PV panels to an existing diesel generator/battery setup

[onni]

Hi all! This is my first post to this forum and I'm quite new to the solar panel world. (I apologize if my english is confusing, it's my third language. Please do correct me if I'm using words incorrectly and feel free to ask me to rephrase if something doesn't make sense.)

My parents in law has a cabin that currently uses a mix of propane (stove and refrigerator/freezer) and batteries (TV, radio, lightning, water pump). The goal is to get rid of the propane powered refrigerator (huge consumption) and greatly reduce the need for using the diesel powered generator for charging the batteries.


This is the current setup
Diesel generator outputs 230V AC to battery charger (12 V/25 A or 24 V/12.5 A).
Battery charger is connected to 4 EnerSys PowerSafe 12V155FS (12V, 150 Ah) batteries, all in parallel (600 Ah).
Batteries are connected to an inverter (12v DC -> 230V AC, 2kW continous output, 4 kW max).
Inverter is connected to an UPS which supplies the appliances.

In short during normal usage: Batteries -> Inverter -> UPS -> Appliances.

Now I'm hoping you could help me choose a small (?) system to charge the batteries using solar panels.


More info
- Cabin is located in Sweden and is mainly used during summer (june-september).
- The roof has about 60 m^2 in the correct direction (south) and has about 8 hours per day without shade.
- Energy usage: 1 refrigerator/freezer + water pump + TV/radio/lightning. My guesstimate is 1 kWh + 0.25 kWh + 0.25 kWh = 1.5 kWh per day.
- During summer it is used by several families and the refrigerator should be kept running. For the rest of the year it's no problem to start the diesel generator to charge the batteries for the occasional visits.


Requirements
- The total cost must be significantly below 1000 €.
- Enough energy in to the batteries to significantly reduce usage of diesel generator during summer time.


My first guess
- About 600 W PV panels should be plenty. 4 150 W ECO-WORTHY cost about 600 € delivered. Are these any good?
- About 8 m cable required from PV panels to batteries. 10mm^2 cable should have low enough losses.
- CM6024Z Solar charge controller connected to batteries as is.


Configurations
1a. The simplest route that uses most of existing things is getting a simple PWM Solar charge controller that only charges the batteries as is (12 V, paralleled) and keeping the UPS connected to the batteries. This does however not solve one of the existing problems: The batteries are not protected against being emptied to much.

1b. A version of the above is to set the Solar charge controller between the batteries and the inverter. The UPS is however marked with 1600 W -> 1600 W/12 V = 133 A. I'm unsure whether this is only when the batteries in the UPS are low or if it's any time it charges them.

2. Change the configuration of the batteries to 24 V and exchange the inverter to one that converts 24 V DC to 230 V AC. This reduces the amperage on the Solar charge controller (cheaper) and the losses in the cables from the panels to the controller (higher voltage).

3a. Using a MPPT controller that accepts a higher input voltage (series PV panels) but keeping the rest connected as is.

3b. Using a MPPT controller and setting it between the batteries and the inverter.


Solar Charge Controllers
This is where I feel I'm more lost than anywhere.
A: CM6024Z. Simple PWM controller. 60 A. About 50 € delivered. Maximum 12 A from, cannot be placed between batteries and inverter.
B: I've seen the Tracer 4210RN being recommended. About 140 € delivered.


Questions
I. Series or parallel PV panels. Are there any downsides with connecting them in series except more expensive controllers (due to higher voltages)?
II. Could the implementation be ramped? Say by buying 2x150 W panels and a decent controller (the Tracer?) and then add more panels if needed.
III. Is there a problem connecting the battery charger (powered by the diesel generator) to the batteries at the same time as the Solar charge controller?

Sorry about the very long post, I felt that there was a lot of info that affects how the solar panels should be implemented.

/Anton

[ILFE]

By my calculations, I wouldn't go with less than a 900 watts array, preferably closer to 1,200 watts.

[onni]

By my calculations, I wouldn't go with less than a 900 watts array, preferably closer to 1,200 watts.

That sounds like a lot, why would I need that much? Care to show me how you did your calculation?

I think that the possibility to use the diesel generator greatly reduces the power needed from solar panels.

/Anton

[ILFE]

That sounds like a lot, why would I need that much? Care to show me how you did your calculation?

You said you had 600AH @ 12vdc. To charge that with solar, it would be 14.5vdc, a 75% efficiency on the panels, and let's say a 10% rate of charge. That would be a 1,130 watts array. At 9% that would be a 1016 watts array. At 8%, it would be a 904 watts array.

I think that the possibility to use the diesel generator greatly reduces the power needed from solar panels.

Of course. That all depends on how much / little you wish to run it. I realize that, if you wish to only use solar to supplement the generator, you would probably go with less. I was thinking of you using solar to be the primary charging source. I am quite happy with my "quiet" power generation where I live.

[onni]

You said you had 600AH @ 12vdc. To charge that with solar, it would be 14.5vdc, a 75% efficiency on the panels, and let's say a 10% rate of charge. That would be a 1,130 watts array. At 9% that would be a 1016 watts array. At 8%, it would be a 904 watts array.




Of course. That all depends on how much / little you wish to run it. I realize that, if you wish to only use solar to supplement the generator, you would probably go with less. I was thinking of you using solar to be the primary charging source. I am quite happy with my "quiet" power generation where I live.

I don't really see how the amount of battery we have affects how much solar panels we need. We get them used (cheap) and will probably have 4 more soon. Isn't it how much we actually consume that should affect the need for panels?

My calculation looked like this:
1.5 kWh per day, 90 % efficiency of inverter, 75 % efficiency of panels, 10 % additional losses - > about 2.5 kWh per day.
5 hours per day with good sun conditions - > 500 W panels.

Are there any errors in my thought process?

/Anton

[Mike90250]

welcome to the forum

Off-grid solar has about a 50% total loss, from the PV nameplate wattage. And you multiply your daily useable sun hours, by that wattage, to arrive at a perfect daily power harvest/usage.

To your benefit, you have a generator that you are used to running. Inversely, you will have others using the cabin and damageing the batteries. (I didn't leave the lights on).

Because of abuse, I would expect the batteries to fail pretty soon.

So, MY thoughts are this.
1) large, 200w grid tie (45V) PV panels are less expensive than 100w 12V panels, per watt. Take that savings and spend it on a quality MPPT controller. (Outback, Morningstar, Midnight) Wire it to the 12V battery bank, and hope batteries last . Batteries in parallel are problematic - see: http://www.smartgauge.co.uk/batt_con.html for details.

2) does your generator "auto-start" or is it manual start ?

3) prepare to replace the batteries and move it all to a 24V system. You have 12v@ 600ah now (7200 wh of storage) moving to a 24V system with 4, 6V, 200ah golf cart batteries gives you 4800wh (can you deal with adding distilled water to batteries, or do you need sealed AGM batteries?). If the 4800 wh is not enough, adding a parallel bank is feasible, bringing it to 9600wh. With large flooded batteries, comes the need to have enough charge current to bubble the cells enough to de-stratify them.

4) many of the better inverters, have internal transfer switches and integral high performance battery chargers (like a UPS on steroids) and will reduce the generator run time from the current times.

5) pure sinewave inverters produce grid quality power that will run motors efficiently, and not fry half your electronic gear. But they cost more, but worth it overall.

[SunEagle]

Hi all! This is my first post to this forum and I'm quite new to the solar panel world. (I apologize if my english is confusing, it's my third language. Please do correct me if I'm using words incorrectly and feel free to ask me to rephrase if something doesn't make sense.)

My parents in law has a cabin that currently uses a mix of propane (stove and refrigerator/freezer) and batteries (TV, radio, lightning, water pump). The goal is to get rid of the propane powered refrigerator (huge consumption) and greatly reduce the need for using the diesel powered generator for charging the batteries.


This is the current setup
Diesel generator outputs 230V AC to battery charger (12 V/25 A or 24 V/12.5 A).
Battery charger is connected to 4 EnerSys PowerSafe 12V155FS (12V, 150 Ah) batteries, all in parallel (600 Ah).
Batteries are connected to an inverter (12v DC -> 230V AC, 2kW continous output, 4 kW max).
Inverter is connected to an UPS which supplies the appliances.

In short during normal usage: Batteries -> Inverter -> UPS -> Appliances.

Now I'm hoping you could help me choose a small (?) system to charge the batteries using solar panels.


More info
- Cabin is located in Sweden and is mainly used during summer (june-september).
- The roof has about 60 m^2 in the correct direction (south) and has about 8 hours per day without shade.
- Energy usage: 1 refrigerator/freezer + water pump + TV/radio/lightning. My guesstimate is 1 kWh + 0.25 kWh + 0.25 kWh = 1.5 kWh per day.
- During summer it is used by several families and the refrigerator should be kept running. For the rest of the year it's no problem to start the diesel generator to charge the batteries for the occasional visits.


Requirements
- The total cost must be significantly below 1000 €.
- Enough energy in to the batteries to significantly reduce usage of diesel generator during summer time.


My first guess
- About 600 W PV panels should be plenty. 4 150 W ECO-WORTHY cost about 600 € delivered. Are these any good?
- About 8 m cable required from PV panels to batteries. 10mm^2 cable should have low enough losses.
- CM6024Z Solar charge controller connected to batteries as is.


Configurations
1a. The simplest route that uses most of existing things is getting a simple PWM Solar charge controller that only charges the batteries as is (12 V, paralleled) and keeping the UPS connected to the batteries. This does however not solve one of the existing problems: The batteries are not protected against being emptied to much.

1b. A version of the above is to set the Solar charge controller between the batteries and the inverter. The UPS is however marked with 1600 W -> 1600 W/12 V = 133 A. I'm unsure whether this is only when the batteries in the UPS are low or if it's any time it charges them.

2. Change the configuration of the batteries to 24 V and exchange the inverter to one that converts 24 V DC to 230 V AC. This reduces the amperage on the Solar charge controller (cheaper) and the losses in the cables from the panels to the controller (higher voltage).

3a. Using a MPPT controller that accepts a higher input voltage (series PV panels) but keeping the rest connected as is.

3b. Using a MPPT controller and setting it between the batteries and the inverter.


Solar Charge Controllers
This is where I feel I'm more lost than anywhere.
A: CM6024Z. Simple PWM controller. 60 A. About 50 € delivered. Maximum 12 A from, cannot be placed between batteries and inverter.
B: I've seen the Tracer 4210RN being recommended. About 140 € delivered.


Questions
I. Series or parallel PV panels. Are there any downsides with connecting them in series except more expensive controllers (due to higher voltages)?
II. Could the implementation be ramped? Say by buying 2x150 W panels and a decent controller (the Tracer?) and then add more panels if needed.
III. Is there a problem connecting the battery charger (powered by the diesel generator) to the batteries at the same time as the Solar charge controller?

Sorry about the very long post, I felt that there was a lot of info that affects how the solar panels should be implemented.

/Anton

Anton

I think both you and I are a little confused with what you want. As of now you have the following equipment: Generator -> battery charger -> batteries -> inverter -> UPS -> appliances.

I am not sure why you have both a battery/inverter system as well as a UPS which also has batteries but if that is what you want then ok.

Now you want to add solar panels to help charge your batteries:

Solar panel -> PWM Charge controller -> batteries -> inverter -> UPS -> appliances
.................................................. .........^
Generator -> battery charger ---------------l

What I do not understand is why you want to put the PWM or MPPT solar charger between the batteries and inverter. The solar charger can only go between the solar panels and batteries.

[Sunking]

Battery charger is connected to 4 EnerSys PowerSafe 12V155FS (12V, 150 Ah) batteries, all in parallel (600 Ah).

Anton why are you using UPS/Telecom batteries? You do know they are made to use very high charge and discharge currents and only can be cycled 200 to 400 times right? That battery will fail very shortly if pressed into cycle service, They are made for emergency standby service and never to be cycled.

Anyway if you were to look at the literature for the battery minimum charge current is C/10. So you have 600 AH which means the minimum charge current 600 AH / 10 H = 60 amps. At 12 volts using MPPT charge controller will require 60 amps x 13 volts = 780 watts. With PWM and battery panels 60 amps x 18 volts = 1080 watts. So take your pick use expensive battery panels with PWM or inexpensive grid tied panels with MPPT.

[ILFE]

Are there any errors in my thought process?

Nope. I think you have it all figured out.

[onni]

I'm going to quote all the replies in order, but first this:

The batteries we have (Enersys 12V155FS) are indeed not designed for this application. But we get them used (1 year old) very cheap. We will try using these at first, if it doesn't work I guess they'll have to be replaced.

Companies that use them for emergency power test them a few times and use them maybe 1 or 2 times a year. After that they are thrown away, and in that condition we get them. The ones we have now are the first we received (about three weeks ago) and are about 1 year old. Before that we only had:
The diesel generator -> UPS -> Appliances.

welcome to the forum

Off-grid solar has about a 50% total loss, from the PV nameplate wattage. And you multiply your daily useable sun hours, by that wattage, to arrive at a perfect daily power harvest/usage.

To your benefit, you have a generator that you are used to running. Inversely, you will have others using the cabin and damageing the batteries. (I didn't leave the lights on).

Because of abuse, I would expect the batteries to fail pretty soon.

So, MY thoughts are this.
1) large, 200w grid tie (45V) PV panels are less expensive than 100w 12V panels, per watt. Take that savings and spend it on a quality MPPT controller. (Outback, Morningstar, Midnight) Wire it to the 12V battery bank, and hope batteries last . Batteries in parallel are problematic - see: http://www.smartgauge.co.uk/batt_con.html for details.

2) does your generator "auto-start" or is it manual start ?

3) prepare to replace the batteries and move it all to a 24V system. You have 12v@ 600ah now (7200 wh of storage) moving to a 24V system with 4, 6V, 200ah golf cart batteries gives you 4800wh (can you deal with adding distilled water to batteries, or do you need sealed AGM batteries?). If the 4800 wh is not enough, adding a parallel bank is feasible, bringing it to 9600wh. With large flooded batteries, comes the need to have enough charge current to bubble the cells enough to de-stratify them.

4) many of the better inverters, have internal transfer switches and integral high performance battery chargers (like a UPS on steroids) and will reduce the generator run time from the current times.

5) pure sinewave inverters produce grid quality power that will run motors efficiently, and not fry half your electronic gear. But they cost more, but worth it overall.

Thank you for taking your time!

1. This is also what I'm starting to lean towards. Where do I buy these (both panels and controller)? About the link: I currently have the batteries with all poles connected as method two but with inverter plus connected to battery 2 and minus to battery three. I'm guessing that the difference would be small to do option 3 or 4.

2. The generator is manual start.

3. See comment above about the batteries. A 24V system would be better, could I just series 2 of our current batteries and then parallel that? We'll get to the battery question later if the ones we have indeed doesn't work.

4. As the batteries (and our inverter) is new we have only used it for two things: water pump and charging the UPS. What kind of inverter do you suggest we get if we switch to a 24 volt system?

5. This is the reason I have been considering having the UPS still connected as is. It delivers clean power to our stuff and it shuts down as the (internal) batteries start getting low plus other protection (short circuit). (They don't protect the other batteries though).

[onni]

Anton

I think both you and I are a little confused with what you want. As of now you have the following equipment: Generator -> battery charger -> batteries -> inverter -> UPS -> appliances.

I am not sure why you have both a battery/inverter system as well as a UPS which also has batteries but if that is what you want then ok.

Now you want to add solar panels to help charge your batteries:

Solar panel -> PWM Charge controller -> batteries -> inverter -> UPS -> appliances
.................................................. .........^
Generator -> battery charger ---------------l

What I do not understand is why you want to put the PWM or MPPT solar charger between the batteries and inverter. The solar charger can only go between the solar panels and batteries.

I'm indeed not on track yet, that's why I'm asking for help

As I said in the reply to Mike: The UPS is mainly there for some protection. We could off course remove it if we have a solution where it doesn't add any value.

Ive seen a lot of solar charge controllers that have: PV connections, battery connections and load connections. They advertise that if I connect our inverter to the load connections I'll get some battery protection. But I guess that's only for lamps and so as they deliver too little amperage on those connectors.

[onni]

Anton why are you using UPS/Telecom batteries? You do know they are made to use very high charge and discharge currents and only can be cycled 200 to 400 times right? That battery will fail very shortly if pressed into cycle service, They are made for emergency standby service and never to be cycled.

Anyway if you were to look at the literature for the battery minimum charge current is C/10. So you have 600 AH which means the minimum charge current 600 AH / 10 H = 60 amps. At 12 volts using MPPT charge controller will require 60 amps x 13 volts = 780 watts. With PWM and battery panels 60 amps x 18 volts = 1080 watts. So take your pick use expensive battery panels with PWM or inexpensive grid tied panels with MPPT.

See my reply two posts up. We get them very cheap. I did not know that they needed to be charged that fast... What happens at a slow charge rate?

[SunEagle]

I'm indeed not on track yet, that's why I'm asking for help

As I said in the reply to Mike: The UPS is mainly there for some protection. We could off course remove it if we have a solution where it doesn't add any value.

Ive seen a lot of solar charge controllers that have: PV connections, battery connections and load connections. They advertise that if I connect our inverter to the load connections I'll get some battery protection. But I guess that's only for lamps and so as they deliver too little amperage on those connectors.

I now understand your desire to use the UPS.

You are also correct that the "load" connections on most charge controllers are for very little loads like some lights. Connecting an inverter to them will probably overload their output.

Thanks for answering my questions.

[onni]

Nope. I think you have it all figured out.

Lol, no... But I still don't get how the amount of batteries is important (except Sunkings comment on charge rate).

[SunEagle]

Lol, no... But I still don't get how the amount of batteries is important (except Sunkings comment on charge rate).

To properly charge batteries you need to have enough amperage from the controller. Too little or too much is not good. The C/10 is the minimum ratio where C = 600Ah.

With a 600AH battery system you will need somewhere around 60 amps which requires 780 watts of panels using a MPPT type charger or 1080 watts of panels using a lower efficient type PWM type charger.

Those are basic math calculations. Depending on where you live and how much good sun you get will allow you to properly size your panel wattage.