Skelufteay
Member
- Location
- Denver, Colorado
I have a question on the DC System Voltage in a battery system. All of the books and examples I have read only consider small application off-grid installations, and I need to understand how a large system would work.
For example if the primary facility currently uses a 500kW generator @ 480V-AC and 240V-AC for lights, trailers, and equipment. So let's say for a PV system size of 300-450 kW. In all the examples I can find, it says the Batteries should be kept at a low voltage, 48-50V-dc, and then inverted to the 480/240V-ac. However, having voltage at that level with long runs would make the voltage extremely high (let alone the high amperge in the lines). I know the NEC says that battery banks cannot be greater than 250V per separated bank, with maximum of 600V, so would it be acceptable to install battery banks at 500V; to keep the voltage loss down? Or is there a reason for keeping the Vsdc low that I am unaware of?
My second question is that I've attempted to do all the calculations using MathCAD, so I could set words as variables, and so it reads it easier than in Excel (imo) here ... View attachment Mathcad - Battery Sizing With Some DataV5.pdf ... I'm told it may be over sized by 25%, but when I tried it using another method, it's actually undersized by 25% in comparison. So am I on the right track for sizing, or is there something I am missing?
Thanks
For example if the primary facility currently uses a 500kW generator @ 480V-AC and 240V-AC for lights, trailers, and equipment. So let's say for a PV system size of 300-450 kW. In all the examples I can find, it says the Batteries should be kept at a low voltage, 48-50V-dc, and then inverted to the 480/240V-ac. However, having voltage at that level with long runs would make the voltage extremely high (let alone the high amperge in the lines). I know the NEC says that battery banks cannot be greater than 250V per separated bank, with maximum of 600V, so would it be acceptable to install battery banks at 500V; to keep the voltage loss down? Or is there a reason for keeping the Vsdc low that I am unaware of?
My second question is that I've attempted to do all the calculations using MathCAD, so I could set words as variables, and so it reads it easier than in Excel (imo) here ... View attachment Mathcad - Battery Sizing With Some DataV5.pdf ... I'm told it may be over sized by 25%, but when I tried it using another method, it's actually undersized by 25% in comparison. So am I on the right track for sizing, or is there something I am missing?
Thanks