Hi Matt,
Short answer is yes, 2 days of autonomy should be fine. I am presently operating our off rid PV/hydro system at well under two days of autonomy. I just crunched some numbers for our situation here in Vermont. Off grid system that is now 4.3kW PV and with a Harris micro-hydro turbine that I run at 325 Watts. · 24v system initially installed 30 years ago and with PV and inverters (dual OutBack) upgraded 7 years ago. · Present Battery bank now over 13 years old, 2v industrial flooded LA's rated at 1200 AH. Originally designed for 3+ days of autonomy. · Our large home has been a true two family home for the past three years, with a full second kitchen along with TV etc. we are now using about 15kWh/day during the winter. Our Tarm wood gasification, forced hot water heating system uses quite a bit of electricity but we can heat the whole deal without burning any oil, or propane, for this 4,000 sq foot two family home in northern Vermont it is well worth it. We harvest the 10 cords of hardwood out of our woods. · 28,880Wh battery bank / 15,000 Wh = 1.5 days of autonomy. I didn't know how well this would work when we added the second living space with the 9 yr old batteries at that point. But I have not had to change a thing. · I have my next set of batteries (sized them a little larger, 1350AH) waiting in reserve in my basement (properly cared for per Surrette/Rolls instructions) as I don't know when the present 13 yr + set will fall off the cliff. I'm watching them closely, no alarming signs of the end yet. Monitoring all cell post terminals with my handheld IR thermometer when battery bank is charging hard and or when the system is under a large load. So far all terminals get up to 86 degrees F at most. Water use has not changed much at all yet and specific gravity readings are all very good. · More numbers: The charge rate with 4.3k of PV only is about a C/8 on the battery bank. · Hydro is 325W, run 24/7 from late October through April, then as needed during rainy periods. · Diesel Gen set charges at 160 Amps, so during the cloudy, snowy winter periods the hydro and gen combined charge at about a C/7 rate. Dave David Palumbo Independent Power LLC 462 Solar Way Drive Hyde Park, VT 05655 802-371-8678 cell 802-888-4917 home From: RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Matt Sherald Sent: Wednesday, April 26, 2017 7:21 AM To: RE-wrenches Subject: [RE-wrenches] Hydro Off-grid Battery Sizing Good morning! I went to bed wondering if the off-grid battery bank sizing rules that I use for PV systems hold true for hydro-based systems. I woke up and I was still mulling this over. My battery bank sizing standard is to use the method outlined in the SEI Photovoltaics Manual. I would presume that since the charging source is fairly consistent (day-to-day and hour-to-hour) that I could then reduce the days of autonomy to 2-days. I'm curious though if anyone has advice for sizing a battery bank for hydro. Any suggestions would be greatly appreciated. Thank you! -- Matt Sherald PIMBY Energy, LLC NABCEP Certified Solar PV Installer® 304-704-5943 www.getpimby.blogspot.com www.getpimby.com
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