New and Confused and in desperate need of some help

[barry]

G'day one and all.

I am in South Africa. Here most South Africans are not doing to well. Power prices are skyrocketing. Businesses selling solar are really taking advantage and hiking prices and their services. Therefore we are considering doing this ourselves.

We run a nursery. This is becoming a difficult enterprise as we use a lot of power.

We have on 40 greenhouse tunnels. Each running a 5.5kw exhaust fan. We are now slowly changing them over to 1kw's. It is going to help but we need to reduce costs further drastically. If not a lot of people are going to be without work as we employ almost 200 people.

What we want to do is a "step by step month by month" kind of solution.

Every month we want to purchase enough equipment to run 1 exhaust fan. Next month the same for the next one and so on. These fans run 24 hours a day. By the way these are 3 phase.

Any help will be great! Cheap and reliable solution.

What would we need:

3phase 1 Kw Exhaust Fan to run 24 hours a day (off the grid)
- Solar Panels
- Inverter (Must it be True Sine Wive?)
- Charge Controller (MPPT? LVD etc.)
- Batteries (Deep Cycle)
- Anything else? Circuit breaker or fuses.

I have been doing some reading. I know what to do with plants but this is way out of my comfort zone.

Thanks a stack.

Regards,
Barry

[thastinger]

I don't know what kind of margins a typical greenhouse operates at but I'm pretty sure that it isn't going to be enough to do that x40. 24Kwh/day via PV is a ton of power and expense. I'm not sure what equipment is available to you or what your insolation hours are but in USD it would cost you probably 15000.00 each and then you would have battery replacement x40 sets every few years after that.

[Robert1234]

You must have a massive amount of floor area to be needing fans with that much hp. If you can drop from 5 kw to 1 kw, can you simply cycle them maybe 15 minutes on, 5 minutes off without harming your crops (or 10 and 2 or some other combination that reduces power consumption)? I think you are going to find out quickly that solar PV power is not your solution, but there are a lot of smart people on here that may be able to help you think up alternate ways to save power.

[SunEagle]

You must have a massive amount of floor area to be needing fans with that much hp. If you can drop from 5 kw to 1 kw, can you simply cycle them maybe 15 minutes on, 5 minutes off without harming your crops (or 10 and 2 or some other combination that reduces power consumption)? I think you are going to find out quickly that solar PV power is not your solution, but there are a lot of smart people on here that may be able to help you think up alternate ways to save power.

Those fans are really not that big in horsepower. The 5000 watt unit is about 7 to 8 hp and the 1000 watt fan is about 1.5 to 2 hp. Although even at those low hp the cost to power via solar will be very expensive.

[Wy_White_Wolf]

First off if you want to go with solar or some other alternate power quit changing the fans. Using 3 phase limits your choices on equipment. It most likely would be better to replace them with DC units designed for solar or single phase AC. No since it adding extra cost of replacing them until you decide how you're going to power them.

WWW

[Naptown]

Does South Africa allow grid tie solar
Even If they so it would take about 5-7 KW to offset the 1 KW fan motor
And it would have to be a net metering scheme.

Is there a way to passively vent them?
That would be the least costly alternative

[Robert1234]

Those fans are really not that big in horsepower. The 5000 watt unit is about 7 to 8 hp and the 1000 watt fan is about 1.5 to 2 hp. Although even at those low hp the cost to power via solar will be very expensive.

As this is a greenhouse and the fans are running 24/7, I'm assuming he is talking about HAF fan arrangement (horizontal air flow) so as to prevent diseases at night and help with respiration during the day. Typically those fans use low hp. For example, a larger one (36") has a 1/2 hp motor, consumes 3 amp @ 230v (0.7 kw), and moves 14000 cfm of air.

A well designed HAF application should have a cfm fan capacity twice that of the square footage of the area being served. Simple scaleup indicates that 5.5 kw should be able to move about 110,000 cfm of air and serve 55,000 ft^2 of greenhouse. That's about 1-1/4 acres of greenhouse - pretty big where I come from.

[SunEagle]

As this is a greenhouse and the fans are running 24/7, I'm assuming he is talking about HAF fan arrangement (horizontal air flow) so as to prevent diseases at night and help with respiration during the day. Typically those fans use low hp. For example, a larger one (36") has a 1/2 hp motor, consumes 3 amp @ 230v (0.7 kw), and moves 14000 cfm of air.

A well designed HAF application should have a cfm fan capacity twice that of the square footage of the area being served. Simple scaleup indicates that 5.5 kw should be able to move about 110,000 cfm of air and serve 55,000 ft^2 of greenhouse. That's about 1-1/4 acres of greenhouse - pretty big where I come from.

That is a pretty big greenhouse. I understand now what you referring to in fan hp size when compared to the amount of cfm needed for the required air flow.

Size is a matter of perspective. For me a 5 hp motor is pretty small.

[Robert1234]

Understood completely. All things are relative to our own experiences.

Being that Barry already referenced dropping the hp by 80% on his fans, I'm wondering if perhaps he is using his exhaust fans to obtain the same benefits he can get from HAF. The HAF fan I referenced is one of the better efficiency MegaBreeze (trade name) fans available, but that's still only maybe 20% more efficient that a low cost HAF fan. I've heard this tounge in cheek adage many times on this forum in many ways... "The cheapest way to produce electricity is not to use it." In my own experience, the power savings I'm obtaining by "going solar" is about twice what I originally calculated it would be each month when it comes to what I'm paying the POCO. I attribute that to simply to being more aware and less wastefull.

Barry, if it is HAF that you are trying to reduce the cost of perhaps this will help.

http://extension.umass.edu/floriculture/sites/floriculture/files/manual/pdf/GreenhouseBMPfb.pdf

Look on pages 104-106. The HAF discussion is short, but it may inspire your thinking as to how to reduce your power useage. I'm sure there are other references available on the web to help as well.

[barry]

Thank you so much for all the response. Trying very hard to keep track of them however a lot of it is going over my head.

I will go through them all again and use the internet as reference.

[thastinger]

Barry. in the "off-grid" section of this forum there is an excel spreadsheet to help you calculate your needs. You're not going to like what it spits out for you though.

[barry]

Barry. in the "off-grid" section of this forum there is an excel spreadsheet to help you calculate your needs. You're not going to like what it spits out for you though.

Thanks mate. Simply reading what is being said here is already getting us a bit down. BUT we are thinking of working things a bit different. We ABSOLUTELY need to find a solution or it is bust.

In SA we get full sun for 6 hours a day. So we are thinking that maybe we will take one of the houses and run it for only 8 hours a day on the 1 kw fan.

If we do this I reckon we might save a bit more (if it works). We are willing to sacrifice this one if need be to see if we can make it work.

[Naptown]

before you go buying new fans for an experiment consider getting a contactor and or timer to turn your existing fans on and off on a 10 minute on or whatever it takes to do one air change and then off for say 50 minutes If you go to 15 on and 45 off that would cut your consumption by 75%

[Sunking]

In SA we get full sun for 6 hours a day. So we are thinking that maybe we will take one of the houses and run it for only 8 hours a day on the 1 kw fan.

Well that is not good, real poor. YOu need complete unrestricted clear view of the horizon east, west, south. Even with that is not top be confused with 12 to 14 Sun Hours. Works out to only be 4 to 5 Sun Hours.

With that said if all you get is 6 hours of direct sun only means you get maybe 2 sun hours at best. So to generate say 8 Kwh per day to run one fan only you are looking at 6000 watt solar panel, Two very expensive 60 amp MPPT charge controllers, and a 48 volt 1250 amp hour 3600 pound battery. Just the battery cost alone here in the USA is around $12,000 USD and will need replaced about every 5 years with tender loving care. Work that out for 5 years and just battery cost alone is 65-cents per Kwh USD. Does your electric company charge you more than 65-cents per Kwh when converted to USD? If not even remotely thinking of taking anything off-grid is economic suicide and bankruptcy.

Barry when we say do not take anything off-grid unless there is no other effective cost solution, we mean it. If you are paying less than about USD 90-cents per Kwh, off-grid solar is not for you. Even if you have Net Metering in SA, unless your neighbors pay for most of it is not likely going to help either as it would take 20 years or more to just break even which means you get to pay 20 years up front for electricity. Something tells me your profit margins and cash flow cannot do it.

[thastinger]

Seems like an air quality study and/or installation of some sort of passive ventilation system/swamp cooler etc is going to be your best bet.