University Project

Re: University Project

I could not find the posts--But we have had a few threads about remote islands that have centralized power using Surrette / Rolls Batteries and SunnyIsland Inverters (multiple locations).

I will say that yes, it can be done, but it does take a lot of attention paid to safety. Very large battery banks need very heavy current bus bars and fusing/protection against short circuits.

The systems (as I recall, I could not find the threads with a quick search) are using the standard Sunny Island and similar AC inverters (something like ~6kW) units and battery banks all cross tied together.

Usually, the first step we recommend is to "know your loads"... Very heavy surges (pumps, and possibly lab gear) can put a strain on the systems. But, usually the biggest issue is are the "smaller loads" that run 12-24 hours per day...

For example, a standard home with a refrigerator my use 130 watts (average) when running but it runs 50% duty cycle 24 hours per day which works out to:

130 watts * 0.50 * 24 hours per day = 1,560 Watt*Hours = 1.56 kWH per day

If this was a cafeteria fridge/freezer making lots of ice and cooling foods for later serving--The power usage can go up a lot.

A simple office microwave may use a lot of power to run, but if it only runs 20 minutes a day--Then it does not use much stored energy:

1,500 watts * 1/3 hour per day = 500 Watt*Hours = 0.5 kWH per day.

But that little 300 watt desktop computer that is used to write papers and run experiments/simulations:

300 watts * 24 hours = 7,200 WH = 7.2 kWH per day

Yes--It is possible to build/run/maintain a larger power system on $0.50 to $1.00 or so per kWH... In California, large users of power (especially durring summer afternoons) can pay upwards of $0.50 per kWH (homes/commercial).

So one can say that is it possible for an Off Grid system properly designed and maintained could be cost competitive with utility power in some locations (or if this was a remote site where power was not available).

If this were a "real" project--There are things that need to be done to support a real school type load... For example, most schools are closed (or reduced occupation) during summer--That is usually when the most solar power is available.

During winter, many places will see 1/3 or less the amount of summer sun... So there are the issues of backup power (generator)--Or if the power is highly variable--Then using a generator to "support" battery power during those times (evening meal prep, student dorm with lights/computers/studying) may be a good option.

The "solar power part" is easy to do a paper design for--The hard part is understanding/estimating the actual loads and what happens if the solar power system is too big (or more likely) to small to support the needed loads without power outages/backup gensets/etc...

-Bill