Designing a solar system in rural communities

[TimGoo]

I am designing the components of a solar system for use in off-grid communities in rural India. Following this thread, I have learnt a great deal about the various components and optimising their size for each system and wanted to double check that my calculations are correct and seek advice as to optimising the design of the system, specifically the battery size.

First of all, I wish to design a system to provide solar energy to 20 off-grid households in rural India. I wish to charge batteries, for each household and then rent the batteries to the households. For each household, I will purchase two batteries - one to be charged and one to be used. I will simultaneously charge a battery for each household through the one (or multiple?) solar panels.

At this stage, I am seeking a rough guide as to the equipment required and feasibility of the plan in order to complete financial projections. I am wondering whether the above plan is feasible and how I can improve upon the design of the system.

Specifically, I remain particularly unsure about the sizing of the battery storage. For each household, I plan to have two batteries - one is that being charged and one that is being used. From this forum, I have read that batteries (lead acid in particular) require a minimum day reserve capacity of 5 days. Does that still apply to micro-scale batteries? Second, in order to avoid overly draining the batteries, beyond 50%, is it advisable to design a system with twice the battery storage as required? Third, I am wary of designing a system in which there is a significant mismatch between battery size and panel wattage. Specifically, is it advisable to design a system with a singular large solar panel and charge 20 batteries simultaneously, or instead, perhaps a separate solar panel for each battery (or somewhere in between)?

Thanks in advance!

[Mike90250]

Keep in mind, that one battery in a house. will only run a fan, a LED efficient light and maybe charge a phone or run a computer for a couple hours.
No air conditioning or refrigeration.

People will still flatten and ruin your battery (the light still works a little bit) and you will be moving around a lot of heavy batteries with acid, Someone will eventually drop one and make a mess.

Each battery will be at a different level, so you need one charge controller per panel & battery.

if we invent a 12V, 100ah deep cycle battery and discharge it to 50%, that is 600 watt hours consumed that has to be replaced in 4 solar hours. Assume only 70% recharge efficiency in the battery, you need to harvest 780 watt hours. Over 4 hours, you need about a 250W panel (well aimed). Panels in warm climates loose efficiency, otherwise
you would only need 230W.
That's now one 250W panel, a MPPT charge controller that manages 15 ~ 20 amps, and 2 batteries. For each house. You need racks for the panels, a shelter for the controllers and a way to store and deliver the batteries. Assume a couple failed controllers the first year, and a couple failing batteries.

[Logan5]

think of batteries as cells, 2 volt cell is common, a 12 volt battery is made up of 6X 2 volt cells. a bunch of batteries is a battery bank. 2X 12 volt batteries is a bank that can be 12 or more efficient 24 volt bank. I do not recommend wiring battery banks in parallel, so if you have 2 X 12 volt batteries, you should wire as 24 volts. if you want insist on running a 12 volt nom. system, you should use 2 X6 volt batteries and wire them in series.

[TimGoo]

Thank you Mike and Logan for the advice, much appreciated! The fact that I now realise that I will need a single panel and battery controller for each household is extremely helpful and will now allow me to assess financial projections.

In relation to energy usage, I have estimated that the daily energy use per household will be 0.91kWh. I have based this assumption on the calculated in this report http://www.sciencedirect.com/science...60148113003832.

In relation to insolation, I currently working off the assumption of 5.65kWh/m^2/day, as that is the average sun hours in Jodhpur, Rajasthan between Feb and Oct.

In relation to battery sizing, am I correct to calculate Ah as 910/24 = 38? Or, it is advisable to size the battery as requiring twice as much energy as required so that the battery is discharged to 50%?

In relation to panel sizing, am I correct wattage as = (0.91*1.5)/5.65 = 242W? With 1.5 being the 'fudge factor'.

In relation to MPPT battery controller, I am calculating Amps as 242/24 = 10.

Are my calculations correct and/or am I missing a critical factor that will throw the feasibility of the plan off?

Thanks!

[DanKegel]

I wish to design a system to provide solar energy to 20 off-grid households in rural India. I wish to charge batteries, for each household and then rent the batteries to the households. For each household, I will purchase two batteries - one to be charged and one to be used. I will simultaneously charge a battery for each household through the one (or multiple?) solar panels.

At this stage, I am seeking a rough guide as to the equipment required and feasibility of the plan in order to complete financial projections.

What is the expected use of the batteries in the households? What outputs will they have? Are you offering an entire system, or just part of one?

For comparison:
http://e360.yale.edu/feature/in_rura..._success/2948/
described a system where each house gets two socketed three-watt LED bulbs and a way to charge cellphones.
Another vendor, m-kopa, offers 2 LED bulbs with cables and switches, a rechargable flashlight, a 5 port USB phone charger, and a rechargable radio.

I'm not sure people will be willing to return each day to exchange batteries, and cost might keep you from being able to offer multiday batteries.
Have you looked at m-kopa's model of putting the solar panel right at the home, so nobody has to travel to exchange batteries?

Also, I'm no battery guy, but my impression is that lead-acid batteries require more care than the average user is willing to exercise. Have you considered a smaller, more expensive per amp-hour, but more carefree battery of some sort?

[TimGoo]

Hi Dan, thanks for the feedback.

I am working off the assumption of 0.91kWh/day per household. I am basing that assumption from the table on page 10 on the following report: https://www.dmu.ac.uk/documents/tech...ergy-paper.pdf.

Considering that I now know that I will need a separate panel and battery controller for each household, I will avoid the logistical issue of transporting heavy lead-acid batteries, and instead will employ the 'panel on site' method such as m kopa. Currently, I am aiming to prepare a financial plan that compares the 'panel on roof' method with the micro-grid method and assess which is the more viable long-term option.

In relation to batteries, thus far I have focused on lead-acid batteries but will research others now too. Thanks!