Suitable solar equipment for diff systems

Re: Suitable solar equipment for diff systems

I think he is out of NW Frontier area of Pakistan...

So, roughly 6-8 hours of "full sun" per day, ~250-300 days per year.

Since we don't know your actual power needs--lets try using a round number of 1,000 Watts of Solar panels, 6 hours per day minimum sunlight (you may have 12+ hours of sun, but "full noon time sun" of ~1,000 watt/sq.meter hour equivalent).

Also, assume 0,77 derating for solar panels + charge controller losses, 0.80 flooded cell lead acid battery efficiency, 0.85 inverter efficiency:

• system derating = 0.77*0.80*0.85 = 0.52 (yes, 1/2 of solar panel rating to AC output)

Put it all together:

• 6 hours per day * 1,000 watts of panels * 0.52 derating = 3,120 Watt*Hours per day

If you want to run 4x laptops around 60 watts:

• 3,120 WH per day / (4*60 watts) = 13 hours per day

Battery bank recommendation is based on a rough rule of thumb of 3 days of no-sun, and 50% maximum battery bank discharge (for long battery life) The number below is probably tends towards a larger battery bank--You may be happy with one 1/2 as large if you have mostly sunny days and want to keep the costs down a bit:

• 3,120 WH * 1/0.85 inverter eff * 1/12 volt battery bank * 3 days * 1/0.50 max discharge = 1,835 AH of 12 volt battery bank

The above numbers are on the conservative side -- However, weather is variable and you will find it difficult to use 100% of available power every day (plus there are times when you may need more power)--so the above daily productions numbers are sort of a maximum value and you should plan for a system somewhat larger than your planned needs (2x larger is not a bad target if you expect loads to grow and want to minimize generator run time).

Inverter wise... You asked about 1.4 kVA system... Sizing the AC wiring and Inverter capacity, kVA (VA) is a good value to know for your AC loads (for inverters, typically KVA rating = KW rating although some have KVA>KW ratings).

For sizing the battery bank and solar panels, you also need to know Watts and Hours of operation. Power Factor may be near 1.0 for resistive loads and modern power factor corrected electronics and motors. For older/less expensive equipment, PF may be on the order of 0.6 or so.

• Power = Volts * Amps * Power Factor

We recommend True Sine Wave inverters over Modified Sine Wave inverters... For ~80% of your typical loads, MSW inverters work OK and are a lot cheaper than TSW inverters. However, for small electronics and enclosed motors (like in refrigerators), TSW are preferred.

Some people use smaller TSW inverters for the "critical loads" (computers) and MSW for other loads (well pumps, etc.).

All About Inverters
Choosing an inverter for water pumping

If you can get a Watt Meter or a Watt*Hour (KWH) meter to measure your loads--that would help you a lot with planning.

In general, PV electric systems cost almost 10x per kWH as utility power (at least here in the US)... Anything you can do to reduce loads will save you a lot of money. Conservation will almost always be the first place you should invest your money (for example expensive laptop computers vs "cheap" desktop systems and monitors). Turning off systems when not in use will can you a lot of money too.

-Bill

Re: Suitable solar equipment for diff systems

Assuming that the OP is affiliated with SKB Engineering:

SKB Engineering:

Established in 1954, SKB is justly proud of its 6th decade of achievements in the field of engineering, construction, operations and maintenance in civil and electro-mechanical sectors.

In the earlier years, the company’s business activities were limited to the Baluchistan Province of Pakistan where it made its mark with projects like the RCD Highway and Hub Dam. However, in the 1970’s its projects expanded to other provinces of Pakistan.

I have worked with PCB Layout Engineers in Pakistan (not SKB that I know of) ~10 years ago (part of time to market--"day time work in the US" , ship job to Pakistan for the other 1/2 of the 24 hour per day process). They were very professional.

-Bill

Re: Suitable solar equipment for diff systems

Ideally, True Sine Wave inverters. Are you 120 VAC 60 Hz or 230 VAC and 50 Hz?

Our host stands by their products. If you are looking for bullet-proof inverters.

Samlex 1500 Watt 24 Volt Sine Wave Inverter. That would be the low-cost TSW choice.

I guess Exeltech Sine Wave Inverters would be another choice. Known for their high quality and rugged products.

I have not heard any issues with the Magnum MS2012 2000 Watt Sine Wave inverter w/charger series inverters. Also includes an internal charge controller for use with a generator or grid power (as backup). Includes an AC transfer relay built in.

Xantrex has been around for a long time. Xantrex Prosine 1800 Watt HW 12V Sine Wave Inverter w/transfer Switch. Less expensive inverter/charger (again for generator / line power charging). Includes "search" mode which drops standby consumption to less than 2 watts. A typical TSW inverter will draw between 6-20+ watts if operating without a load. May save you having to put a DC switch to turn off inverter when there are no loads. Search mode typically works by turning on AC output for a short time looking for > 6-8 watt connected load ever few seconds -- Turns on 100% if load is detected.

The Xantrex XW system Xantrex XW4024-120/240-60 Hybrid Inverter-Charger may be way over-kill (and expensive) for your needs. Includes two AC inputs (grid and generator), search, generator control option, highly programmable. In the US, we use 120 / 240 VAC split phase power (basically a 240 VAC center tapped transformer). One of the few inverters that does not need extra hardware to support 120/240 VAC power.

For your region, you can probably get good quality (and not cheap) European Inverters. And obviously China (and probably India) would make units that suit your needs too. Many of the above also have 230 VAC 50 Hz versions too--but those would most likely be special order from a US retailer/wholesaler.

I would look at the above products and figure out which features would make your life easier (search mode, generator charging option, etc.). For many users, you have to stock your own spares--so buying several inverters as spares may be a better choice than one very expensive inverter (if you have budget limits).

Also, be aware that somebody may try to sell you a MSW (Modified Square / Sine Wave) type inverter and tell you it is a "Sine Wave" type inverter. In general, TSW (True Sine Wave) inverters are much more expensive than MSW--So if they tell you "Sine Wave" and the price is "too good"--suspect that the inverter is not what you are being told.

Regarding Solar Charge Controllers--The MPPT type MorningStar Solar Charge Controllers are currently probably among the best out there right now. Available in 15 amp, 45 amp, and 60 amp output versions. The 45/60 Amp are the most flexible. The Morningstar TriStar 60 amp MPPT solar charge controller actually includes an internal HTTP (Internet) server that you could plug right into your network for remote monitoring.

MPPT type charge controllers are ~2-3x the expense of a PWM charge controller.

Yours sounds like a large system (at least you have a big battery bank) and you should use 2x 60 amp charge controllers (and a recommended ~1,700 to 2,300 watts of solar panels per controller just based on battery bank size). You could "get away" with using just one 60 amp charge controller and connected solar array--but that would be the minimum size I would recommend for a 1,200 AH 24 volt battery bank (a good rule of thumb is 5-13% of 20 Hour battery capacity rate for proper charging--10% of a 1,200 AH battery bank would be 120 Amps of rated charging current).

Knowing your equipment loads and then sizing the battery bank, solar array, generator, etc. to support those loads. Too large of battery bank can actually be a real issue. Large batteries need lots of current to properly charge and make up loses for self discharge (especially flooded cell batteries) as the bank gets old.

MPPT charge controllers allow you wire high voltage solar arrays (Vmp~100 volts maximum for current range of off-grid MPPT charge controllers) allows you to use smaller gauge wire between the Solar Array and the Battery shed/installation. 1/3rd the current for ~100 VDC on a MPPT controller vs the ~35 VDC that would required for a PWM type controller. Allows you to use less copper and also place the array farther from the battery shed (if needed).

All About Charge Controllers
Read this page about power tracking controllers

If you use a backup generator--sizing your charger + genset can save yo lots of costs too (especially fuel). Most generators are fairly efficient down to ~50% rated load. Below that, the fuel flow hardly drops even though you are not taking much energy. Diesel gensets should typically be operated at 50-60% minimum load for long life and to burn clean. Lots of low power running can glaze cylinder walls and "coke/carbon" the combustion chamber/exhaust valves.

You have not talked much about a genset--but you really want to keep your battery bank above ~75% state of charge. Storing/using batteries below 75% SOC for days/weeks/months can really shorten the useful life of your battery bank.

Off grid folks on the board here typically run the genset (if needed) early in the morning to get the battery bank >80% charged--then let the solar finish charging the battery bank.

Take some time and read through the Battery FAQ's if you are not that familiar with battery requirements:

Deep Cycle Battery FAQ
www.batteryfaq.org

Lastly, I would also recommend a Battery Monitor (in addition to a hydrometer+thermometer for flooded cell battery banks). Very helpful for non-technical people that need to operate an off-grid power system. Victron Energy out of Europe has also had a couple recommendations here too.

Most of the rest of the equipment can be abused pretty badly without much issues. Batteries on the other hand will not last long if not properly maintained.

I would suggest reading through the various models/options in the links I have provided--and make a list of requirements / vendors / models that meet your requirements (include those that are available locally) and ask here for feedback on your choices.

There are others here with a lot more experience than I that can give you more detailed answers on specific units/needs.

-Bill