newbie - mini shed install!

apples12apples12 Posts: 3Registered Users
Hi all,
I'm new to solar and this will be a DIY install, hoping to get some help with this.

I will be connecting a single device which as a maximum power rating of 60w and a bulb with a rating of 10w

I have sourced a panel

It is a Canadian Solar CS6P-255P

http://www.solardesigntool.com/components/module-panel-solar/Canadian-Solar/2613/CS6P-255P/specification-data-sheet.html


What sort of inverter would I need with this and what kind of battery to reliably power the above load for a continuous 24 hour cycle? I.e. this will be 'always on'

Any help/tips are appreciated - off I go to read the stickies!

Thank you


Comments

  • EstragonEstragon Posts: 2,447Registered Users ✭✭✭✭
    Hi. Welcome to the forum.

    If the 60w device and/or 10w bulb aren't purely resistance loads (eg. heaters, incandescent or halogen bulbs), I'd use a pure sine wave inverter. Electronics and other non-resistance loads may run fine, but may run hot, or not at all on modified/square wave inverters. If the 60w load is a motor/pump, check for locked rotor amps in the specs, as a 60w max running amp pump could draw several times that to start. Assuming no high pump start needs, something like a PST120-12v Samlex could work.

    70w x 24hrs = 1680 watt-hours/day. With inverter/charging losses, that's ~2000w/day needed for charging and the loads. In most locations, most of the year, it's reasonable to expect ~4-5hrs of equivalent to full sun on average daily, and for panels to output ~NOCT spec power, or about 75% of the STC rating. For your panel, that's ~255x75%x4hrs=765w average per day. You can estimate power more accurately for your location at pvwatts.nrel.gov

    In order to get 2000w, you will likely need 3 of those panels. If you can be certain of enough sun every day (few locations can), or have a secondary means of charging, you can get away with 1 day reserve. 2000w÷50%discharge = 4000wh battery required, ÷12v nominal = 333amp-hours. 2x6v L16 flooded batteries would be a good choice for this. 2 strings of 6v golf cart batteries in parallel (4 total) would also work. To go more than 1 day, you would need to add panels, batteries, etc proportionate to desired days of autonomy.

    To charge with those panels, you'll need an mppt type charge controller with ~60a or greater capacity. You could get away with a much cheaper controller by going to 24v nominal, but good, small, 24v PSW inverters are harder to find and can be expensive. Depending on the nature of the 60w load, whether an integrated AC charger would be of value, and whether future expansion might be desirable, it might be worth considering though.

    You will also need some installation parts such as combiner box, breakers, wire, racking, etc.

    Anyway, some thoughts and numbers to get started with.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • apples12apples12 Posts: 3Registered Users
    Many thanks for the reply

    The 60w load will be a usb hub running a raspberry pi (needs 5v input)

    Even if the solar only provides power and charging for the pi and it's accessories then that would be sufficient.

    If I obtained 4 panels and 3 strings of batteries I'm assuming an mppt controller greater than 60a will be required?

    Thank you
  • karrakkarrak Posts: 277Solar Expert ✭✭✭✭
    If you are only running a Raspberry Pi and a USB hub I would think the power requirements will be less than 6W, nowhere near 60W. What else is running off the USB hub?

    Simon
    Off-Grid with LFP (LiFePO4) battery, battery Installed April 2013
    32x90Ah Winston cells 4p8s (24V), 4kW Latronics Inverter, 1160W of Solar Panels, homemade MPPT controller
    Homemade BMS https://github.com/simat/BatteryMonitor
     

  • EstragonEstragon Posts: 2,447Registered Users ✭✭✭✭
    A rPi typically uses a 1a 5vdc power supply. Mine runs around 200milliamp, or .2x5 or 1watt with a USB keyboard and optical mouse plugged into onboard USB ports, and with wifi and bluetooth radios on, and ethernet enabled. As Karrak notes, this is a much smaller load, which can be supported with a much smaller system.

    To answer your question though..., I wouldn't recommend going to 3 strings of batteries for 3 reasons. First, more than 2 strings can be difficult to keep balanced, requiring careful wiring, monitoring, and corrective action to keep each string at about the same capacity. Second, more than two strings need overcurrent protection for each string. Third, the number of cells gets unwieldy for proper maintenance. Instead of three strings, it would be better to use larger batteries (eg L16s vs golf cart) and/or increase string voltage (eg [email protected] for [email protected]). Higher battery voltage would require less controller current capacity (eg [email protected] nominal vs [email protected]), and may allow for the use of cheaper PWM type controller(s).

    Getting back to your actual load though, it may be worth rethinking the need to invert 12v(or 24v) dc to 120vac, then back to 5vdc for the pi. 12v lighting is widely available from marine/rv places, as is 12vdc USB power. If the shed is heated, or not in a cold climate, lithium battery may be a better storage choice. Lead acid batteries are damaged if left discharged for long periods, whereas lithiums are fine with sitting partially charged. Lithium are ok discharging cold, but don't like being charged below freezing.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • apples12apples12 Posts: 3Registered Users
    The total load will be 4x 10w mining computer asics along with the pi itself and a couple of small fans (12v, 0.4a)

    By lithium would a bank of 16550 batteries work?
  • EstragonEstragon Posts: 2,447Registered Users ✭✭✭✭
    That load running 24x7 puts the numbers back to close to the first run through.

    A lithium bank is a possibility, but would have to be a fair sized bank to support. You can use a bit more of the capacity with lithium (~80% vs 50% for lead acid), so (eg) a [email protected] lead acid would be roughly equal to a [email protected] lithium. L.A. would run maybe $4-500 for a pair of L16 flooded vs ~$2,000 for lithium with required bms for cell-level control.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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