Introduction with Questions about system upgrade

Fe-WoodFe-Wood Solar Expert Posts: 96 ✭✭
Hi everybody!
My name is Peter and I live in the Sierra Foothills and run my Art/Manufacturing business off-grid. Currently I run a 15KW Lister Diesel for the shop power needs. I want to add battery power for music and some lights. I'm wondering what people think about Trojan, Rolls and Crown Batteries. I'm going to be buying batteries for the shop power as well as an upgrade/conversion for my Grundfos SQFlex water system.

My other and more pressing question is: I am going to be building a small utility/bathhouse as support for a travel trailer I will be living in shortly.

My current water pumping System is a Grundfos 6SQF2 with a CU-200 Controller and 4 Kyocera 130w x12v panels. My well pump runs about 3-4 hrs a day off and on in the summer. It has 4000 gl storage and a float switch.
I would like to combine this system into another system so I can produce more power to run the trailer and washer/dryer etc.
I am looking at adding 4 more Kyocera 135W X12v panels and a Outback VFX2812 Inverter. For battery storage, I'm thinking 2 of the Rolls Surrette 6CS21P batteries. I'm looking for true sine-wave electric for computer use. Am I missing or overlooking something?

I should also add the shop and utility house will be about 400' apart...

I haven't looked into Solar power for about 5 years now and it seems a lot has changed for the better!

Thanks for looking and any help or guidance:D

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Introduction with Questions about system upgrade
    Fe-Wood wrote: »
    Hi everybody!
    My name is Peter and I live in the Sierra Foothills and run my Art/Manufacturing business off-grid. Currently I run a 15KW Lister Diesel for the shop power needs. I want to add battery power for music and some lights. I'm wondering what people think about Trojan, Rolls and Crown Batteries. I'm going to be buying batteries for the shop power as well as an upgrade/conversion for my Grundfos SQFlex water system.
    I will leave it to others that have more off-grid experience than I--But many people have certainly been happy with either the Rolls or Trojan batteries on the forum here. I have not heard as much (either way) about Crown.

    In the end, treating the batteries well will go a long way towards a long life.

    Read the couple battery FAQ's for a start:

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    Avoiding over discharging, over charging, boiling dry, cycling often below 50% state of charge, never below 20% state of charge, and getting batteries above `75% state of charge reasonably quickly (day or so) to reduce sulfation all help.
    My current water pumping System is a Grundfos 6SQF2 with a CU-200 Controller and 4 Kyocera 130w x12v panels. My well pump runs about 3-4 hrs a day off and on in the summer. It has 4000 gl storage and a float switch.
    I would like to combine this system into another system so I can produce more power to run the trailer and washer/dryer etc.

    Personally, I would be tempted to leave this setup alone... Just switching from a Solar PV + Pump setup to Solar+pump+charge controller+batteries really increases the costs (by ~4x or more) of the installation and operational costs (batteries need replacement every 4-8+ years, more losses in system mean more panels to make up extra losses, etc.).

    That means setting up a second off-grid PV + battery system would probably be much better (if it is going to be a smaller system--if a large system, then perhaps rolling the pumping requirements into the system won't hurt--especially if you pump mostly during the sunny 6-9 months of the year).
    I am looking at adding 4 more Kyocera 135W X12v panels and a Outback VFX2812 Inverter. For battery storage, I'm thinking 2 of the Rolls Surrette 6CS21P batteries. I'm looking for true sine-wave electric for computer use. Am I missing or overlooking something?

    Loads? How much power (peak watts, and Watt*Hours) are you looking to supply.

    Solar PV power is expensive--Currently you have a 15kW diesel genset which probably supplies more power than I would ever use in my suburban home (I probably peak around 2kW and average around 8kWH per day for my grid connected home).

    You may end up breaking the loads into several parts:
    • Pumping--Existing system as is
    • Shop Tools / Heavy loads (exterior work lights, tools, perhaps even vacuuming/etc.)
    • Small loads for evening/night/quiet time (laptop, modem, lights, radio, small TV, recharging cell phone, etc.).
    Also, if your loads are seasonal (irrigation/fan/air conditioning during summer, etc.). you can size the system to run with fewer panels than if you have constant loads all year long (winter, need more panels and/or genset for bad weather).

    Inverter wise--There is a lot of interesting product... From a very nice 12 volt 300 Watt TSW with "search mode" and "DC inhibit" to large inverter/chargers that can supply 120/240 VAC split phase power and even support Grid Tied / Off-Grid modes with the same unit.

    I would suggest looking at a Battery Monitor option for the battery bank... Very handy for understanding how well the battery is being recharged after supplying power. Not perfect--but saves measuring specific gravity for flooded cell battery banks--and is the only "real time" monitoring option for AGM/Sealed batteries.

    And, a Kill-a-Watt meter is great for measuring your 15 amps 120 VAC loads (kWH per day).

    I would also suggest placing a Watt*Hour meter (a surplus utility kWH meter is cheap these dasy) on your genset. And, with logging your fuel usage (per day/per month) you will get a good handle on your power costs so you can make the comparisons between how much power you use today and how much it costs you ($$ of fuel+generator costs / kWH).
    I should also add the shop and utility house will be about 400' apart...

    One of the things we always try to point people to is conservation and understanding their loads. Conservation because it is almost always cheaper to conserve a watt than to generate a watt... And understanding loads to invest the time and money as appropriate (off-grid power still costs around ~$1-$2+ per kWH--or ~10x what grid connected power costs).

    Using a small TSW inverter for the "sensitive loads" like electronics, wall transformers (and low standby losses). Use a medium sized 1,200-1,500 watt TSW for a refrigerator. And possibly a large MSW for shop tools (if a large TSW is too expensive).

    Also, choosing the right battery bank voltage of 12/24/48 volts (12v good for 1,200-1,500 watts max; 24 for 2,400-3,000 watts; above that think about 48 volt bank).

    I haven't looked into Solar power for about 5 years now and it seems a lot has changed for the better!

    Sending a lot of power 400' is not cheap and easy. If you have to send a lot of power (shop tools)--using a step up / step down pair of transformers will save you for power line costs--but they can give you 5% or so losses just idling with no loads (turn off branch circuit if no active loads?).

    However, if you only need a little power for the RV and a lot at the shop 400' away--installing the main PV system there and sending a "small" amount of power to your home may be a good alternative.

    In the end--It is difficult to give you a good answer without better understanding your needs/requirements.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Fe-WoodFe-Wood Solar Expert Posts: 96 ✭✭
    Re: Introduction with Questions about system upgrade
    BB. wrote: »

    I would also suggest placing a Watt*Hour meter (a surplus utility kWH meter is cheap these dasy) on your genset. And, with logging your fuel usage (per day/per month) you will get a good handle on your power costs so you can make the comparisons between how much power you use today and how much it costs you ($$ of fuel+generator costs / kWH).

    Thats a good idea! I have an hour meter but have always wondered what I'm actually using. Presently, on average it cost me about a $1.25 to run the generator for 1 hour. This includes Oil changes and fuel.
    BB. wrote: »
    I will leave it to others that have more off-grid experience than I--But many people have certainly been happy with either the Rolls or Trojan batteries on the forum here. I have not heard as much (either way) about Crown.

    In some recent reading I did, I understood Rolls Surrette made the Trojan line of batteries. Is this correct? Also I like the Surrette business model. Just an aside...
    BB. wrote: »
    Personally, I would be tempted to leave this setup alone... Just switching from a Solar PV + Pump setup to Solar+pump+charge controller+batteries really increases the costs (by ~4x or more) of the installation and operational costs (batteries need replacement every 4-8+ years, more losses in system mean more panels to make up extra losses, etc.).

    What I'm looking to do with this system is split it. I want to leave the pump system "as is" but when there is no power demand from the pump I would like the power to be able to charge batteries. So I guess what I'm looking for is a switching device that will read the demand from the pump and switch from charging to pumping or visa-versa.
    BB. wrote: »
    Also, choosing the right battery bank voltage of 12/24/48 volts (12v good for 1,200-1,500 watts max; 24 for 2,400-3,000 watts; above that think about 48 volt bank).

    This is good info. What kind of loss will I see with a 2500watt inverter on 12vDC such as the one I mentioned in my post? I have basically sized the inverter for spike loads rather than run loads. Think 9amp cloths washer
    BB. wrote: »
    In the end--It is difficult to give you a good answer without better understanding your needs/requirements.

    Thank you BB!! You have raised some great questions and provided great info with your response.

    So in a nut shell-
    *Shop will be run by the genset and will run a charger for batteries that will run basic safety lights and music system on 12vdc. I may run a 12/2 line to untility/bathouse for a small backup charger.

    *Water pumping system will be split between pumping demand and battery charging demand. I believe the CU-200 controller has the capacity to switch. I'm going to have to check that out. I know it can go from various power supply types, wind ,sun and genset. It may need to have a switching device. Regardless it won't be run by the inverter.

    *Additional 4 panels will be for battery charging only. I should add that high power demand will be made during peak sun hours when possible.
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Introduction with Questions about system upgrade

    Just to be clear, the Surrette are certainly both more expensive and should last longer---is it 2x the price for 2x the life--I am not sure. (I believe Rolls/Surrette is a different company than Trojan).

    Regarding inverters--Choosing the right one is always a tricky job.

    Too small, and they will not handle the starting surges. Too large, and the standby losses will kill you. Equipment runs better/more efficiently on a TSW inverter, but their tare losses are about 2x the same sized MSW.

    If you start with a small system--The Morning Star 12 volt 300 watt (600 watt surge) TSW inverter with "search mode" and "DC inhibit" is not a bad one to start with. Even for a small system--you can leave it in "search mode" (it looks for a >6 watt AC load while ~0.6 watts on search mode, then switches "on" with ~5 watts tare + AC loads--PDF Glossy).

    Should work well to run 120 VAC AC power to a few CFL lights, radio, cell phone chargers, etc.--while left in "search mode". Or you can set it to be turned on manually when you want AC power (low current/voltage switch).

    Here are a couple inverter FAQ's which will help:

    All About Inverters
    Choosing an inverter for water pumping

    Being able to switch the pump panels to the solar PV system... There are various ways of doing it, and various issues. Matching the panel voltage/setup to the charge controller chosen. Possibly changes to series/parallel connections to change Vmp-array between pump and charge controller. Needing a second charge controller if you cannot parallel with existing off-grid array (Vmp/Imp matching for series/parallel connections). How far the pump array is from the battery bank/charger, etc.

    I can start "making stuff up"--but is probably less confusing for both you and me if you can give me some suggested loads (watt*hours per day) and we can get some basic system specification.

    In general, people over estimate how much a solar system generates and underestimate their loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Introduction with Questions about system upgrade
    Fe-Wood wrote: »
    What I'm looking to do with this system is split it. I want to leave the pump system "as is" but when there is no power demand from the pump I would like the power to be able to charge batteries. So I guess what I'm looking for is a switching device that will read the demand from the pump and switch from charging to pumping or visa-versa.

    You could do it, but it sounds like more trouble than it's worth. I'd run the pump PV to a charge controller to the batteries, and then just run the pump off the batteries. Achieves the same basic goal without having to rig up special switching.

    The main problem with the switching, is that it requires power to the pump control. I.e., it has to detect when the pump is going to run, then trip a relay to switch the PV output from the battery charge controller to the pump control...which is useless since the pump control has to have power all the time or there is nothing for the switching system to detect and react to.

    So, if you have the PV output switched to the charge controller, where does the power for the pump control come from? Has to come from the batteries, no? And if you are going to feed the pump control from the batteries - then why bother with the switching in the first place?
  • Fe-WoodFe-Wood Solar Expert Posts: 96 ✭✭
    Re: Introduction with Questions about system upgrade

    Great comments and questions, Thanks!

    dwh-
    I believe grundfos makes a controller that is for using generator power (ie.110vac) or is the CU-200 capable of regulating the demand and capacity of a battery tied pump. Currently the pump maxes out at about 210watts tied directly to the panels. Would the batteries provide to much power if tied directly to the controller?

    BB-
    I have done a few calculations and have a few questions about MSW vs TSW. From the reading you linked to (good stuff) it sounds like MSW is not really worth it when you compute the added draw and reduced life of the motors. Did I understand this correctly?

    My biggest load will be the cloths washer with a start up load of about 3400 watts. Add to that the misc. phantom loads of about 550 watts and I will have a spike load of 4000 watts. The inverter I'm looking at, the outback VFX2812 Inverter is rated at 6000 watt spike load, If I'm understanding the specs right. My run load would be 1300 watts. My panels will put out 864 watts at 80% efficiency. I've looked up my locations sun index but I don't remember what it is from the chart. I'm thinking it is about 5 hrs in the winter and about 9 hours in the summer.

    I guess my question has become- Is this system sized right for the demand I'm looking for and how do I tie in the water pumping system the most efficient way.

    I'm thinking I will run a 110vac line from the shop generator to the pump when I run the water line. Its only pipe and wire and I will have the trench anyway for the water line. I am also looking at scaling this system up when I build the house. Given my philosophy, I would rather spend more up front for the better batteries and components that do it on the cheep and have to fight it all the time. I have done the Costco deep cycle batteries for another stand alone system and they seem to last only about 4 years.

    Comments?
    Thanks again!
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Introduction with Questions about system upgrade
    Fe-Wood wrote: »
    dwh-
    I believe grundfos makes a controller that is for using generator power (ie.110vac) or is the CU-200 capable of regulating the demand and capacity of a battery tied pump. Currently the pump maxes out at about 210watts tied directly to the panels. Would the batteries provide to much power if tied directly to the controller?

    Looking at the specs, the CU-200 can run off AC or DC, but the DC has to be 30-300v, so to run it off batteries you would have to rig your batteries in either 36v or 48v (nominal) configuration.

    The pump motor spec sheet shows the same specs.

    That spec sheet shows the system running off batteries - Page 14:

    http://www.affordable-solar.com/admin/product_doc/Doc_Product%20Guide%207-07_20080206105112.pdf


    What you have now is on page 13, and what you are talking about doing is on page 14. The only thing is, that you'll have to design and build the rest of your solar/battery system around the nominal voltage of the battery bank - 36v or 48v. 36v isn't too common, but 48v is and there are advantages to rigging for a higher voltage.

    Voltage drop over 400' becomes more of an issue as voltage decreases, so your 48v PV panels and batteries really should be close together (near the pump), then invert to 120v AC for the 400' run to whatever.

    The alternative would be to relocate the pump solar panels to be near the batteries and the new solar panels, then invert to 120v to run back to the pump/controller which can run off AC as well as DC.
  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: Introduction with Questions about system upgrade

    I'm with DWH on the supply for the pump.... don't do two systems.

    I run a Grundfos pump through a CU200 controller normally from a 2500w inverter, but that inverter converts to a charger when the generator is running, so if I'm pumping when the gen is on, the pump gets power from the gen. I have posted to a recent thread in the 'solar pumping' section detailing how my Grundfos can draw from either of my inverters or the generator.

    That Grundfos system will use voltages from 30 to 240, AC or DC. I'm still amazed at that. I use 120VAC because it's convenient, having three inverters online and generator backup.

    I used an MSW inverter for years to power the pump that supplies pressure to the house and eventually the pump motor failed, not unexpectedly. I've since replaced that inverter with one that has a better waveform. I could hear the pump motor straining when it was on the MSW inverter. (Every now and again I'd have to 'thump' the motor to get it going). No problems like that using a better inverter.

    One problem you've likely already been considering is that of supplying power to an RV from a solar battery bank. For simplicity: 12VDC from the solar panels into the batteries. Then invert to 120VAC, send to the RV, then convert back to 12VDC to keep the RV batteries charged. Pretty inefficient way to do things. Having lived in an RV for almost a decade, I understand. Running 12VDC long distances isn't good either. (you can substitute whatever DC voltage you prefer, the inefficiencies are still there)

    My mobilehome, watershed, pumphouse (includes the power system) and RV are all about 50 to 75 feet apart from each other. I have buried conduits and water pipes to each.

    We are 'neighbors' and I'll be glad to assist in any way that'd be helpful. My first question, tho, is about how you want to handle powering the RV. You can PM me if there are details or questions that you don't think would benefit others (but I'm not usually online weekends... we have a slow dialup at home, lightning fast DSL at work).

    Phil
  • soloronesolorone Solar Expert Posts: 254 ✭✭✭
    Re: Introduction with Questions about system upgrade

    400 feet is obviously a long run. I know nothing of the new controllers, but I have been running my system 24V, 220' which is about the max for 4 runs of 4 ought copper wire.

    It would seem at higher voltages, #2 wire might suffice. I have no idea what wire cost now, but I think I would start here and seek a balance between transformer cost, and idle/energy loss, and the cost of wire and conduit.

    As for the Rolls batteries, mine are 9/10 years old, and I have not treated them well, they have taken a lot of punishment, and are still hanging in there, but current capacity may now be only 50/60%. I expect them to last maybe another year or two. I hope I can afford another set of Rolls/Surretts.
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Introduction with Questions about system upgrade
    Fe-Wood wrote: »
    I believe grundfos makes a controller that is for using generator power (ie.110vac) or is the CU-200 capable of regulating the demand and capacity of a battery tied pump. Currently the pump maxes out at about 210watts tied directly to the panels. Would the batteries provide to much power if tied directly to the controller?
    As I understand--the "smarts" is actually in the pump motor/electronics. Basically the MPPT and AC/DC conversion circuitry is all in the pump body itself.

    The higher the voltage, the less current and smaller wire gauge you will need.

    And, I guess I will continue to say look at laying out your system without regards to the pump. If the pump is close to the energy source (keep wires short) and it will not be a huge fraction of the total energy usage--then look at what it would cost/take to integrate the pump into the new system.

    Also read the specifications closely---The pump at lower voltages is current limited (and therefor limited in its pumping capacity). If the "lower voltage" will still meet your pumping needs--Great.
    I have done a few calculations and have a few questions about MSW vs TSW. From the reading you linked to (good stuff) it sounds like MSW is not really worth it when you compute the added draw and reduced life of the motors. Did I understand this correctly?
    Certainly, if you can justify TSW inverters, they will be better for your loads and more efficient when driving those loads... However, the much higher costs of TSW and the higher idling losses (tare or unloaded power usage) of the TSW inverters do certainly impact your system design.

    Some folks will use a small TSW for the critical loads and a big MSW for shop tools and such. It may not be perfect--but you can save some money and/or add panels/batteries to your system. Driving larger motors, old fashion washing machines (those with non-electronic timers) and such--people the world over use MSW.

    Perhaps some other off-grid folks here can relate their TSW / MSW choices.

    I am not trying to push TSW as the only solution... But with all of the load/inverter options--it is very difficult to make large sweeping statements (that are anywhere useful and accurate :roll:).,
    My biggest load will be the cloths washer with a start up load of about 3400 watts. Add to that the misc. phantom loads of about 550 watts and I will have a spike load of 4000 watts. The inverter I'm looking at, the outback VFX2812 Inverter is rated at 6000 watt spike load, If I'm understanding the specs right. My run load would be 1300 watts. My panels will put out 864 watts at 80% efficiency. I've looked up my locations sun index but I don't remember what it is from the chart. I'm thinking it is about 5 hrs in the winter and about 9 hours in the summer.

    I really cringe at pulling 3kW/6kWatt surge on a 12 volt battery bank.

    Running 3kW on a 12 volt system, assuming 85% efficient, 10.5 volt cutoff, and 1.25 NEC safety factor for fuses/wiring:
    • 3,000 watts * 1/10.5 volts cutoff * 1/0.85 eff * 1.25 = 420 Amp circuit/breaker/fuses
    For the size system you are talking about--I really would be looking a 48 volt battery bank. That will cut the current to 1/4 and give you a lot more voltage drop across wiring/fuses/breakers.

    Also, if you have a lot of Watt*Hours / Amp*Hours per day of power usage--you may be able to use fewer solar charge controllers (they are typically limited to 60 or 80 amp output--whether at 12 volts or 48 volt battery bank) if you have a large PV array.

    Without knowing the average loads, it is difficult to estimate an "optimal" system.

    Motor surges are a pain--but a good inverter+battery bank should be able to power a washing machine pretty well.

    Again, perhaps a few people can suggest their favorite off-grid appliances here too.
    I guess my question has become- Is this system sized right for the demand I'm looking for and how do I tie in the water pumping system the most efficient way.

    It looks like your pumping system is current configured to ~60 volts--Perhaps a 48 VDC battery bank will be a nice fit.

    Do you have a lot of 12 volt loads and that is the reason you are leaning towards a 12 volt battery bank? Can you use 120 VAC (efficiently) instead?
    I'm thinking I will run a 110vac line from the shop generator to the pump when I run the water line. Its only pipe and wire and I will have the trench anyway for the water line. I am also looking at scaling this system up when I build the house. Given my philosophy, I would rather spend more up front for the better batteries and components that do it on the cheep and have to fight it all the time. I have done the Costco deep cycle batteries for another stand alone system and they seem to last only about 4 years.

    Whatever you run--I would plan on running some extra wire (enough for 240 VAC split phase) and/or some extra empty buried pipe/conduit that you can pull other stuff through later (communications, extra 120/240 VAC, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Fe-WoodFe-Wood Solar Expert Posts: 96 ✭✭
    Re: Introduction with Questions about system upgrade

    I have to say you guys are really helping me work this out. thanks a bunch!!
    My shop runs on the 15KW genset. Its about 350'-400' from the pump house. The power line I will run from the genset to the pump house will be 120vac for extra battery charging at the pump house. This line will be switched in the shop for on-off control and will run a small dedicated battery charger, 10 amps max. The trailer will run on a 120vac hookup rather than through the trailer batteries and on board inverter. This will be powered from the pump house. My draw in the trailer should be in the 1000-1500 watt range max. I'd rather not run the well pump off the inverter to reduce inverterted power draw. I will read up on the specs for the pump to see what my options are. I'm not opposed to running 48vdc for the battery bank because through this discussion I realized I can re-wire the existing panels to produce 48vdc to charge the batteries, They may already be this way for the pump, come to think of it. The panels, batteries, inverters and pump controller will all be within 5'-10' of each other so line loss and proper wire size is not an issue. All long runs will be 120vac.

    At this point there hasn't been a strong enough argument for a MSW inverter so I'm still leaning towards the TSW inverter. It seems innovation will remove MSW inverters from the market over time anyway and I am looking at expanding the system in 3 to 5 years. Also, space for panels is not an issue.

    To answer some of the load questions- I'm in the building/designing stage so I can make the system what I need and make the demand to suit the system, if that makes sense. 48vdc will require more batteries but I suppose thats good?
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Introduction with Questions about system upgrade

    Technically, for a given amount of power/energy... It does not matter (for example) 4x12 volt batteries in parallel (4x the AH capacity) or 4x12 volt batteries in series (4x the voltage)... Remembering:
    • Power=Voltage*Current
    • Power= Voltage *4xCurrent = 4xVoltage * Current
    From a transmission and energy usage point of view, it is generally easier to manage 48 volt and 100 amps (4,800 watts) vs 12 volts and 400 amps (still 4,800 watts).

    The other missing connection is the actual Watts * Time or Watt*Hours of energy use.

    1,500 watts peak is a pretty hefty load for an off-grid system. But the big issue is time... For sample run a 1,500 watt microwave 20 minutes a day vs running a 200 watt desktop computer + monitor + laser printer + network + etc. for 10 hours a day:
    • 1,500 Watts * 20 min/60 min per hour = 500 Watt*Hours per day
    • 200 Watts * 10 hours = 2,000 Watt*Hours per day
    So the "smaller" load ran all day would require 4x the panels and 4x the batteries of a microwave oven only running 20 minutes a day.

    In general, a good starting point is around 3,300 Watt*Hours (3.3 kWH) per day for a good size cabin/off-grid home setup (100 kWH per month).

    Above that size of system (around 1,500-2,000 watts of panels), becomes a pretty large system and not at all inexpensive to build/install. Even this "smallish system" may cost around $15,000 or more to build.

    Remember too--You have to replace the batteries every 4-8+ years and the electronics probably every 10-15 years. A larger system will require more costs over time to maintain too.

    Not to say a larger system cannot be done--But you really want to quantify the loads first before you lay out that amount of cash.

    All the above examples/numbers/costs are just really wild estimates to get a ball park idea of what you are aiming for. With better power usage estimates we can get more exact on the hardware and you can work out the exact costs.

    Off Grid solar power prices have come down in the last decade by a lot... But it is still not cheap. Off-Grid power still costs (very roughly) around 10x watt grid power costs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Fe-WoodFe-Wood Solar Expert Posts: 96 ✭✭
    Re: Introduction with Questions about system upgrade

    BB-
    My biggest draw will be cloths washing and drying say 1800 watts for 2 hours, 2 or 3 times a week. The other draw will be lights, computer, router, modem, answering machine and printer. Maybe a microwave. the modem (satellite internet), answering machine and router will be on all the time. I'm hoping for less than a 20 watt draw but have no idea yet. Most of the converters I have looked at for this stuff are measured in Milly amps. So I guess its 24 * 20 =480 watt hours a day plus 3000 watt hours 3 times a week. then lights and computer at 500 watts for 5 hours a day = 2500 watt hours. so looking at it from a weekly perspective- (480*7)+9000+(2500*7)=29,860 watt hours a week consumed. My panels will generate about 850 watts (conservative) for an average of 7 hours a sunny day. so 850*7=5950 watt hours a day or 41,650 watt hours a week. Am I doing this right? Looked at from the winter power production, I produce 29,750 a week with 5 sunny hours a day. This is when the generator will come in...

    I'm gone for the weekend and first part of the week but I look forward to more discussion when I get back.
    Thanks for all the help so far everyone!!!!
  • BB.BB. Super Moderators, Administrators Posts: 29,823 admin
    Re: Introduction with Questions about system upgrade

    Is this an electric drier?...

    Perhaps you can find a more efficient set of units? My Fisher Paykel washer and natural gas drier each take about 0.250 kWH per load.

    29,860 WH per week or 119.440 kWH per month.

    Assuming Sacramento type weather with PV Watts, 0.52 derating for off grid system, fixed array, use 1kW worth of panels (even number):
    "Station Identification"
    "City:","Sacramento"
    "State:","California"
    "Lat (deg N):", 38.52
    "Long (deg W):", 121.50
    "Elev (m): ", 8
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 38.5"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:","12.5 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 2.75, 41, 5.12
    2, 4.23, 57, 7.12
    3, 5.27, 79, 9.88
    4, 6.33, 90, 11.25
    5, 6.83, 97, 12.12
    6, 6.93, 93, 11.62
    7, 7.23, 99, 12.38
    8, 7.30, 101, 12.62
    9, 6.96, 95, 11.88
    10, 5.67, 82, 10.25
    11, 3.68, 52, 6.50
    12, 2.71, 39, 4.88
    "Year", 5.50, 927, 115.88

    Assume that 9 months of the year no-generator or February with 57 kWH per month minimum production (20 year average):
    • 119.440 kWH per month / 57 kWH per month per 1 kWH of panels = 2.095 kW of panels minimum
    So, for your system, I would suggest a minimum of 2,100 watts of solar panels. For 3 months of the year (winter) you will make up production with a genset (as needed). Outside of February you should not need a generator for normal weather/operation.

    Your battery bank assuming 1 to 3 days of "no sun" with a minimum of 50% discharge (for longer battery life):
    • 119,440 WH per month / 30 days = 3,980 Watt*Hours per day
    • 3,980 WH per day * 1/0.85 inverter eff * 1/48 volt battery bank * 1 day no sun * 1/50% max discharge = 195 AH @ 48 volt bank and 1 day no sun
    • 3,980 WH per day * 1/0.85 inverter eff * 1/48 volt battery bank * 3 day no sun * 1/50% max discharge = 585 AH @ 48 volt bank and 3 days no sun
    Note, for a 6kW inverter (12kW surge) on 48 volts--you are probably looking at 600 AH @ 48 volts minimum.

    There are some more rules of thumb to look at--but the above is probably the "minimum system" that would meet your needs (from my point of view).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Introduction with Questions about system upgrade

    Sounds like you are being optimistic. I wouldn't assume 7 hours of production a day unless your existing PV is already getting that much. Computer, modem, etc...20w? Not a chance. My Acer netbook (the power saving model) draws 9-14w all by itself.

    You have a handle on the math, but you are also leaving out the derating factors - for instance the batteries are only 80% efficient and the charge controller somewhat less than 100% (though the good MPPTs are rated up in the 90's)- so toss out AT LEAST 20% of your estimated harvest. Then the inverter is less than 100% as well, and then there is the line loss from a 400' run of wire.

    The rough rule of thumb is that from PV->charge controller->battery->inverter you'll end up with about 50% of your PV harvest in the form of usable power after system losses.

    6000wh/day divided by 48v works out to about 125ah/day. You don't want to take the batteries below 50% so you'll need at least 250ah of battery at 48v. That would be 8 [email protected] batteries, or 8 [email protected], etc.

    And that only gives you one day's reserve capacity...so you are looking at running the gen every single day the sun doesn't shine. Or, I should say, A gen. You could keep a little Honda eu1000i in the pump house to run a battery charger on cloudy days instead of having to run the big gen just to charge batteries.

    If you wanted to have your batteries last a long time by only taking them down 25% regularly, then you'd have to double the bank size. That would also serve to give 2 days reserve for the occasional drain down to 50%.


    Putting the PV/battery/inverter/charger at the pump house end of a 120v line is good. Assuming that runs underground, don't forget to run an extra large conduit in case of future expansion, but also to run another (also oversized) conduit for low-voltage communications lines - you will want to monitor what is going on in the pump house.
Sign In or Register to comment.