Solar panel connection

zviedris · March 2019

I do want to build a solar wood kiln. Part of it has fan ventilation that should work when there is high temperature or high humidity.

Basically when there is sun - fans should work. Still, need some power management when there is a bit cloudy. Also would like to have that there is regulated voltage.

I understand how to wire panels to mppt, but has problems how to wire fans to mppt. First - mppt port for DC load is more for 50-60W 12V, that can get to run 1 fan. So how to wire fans to mppt? I do not want to wire them all through battery. Then in case of clouds battery will be drained very fast.

Other question - how to do wiring if there is not 12V fans, but 24V fans?

Estragon · March 2019

2 x 100w panels might produce ~ 150w in full sun with proper tilt - not enough for 4 x 80w fans (at full speed).

You could hook fans to the battery via a normally open relay controlled by the load terminals.

Estragon · March 2019

Some charge controllers can output 12 or 24v. If using 24v fans, set for 24v output, and wire two 12v (or four 6v) batteries in series (+ive on one battery to -ive on the next) for 24v.

mcgivor · March 2019

The fans need to be wired in such a way so as to prevent over dischargeing the battery, thereare various ways to achieve this, the simplest way would be to use a controller which can be used as a load controller, such as a Morningstar TS.

https://www.solar-electric.com/trts12vochco.html

A second controller would be needed to charge the battery, the voltage would be dependent on the load needs as well battery nominal voltage, in the case of the TS it can be 12, 24 or 48V., using a voltage higher than 12V is something I would recommend.

The capacity of the battery will be determined by the load demands, current multiplied by time, for the above example the load would be 26.6A which would deplete the 60Ah battery to 50%, the maximum recommend, in ~30 minutes. The PV also needs to be sized appropriately to recharge the depleted battery as well as support the load, so an accurate calculation need to be done to result in a reliable system.

Some cheap controllers have load terminals which can be used to either control the load directly or via a relay, unfortunately they are often not well suited as they generally allow the battery to over discharge. The Morningstar can be adjusted to cut in and out at higher values to protect the battery. It really comes down to economics, if this is an important installation then don't cheap out, but first do a calculation, without actual figures, fan voltage / current, backup run time requirements and so forth, it's impossible to begin.

BB. · March 2019

In a battery based off grid solar system... Think of the battery bank as the "heart" of your system. You design your loads to connect to the battery bank (or through an AC inverter for AC loads).

And the solar panels+charge controller (MPPT or PWM) as simply battery charging (you may have to account for your loads during daytime--These loads "subtract" from battery charging current).

Standard MPPT controller only work when connected to a battery bank. They cannot run without one (usually their at is "brains" aka computer is powered from the battery bank--stable day/night voltage/energy source).

I would ask for more details on your loads... Very roughly, it costs almost 4x as much to build/run a battery based solar->charger->battery bank-> DC loads (or AC inverter->AC loads).

If, for example, you can run your main fans from solar panels directly... You save a bunch of money and maintenance issues (typically around the battery bank and the fact the batteries will only last around 3-5-8 years for "typical" flooded cell lead acid batteries).

What is commonly done for off grid power where they only run during the day (typically water pumping for irrigation or filling a cistern), is to run solar panels -> fans (DC fans that are in the "voltage range of the panels).

A different device to use is a LCB "Linear Current Booster"... More or less, they are the MPPT controller between the solar array and the loads, without using a battery bank. DC motors typically require high current/not too much voltage to start turning (especially if it is a pump with air/water load). An LCB takes the "high voltage" and "low current" of the solar array (mornings, evenings) and efficiently down converts to "lower voltage" / "higher current" needed to start/run the DC motor (at lower RPMs). Here is one example (LCB's are "going away"????):

https://www.solar-electric.com/902-100.html

Use for 24 volt fans, and a Vmp~36 volt array (or two "12 volt" Vmp~18 volt panels in series). This is a smaller unit (around 5 amps @ 24 volt output, others may be available).

Then there is the "high end" version of the LCB... Those are VFDs (Variable Frequency Drives) that take DC from the solar array and outputs 240 VAC @ 3 phase into a 3 phase induction motor. Obviously for larger 3 phase induction motors... These will vary the output frequency (and voltage) based on the available input solar power. Used mostly for 3 phase water pumps.

Solar input VFDs are a bit on the new product side--But can be really nice for larger "daylight only" power systems.

And the folks above, have covered the basics for a true off grid power system.

Note that many DC fans have relatively short lives (DC brushed motors, may last 5,000 hours between brush replacements). "Better" DC fan may last 10,000 to 50,000 hours (~8,000 hours in 365 days/1 year).

Many times, DC fans seem "more efficient"... However, mostly they move less air against lower back pressure. A larger AC fan (really designed for the application) will move more air against more back pressure.

-Bill

mike95490 · March 2019

Many mid size controllers have a "dusk-dawn" lighting control, and a inverting relay could run fans in day light hours, or a simple voltage controlled relay sensing higher battery voltage.

zviedris · March 2019

Hi!

Thanks for valuable information.

This ir more like a hobby project because doing it full solar way could be interesting. Still, I want to see it also from investment side as if I put money in solar system that I can't get back in 5-7 years in saved energy costs then why to do it ;)

My main problem is that there is a lot of unknown things. It is not easy to find fans either 12/24V, neither 220V. Fans require quite a large loads (12V 80W, 220V 1KW). This adds complexity to controllers between solar panels and fans. If I need to buy like one water pump controller for each fan then it is a bit costly. If I need to buy more than 4 batteries so that system runs normal and they are not depleated too fast and they need to be changed like every 2 years then maintainance costs is too high.

I will run the solar system between march/april till september/october. Also it will run avarage 10 hours a day.

What are options to run 220V fans from solar panels and add just grid power as a backup?

BB. · March 2019

A battery based "off grid" / hybrid AC output solar power system runs around $0.50 to $1 to $2+ per kWH (all up costs, installation, maintenance, replacement batteries ever 3-8 years, replacement electronics every 10+ years). SWAG guess, but it usually pencils out this way... $1+ per kWH is common, less if you really work at it (keep costs low). And >$2 per kWH if things go wrong, kill a battery bank or two, or have only seasonal usage (electricity not used, is lost in off grid solar--You can only store ~2-3 days of solar harvest cost effectively with batteries).

Small Generators may be ~$1 per kWH -- Just based on fuel costs (highly variable, and trending upwards).

Solar panels + some sort of LCB or VFD -- You can get down into the $0.20 to $0.10 per kWH (electronics last 10+ years, solar panels 20+ years).

If you are some distance from utilty lines--Perhaps it can make sense. If you have utilty power close/on site, usually battery based solar does not make economic sense (get a genset for emergency backup power, if needed).

My suggestion--Spend your time on figuring out the "optimum" fans (AC, DC, Big, Small, etc.) so that you are using the least amount of energy to do the job. Once you have done that, then work on a paper solar design and see if it makes sense now.

You will save money on your fan/air circulation design -- Either if you stay with utility power (lower bills) ro with solar (smaller system that meets your needs).

It is kind of like asing what truck to you need. A golf cart size? 1/2 ton pickup, or a Mac Diesel 18 wheeler. Each has its place, but until you know your needs, no idea what is best for you.

-Bill

zviedris · March 2019

Non related question - how can I transform 12V 80Wats to 220V whats?

Do I understand correctly that 12V 80W is 80/12 Amps then 80/12 (amps) *220 (volts) = 1466 whats? I just try to understand how many 220V kWh will be used by 12V 80W fan in an hour.

Maybe someone can give some link where to read more about LCB and/or VFD?

Estragon · March 2019

80w at 220v is 80/220= 0.363a

Assuming the 220v is AC, you'd need an inverter to go from 12(or 24) vdc to 220vac.

BB. · March 2019

Assuming you are in Latvia or Europe in general (and need ~230 VAC at 50 Hz), here is a good lower cost AC inverter Mfg:

https://www.samlex.com/product-category/inverters/

https://www.samlex.com/product/pst-25s-24e/

This is from a 24 volt battery bus--But gives you the basics of what can be used.

-Bill

zviedris · March 2019

Yeah, I am from Latvia :)

Thanks for information. This is very positive and helpful forum.

Will try to get my schema together and repost it later on for verification.

zviedris · March 2019

Have found PWM - https://www.aliexpress.com/item/EPever-60A-PWM-Charge-Controller-12-24V-36V-48V-Auto-Work-for-Solar-Battery-Charging-LCD/32981854878.html

I think I will try with this one in the middle, without battery. Will have 600W 18 V (Voc) panels and four 90W 12V car fans.

As I understand this setup should work when there is sun outside.

BB. · March 2019

If you want to do the fans without a battery bank, usually a PWM solar charge controller is not going to do anything like you need.

Instead Look for DC to DC Buck converters (takes high DC voltage and drops it down to low DC voltage). They are "EVERYWHERE". Here is an Amazon (USA) link, but you should find similar in your region:

https://www.amazon.com/s?k=dc+to+dc+buck+converter&ref=nb_sb_noss

And, here is a specific converter that may do what you want:

https://www.amazon.com/Converter-DROK-Voltage-Regulator-10V-75V/dp/B071LGTTRN

I have not used any of these units. But the basic function should work. Take 18-70+ VDC in, and programed for 12 volts out (or whatever you need).

Buck converters (drop or "buck") from high voltage to low voltage (the input has to be a few volts higher than the output to work correctly).

There are Open Frame fancy units (like the one I linked tod), and others that are sealed units and no display...

I would suggest a Higher Input Voltage Buck converter, and set your panels, 2x series for Vmp-array~36 volts, and it will run 12 volt fans nicely.

They are not specifically LCB (linear current boosters) but should give you a good start.

I suggest just buying one unit and see how it works. You want to make sure that it does not (for example) you to manual restart the converter every morning (some have "hard" shutdown if there is a "brown out", or other issues).

Buy one and run it for a few days/weeks and see how it goes. Buy one "expensive unit" and one "cheap" unit and see out they compare.

And you have to read the specifications very closely to make sure they meet your needs. The one above is a ~18 volt to 75 VDC input voltage, and at 12 VDC is adjustible to 12 Amps maximum:

12 amps * 12 volts = 144 Watts maximum output

Here is another unit:

https://www.amazon.com/Daygreen-Voltage-Regulator-Transformer-Converter/dp/B07DH398DW

Daygreen Voltage Regulator DC DC 48V 60V 72V Step Down to DC 12V 10A Buck Transformer Converter

Lots of options.

-Bill

Solar panel connection

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