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 –Use less energy! produce the Negawatt! –Efficient appliances CF lighting Newer models (EnergyStar) –Divert heating loads to solar, gas, etc…

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

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 = 2.25 kWhrs

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

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

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

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

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

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)

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

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

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

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)

Davis Rating Scale 1. Basics 2. Essentials 3. Modern Conveniences 4. Hot Water Heat 5. Space Heating 6. Full Service Household

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

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

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

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

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

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