Starting out sizing question

vcallaway
vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
After reading hundreds of posts I'm down to a couple of simple questions.

I'm going to take one room, the master bedroom and run it off of solar. I already have that room and the living room setup on a battery backup system. The plan is to pull a couple of batteries from that and move to solar only.

This is my worksheet on power requirements:

Device Watts Hours Watt Hrs
Laptop 60 24 1440
Network Devices 20 24 480
Master Bath Lights
(4 @ 14W) 56 2 112
Bedroom Light 14 1 14
Clock 1 24 24
Night Lights (2 @ 1W) 2 22 44
Outdoor Lights
( 3 @ 14W) 35 6 210
CPAP 25 7 175


Total Watt Hours 2499
Max Load in watts 213

Tried to clean up the formatting, it is a cut and paste from my spreadsheet.

The laptop and network hub have to stay running 24x7. It is our phone system and ties into work. I'm always on call and have spotty cell service.

My batteries are 8D lead acid batteries. Basically big deep cycle RV batteries. They are rated at 220 AH @ 20 hrs. Would like a recommendation as to if I should use one or two. I have a good source for them at $100 each so the cost is not really an issue, just longevity.

I currently have a 400 watt MSW inverter. Everything seems to work fine with that. With max load being 50% it looks like that is good to go.

I'm at 47 degrees north. Summers have good sun, but winter is not so good. I'm near the water so I get good wind. I'm thinking that I should size the solar for summer now and add wind and maybe additional panels when winter comes in.

The problem is that I can't seem to figure out how much wattage I need in panels. I've read trough the site and I just get more confused. And should I consider the over 100 watt panels? The store front states that they are primarily used in grid tie systems. This will be stand alone.

Since this is still in hobby/learning stage budget and marital bliss are a consideration. I also don't want to go too cheap and wind up having to replace things later.

Thanks.

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Starting out sizing question

    Try readnig this thread:
    http://forum.solar-electric.com/showthread.php?t=5287
    I answered some questions and did some calculations there, that you can apply to your situation. write again if you have more questions.


    Panels & Charge controller, It's not the "size" that counts, it's the voltage, you won't need over 20V to power your controller, unless you get a MPPT type controller
    - see the controller FAQ about them.
    http://www.windsun.com/ChargeControls/ChargeCont.htm

    Also - the Morningstar Suresine
    http://store.solar-electric.com/mosu300wasiw.html
    inverter is quite efficient, and if you bolt it to a nice heat sink, you should be able to run at 300W all the time
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Starting out sizing question

    You should be aware that your inverter will probably pull between 15 and 25 watts full time, just by itself, and most of the cheap MSW inverters are not very efficient, so you would have to add probably another 20% for that.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Starting out sizing question

    You figure you need 2500 watts a day. Figure 4 hours a day of good sun, so:

    2500 / 4 = 625

    You need at least 625w of PV panels.

    That is of course not figuring in cloudy days or inefficiency of the charge controller or inverter. Might as well just bump that up and say 800w worth of panels.

    You can of course use whatever combination of panels you want, but to keep it simple you should probably use all the same type - or at least all the same voltage.

    You need to store 2500w x 2 (to keep the batteries from draining below 50%) so you need 5000w of storage at say 12volts that would be 417 amps. Your batteries are 220 so you need two of them.

    You could probably get by on one battery, but by draining it below 50% on a daily basis, it won't last nearly as long.

    Batteries have a cycle rating. At 20% discharge they are good for X cycles, at 50% they are good for Y cycles, at 80% discharge they are good for Z cycles. The numbers aren't what you might think... X might be 3500, Y might be 1000 and Z might be 50.

    Normally, you want to keep deep cycle batteries from going below 50%.


    Now, that's the absolute minimum to supply one day's power. If you get two cloudy days when the batteries don't charge, then they'll be dead (100% drained).

    Figure out how much of a comfort zone you need, and scale the system up accordingly.
  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    Re: Starting out sizing question

    So If I pull out the laptop and network I can drop the need down to 579 wH.

    With that in mind does this sound doable?

    a single battery
    Two of the Kyocera KD135GX-LP panels.
    Morningstar Dual battery Controller

    If I understand the controller info I can send some of the charge current to my other battery bank. It looks like it is a good option for my current setup.

    The controller looks like it can handle three of those panels with maximum output.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Starting out sizing question

    220a @ 12v = 2640w

    2640w / 579 = 4.5

    So a single battery would supply your new load for 4.5 days, or at 50% DoD (Depth of Discharge) - 2.25 days.

    With 270w of panels, you could generate about 1000w per day (and probably more most days, maybe 1200w/day), so you would have about 400w or more extra to charge a second battery.

    The dual charger will work but I have no idea what your second battery is.

    Also, for max efficiency in battery charging, you should use a battery temp sensor, but I think that dual charger only supports one remote temp sensor.
  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    Re: Starting out sizing question

    Thanks! Looks like I have a starting point.

    As for the other batteries they are a bank of 8D's. I have a 3-way automatic transfer switch with an inverter and batteries for power outages. We have lots of short outages and the occasional long one. Longest was almost a month. I have an Onan generator that kicks on when the batteries get low. The house is starting to resemble a large RV.

    I promised my wife last winter that I would spend the summer making our home less reliant on the grid for comfort. I'm running gas lines this weekend so we can convert our dryer and stove. We are also going to buy a gas fireplace. Our home is only 1400 sq ft so it is easy to heat.

    I'm sure I will be broke by fall :p
  • quid_non
    quid_non Solar Expert Posts: 48
    Re: Starting out sizing question

    Also - the Morningstar Suresine
    http://store.solar-electric.com/mosu300wasiw.html
    inverter is quite efficient, and if you bolt it to a nice heat sink, you should be able to run at 300W all the time[/QUOTE]

    Hi Mike!
    Can you offer an idea/material for a heat sink for this 300W inverter to allow continuous 300W use? Perhaps a 1/4'' steel plate or similar?
    Thanks
    Wayne
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Starting out sizing question
    quid_non wrote: »
    Hi Mike!
    Can you offer an idea/material for a heat sink for this 300W inverter to allow continuous 300W use? Perhaps a 1/4'' steel plate or similar?
    Thanks
    Wayne

    Steel is a poor heat conductor. The Suresine looks like (I have not actually seen one, only photos) it would have a flat back, that you would ordinarily bolt to a wall. If there was some 1/4 or 1/2" aluminum plate, and a dab of heatsink grease between them, you would gain a lot of thermal area. It's inner parts can handle a 600W load, for 10 minutes. I'm guessing it could do that a LOT longer, if it was heat sunk to something that could radiate the heat away, 300W would be cool as a cucumber, and 400 or 500 might be achievable for longer times than a wood mounted part would take. I'm not saying to abuse it, but for electronics, cooler is usually better. A heatsink should not void the warranty, but use your own common sense.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Starting out sizing question

    The suresine 300 is a very robust, heavy unit. While running ~325 continuously for ~1 hour, the case gets luke warm to touch. The case is cast aluminum I believe and is deeply finned to allow convective cooling.

    I have run mine with a 225 continuous load and it works great. I would think it would drive 300 (if it was in free air) continuous without ill effect indefinitely.

    Tony