Battery back-up determining
For the size of your daily usage I would look at the size of your daily usage. 10kW/hrs is massive for off-grid. Sounds like some people need to learn that switches have two positions, and one of them is "OFF".
Trying to supply that much power with solar is daunting ... and expensive. I agree with audredger; 15 panels won't do. You've got to get that 10kW into the bank in about 4 hours of good sun. That's 2500 Watts per hour, and with the usual panel de-rating that means roughly 3200 Watts of panel minimum - and that on a good day.
Hi, I'm new to this forum. I felt compelled to join because I'm here doing battery backup research. The kinds of quotes I'm getting definitely reflect the thinking and discussions that I see here. There is a completely different paradigm because of my starting up as a grid-tied urban desert dweller. My system is sized based on the contractor asking how much solar power I wanted -- my answer was "How much can I get?". You see the answer is based on pay-back of the original costs using HIGH ELECTRIC BILLS on a house with no upgrades since it was built in 1980. There's a pool, two conventional electric water heaters, two 10 S.E.E.R. package AC units, and a lot of older appliances... at least that's how I bought the place 2 years ago. Now with 23,760 Watts of PV grid-tied co-generation, increased shading and insulation, a hybrid electric water heater, a 2-hour limit timer on the conventional water heater, an upgraded 16 S.E.E.R. AC and a programmable t-stat on the 10 S.E.E.R. to reduce it to night-time use on the master bedroom, and a new pool pump motor -- my payback on this system (after taxes) is May 2014. It was commissioned in March 2012. You can see that this is very rapid payback and I have the numbers to back this up. But my point is that I don't need battery backup for 160kWh per day that I produce. I need enough to get through one night with one AC running. I can survive comfortably on 5kW peaks at night and my system generates more than I use even on rainy days in winter. The only time I need backup is when the grid fails because I have beaucoup surplus in our net metering account. But I asked for a quote from Blue Pacific Solar and they wanted to sell me 48 Full River DC400-6 6V 400AH L16-AGM batteries in 6 enclosures. My house is equipped with a "load controller" which can easily be activated to limit major appliances to below 7kW (measures total to throttle the appliances and AC back). So I discussed with Blue Pacific Solar that I wanted to handle grid failure by 1) disconnect from grid, 2) switch on load controller, 3) activate battery backup or generator. The problem is they assumed I need the power I generate on the roof. I make 50% more than I can use on the hottest day of the year.
So I'll be looking at reducing my loads too. No worries. How do I size my battery backup for 1 AC unit and a new efficient fridge overnight. I assume my Sunny Boy inverters (3 SB7000US) will carry me through the day with 2 Sunny Island 6048 control units.
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