property:development:construction:services:electricity:solar

Summary

Calculations

Assuming for a tiny home:

Calculate max instant power load:
- Note:
  - Average Tinyhome is 4000W.
- 5 x 10W lights = 50W
  - 1 x 250W fridge = 250W (an economy fridge can get down to 70W)
  - 1 x 2000W oven/microwave = 2000w
  - 1 x laptop = 100W
  - 2 x 200W chargers = 100W
  - 2 x 10W chargers = 20W
  - = 2520 W
  - An average kiwi house will also have:
    - more lights: 6 x 10W = 60W(normal house)
    - ext lights: 4 x 20W = 80W (outer lights, etc.)
    - Dish washer: 1 x 1.6kW = 1.6kW
    - Washing machine: 1 x 1kW = 1kW
    - Dryer: 1 x 3kW = 3 kW
    - Water heater: 1 x 1.5kW = 1.5kW
    - Heating: 2 x 2kW = 4kW
  * Calculate daily power needs:
- Note the max load is not for one hour, nor every hour of a full day.
- Note:
  - Average Kiwi Household is 20kwH.
  - Average US household is 30kwW.
  - Average is NOT the same as Max Daily (eg: winter).
  - We use 27hwH. Up to 40kWh.
- The energy consumed is:
  - Lights: 50w x 6h = 300Wh
  - Oven/Kettle: 2000w x 1h/3 = 666Wh
  - Fridge: 250w x 24h/3 = 1000Wh
  - Laptop: 60w x 10h = 600Wh
  - Chargers: 100w x 4h = 400Wh
  - Chargers: 10W x 12h = 120Wh
  - = 3.1kWh, rounded up to 4kWh, which is pretty average.
  - Compared to an average house, which has in addition:
    - Lights: 60W x 6h = 360Wh
    - Outdoor lights: 80W x 3h = 240Wh
    - Dishwasher: 1.6hW x 2/31h = 1.2kWh * Washing machine: 1kW x 2/31h = 1kWh
    - Dryer: 3kWx 2/31h = 2kWh * Heating: 4kW x 4h = 16kWh * Water heater: 4kW x 2.5h = 10kWh * So that's the base 4kW + 6.2kW = 8700kWh + 10000kWh ⇒ a whopping 27,0000kWh (The average for NZ is 20kWh. The average for US = 30kWh. But then there's winter, where it rises considerably due to heat needs). * So, as a recap, the daily load is: * after adding a 25% margin of omissions and future needs (electric car) * Tiny Home: 2553Wh * 1.25 = 3830kWh. * Bump it up to 4kW, and you have enough to run a dishwasher. Or washing machine. But not both. And no drier of course. * Average House: 20000Wh * 1.25 = 25000Wh Calculate solar panels array:
- If not using a battery, one would be working with use max load…noting you'll only really be able to use it 3hours a day. Kinda useless.
- But if using a battery, use the daily power needs as a starting point.
- Need is equal to 'Total Daily Power Consumption (Wh) / Peak Sun Hours per Day = Solar Panel Wattage (W)'
- Tiny home needs: 4kWh / 3h (max kiwi sun in summer) = 1200W needed from panels.
- House needs: 25kWh / 3h = 7250W needed from panels.
- Which can be developed by eg: 5 x 200W, 7x150w, 4x300w, 4x320W or 3x350w would work. 3x310W is a bit light.
Calculate battery bank needs:
- Total Daily Power Consumption x Days of Autonomy / Battery Voltage = Battery Capacity (Ah)
- 3125 Wh x 3d / 12V = 9375Wh / 12V = 781Ah
- One could use:
  - 4x200Ah battery…a whopping 4x$2129.Ouch.
  - Or cut down to 2d:
  - 3125 Wh x 2d / 12V = 6250Wh / 12V = 520Ah. Which is 3x200Ah batteries. Still Outch.
  - Or start with just one day backup (note more wear on batteries due to full discharges):
  - 3125 Wh x 1d / 12V = 3125Wh / 12V = 260Ah. Which is 2x200Ah battery
  - While you technically can, don't change size in batteries (eg: 2x200Ah + 1x200Ah) as uneven dis/charging ages batteries fast.
  * Calculate the solar charge controller:
- used to control flow from solar panel to battery to not overcharge it.
- important to choose one that is larger than both the source panels and closer to the target batteries current.
- Read the panel's specsheet or calculate A from known V to determine maximum current all panels can generate:
  - Assuming 3x340w panels, at 34.73V,
    - 340/34.73V = 9.79A per panel
    - So it's 3 panels x 9.79A ⇒ 29.37A Max current output.
    - Calculate the max current the battery can accept:
    - It is probably not the same as what the battery can produce. eg: Specs says max charge rate is 50A.
    - So, min 30A, better if one can afford 50A.
    * Calculated the Dump load:
- used to dissipate excess electricity generated by solar panels, as heat
Calculate inverter: