buying a complete system

Legolas

Dear all,

I am going to China to buy a complete solar system for my house. I am totally new to the business and would need
advise on what to get. Mainly i would need to have an output of about 30 amperes of 220 DC.
so far i found a system as per attached photos, would this be enough to produce what i need ? do i need any extra
parts ?
thanks for any help

Robert
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BB.

Re: buying a complete system

Welcome to the forum Robert.

I am guessing you are out of Beirut or so...

Usually, we like to start with your loads. In general, off grid solar power is pretty expensive to buy and to maintain (new batteries every 4-8 years, new electronics every 10+ years, etc.)... So you do not want to build a system that is too large--And you do not want to build a system that is too small and not support your needs either.

Looking at your loads--That is a pretty large off grid power system. 28,000 WH per day, with 20,000 Watts being AC and 4,300 WH being the refrigerator.

The refrigerator numbers may be high... In the US, you can get a pretty large refrigerator/freezer down to near 1,200 WH per day (although, in hot weather, the power usage can double). Air conditioning weather appears to be in the May through October range.

Lets say you use 1/2 the power during the day, and 1/2 the power at night (and during bad weather, only 1/2 the power in winter).

So, lets try sizing the battery bank for 2 days of storage, 50% maximum discharge and to only carry 14,000 WH per day:

14,000 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 1,373 AH @ 48 volt battery bank

I see you have GEL type batteries called out... In general (at least for the US market), GEL batteries are not good for solar/off grid power. We need to charge the batteries very quickly, and GEL batteries (again in the US) are only rated for 5% or 1/20 Hour charge rating--If you charge them faster, the gas and GEL develops bubbles which kills the battery.

For a full time off grid system with lots of day time loads, I would be suggesting something like a 10% to 13% or 1/8 hour rate of charge:

1,373 AH * 59 volts charging * 1/0.77 panel+charge controller derating * 0.13 rate of charge = 13,677 Watt array

And if you want to collect power in the summer months to run everything--We need to get the average sun for your location. Using a fixed array and the solarelectrichandbook:

[h=3]Beirut
Average Solar Insolation figures[/h] Measured in kWh/m²/day onto a solar panel set at a 56° angle from vertical:
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun


3.81

4.48

5.50

6.22

6.80

7.00



Jul
Aug
Sep
Oct
Nov
Dec


6.94

6.95

6.74

5.88

4.47

3.58



So that would give us October at 5.88 hours of "minimum average" noon time equivalent sun for "summer" months:

28,000 WH * 1/0.52 off grid end to end efficiency * 1/5.88 hours = 9,158 Watt array (October is "break even" month)

So, somewhere between 9,158 to 13,677 Watt array would be "optimal" (if you really plan on using so much AC+refrigerator, then the larger array would be easier to maintain the battery bank).

I don't see any solar charge controllers listed, but if you use an 80 Amp MPPT type charge controller, then for a 13,677 Watt array, you would need:

13,677 Watt array * 0.77 derating * 1/59 volt charging = 178.5 Amps typical maximum charging current
178.5 amps / 80 amp charge controller = 2.2 charge controller ~ 3 charge controllers for that size array

Anyway, that is a start... And some guesses on my side. If you did not need the Air Conditioning (or did not need 20 kWH of AC) and had a more efficient refrigerator, the system would be dramatically smaller and less costly.

Questions/corrections to my guesses?

-Bill

westbranch

Re: buying a complete system

Another recommendation for first time solar users is to start with a set of Golf Cart (GC) batteries. Why, because the first set has a tendency to be murdered very quickly due to a lack of knowledge by the user...
these batteries are relatively accessible in many locations..

hth

Legolas

Re: buying a complete system

Gents,
thanks for the info very helpful indeed...i would like to know a bit more about basics on how the system works. what will i need after
i install the panels on the roof ! what exactly will i need to get take power from batteries and convert to 220 dc ? thanks

BB.

Re: buying a complete system

Legolas wrote: »

thanks for the info very helpful indeed...i would like to know a bit more about basics on how the system works. what will i need after
i install the panels on the roof ! what exactly will i need to get take power from batteries and convert to 220 dc ? thanks

Can you confirm you need 220 VDC? Usually, most people need ~220 VAC and 50Hz power (if you are in Lebanon or the area?). We would also need to know how much power it would need (a few watts/amps, or 1,000's of watt, etc.).

If you are familiar with an automotive electrical system--It is very similar to how a solar power system works. The battery is "always on". So, if you have loads and no sun, the battery supplies all of the current. If the sun is up, the solar panels go through the charge controller which measures the battery voltage and decides if the battery needs charging or just holds the battery voltage stable so that the panels can supply load current (just like a car alternator--When the engine is running, the alternator both charges the battery ans supplies load current).

There are a lot more details, but that is is the basics. You will have a choice to make, either a PWM (Pulse Width Modulation) or an MPPT (Maximum Power Point Tracking) solar charge controller. For smaller systems (less than ~400 watts of solar panel), a PWM system maybe "good enough" (PWM controllers are less expensive). MPPT controllers are more expensive and usually are used for systems > 800 watts of solar panels.

Also, there are two different "classes" of solar panels. The ones with Battery Compatible output voltage (Vmp~18 volts for 12 volt battery bank, ~36 volt for 24 volt battery, and ~72 volts).

The other class of solar panels are usually called GT panels (grid tied solar panels). Basically these panels have Vmp (voltage maximum power) that does not match the Vmp:Vbatt numbers I gave above. Their Vmp maybe ~30 volts, or other voltage (some have Vmp~36 volts, which can be OK for 24 or 48 volt batteries--Two panels in series). For GT panels, they usually are available for over ~200 Watt panels, and many times, are less expensive ($$$/Watt) and the "Battery Compatible" panels are generally smaller than 200 Watt.

You have to be careful... There are a lot of design issues that you should address before you buy the hardware. Loads define battery bank. Battery bank and loads both define the solar array Wattage. And size of the system help set the battery bank voltage. And amount of sun/seasonal use of power also sets array Wattage.

Once you have a paper design based on your needs--Then you can start looking at hardware that will meet your needs.

-Bill

softdown

Re: buying a complete system

Unless you have an electrical background with a solid solar education, knowing what to buy is exceedingly difficult. Buying an assortment of bargains for, say, $2000 has a good chance of yielding, say, $1000 worth of the right parts.

The vast majority of people are better off buying an entire kit that is designed to work together. Unless you are pretty savvy, pretty lucky, and have a LOT of time to play with things. Thats just my .02.

Legolas

Re: buying a complete system

@ BB
thanks again this is very informative but will take a while for me to understand how the system is built in all its details.