Is 3.5kw ok for a 1st diy system?

Audley A

New Member
Joined
Nov 15, 2020
Messages
1
Hi Solarites,
I want to install an off grid system using 16 Chinese made LiFePo4 3.2v 310Ah batteries (the blue ones - US$1,900) in a 48v configuration fed by 8 x 445w panels (currently US$185 each) = 3.56kw mounted on a southern facing roof with a 30° slope. This is in Jamaica at 18° latitude.

Keeping the battery capacity between 10% and 90% should give me at least 10kwh which should be more than enough to take me through a night as my average daily usage ranges from a high of 12.7kwh last summer to a low of about 7kwh last month (winter). Current monthly electricity cost is about US$0.28/kwh for the first 100 kwh then US$0.37/ kwh thereafter. At present, I have no air conditioning but plan to get at least one small inverter unit installed by this summer.

Ideally I would like to do this as diy but there is so much that I am not sure about. A part time installer has offered to do it for $1,200 which would raise my total system cost from about $7,800 to $9,000. Our solar setup here is tax-free but we do not get any other incentives or rebates. Payback is estimated to be 8 years if I cover my whole bill and my usage remains the same as last year and increasing electricity prices are not taken into consideration.

Maybe someone on this site will volunteer to spoon feed me re the procurement and installation so that I could do it myself. The owner of a similar LiFePo system would be great to have as a collaborator. I have read a bit and watched youtube videos but never worked with solar. There are no regulations here controlling off grid solar as yet. I have had basic electrical training and my main electrical experience was in computer repairs many many years ago.

The few persons that I know of here have installed 24v lead acid systems but cannot give me a good reason why the preference for 24 over 48v. (Actually one of them has recently gone with lithium at 48v.) I intend to keep the grid as standby so no planned backup storage for the few days annually without sufficient sunlight.

Any comments or suggestions would be welcome.

System components proposed by part time installer:
8 SOLAR PANEL 445W MONO SOLAR PANELS (36VDC) , 1 48V 310AH Lithium-ion (Lifepo4) battery (16 × 3.2V x 280Ah) With DALY BMS, 1 SOLAR POWER 6kW 48V INVERTER (BUILT IN MPPT CHARGER), 1 OUTBACK 250AMP PANEL MOUNT BREAKERS, 1 6 STRING COMBINER BOX, 6 ALUMINIUM MOUNTING RAILS, 8 END CLAMPS, 12 MID CLAMPS, 1 MANUAL TRANSFER SWITCH 63Amp 120/240V, 4 DRANCH CONNECTORS (PAIR), 3 MIDNITE LIGHTENING ARESTOR (AC/DC), 2 OUTBACK 80AMP PANEL MOUNT BREAKERS, 30' 6 AWG DC WIRE 3 CORE, 100' 10 AWG DC WIRE 4 CORE, 20' 1/0 AWG BATTERY CABLE, 6 2/0 BATTERY LUG ENDS, 6 6 AWG BREAKER LUG ENDS, 6 FlAT ROOF LEG PAIR, 6 MC4 PV CONNECTORS, 2 8 WAY DISTRIBUTION PANEL, 0 BATTERY BUS BAR (POSITIVE & NEGATIVE), 1 GROUND ROD, 30' GROUNDING CABLE (16 MM2) PVC GREEN, 1 CONDUIT , TRUNKING & WEATHER PROOF BOXES
 

snoobler

Solar Honey Badger
Joined
Jul 10, 2020
Messages
8,430
Location
HBR, AZ
Welcome to the forum.

Rhetorical question: Do you think the solar component list is provided in a way that's easy to digest?

How much solar do you have available?
 

MichaelK

Photon Sorcerer
Joined
Mar 21, 2020
Messages
1,517
Hi Solarites,
I want to install an off grid system using 16 Chinese made LiFePo4 3.2v 310Ah batteries (the blue ones - US$1,900) in a 48v configuration fed by 8 x 445w panels (currently US$185 each) = 3.56kw mounted on a southern facing roof with a 30° slope. This is in Jamaica at 18° latitude.

The few persons that I know of here have installed 24v lead acid systems but cannot give me a good reason why the preference for 24 over 48v. (Actually one of them has recently gone with lithium at 48v.) I intend to keep the grid as standby so no planned backup storage for the few days annually without sufficient sunlight.
You need a charge controller to receive the raw solar DC and transform it to the voltage the batteries want. You may wire batteries in series to increase voltage and reduce voltage drop, but you need to make sure the combined Voc does not exceed your controller limit.

You will need an inverter to convert your battery power to standard AC. Does Jamaica use split-phase 120V/240VAC like the US? For things with a motor, ie: refrigerator, air-conditioner, pumps, ect you need an inverter with good surge capacity.

You will need all the correct sized wire to handle your loads along with the fuses/breakers to keep everything safe, and to not burn your house down.

The voltage of your battery bank is proportional to your loads. It is all about how many amps you have to pull from the battery to run your load. For loads less than 1000W, 12V batteries are generally OK. For loads between say 1000 and 2000W, 24V is OK. For loads greater than 2000W, then 48V is the best choice. For example lets say you wanted to run a pump that draws 2000W. At 12V it would take 167amps to power it. At 48V it would be only 42amps, easily supplied by most batteries.
 
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