Is my thinking correct?

SystemSystem Posts: 2,511 admin
Hey guys... new here obviously (which is why i'm in the beginner's section =)). I have been doing a lot of research on a small solar system that i can ultimately use for space heating/cooling my small home. I can get 10 175w panels (Voc=43.6v ea, Current at Pmax=4.9amps ea) for a reasonable price, so i would be looking at a 1750w system total. I have looked on these forums but i can't get exact answers to my questions, so please help me if you can.

I know I would need to get the following system components, but I am confused about somethings (explained below):
1. Solar Panels 2. Some type of combiner (as shown here http://www.freesunpower.com/example_systems.php). 3. Charger Controller 4. Deep Cycle battery bank 5. Inverter.

If I missed something let me know.

My main questions are these: How do I decide which controller to get? And are there any resources that anyone can suggest for how to hook it up? From what I am finding, I will need multiple controllers for this 10-panel system. I have found conflicting information about how to decide this... (as shown here http://www.sunsoglobal.com/faq/How%20to%20Size%20a%20Solar%20Charge%20Controllers.pdf, vs. here http://www.freesunpower.com/chargecontrollers.php). In other words, do I need to use 2 50amp (due to the sum of the max amp output of 5 panels) controllers? and how to I decide what voltages they should be rated to? Is this determined by what one of my batteries is (which will be 12v) or by the sum of all of the volts of my batteries?

Thanks in advance for any and all advise and/or references...

Comments

  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Is my thinking correct?

    Generally, heating and cooling with solar PV system is quite expensive (requires a lot of solar panels and batteries).

    What are you planning on using for heating and cooling? Something like a mini-split heat pump system? Or resistance heater and swamp cooler?

    Regarding the the solar panels+charge controller--You should define your loads (maximum/average power) and the battery bank voltage.

    Then you can choose a charge controller... With "non-standard" Vmp solar panels (non-standard regarding battery bank 12/24/48 volt charging for a battery bank), you probably will need a MPPT type charge controller... Those run around $500-$700 each. And how many you will need depend on the battery bank voltage and the number of solar panels/wattage/configuration.

    There are a lot of questions here, typically we like to start with the loads, then define the battery bank, and then pick the inverter/charge controllers/solar array.

    You can go the other way, start with XXXX watts of solar panels and then figure out how much power you can get from them and how large a battery bank you can support... But it would be helpful to know, roughly, were your system will be installed (sunny southwest, cloudy northeast, etc.)...

    It will be kind of confusing starting in the middle and know knowing where you really want to go.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: Is my thinking correct?

    another question might be how long you intend to press the heating/cooling timewise every day? to use a heavy load for many hours day and night means not only more pvs necessary to provide that power, but the storage of that power in batteries will need to be quite large. when it comes to heating and cooling there is no such thing as a small system for this and 10 175w pvs is not a small system in my book, but for heating and cooling it is small.
  • jcgee88jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Is my thinking correct?
    in_dmand wrote: »
    I have been doing a lot of research on a small solar system
    that i can ultimately use for space heating/cooling my small home.
    If I missed something let me know.
    ...

    You didn't mention if your home is already connected to the
    grid. If it is not, then a battery system makes sense. If it is
    connected, then doing a conventional grid-tied system, i.e., no
    batteries and no charger, is more straightforward, less
    expensive to buy and maintain, and more efficient in terms
    of energy harvest. What you would lose in a battery-less
    config is the ability to run standalone should your utility's
    power fail (but you could plug that gap by buying a generator).

    So, is your home currently connected to the grid?

    John
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Is my thinking correct?

    Using solar directly to heat air or water is orders of magnitude cheaper and more efficient than using PV. Solar hot water might capture 4-5 times as much energy per square foot with a much cheaper cost, making a system much more cost effective.

    Tony
  • System2System2 Posts: 6,290 admin
    Re: Is my thinking correct?
    BB. wrote: »
    Generally, heating and cooling with solar PV system is quite expensive (requires a lot of solar panels and batteries).

    What are you planning on using for heating and cooling? Something like a mini-split heat pump system? Or resistance heater and swamp cooler?

    Regarding the the solar panels+charge controller--You should define your loads (maximum/average power) and the battery bank voltage.

    Then you can choose a charge controller... With "non-standard" Vmp solar panels (non-standard regarding battery bank 12/24/48 volt charging for a battery bank), you probably will need a MPPT type charge controller... Those run around $500-$700 each. And how many you will need depend on the battery bank voltage and the number of solar panels/wattage/configuration.

    There are a lot of questions here, typically we like to start with the loads, then define the battery bank, and then pick the inverter/charge controllers/solar array.

    You can go the other way, start with XXXX watts of solar panels and then figure out how much power you can get from them and how large a battery bank you can support... But it would be helpful to know, roughly, were your system will be installed (sunny southwest, cloudy northeast, etc.)...

    It will be kind of confusing starting in the middle and know knowing where you really want to go.

    -Bill

    Thanks everyone for the quick responses!... Yes Bill, I was planning on getting a MPPT type controller for sure. I am wanting to run something like this window heat/ac unit (http://www.overstock.com/Home-Garden/LG-7-000-BTU-Heat-and-Cool-Window-Air-Conditioner-Refurbished/5639124/product.html?cid=123620) which is a 1000w load. According to my calculations (which could definetely be off) I would have a 1750w system (in full sunlight)... which would give me 1k watts to run the window unit in full sunlight, but also be charging the battery bank at the same time, right?

    As far as the battery, could I get away with 2 batteries with a lot of aH (so that way I don't discharge them too much)? like this one http://www.batteriesinaflash.com/deep-cycle-lead-acid/12v/fullriver-group-8d-12v-260ah-agm-sealed-lead-acid-battery?source=google_products . I can't remember where I found the formula, but does anyone know how I would figure how fast the listed solar panels could charge 1 of the above batteries from 50%?

    I forgot to tell you guys that I will probably have about 5 hours a day in direct sunlight on average.

    I am just wanting this system (for now) to be able to help me cut down on my heating and cooling system costs. I don't want to tie it into my grid, just basically make my own type of solar generator... kind of like the SUNRNR found in this link http://www.sunrnr.com/Products-Pricing.html . I just figure I can do it for much cheaper than what they have it listed for since I can get a good deal on used panels. I am just wanting to be able to run an extension cord into my house, or if i have to keep the battery bank inside or under my house (due to temps) then I would just want to run an extension cord through my house to this window unit. Lastly, I live in the north part of South Carolina in case anyone of you were wondering.

    I am just overwhelmed with all of the information I need to do this myself =/ But thank you guys so much for your help! I am learning a lot!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is my thinking correct?

    Solar electric in a nutshell (the simple form):
    Will it save on your utility bill? Yes. Will it save you money? No. Money is better spent on conservation.

    As for that unit you link to, probably 1000 Watts running. The start-up will knock out a small inverter and the power consumption over time will be large. You have to look at system planning like this, regardless of how it is used:

    1). Maximum load at any time (including start-up surges for motors) to determine size of inverter (cheaper MSW inverters do not work well with AC induction motors and other things).
    2). Daily Watt hours and maximum Depth Of Discharge determines size of battery bank.
    3). Size of battery bank sets the specs for solar panels and appropriate charge controller.

    The unit you cite probably would require a 6 kW pure sine inverter just to start. That would be a very expensive inverter: http://www.solar-electric.com/xaxwhyin1.html Getting compressor motors to run is very difficult; they need a lot of initial power. Then consider it running for 1/3 of the day: 8 hours * 1000 Watts is 8 kW hours. So you're look at over 334 Amp hours @ 48 Volts for 25% DOD. Then to recharge that, about 3kW of panel. These numbers aren't precise, because I don't have a precise figure on the AC unit's consumption or how long it would be running et cetera.

    But I'll bet there's a better way to invest to save on the energy bill. Conservation, conservation, conservation.
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: Is my thinking correct?

    Grid Tied solar (solar panels + GT inverter) which connects directly to your utility power is usually the most cost effective method to generate power at home today. The basic system does not give you emergency power (no battery, wrong type of inverter) so is not the answer for everyone...

    If you have long periods of power failure (typically after storms) or want to plan for periods of outages of weeks or longer, then a hybrid (Grid Tied or Off Grid) or a pure off grid inverter may be the solution... But hold onto your socks because a large enough system to run an A/C unit is going to cost you in the $10-$20k+ range. Plus you will need to replace batteries every 3-15 years and probably need to replace the inverter and charge controllers every 10-15 years or so...

    Very roughly, the cost per kWH of electricity assuming a 20 year design life and typical maintenance costs:
    • $0.10-$0.20 per kWH for Grid power
    • $0.15-$0.35 for GT solar
    • $0.45-$0.75 for Hybrid solar (GT+Off Grid capable)
    • $1.00-$2.00+ for Off Grid solar (roughly the same for fuel costs of a backup generator)
    Conservation should be your first goal (insulation, reduction of power usage, etc.).

    Next, picking appliances that are the most energy efficient you can (and in the case of A/C and Heat Pumps, those that are more "off grid friendly" is definitely worth the extra costs).

    And if you want off-grid power, then you probably also need to look at an emergency backup genset + fuel supply/storage too for an effective system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 4,254 ✭✭✭✭
    Re: Is my thinking correct?

    Lots of good information out give already!

    I run a small AC on solar so I can give you some good round numbers, after losses inherent with solar, likely you would be about net even with the 1750 watt array and a 1000 watt AC if you running it in lue of your central air, as it would be running almost constantly.

    As for heating most electric heaters are equally effiecent as they basically heat is a product and the desired effect is to use/loose energy as heat (as heat is typically the ineffiecent part of other systems) Most small room heaters are 1500 watts I can't see this as practical, with out doubling your array. (with out considering the fewer hours of sun in winter.)

    So on average you would get 5 hours of Cooling per average day, from your system. or 1/5 of your daily needs before the fride and lighting, would this be worth it to you, before considering batteries, inverters, wiring, code, permits?

    Now how good a deal are you getting? I paid less than $1.70 a watt for New UL listed panels after the 30% tax credit, and I'll bet I could get them even cheaper today.

    Have you done the practical long term things at the house, an energy audit(often free from the prower company) extra insulation, better windows,vapor barriors?
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Is my thinking correct?
    in_dmand wrote: »
    I am just wanting this system (for now) to be able to help me cut down on my heating and cooling system costs. I don't want to tie it into my grid, just basically make my own type of solar generator... kind of like the SUNRNR found in this link http://www.sunrnr.com/Products-Pricing.html . I just figure I can do it for much cheaper than what they have it listed for since I can get a good deal on used panels. I am just wanting to be able to run an extension cord into my house, or if i have to keep the battery bank inside or under my house (due to temps) then I would just want to run an extension cord through my house to this window unit. Lastly, I live in the north part of South Carolina in case anyone of you were wondering.

    I am just overwhelmed with all of the information I need to do this myself =/ But thank you guys so much for your help! I am learning a lot!
    If you have grid power available, and unless you are subjected to long periods of time where the grid goes down, a battery based system doesn't really make sense. A system with batteries is much more expensive and much more complex than a straightforward grid tied system. My advice would be to take a serious look at your situation and decide if the significant extra expense, complexity, and maintenance of a battery based system is really necessary.
  • TobyToby Solar Expert Posts: 56 ✭✭✭✭
    Re: Is my thinking correct?

    Has anyone ever tried an HVAC hard start capacitor with inverters to limit the start-up power surge?

    From what I recall, they are used when HVAC units cause lights to dim on houses connected to commercial power.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Is my thinking correct?
    Toby wrote: »
    Has anyone ever tried an HVAC hard start capacitor with inverters to limit the start-up power surge?

    From what I recall, they are used when HVAC units cause lights to dim on houses connected to commercial power.

    Motor start capacitors can help, but they don't reduce the power need; just put it on a better part of the curve (improved power factor). And they have to be sized for the particular motor involved. In the case of some units that are designed to be used with this option, that quantity is known. With an off-the-rack AC unit you'll be doing some guessing 'til you get the right size.
  • Peter_VPeter_V Solar Expert Posts: 213
    Re: Is my thinking correct?
    in_dmand wrote: »
    I am just wanting this system (for now) to be able to help me cut down on my heating and cooling system costs. I don't want to tie it into my grid, just basically make my own type of solar generator.

    Can you tell us WHY you want to spend 3 or 4 times as much money to get the same results?
    Off grid systems are MUCH more expensive than grid tied for the same energy output.

    Aside from the expense of the Batteries and Charge controllers, you'll need a larger array to account for losses in the batteries and charge controller.
    Plus there are probably many days when you won't need heating/AC, but the sun is still out and shining. With a grid tied setup you can harvest that energy and push it to the grid to get credit for when you need it, this means you can get away with an even smaller array on a grid tied.

    I.e. if your heating/AC needs 10 kwh a day, but only runs for 1/2 the year, then with a grid tied array you only need to produce an average of 5kwh per day year round.

    Plus you can't just toss the batteries in the house somewhere. You need either a special room/shed for them or you need approved battery boxes that are located outside the living area of the house. Some areas will allow you to put them in your garage or basement, IF they are properly ventilated.

    Batteries need monthly maintenance, measuring specific gravity and topping them up with distilled water, etc.
    And to top it off, after 4 years or so, you'll have to buy a whole NEW set of batteries.

    Grid tied is not only cheaper, it's easier.
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: Is my thinking correct?
    Grid tied is not only cheaper, it's easier.

    No only cheaper and easier per say but a way more efficient use of both money and power! 1/2 as much cost per watt for twice the output in round numbers,,, it is a no brainer.

    Tony
  • bmetbmet Solar Expert Posts: 630 ✭✭
    yeah

    until the power goes out

    then it's dead.

    how cheap is that?
  • BB.BB. Super Moderators Posts: 26,837 admin
    Re: yeah
    bmet wrote: »
    until the power goes out

    then it's dead.

    how cheap is that?
    We are getting a bit ahead of the original poster... But from his second post:
    I am just wanting this system (for now) to be able to help me cut down on my heating and cooling system costs.

    If we are looking at that vs an off-grid system or emergency backup, then Grid Tied is much cheaper, and for short outages (less than 1 week or so), a genset plus backup fuel supply is also much cheaper than any Hybrid or Off Grid system.

    If somebody has weeks or months of outages (ice storms, fire storms, hurricanes, etc.) because they are at the end of the utility's service (last person to get their power up), then other solutions, such as hybrid (grid tied/off grid capable) solar + backup genset make better economic sense.

    But one thing to remember, there are a lot of small utilities that do not support Grid Tied power--which does limit the ability for many rural folks to install the most cost effective solution of a pure Grid Tied Solar system.

    In any case, usually the cheapest solution is going to involve the use of conservation--And for A/C and heating--That is going to involve some sort of high SEER heat pump system0--which most inexpensive window A/C units do not come close to competing with in terms of efficiency.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: yeah
    bmet wrote: »
    until the power goes out

    then it's dead.

    how cheap is that?
    Which is why we all have said that GT is easier, cheaper, etc., etc., UNLESS the grid is undependable. Even then, you have to consider how much it costs you when the grid goes down vs. how much it will cost you to protect yourself against that occurrence.
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