Arthur Götz

I so appreciate honesty! I spoke to a supplier this morning who reported that he didn't have any problems with Goodwe, but one, which was replaced promptly. "Upgrading" to a bi-directional Goodwe 5048D-ES , keeping to 5kW and a 240Ah 48V battery bank, but maxing out on the number of panels, will see a payback period of just 31 months for the price difference of the upgrade. This is a rough estimate only, but it definitely warrants a closer look. Yes, the Victron BMV is definitely the way to go. A tad expensive, but still cheaper than a single battery, never mind 4. Thank you for your honest advice.

Dear Forumites I have grid power at my house, but would like to go solar anyway, in order to become as independent as possible, and have cleaner (read more stable) power. I don’t want to disconnect from the grid completely, not yet. At first I'm going for a minimal system, and will later fill up the holes in my calculations and naivety. I need advice please, as will become apparent, my electrical knowledge, never good to start with, is now rusty to boot. I’m designing for 4.2kWh during daylight hours, 3.3kWh during the night and no autonomy beyond a single night. These are worst-case measurements over two weeks, not an average. I’ve settled on the following equipment, mostly trying to stay within my financial limits: • Axpert inverter MKS 5K • 6x Canadian Solar CS3K-300P, in two strings • 4x OmniPower 240Ah 12V sealed batteries in series. Solar panel output: At our location, north of Windhoek, Namibia, we have about 6.17kW/m²/day at a panel angle of 67°. At a panel efficiency of 18.05%, 156x78mm cells times 120, I can expect 9.76kWh per clear day, which is 30% more that my total daily need. Then again, much of this will probably go towards re-charging inefficiencies. MPPT range: The MPPT range is 60-115VDC, max PV panel VOC is 145V. With two strings, optimal operating voltage (Vmp) 32.7V, Voc 39.3V, I have an optimum power point voltage of 98.1V and a VOC of 117.9V, so I’m on the safe side? Voc @ -5°C = 128.4V Batteries: I’d like to stay within a 25% discharge window, if possible. The batteries can provide 240 x 48 x 0.25 x 0.9 (inverter efficiency) = 2.6kWh. Which is 80%of what I need, so can I set the low DC cut-off voltage to some as yet unknown value and use grid power for the rest? I could also switch off the fridge and evaporative cooler at 01h00, and restart at 08h00. In which case I should probably be covered 100%. Feed back into the grid Incidentally, what is the cheapest, but still good, 48V 5kW inverter that can be used to charge and run off batteries and also feed excess power into the grid? I believe that would be called a bi-directional hybrid inverter? We are quite a few houses and offices that run off a single transformer, and the power that I can feed into the grid behind the utility's transformer will never be anywhere close to covering our consumption.