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Hydro Load Assessment

Hydro Load Assessment. How do you know how much energy you need? Electric bill Average US household uses 850 kWhrs/month = 28 kWhrs/day Also need capacity : what is the largest load to run? Do a load assessment!!. Load Assessment. A house on RE must use less electricity

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Hydro Load Assessment

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  1. Hydro Load Assessment • How do you know how much energy you need? • Electric bill • Average US household uses 850 kWhrs/month = 28 kWhrs/day • Also need capacity: what is the largest load to run? • Do a load assessment!!

  2. Load Assessment • A house on RE must use less electricity • Use less energy! produce the Negawatt! • Efficient appliances • CF lighting • Newer models (EnergyStar) • Divert heating loads to solar, gas, etc…

  3. Frugal Lighting Rule • One light per person • One light for the room Task lighting is good for the eyes

  4. Load Assessment • You’ll need for each appliance… • Power consumption • In Watts • Rating will be stamped on appliance • Number of hours/day appliance is on • Simple example: a 15 W CF bulb is on for an average of 5 hrs/day day: (15 W)(5 hrs/day) = 75 Whrs/day month: (75 Whrs/day)(30 days) = 2,250 Whrs = 2.25 kWhrs

  5. Load Assessment • Some special cases • Cycling loads • Most heating appliances are on a thermostat – not on 24/7 (space heating, fridge, water heater, etc) • Surge requirement • Motors requires additional current when starting • Rule of thumb: starting power = 3 times rated power • Important for “large discharge current at C/10” • Phantom loads • Many appliances consume power even when off (24/7) • Timers • Transformers

  6. Load Assessment • Potential errors? • Usage changes with season • Appliance efficiency often decreases with age • Most “duty cycles” must be measured

  7. Load Assessment • Example: summer cabin • Loads: • Lights: all 15 W CF, on a total of 10 hrs/day • Radio: on 2 hrs/day (20 W) • TV: on 2 hrs/day (40 W) • Small fridge: on 8 hrs/day {you measured it} (400 W) • Water pump: on 2 hrs/day {fills cistern} (500 W) • Other loads diverted to propane

  8. Load Assessment • Average daily usage • Lights: (15 W)(10 hrs/day) = 150 Whrs/day • Radio: (20 W)(2 hrs/day) = 40 Whrs/day • TV: (40 W)(2 hrs/day) = 80 Whrs/day • Small fridge: (400 W)(8 hrs/day) = 3200 Whrs/d • Water pump: (500 W)(2 hrs/day) = 1000 Whrs/d • TOTAL: 4510 Whrs/day = 4.5 kWhrs/day • Assume all 120 V loads

  9. Hydro Sizing • Energy required = 4.5 kWhrs/day • Or (4.5 kWhrs/day)(30days/month) = 135 kWhrs/month • Hydro Power = (135 kWh/mo)(1mon/720h) = .188 kW or 188W • So, we need a hydro system producing at least 188W all the time. • Say we have 50’ of head, we’ll need to use at least 38 GPM of flow

  10. Battery Bank Sizing • Battery storage for PV and Wind systems typically require 3 or more days of battery storage • Hydro systems run all the time • Batteries in a hydro system typically need to store energy for less than a day • Often, the battery is sized to provide sufficient current to the inverter rather than an amount of storage (at the C/10 max rate)

  11. Battery Sizing • Average daily usage = 4510 Whrs/day • Size of battery bank needed? • Must choose system voltage! • Usually 12, 24, 48VDC • Choose 48 V • 4510 Whrs/day / 48 V = 94 Ahrs/day

  12. Battery Bank Sizing • Storage needed: 94 Ahrs/day at 48 V • Inverter efficiency: 94 Ahrs/d/0.9 = 104 Ahrs/d • 1 day res.: (104 Ahrs/day)(1 d) = 104 Ahrs • Temp penalty at 60°F: (104 Ahrs)(1.11) = 116 Ahrs • Leave a 20% reserve: (116 Ahrs)(1.20) = 139 Ahrs • Choose 220 Ahrs, 6 V batteries: need a 48 V battery • The 48 V battery will need (8) 6 V batteries in series • Total = 8 batteries, 48V, 220 Ahrs

  13. Battery Bank Sizing • Should pump and fridge run at the same time? • Max discharge rate = C/10 • C/10 = 220 Ahrs/10 hrs = 22 A • Pump + fridge = 900 W/48 V = 19 A • Should be able to handle this possible surge

  14. Check the charge rate • We can charge the battery at a max rate of C/10 or 22A • If we end up with a 250W hydro system at 48V, the current will be 250W/48V = 5.2A, no problem, nice and slow • At this charge rate, it would take 220Ah/5.2A = 42 hours to charge or C/42 • Sounds slow, but we will typically only partially drain the batteries, say 20%. • (.2)(220Ah)=44Ah removed during the day • At 5.2A, it would take 44Ah/5.2A=8.5 hours to charge back (overnight)

  15. Davis Rating Scale • Basics • Essentials • Modern Conveniences • Hot Water Heat • Space Heating • Full Service Household

  16. 1. Basics • Lighting, weekend cabin, small RV • A small PV system may be the most appropriate • 50 to 250W inverter • If you need power in the winter, nano-hydro may outperform PV

  17. 2. Essentials • “Lights and Music” • Lights, small appliances like stereo, blender, laptop • 35 to 70 kWhrs/month • 50 to 100W hydro system • 300 to 1000W inverter

  18. 3. Modern Conveniences • Lights, stereo, blender, laptop, refrigeration, freezing, water pumping….everything that doesn’t require much heat • 75 to 125 kWhrs/month with efficient appliances • 100 to 200W hydro system • Need a sufficient inverter capacity for max loads • An “easy start kit” can reduce starting surge • A nice 2.5 to 4kW true sine wave inverter should do it

  19. 4. Hot Water Heating • Will require an AC system, lots of water • Batteries and large heating loads don’t mix • Recovery time may be slow (3412 BTUs per kW), hot water heaters usually have two 4500W elements for fast reheat • More efficient to use solar or low-grade energy for heating water • High grade energy: electricity • Low grade energy: gas

  20. 5. Space Heating • Will require a full sized AC system • 1000 to 2000 kWhrs/month • 1 continuous kW heats a little better than a cord of firewood • For a six month heating season, a 10kW hydro system = 12 cords of firewood

  21. 6. Full Service Household • More power than you know what to do with • High current appliances (ranges and dryers) • Usually a surplus of power which can be sold $$$$$$$$$$$$ • Many thousands of kWhrs/month

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