Need help Designing 10KW S PV System on Paper

Re: Need help Designing 10KW S PV System on Paper

Assuming you are somewhere around New Delhi India, a fixed solar array will output around (noon time equivalent hours of sun per day):

Month      Solar Radiation (kWh/m2/day)
1      5.56     
2      5.90     
3      6.65     
4      7.01     
5      6.91     
6      6.34     
7      5.28     
8      5.25     
9      5.89     
10      6.17     
11      5.74     
12      5.56     
Year      6.02

Battery bank, assuming 2 days of storage and 50% maximum discharge at 48 volt bank:

• 9,000 watts * 1/48 volt battery * 8 hours * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge = 7,059 AmpHour @ 48 volt battery bank

The size of solar array to supply rated output in January would be:

• 9,000 watts * 8 hours * 1/0.52 off grid sys efficiency * 1/5.56 hours average sun Jan = 24,903 Watt Array minimum

Add a couple of large AC inverters, backup genset (you need that anyway), plan on replacing the batteries every 5-10 years or so (depending on batteries and how well they are taken care of), etc... Not an inexpensive system.

Maybe around $50,000 USD for solar panels and $70,000 USD for industrial "fork lift" type batteries (could last upwards of 10-20 years), plus mounting hardware for array, wiring, inverters, backup battery chargers, etc... Probably $200,000 just for material in the US (as a first guess). I would not begin to guess what the costs in your region would be--But something more than 10x what you were hoping to pay for off grid solar power.

I understand that energy and fuel costs are not cheap... But utility power at $0.10 per kWH (USD?) is not a bad price. You could design a battery+AC Inverter system (with backup gensets) first that used utility power first, then add solar panels as it makes economic sense later.

In the US, off grid solar power costs around $1 to $2+ per kWH or about 10x the cost of utility power. This puts a huge incentive on you to conserve. Computer systems, lighting, Air Conditioning all use huge amounts of energy and can be reduced by a lot (50% or more) with the correct choices in equipment and construction.

-Bill

Re: Need help Designing 10KW S PV System on Paper

More or less, first look at your loads. Both peak power (say 9kW peak to support starting motors, lunch at a cafeteria, perhaps night time peaks for a call/engineering center supporting world wide customers, etc.--That is the maximum power supplied by the inverter/generator). And then there is the average power--everything running normally. Computers, lights, Heating and Ventilation, water pumps, etc... That may be a 3 kW load (say times 16-10 hours per day for two shifts)--That is the gallons per day of fuel, kWH per day electrical, AH/kWH of battery storage, and kWatt of solar array required to support.

Remember, full noon-time equivalent sun hours per day (one method of measurement based on the average noon-time sun of ~1,000 Watt per square meter) is only ~5-7 hours per day for your area (again, if I have your location correct) with a fixed array facing the equator, tilted to latitude.

So, if you had (for example) a 9kW average load off grid with ~52% system efficiency (conservative average) with 5 hours of sun per day, then the array needed to support that amount of power for 5 hours of sun per day:

9,000 watts * 18 hours per day * 1/0.52 system efficiency * 1/5 hours of sun per day = 62,308 Watt Solar array to "meet" required loads

Or if it is 9kW peak loads and 3kW average load over 18 hours:

3,000 watts * 18 hours per day * 1/0.52 system efficiency * 1/5 hours of sun per day = 20,769 Watt Solar array to "meet" estimated "average" loads

So, yes, it is very likely to have a solar array several times larger than the estimated average load.

To size a Grid Tied system--You can use ~77% system efficiency, and because the solar power is only an "assist", the array and inverter do not have to supply any loads. The Utility will do that. The GT system only assists by reducing power consumption (utility meter turns slower). Or even turns meter backwards in middle of sunny day (credit on your utility bill) and during less sunny times, the meter turns forwards.

A grid tied system, for all the world really looks like a car's electrical system. The "battery" is the utility system (really for all the world like a giant AC battery bank), and the car's alternator is your GT system. When the engine is off, the battery supports all of the loads. And when the engine is running, the alternator supports most/all of the loads, and pushes back energy to "recharge" the car's battery (of course, the utility does not "recharge", your "excess energy" is simply sent to nearby buildings in parallel with the normal utility power flow).

-Bill