Boosting off grid capacity

surveyor1

Hi Folks......pls help!!! if you can :cool:
I am currently running an outback radian off grid with two fm80 CC . I have 24 - 300 watts Helios panals and 1300 Ah of AGM storage. On average i am inverting about 1.2 kw continuously. This works fine for now for everything am doing. However, i want to start running some continuous heavy (say 25 amps @ 240 volts) loads with the system. What must i do to accomplish this. The heavy loads will run only during the day time. My options are:
1. Add more panels and an additional CC?
2. Add an additional radian by staking the two and add an additional CC?
3. Any other suggestion?

thanks in advance for your ideas

solar_dave

Re: Boosting off grid capacity

Can you tell us more about that load. That is a lot of power consumption for off grid.

Cariboocoot

Re: Boosting off grid capacity

Welcome to the forum.

Let's see what you've got.
An 8kW Radian inverter.
Twenty-four 300 Watt panels totaling 7200 Watts, as 3600 Watts on each of two FM80 controllers. That would be approximately 58 Amps per controller.

You want to add a 25 Amp 240 Volt or 6000 Watt load, on top of 1200 Watts average. That would total 7200 Watts, or about as much panel as you've got.

But panels do not put out their full rated Wattage. On average your two arrays produce about 5500 Watts. You can increase each array from 3600 to 4800 Watts if you can get matches for the existing panels. This should bring the current up to 77 Amps on each FM80.

At this level (152 Amps combined) that 1300 Amp hour battery bank will be less stressed and will charge more easily. As it is your rate is about 8.9%, which is good. With the increase in panel it will be 11.7%, which is even better without being too high.

I would not add another inverter for occasional loading.
If you can't get identical panels or adding in to the existing array is too difficult for other reasons, then adding another 1kw to 2kw on a separate controller would be possible.

surveyor1

Re: Boosting off grid capacity

the heavy load will be a few power tools and inverter a/c units. they draw a total of 25 amps @ 240 volts..but we only intend to use these in the day time. What we are trying to accomplish is to use some of the panels to charge the batteries during the day and use the excess solar energy to run the heavy loads. With our current setup with the 24 panels, and without the loads, the battery bank is fully charged by 1300 hrs. Therefore, we want to harvest this excess energy and if need be add what it takes to be able to use the additional equipment

solar_dave

Re: Boosting off grid capacity

surveyor1 wrote: »

the heavy load will be a few power tools and inverter a/c units. they draw a total of 25 amps @ 240 volts..but we only intend to use these in the day time. What we are trying to accomplish is to use some of the panels to charge the batteries during the day and use the excess solar energy to run the heavy loads. With our current setup with the 24 panels, and without the loads, the battery bank is fully charged by 1300 hrs. Therefore, we want to harvest this excess energy and if need be add what it takes to be able to use the additional equipment

Well it is not a continuous load then, power tools and AC units have duty cycles.

BB.

Re: Boosting off grid capacity

Welcome to the forum Surveyor1,

Do you have a better estimate of the loads? Basically something like this:

1.2 kWatts * 24 hours per day = 28.8 kWH per day of steady state load
25 amps * 240 VAC * 3 hours per day = 18,000 WH = 18 kWH per day

Adding the wattage together:

1.2 kW + (25a*240v)/1,000 w/kW = 7.2 kWatts

That is a heavy load for an 8kW AC inverter... Depending on your needs, you may want to use the 8kW inverter for the 6kW load and a second, smaller AC inverter for the 1.2 kW loads... Or tie them together for one big 16 kW capable AC inverter.

Now--Some other issues... Assuming you are in a relatively sunny region and get an average of 4 hours of sun minimum 9+ months of the year:

(28,800 WH + 18,000 WH) * 1/0.52 system efficiency * 1/4 hours of sun per day = 22,115 Watt solar array minimum (based on my guesses)
22,115/300 watt panels = ~74x 300 watt solar panels minimum (have to adjust for controllers/proper array voltage)

Also, you may end up needing a larger battery bank too with that large of solar array... It is nice to have ~100 AH @ 48 volts of battery bank for every 1 kWatt of solar panels or ~800 AH minimum for AC inverter and perhaps 2,200 AH minimum 48 volt battery bank for a 22 kW solar array (there have been reports of MPPT charge controllers taking a "too small" out of regulation--over 72 volts battery bus voltage--I think when the controller does an MPPT sweep--Not sure, but you should talk with Outback about the ratio of solar panel to battery bank size).

Anyway--That is sort of what we are looking at... Depending on the load profile, may need to look at the size of the solar array.

-Bill

surveyor1

Re: Boosting off grid capacity

We have enough space for an additional 24 pcs of 300 watts panels. That should bring our array to 48 pcs or 14.4 kw of panels. But you blew me away suggesting that I would need 74 pcs total. I was under the assumption that i was ahead of the game. As suggested, I will have to ask outback about the pv: battery ratio. i guess i have to look at my #s again.
But let me get the bottom line: To accomplish my goal, I need to get an additional radian, atleast 74 panels total, 2 additional cc and perhaps a larger battery bank?

BB.

Re: Boosting off grid capacity

Again--that was with my completely SWAG estimate of your power usage... Was the 1.2 kW 24 hours per day? Was the 6kW for 3 hours per day--I have no idea.

Was just using numbers to do the math instead or writing (A+B)*1/Inv-eff ... (Algebra tends to scare a lot of people away and make things a bit less clear).

Also, I know nothing about your power usage--Conservation is usually a huge deal with off grid power. It is not unusual to cut power usage by upwards of 50% for homes where conservation has never been performed. And sometimes industrial power usage is can be cut too--Many times, off grid power is provided by (what used to be cheap) portable generators. With the price of fuel and (sometimes) pollution regulations, taking a look at the industrial power needs and addressing overall power efficiency can save a fair amount of power--And cut your off grid system capacity.

And I guessed about the amount of sun you have and there are questions if your power usage is seasonal (winter in/monsoon seasons can really cut power production from solar).

In general, it is almost always more cost effective to spend time/money on extreme conservation vs just building out a larger off grid power system.

-Bill "more questions than answers" B.

solar_dave

Re: Boosting off grid capacity

Just as an FYI, I just went back and reviewed my office/shop for loads per day, it has a 3 ton mini-split with 3 wall units. On a 95+ degree day with the cooling set to 78 F, the whole building, lights, cooling, stereo playing and occasional equipment usage draws about 1.0-1.5 kWh per hour after the initial cool down which can run up to 2.0+ kWh during that 1 hour time frame. The lighting alone is about half of that running load with nine 4 foot florescent fixtures pulling about 500 watts. That being said the building is really well insulated, 2X6 walls with exterior application of 2 inches of Styrofoam exterior board under the stucco and about 18 inches of attic insulation. The worst part of the envelope is the insulated overhead door which faces north. The duty cycle on the AC unit with inverter technology shows a soft ramp up and ramp down every few minutes with the duty cycle well under 50%, looks like more like 30%.

I will get you a graph of the usage after today's 90F afternoon.

Cariboocoot

Re: Boosting off grid capacity

surveyor1 wrote: »

We have enough space for an additional 24 pcs of 300 watts panels. That should bring our array to 48 pcs or 14.4 kw of panels. But you blew me away suggesting that I would need 74 pcs total. I was under the assumption that i was ahead of the game. As suggested, I will have to ask outback about the pv: battery ratio. i guess i have to look at my #s again.
But let me get the bottom line: To accomplish my goal, I need to get an additional radian, atleast 74 panels total, 2 additional cc and perhaps a larger battery bank?

In my opinion you do not need an additional forty-eight 300 Watt panels. You need an additional eight 300 Watt panels to max out the two FM80's you have now.

These loads are not constant or singular; they will not pull the full 7.2 kW the whole time they are on. They will not be used when PV power is unavailable. At least that is what I gathered from your posts. Therefor it is not necessary to boost the entire system up to the level where it can handle all this power 24 hours per day. If the total loads do not exceed the output capacity of a single Radian (and do not worry about surges; it can handle thousands more Watts for a moment) you do not need an additional inverter of any kind.

Maybe I'm just wasting my time here explaining things. After all, I'm no diesel mechanic; just a guy with years of experience fixing systems designed by people who don't know what they're doing (and some of them are 'experts').

surveyor1

Re: Boosting off grid capacity

I will await your submission.

BB.

Re: Boosting off grid capacity

surveyor1 wrote: »

I will await your submission.

I am not sure who this is for?

So, what are your daily loads (Watt*Hours/kWH per day, mostly during the day/night, if the sun does not shine, are your loads less, seasonal loads, backup genset, etc.)? And where is the system installed/how much sun do you get by season?

-Bill

surveyor1

Re: Boosting off grid capacity

Cariboocoot wrote: »

In my opinion you do not need an additional forty-eight 300 Watt panels. You need an additional eight 300 Watt panels to max out the two FM80's you have now.

These loads are not constant or singular; they will not pull the full 7.2 kW the whole time they are on. They will not be used when PV power is unavailable. At least that is what I gathered from your posts. Therefor it is not necessary to boost the entire system up to the level where it can handle all this power 24 hours per day. If the total loads do not exceed the output capacity of a single Radian (and do not worry about surges; it can handle thousands more Watts for a moment) you do not need an additional inverter of any kind.

Maybe I'm just wasting my time here explaining things. After all, I'm no diesel mechanic; just a guy with years of experience fixing systems designed by people who don't know what they're doing (and some of them are 'experts').

I catch your point. However, i currently have the panels connected in series of 3 pv. Therefore, do you think i can use 3 or 4 (to even out) strings on these cc?

surveyor1

Re: Boosting off grid capacity

BB. wrote: »

I am not sure who this is for?

So, what are your daily loads (Watt*Hours/kWH per day, mostly during the day/night, if the sun does not shine, are your loads less, seasonal loads, backup genset, etc.)? And where is the system installed/how much sun do you get by season?

-Bill

this reply was for solar dave

BB.

Re: Boosting off grid capacity

Sorry.

-Bill

surveyor1

Re: Boosting off grid capacity

BB. wrote: »

Sorry.

-Bill

No love lost........but to answer your questions, take a look at my original post

BB.

Re: Boosting off grid capacity

Still not sure... Are you drawing 1.2 kW * 24 hours per day? And how many hours per day do you draw 6kW per day. Do loads change over season (A/C, water pumping in summer, heating in winter, etc.)?

And where is the system located, roughly. PV Watts is a quick way to figure out your hours of useful sun per day by month.

The peak power needs define the inverter... The hours per day * x kW define the battery bank and solar array.

-bill

surveyor1

Re: Boosting off grid capacity

BB. wrote: »

Still not sure... Are you drawing 1.2 kW * 24 hours per day? And how many hours per day do you draw 6kW per day. Do loads change over season (A/C, water pumping in summer, heating in winter, etc.)?

And where is the system located, roughly. PV Watts is a quick way to figure out your hours of useful sun per day by month.

The peak power needs define the inverter... The hours per day * x kW define the battery bank and solar array.

-bill

BB. we draw 1.2 kW @ 24hrs.....We want to draw the additional 6 kW for 8 hrs (assuming a continuous load). this load will not be used in the night. During cloudy days we would scale back the heavy load to about 4 kW. We are in the Caribbean with sun on most days but for calculations assume 5 hrs per day. I currently have 7200 pv watts but is seaking advice on what to do to handle the additional load. I currently have 1300 kAh @ 48 volts battery bank. This serves me very well with the current load.

Cariboocoot

Re: Boosting off grid capacity

surveyor1 wrote: »

I catch your point. However, i currently have the panels connected in series of 3 pv. Therefore, do you think i can use 3 or 4 (to even out) strings on these cc?

So you have four strings of three in series per charge controller?

If so, you can add a fifth string of three; another 900 Watts on each controller. This would bring the total up to 4500 Watts and output around 72 Amps. Not maximum, but certainly and improvement.

A sixth string of three would hit 5400 Watts and would max out the 80 Amp controller more often, with about 6 Amps not realized (although MidNite Classics may make use of it). It would improve output on less-than-perfect insolation days.

The question here is can your combiner boxes take one or two more strings, or are they limited to four? And then you have to check the wire gauge and see if it can handle the additional current and what the Voltage drop would be over the distance.

If you have to change out combiners and wiring it may actually be cheaper (or at least easier) to build a third array of 3600 Watts and use an additional charge controller. Weigh the approximate $500 cost of an MPPT controller plus wiring and combiner against altering the existing arrays to accommodate the additional panels.

BB.

Re: Boosting off grid capacity

surveyor1 wrote: »

BB. we draw 1.2 kW @ 24hrs.....We want to draw the additional 6 kW for 8 hrs (assuming a continuous load). this load will not be used in the night. During cloudy days we would scale back the heavy load to about 4 kW. We are in the Caribbean with sun on most days but for calculations assume 5 hrs per day. I currently have 7200 pv watts but is seeking advice on what to do to handle the additional load. I currently have 1300 kAh @ 48 volts battery bank. This serves me very well with the current load.

OK:

1.2 kWH* 24 hours per day = 28.8 kWH per day
6 kW * 8 hours per day = 48 kWH per day
====================================
Total = 76.8 kWH per day

The typical end to end off grid system efficiency is around 52%. With 5 hours per day of sun, the minimum array would be:

• 76,800 WH * 1/0.52 eff * 1/5 hours of sun per day = 29,500 Watt array

You are asking your present system to supply 76.8/28.8 = 2.7x more power than you use today... That would indicate ~19.44 kWatt of solar array based on your current loads to support your "new" loads.

If you do run your heavy loads during daylight hours (when the sun is up and shining), you save ~10-20% losses based on supplying power directly from the array vs charging the battery bank.

-Bill

ggunn

Re: Boosting off grid capacity

surveyor1 wrote: »

No love lost.......

You may want to consider the way that phrase is normally interpreted...

Usually when someone says that there is no love lost between two people, they mean that the folks dislike each other intensely and make no secret of it.

surveyor1

Re: Boosting off grid capacity

Hi guys, just wanted to update you on my adventure. I have resolved my problems by increasing the number of pv and charge controllers. I now have enough power to run all my heavy loads and charge my batteries. It's a great feeling to watch your systems produce over 9kw of power!