month between full charges--AGMs can go upwards of 6 months, but they are more expensive and possibly not as rugged for these applications).
    I was hoping there was a built-in charger controller for the inverter that would handle battery charging without having to invest in a separate circuit. For example, set it to a 50% discharge depth then shut off when the threshhold is exeeded. So when the inverter specs say it has a built-in solar charger controller this does not control the inverter output?

    There are quite a few inverter/chargers with automatic transfer switches--And many of these inverter/chargers have some pretty nice programmable battery chargers (is more difficult to get a programmable stand-alone battery charger).

    However, I do not know of any that use a Battery Monitor (current shunt+timer) to estimate battery state of charge and let you set a "shutdown" value (i.e., 50% SOC). It should be possible--and probably some of the inverter/chargers have enough hardware/brains to do that--But they have not (again, to my limited knowledge).

    There are a fair number of inverters that do have the ability to shutdown on battery bus voltage--But I am not sure how they exactly implemented (i.e., 5 minute/30 minute timers, a few may have current offset estimates). The higher end inverters are going to have more configuration options (but cost a lot of money too).

    There are quite a few inverters that will auto control a genset based on battery voltage/time.
    Does a solar charger controller provide overcharging limits on AC charging of the batteries? I like the idea of employing a circuit for self protection of the batteries, but I would have thought this would be integrated with the inverter.

    More or less, all of the Solar Charge controllers today each behave as if they are the only power source on the battery bank. And respond according to the voltage/time curves they observe. A few can have the controllers coordinate operation (all in bulk, all in absorb, etc.). And a couple have data buses to share information and control--But at this point, there is not much that you can adjust down deep in the programming.

    Talking with folks at Midnite (boB, Robin, Ryan/Halfcrazy) or calling up somebody at Midnite may give you more ideas/options. The other companies (Outback and Xantrex/Schneider) certainly have capable hardware and software--But you may have difficulties getting "off book" type of answers.

    This is a very helpful equation. So in my case does that mean a 4-way battery bank (200Ah @24V each string) could only power a sole 1.5 KW refrigerator or deep freezer for only 6.4 hours? Somehow that does not seem to be a very economical solution. We would need additional battery power just to be able to turn on some lights. So I must say it doesn't seem to be a very balanced system.

    A refrigerator/freezer usually will only run 1/3rd to 1/2 of the time--So they will "run" 2-3 longer than their average operating Watts would indicate:

    1,500 WH per day Fridge / 24 hours = 62.5 watts average power

    But its operating Wattage (to run the pump) may be ~120 watts. And it can draw 400-600 watts a couple times of day if it has automatic defrost heaters.

    Normally, we assume a refrigerator that is not opened could go ~24 hours or so without power--So it is up to the customer to decide if they want to pay for 10 hours of backup power or not.

    And--that is the problem with batteries... The do not really store that much energy for their size/weight/cost.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Help Designing Backup Power System for Home Use in Africa

    You will want to source the heavy batteries in Africa. Try the golf course, or a warehouse and see where they get the batteries for the golf carts or forklifts. Forklift batteries are a giant 3,000 pound cube of lead acid. You are not going to move one by hand.

    Batteries can provide power instantly, when the grid goes down, and the generator takes about 30 to 60 seconds to start up and get to a stable speed.

    If no grid-tie, adding solar to the mix, will be a expense that seldom gets used.

    You could use the Xantrex XW series inverter charger, with a minimal battery bank, and a generator auto start module. When the batteries deplete, the command is sent to start the generator, when Grid returns, or when batteries are full, generator shuts off.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,