Solar for Tanzania

Anosha

Hi, I am looking to set up a solar system for a small Maasai Boma/house to run a small fridge, laptop, small LED TV for maybe 2 hours per night, charge several phones, and several LED lights.  I am a total technophobe, so know nothing.  HELP please.  Normally we do get a lot of sun each day and am considering adding a wind generator to supplement in the rainy season.  All advice gratefully received.

BB.

Welcome to the forum Anosha,

Ideally, you really need to measure your power usage... xxx Watts peak power (sort of like km/hr), and yyyy Watt*Hours per day (like km driven).

A good device is a Kill-a-Watt (brand name or similar) Watt*Hour meter... Example of some:

https://www.amazon.co.uk/s?k=kill+a+watt+meter+uk&sprefix=kill+a+watt
https://www.amazon.co.uk/s?k=230+vac+power+meter&crid=1MLMQ7SCDZ0BO

Just be aware--A refrigerator (even a small one) really pushes the energy usage up from a "small" to a medium size solar power system (which is not "cheap").

What you are looking is (just examples). What a Peak Watts calculation looks like:

• 600 Watts minimum starting surge for "average" AC refrigerator compressor
• 30 Watts typical for mid-size laptop computer
• 2x 13 Watt LED lights = 26 Watts
• 15 Watt charging phone or tablet computer
• 600+30+26+15=671 Watts max load
• And for a standard (simple) AC compressors, probably need a 1,200 Watt minimum AC inverter to reliably start/run a fridge (even a small one).

I don't know what is available in your region, but see if you can find a 12/24 VDC battery powered refrigerator... DC refrigerators (and more modern "inverter refrigerators" can be very nice for solar... Don't need an AC inverter, or can use a much smaller AC inverter (inverter refrigerators tend to have very low starting surge).

And for Watt*Hours per day--This is to size your battery bank. A Watt*Hour meter (or for DC systems, a Watt*Hour / Amp*Hour meter) tells us how much energy you use in a day. Just some guesses:

• 900 Watt*Hours per day small/efficient refrigerator
• 30 Watt computer * 4 hours per day  = 120 WH per day
• 2 x 13 watt LED lights * 3 hours per night = 78 WH per day
• 15 Watts * 2 hours phone/tablet charging = 30 WH per day
• 900+120+78+30=1,128 WH per day

A typical flooded cell lead acid battery bank, would suggest 2 days of storage (for bad weather) and 50% max planned discharge (for longer battery life):

• 1,128 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/12 volt battery bank = 442 AH @ 12 volt battery bank
• OR using 6 volt @ 220 AH "golf cart" batteries, => 2x batteries in series (12 volts) and 2x parallel strings => 440 AH @ 12 volt batter bank

Here is where we get into an issue... Simple refrigerator compressors take a lot of power to start (surge). And a 442 AH @ 12 vol battery bank will supply around a 1,200 Watt max AC inverter. If you can find a DC refrigerator or an "AC Inverter" type refrigerator--That can help ease the peak surge current draw on your system.

Anyway... The rest of the calculations for solar panels. Two calculations, one based on Minimum rate of charge and the second based on how many hours of sun per day you get... Fixed array somewhere in Tanzania:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Dodoma Tanzania
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 84° angle from Vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.79	5.83	5.80	5.71	5.70	6.50
Jul	Aug	Sep	Oct	Nov	Dec
6.76	6.71	6.70	6.67	6.54	6.07

• 1,128 WH per day * 1/0.52 off grid AC lead acid system eff * 1/5.71 hours per day of sun (May average) = 380 Watt minimum May "break even" array

Normally, suggest that you only use 50% to 65% of daily predicted power--Allow for a few days of bad weather, higher energy usage, etc.:

• 380 Watt array * 1/0.50 "daily usage factor" = 760 Watt array "comfortable" array (little or no backup genset charging needed)

And charging based on 5% (for weekend/couple weeks at a time usage) to 10%-13%+ rate of charge for full time off grid:

• 440 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 414 Watt array minimum
• 440 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 829 Watt array nominal
• 440 AH battery bank * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,077 Watt array "typical" cost effective maximum

Assuming I got close to your location in Tanzania, you have lots of sun per day all year round... So, you can probably do OK with a slightly smaller array for full time off grid (less than 829 Watt array @ 10% rate of charge)--But that is still very close for a "conservative" array of 760 Watts... I would not "agonize" over 10% different array Wattages--That is pretty much "the same" size (hard to even measure the differences between 760 and 829 Watt array and their daily harvest).

For a charge controller--You will have to see what is available in your region... Suggest going with MPPT type (more flexible)... Roughly:

• 829 Watt array * 0.77 panel+controller derating * 1/14.5 Volt charging = 44 Amp suggested minimum rated MPPT controller

Anyway, lots of information here--And lots of guesses on my part.

The above design guidelines are relatively conservative--And if you are pressed for money--You can look at reducing the sizing a bit, use a genset during a few days of bad weather, or clean out the refrigerator and turn it off during bad weather/when not needed.

I am sure you have lots of questions... Always highly suggest doing lots of back of the envelope (above) and paper designs before you start buying hardware... It is pretty easy to buy stuff that may not plug and play together well if you go for "here is a good sale" shopping spree.

Take care,
-Bill