Current plan is DC to AC to DC using off the shelf tech. That way any excess KWH is sold to power company. The grid becomes our "battery bank".
Am exploring a 600V to 48V Battery Bank system to power the miners.
So it would be 600V DC (solar array) to charge controllers (Morningstar MPPT 600's) to 48V Batteries (probably US Battery 425A/hr L16 HC's in strings of
to 48V/12V DC/DC converters to the miners. System would include AC/DC battery charging for those non-sunny days. Backup genny for battery charging when/if the grid goes away (I own a continuous duty rated 35Kw Onan that is just looking for a purpose in life). This is a grid isolated system technically.
Downside of that route is conversion inefficiencies, cost of batteries, cost and complexity of DC/DC conversion(s). Upside is that the miners are effectively UPS'ed and battery backed up.
Am also looking at using Syn-Gas to power a genny. Which is wood gasification, purify and warehouse the gas (methane, CO, and minor amounts of H2 in suspension, Nat Gas effectively), then use the Syn-Gas to power the genny to do battery charges periodically. Logging scrap is plentiful here and currently considered an annoying waste product of the logging industry.
Am also investigating using wood gasification Syn-Gas as a feed stock to a Fisher-Troops processor to make liquid fuels (diesel/gasoline, GTL-Gas to Liquid).
http://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_processAnother possibility is using wood gasification Syn-Gas in Bloom Energy processors. Like the ones used by eBay, Google, and Walmart.
http://en.wikipedia.org/wiki/Bloom_Energy_Server.
We have time to sort all this out and make an informed decision. As we move forward I'll try to remember to post pics.
Is it possible to use the grid power for mining and simply use solar to kick the power back to utility. Such setup would be simpler, I guess.
Yes, absolutely.
The 2 systems need not be tied together. And, in fact, can be geographically distant.
The downside is that the power sold is at a lower $$$/KWH than the power bought.
So it makes monetary sense to use what you generate and sell the excess.
Hence the need/desire to tie the systems together and let it "load balance" itself. Buying some at times and selling some at times.
But how due to the very low solar power available time (<= 6hrs) per day the break even on such a setup will be too long.
The breakeven on the panels currently installed is 24-26 months. Which were purchased 2 years ago year from ML Solar @ $0.76/W. At the time of installation, cost per KWH from Lake Country Power was $0.134/KWH. So these panels are about to hit the breakeven point.
This includes accounting for being @ ~45 degrees latitude which effectively derates a panels output by 30% (70% of rated output, have always found it interesting that the output is roughly the sine of the angle of the latitude, oh shit physics really does work in real world everyday life). Panels are typically rated @ 1000W/meter squared (which is somewhere near the equator). Here in Northern Minnesota that figure drops to ~700W per square meter due to us being higher up on the planet making the photons travel through more atmosphere. Hence less of them reach the surface and energy density is less.
Regarding the Solar charging hours per day issue, this is mitigated by using extremely efficient charge controllers and/or grid tie inverters. Hence my favoritism of enphase microinverters and the Morningstar MPPT charging controller product line.
In conjunction, in battery bank style systems, by designing the battery bank to the lowest feasible voltage. Charging hours are expanded. Because the panels have to overcome a lower voltage to cause battery charging to happen. Thereby expanding the charging hours per day on both ends (morning and evening).
In the current system, which is charges a 12V battery bank, three solar panels are connected in series, which means to cause charging to occur each panel (Voc 37.35V, Vmpp 29.29V) only needs to output 4.4 volts (13.2V combined). This occurs ~8AM and ceases ~6PM. Now is the panel putting out rated current at those times, No. But what it does do is expand the effective hours per day to something closer to 8+.
By changing the battery bank nominal voltage to 48V charging would occur much later in the morning and would cease much earlier in the afternoon. Consequently losing or wasting all the energy the panels were capable of supplying during those early morning and evening hours. The lower nominal battery voltage accounts for a 20%-30% increase in harvested energy (time of year dependent).
To your point, in badly designed systems the effective charging times per day can be as short as 4 hours per day. The devil really is in the details.
Low hours per day charging propaganda is bantered about by fossil fuel dependent energy sources as a means to dissuade consumers from closely examining alternative energy sources.
