solar system

robocop · March 2017

Hi

again trying to get some info.

Will use a 5000w a continious solar pure sine inverter 48v vdc

How many watt in solar panel should I or can use with this inverter?

thx for reading

Robert

mike95490 · March 2017

That's a pretty large load, 5Kw and will require a VERY LARGE PV array and battery bank to run that 24/7

But if you are saying you have a 5Kw inverter and want to connect a reasonably efficient house to it, then it becomes a good possibility. So we need your actual load estimates and location to figure out the size of things

robocop · March 2017

It is just for 2 airco one 12000bru and the other 24000 btu for about 3 hours maybe wqith a bettary bank of 600ah

robocop · March 2017

But most I would like to have somebody who can tell me how it work as nobody has given me their email.

When I do have that way of thinking I can ask more specific thnx

mcgivor · March 2017

robocop said:

It is just for 2 airco one 12000bru and the other 24000 btu for about 3 hours maybe wqith a bettary bank of 600ah

You need to post the specs of the AC units, when they need to be run, time of day, inrush current if not inverter type, there is no "just", also 3 hours run seems a very short run period , AC is a major consumer and has to be well engineered to work. The best 12000 BTU AC units can draw as little as 4A at 230V no inrush for efficient inverter technology , non efficient could be 8A with 80A or more inrush, so the DC-AC inverter needs to be sized correctly to cope with whatever loads you have.

BB. · March 2017

Robert,

Please post your questions here... You are not the only person that may have confusion how everything works. If we did everything by private message and emails, then only one person benefits. If we post the Q&A here, then tens to hundreds of people benefit.

OK.. Let us take a guess about your stated energy usage. Say you use 4 amps @ 230 VAC for the small one and 8 amps for the large, and have a 100% duty cycle (you turn on full) and run for 3 hours until you take the heat off the home. Assume you are in Curaçao (Dutch island ~60 miles north of Venezuela for us geographically impaired).

Battery size, based on two calculations. One based total energy used (Watt*Hours per day) and the other based on your peak loads (starting the A/C units).

Battery sizing, for many reasons, 2 days of storage (good for a couple of days of bad weather) and 50% maximum battery discharge (longer battery life) for flooded cell lead acid batteries seems to work well:

12 amps * 230 VAC * 3 hours per day = 8,280 WH per day = 8.28 kWH per day (a fairly large off grid system for self install)
8,280 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 maximum discharge * 1/48 volt battery bank = 812 AH @ 48 VDC battery bank [fixed equation--missing "/" sign]

Your 600 AH battery bank is a bit small--But certainly within the area of a reliable off grid power system.

Then there is sizing the battery bank for your loads. Ideally, I would suggest a C/8 maximum continuous discharge rate (20 hour battery capacity divided by 8). This gives good life for the battery and good surge current for starting the AC systems.

12 amps * 230 VAC * 1/0.85 inverter eff * 1/48 volts * 8 Hour discharge rate = 541 AH @ 48 volt battery bank (based on average load)
12 amps * 230 VAC * 1/0.85 inverter eff * 1/48 volts * 5x starting surge for compressor * 2.5x discharge max discharge rate for battery = 898 AH @ 48 volt if you tried to start both AC units at the same time

Your 600 AH battery bank @ 48 volts is probably not large enough to reliably start two standard AC systems at the same time. Make sure that you start one, then the second.

And this shows how picking the right AC system can affect your system costs. Newer "inverter" type AC system (mini-splits and such) have a "soft start" function that means their starting surge is not much more than their normal running current.

And then we have sizing the solar array. Making some guesses here. Assume you have a shallow pitch roof (18 degrees) facing south (suggest minimum of 5 degree tilt so that dirt, dust, leaves fall off/washed off during rains--self cleaning). Fixed array for Curaçao:
http://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation ( kWh / m2 / day )
January	5.67
February	6.04
March	6.09
April	5.33
May	4.95
June	5.24
July	5.02
August	5.82
September	5.88
October	5.31
November	5.10
December	4.86
Annual	5.44

Say you run the A/C 12 months a year (heat in summer, humidity reduction non-summer), the minimum average sun is December at 4.86 hours (assume you use a genset during bad weather, or reduce A/C usage):

8,280 WH per day * 1/0.52 typical off grid system eff * 1/4.86 hours of sun (December, long term average) = 3,276 Watt array (break even month for December)

And we need to size the battery bank. Recommend 5% to 13% rate of charge (20 hour battery capacity number), and 10%+ for full time off grid system (5% can work for weekend/seasonal systems). Will use your present battery bank of 600 AH--Note an 800-900 AH battery bank @ 48 volts would require a larger array "to keep the batteries happy".

600 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 2,299 Watt array minimum
600 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 4,597 Watt array nominal
600 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 5,977 Watt array "cost effective" maximum

Somewhere around 3,276 Watts to 4,597+ Watt array recommended for your system. Full time off grid, 4,597+ would be better (and reduce genset run time during bad weather).

Those are my guesses--Please feel free to ask questions and "fix" any incorrect guesses on my part. There is a lot of information here (and assumptions).

-Bill

robocop · March 2017

for BB Mike and others keep thanking you for your time gods bless

added panels suniva 330 w (how many panels if no battaries used?)

If using batteries how many panels?

inverter MUST ph 1800 MPK plus 5000w inverter 48 vdc or similar

4 pcs vdc 12v gel deep cycle 200ah(800AH) is this sufficient is more than the 600ah mentioned before

to drive a 12000btu inverter and a 24000 inverter btu airco

for 3 hours a day at least

hope this info will help

littleharbor2 · March 2017

robocop said:

inverter MUST ph 1800 MPK plus 5000w inverter 48 vdc or similar

4 pcs vdc 12v gel deep cycle 200ah(800AH) is this sufficient is more than the 600ah mentioned before

At 48 volts your 4 200Ah. 12 volt batteries are still 200 Ah. When you series wire the voltage adds. The amperage remains the same. You would need 16 of those batteries in series/parallel to achieve 800 Ah. but you really shouldn't run 4 parallel strings of batteries. You could use larger 6, 4 or 2 volt batteries to achieve this without having to use so many parallel strings.

BB. · March 2017

Robert,

You first need to define your loads (and pick loads that are very efficient).

Solar panels are not batteries... They sort of look like batteries (sun on panel, voltage/current available for use). However--Solar Panels do not have any surge ability--I.e., if you have a 100 watt panel and need 200 watts to start a small pump, there is no surge current/power available for the few seconds to start the pump.

Solar panels, more or less, output current in proportion to the amount of sun hitting the panel. The voltage output of the panel will vary between (roughly) Vmp and Zero volts. Solar panels are "current sources". If you have 100% sun on a 300 Watt @ 10 amp & 30 volt panel. If you draw 10 amps, the panel voltage will roughly be 30 volts (Vmp-voltage maximum power). If your loads tries to pull 10.5 amps, the voltage will collapse to near zero volts.

So--While it is possible to put a set of solar panels on the input of an off grid AC inverter (that was designed for battery bank)--It usually does not work out well. The OG inverter is designed for a standard operating input voltage (10.5 to 15.x volts typically)--And that there is a lot of surge current available from the battery bank to start motors/pumps/etc. Many OG inverters will "latch off" if the input voltage drops below ~10.5 volts, and you need to turn off the DC power and turn it back on to restart the inverter.

And a typical "12 volt solar panel" has Vmp~18 volts and near 21 volts for open circuit (no load)--The solar panels can over voltage the input of the OG inverter if there are no loads on the inverter.

Either you have to put a very large array (no battery) to run from morning to evening and support your loads. One solar mfg. makes a device that resets the DC input to reset the inverter (direct solar panel to OG inverter).

And because the sun+weather+starting surge+etc. makes the AC power "unreliable" during the day (lots of shutdowns/restarts)--You have to accept that behaviour (perhaps a fan can be turned on and off--Lights inside/tv/radio/refrigerator--The "unreliable nature" of battery less AC power may not be acceptable to you).

If you want "grid quality" power for your off grid system (i.e., turn on the appliance and it starts--Can run your loads at night, during bad weather, etc.)--You really need a battery bank to store the energy (typically, your battery bank stores 4x your daily energy usage).

If you have optional loads (no irrigation needed during bad weather/winter, run AC during the day only, etc.)--You can get away with a smaller (lower capacity) battery bank--But no battery bank is still not useful for many people. Some things can work nice--Daytime water pumping to a pond/water tank works well (the water tank is your "energy storage").

-Bill

oil pan 4 · March 2017

You can't run the inverter with out batteries.
The voltage will be so high the inverter will not turn on, then if you did get it to turn on the inrush of an older style air conditioner would cause the inverter to under volt and turn off.

robocop · March 2017

Hi

I you use 24v vdc inverter (are the 48v inverters switcheable to 24 vdc?) batteries at 200ah 8 pcs 12v batt 200ah are enough

robocop · March 2017

I forgot using 330 w panel how many panels do I have to use ?

BB. · March 2017

I have never seen a 24/48 VDC input inverter. But, I am not in solar power sales, so I cannot say it is impossible to find one.

Battery size/capacity/voltage depends on your loads and your inverter size... Roughly, for 12 VDC @ 200 AH batteries, 8x, wired in series/parallel for 24 vdc or 48 vdc, the maximum Watt inverter I would suggest for use with flooded cell lead acid batteries would be:

8 * 12 vdc batteries * 200 AH * 1/8 hour discharge rate * 0.85 ac inverter eff = 2,040 Watt typical maximum supported Inverter
8 * 12 vdc batteries * 200 AH * 1/5 hour discharge rate * 0.85 ac inverter eff = 3,264 Watt max recommended ac inverter

Your battery bank will not support any larger continuous loads reliably over time/temperature/state of charge.

-Bill

BB. · March 2017

The size of solar array (not knowing anything about your loads), based on battery bank capacity:

8 * 14.8 vdc charging for batteries * 200 AH * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,538 Watt array minimum (weekend/seasonal usage)
8 * 14.8 vdc charging for batteries * 200 AH * 1/0.77 panel+controller deratings * 0.10 rate of charge = 3,075 Watt array nominal (full time off grid)
8 * 14.8 vdc charging for batteries * 200 AH * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,998 Watt array "cost effective" maximum

-Bill

mcgivor · March 2017

@robocop
So far there has been no indication of actual loads, these are important figures. nobody can speculate what the requirements are based on vague information. Start with the actual load figures, inrush, followed by run current, for each unit. It would be almost impossible to figure out based on the information provided. Thinking one could run an A/C unit on solar without a battery is absurd,, in my opinion, although it may be possible with 3 phase. Rewind and start from the beginning, post the loads first, including inrush then move forward, you can't reach the finish line without running the race, so to speak.

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