Thinking out of the box

**SunEagle** · 07-12-2016, 08:56 AM

Just be careful with that system. Anything over 50volts AC or DC is considered dangerous to people and is restricted in the US unless there is the proper warning signs and safety equipment to protect the user from getting electrocuted.

**bcroe** · 07-12-2016, 07:45 PM

Originally posted by Garouda

How much am I willing to invest in my battery bank?
What do I need in order to charge it?
How do I manage my power consumption in order to fit into the frame I’ve designed?
Like: ‘do not open the fridge after dusk...’
How can I preserve my batteries?

You certainly can greatly reduce your long term battery costs, by running your heavy loads only when the sun is shining. Store water in
a water tower over night. The more batteries are charged and discharged, the more money will be spent. Bruce Roe

**Garouda** · 07-12-2016, 07:52 PM

Thanks SunEagle, this also is an answer to my question about the online solar calculators or tutorials that are always restricted to 48Vdc.
I live in Thailand now and the standards here are quite flexible, but I will apply western standards.
My background Engineering - Business Management - Financial Analyst, I have some practical experience in electric circuits beside my background in Engineering so I'm more than aware of the danger. There will be a fence with warning signs around the installation.

**Garouda** · 07-12-2016, 07:55 PM

Originally posted by bcroe

Store water in a water tower over night.
Bruce Roe

Thanks Bruce.
That's the idea beyond the PV array reconfiguration, pump water into a water tower, when sun is available and when necessary.
Contingency plan: the genset.

**SunEagle** · 07-12-2016, 07:57 PM

Originally posted by Garouda

Thanks SunEagle, this also is an answer to my question about the online solar calculators or tutorials that are always restricted to 48Vdc.
I live in Thailand now and the standards here are quite flexible, but I will apply western standards.
My background Engineering - Business Management - Financial Analyst, I have some practical experience in electric circuits beside my background in Engineering so I'm more than aware of the danger. There will be a fence with warning signs around the installation.

Sounds like you understand the dangers. Even I once didn't worry about being around industrial electrical system at 480v AC but after seeing a number of friends and workers get shocked or be subjected to an ARC Flash I will say that wearing proper protective clothing is a very smart action.

Never take electricity for granted. It will reach out and bite even the most experienced electrical person if you let it. And becoming complacent with it is when that snake bites.

**Garouda** · 07-12-2016, 08:45 PM

Originally posted by SunEagle

Sounds like you understand the dangers. Even I once didn't worry about being around industrial electrical system at 480v AC but after seeing a number of friends and workers get shocked or be subjected to an ARC Flash I will say that wearing proper protective clothing is a very smart action.

Never take electricity for granted. It will reach out and bite even the most experienced electrical person if you let it. And becoming complacent with it is when that snake bites.

Frankly speaking, I'm hesitating . I know the danger myself, but what's going to happen when I won't anymore be able to maintain the system? I'm 64 now, what about myself within ten, fifteen years?
I'm reluctant to design a system resulting in high currents and we all know the benefits of a high voltage, or the drawbacks to high amperage. I'm also against batteries strings in parallel, but I'm concerned by the risky legacy

I'm leaving with the above described configuration.

**Mike90250** · 07-13-2016, 01:22 AM

Tell us a bit more about the solar water pump. Does it use a MPPT controller internally ? If so, connecting it to 96V batteries may fry it as it tries to find the MPPT point and does not have a PV panel as a current source, MPPT cannot work with a voltage source (batteries)

**Garouda** · 07-13-2016, 03:32 AM

Originally posted by Mike90250

Tell us a bit more about the solar water pump. Does it use a MPPT controller internally ? If so, connecting it to 96V batteries may fry it as it tries to find the MPPT point and does not have a PV panel as a current source, MPPT cannot work with a voltage source (batteries)

There is a solar pump inverter which is fed by the PV array, that's why I need to reconfigure it from 2 strings of 5 in series (Power) into 1 string of 10 in series (Water)
What I wrote is I do not want to have the batteries involved in the pumping process in order to preserve the battery bank.
Config (1) 2 x 5 PV panels -> MPPT controller -> batteries -> inverter -> AC loads
Config (2) 1 x 10 PV panels -> pump inverter (MPPT solar + PWM pump driver) -> pump (3-phase 220V AC)
Reconfiguration Config (1) -> Config (2) of the PV array through a combiner box with two 4-pole DC isolator switches, on demand, when necessary and when sun is available.

**Mike90250** · 07-13-2016, 03:22 PM

You are on your own, I don't know of any device like you are describing:
> Config (2) 1 x 10 PV panels -> pump inverter (MPPT solar + PWM pump driver) -> pump (3-phase 220V AC)

**sensij** · 07-13-2016, 03:46 PM

Originally posted by Garouda

Power: two strings of five panels in series, Voc= 5x39.5Vdc=197.5 Vdc.
Current: 250W nominal, Power tolerance 0, +5; 262.5W. 262.5W x 10= 2,625W.
Battery bank: 16 x 7.2V (bulk) = 115.2Vdc; 2,625W÷115.2V=22.8A, let’s consider a 30A MPPT controller charger, 96VDC, 300VDC PV input Max, 3400W PV input Max.
Inverter: 245Ah C8, 245÷8=30A 30X 220VAC=6600W; a 6kW inverter charger. (96Vdc-220VAC, 50Hz)

This part looks wonky to me. I'm not sure what C8 (C/8?) has to do with the inverter in this context. If the battery is 245 Ah, C/8 discharge current is 30.6 A, at 96 V that is 2940 W. Doubling that to account for surges seems reasonable, but that isn't what the OP wrote and it isn't clear if that is needed for the intended loads, which is how an inverter is normally sized.

Also, a reasonable guess at max sustained charge current would be something like STC rating * 0.85 / 96 V = 250 * 10 * 0.85 / 96 = 22 A, depending on the panel orientation. That is on the light side for a 245 Ah bank (C/11), but not exceptionally so.

Originally posted by Garouda

First the battery bank: 16pcs 6-volt 245Ah deep cycle batteries in series, or 23,520 Wh, 96Vdc.
25% DOD: 5,880 Wh available solar irradiance: 4.91 h/d 5,880÷4.91=1,190W

That is the first time I've seen insolation listed at two decimal points! Although there are plenty of fudge factors built in later to account for losses, it isn't clear if the seasonal differences in insolation (and possibly load) are being considered.

**Garouda** · 07-13-2016, 09:55 PM

Originally posted by Mike90250

You are on your own, I don't know of any device like you are describing:
> Config (2) 1 x 10 PV panels -> pump inverter (MPPT solar + PWM pump driver) -> pump (3-phase 220V AC)

I haven't decided yet which solar pump inverter I eventually will buy though...
I hope I won't have problems with the moderators... it's as Leonics Apollo SPN-216 at www.leonics.com/product/renewable/inverter/dl/SPN-223.pdf

**Garouda** · 07-13-2016, 10:05 PM

Originally posted by Mike90250

You are on your own, I don't know of any device like you are describing:
> Config (2) 1 x 10 PV panels -> pump inverter (MPPT solar + PWM pump driver) -> pump (3-phase 220V AC)

Hi Mike, I tried to post a reply with a link but this was obviously against the rules on this forum. If you use a search engine with solar pump inverter, you may find it. It's a Leonics Apollo SPN 216 inverter. In fact I haven't decided yet the one I will eventually buy, there are many models. I guess they are not common in the States due to the 50V limitation.

**SunEagle** · 07-14-2016, 09:02 AM

Originally posted by Garouda

Hi Mike, I tried to post a reply with a link but this was obviously against the rules on this forum. If you use a search engine with solar pump inverter, you may find it. It's a Leonics Apollo SPN 216 inverter. In fact I haven't decided yet the one I will eventually buy, there are many models. I guess they are not common in the States due to the 50V limitation.

There are automatic software safeties that do not allow a post with a link attached. It gets unapproved which then takes a MOD to review it and take action from there.

**Garouda** · 07-14-2016, 01:54 PM

Originally posted by sensij

This part looks wonky to me. I'm not sure what C8 (C/8?) has to do with the inverter in this context. If the battery is 245 Ah, C/8 discharge current is 30.6 A, at 96 V that is 2940 W. Doubling that to account for surges seems reasonable, but that isn't what the OP wrote and it isn't clear if that is needed for the intended loads, which is how an inverter is normally sized.
C8 rating is considered as the fast discharge rating to take into account for an FLA battery, I must have read this somewhere.
You are right, it's 2940W, and I initially had in mind a 3500W inverter. The model is able to cope with a surge nominal x 3, but I won't have any big inductive loads which usually cause such a surge. Then I considered I could afford a bigger one, in case of, but mixed up my numbers and wrote some BS calculation. An inverter is indeed sized according to the loads when the whole system is designed the same way. If your inverter is too big (say your loads are too heavy) it'll be at the expenses of your battery bank lifetime...
Also, a reasonable guess at max sustained charge current would be something like STC rating * 0.85 / 96 V = 250 * 10 * 0.85 / 96 = 22 A, depending on the panel orientation. That is on the light side for a 245 Ah bank (C/11), but not exceptionally so.
Here I can't follow you. First it's not 96V, but 16 x 7.2V (bulk-absorbtion) = 115.2Vdc one has to consider. Second I do not use such rules of thumb like current times 1.3, voltage times 1.2 or other .85 but take the temperature characteristics out of a real PV panel datasheet and adjust according to my own situation.
That is the first time I've seen insolation listed at two decimal points! Although there are plenty of fudge factors built in later to account for losses, it isn't clear if the seasonal differences in insolation (and possibly load) are being considered.
That's because it's the first time you see one I calculated myself by crunching lots of numbers... I may have made some mistakes, but my value seems to be acceptable. Indeed I found a study by the School of Renewable Energy Technology, Naresuan University mentioning 5.06 as total yearly average for Thailand, sorry about that, but it's also with at two decimal points. I also calculated the yearly average for my location, and not the lowest month because my system will have a genset as back-up anyway.

see above

Thinking out of the box

Thinking out of the box

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