Time of use is important but if they can’t kick off the motor in question, then it’s a moot issue, right?
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Netscape. Just the Net You Need.
No thats not right. What does it matter if you install a 500 HP motor in a car because you are concerned about having enough torque to pull a hill, if there is no gas in the tank to drive down the road after it starts?
Run time of all electrical loads is the main design factor when sizing an off-grid solar system and it determines how fast you will drain the battery bank and how much solar array you will need to keep it charged. Surge loads and peak loads are used to size the inverter, switchgear, and wire, but total amp-hours (or kWh) per day of all loads determines the array and battery bank size. Designing an off-grid system is nothing like designing an on-grid or a generator based power system as you have "X" amount of amp-hours per day and thats it. Starting and running a 1500 watt microwave for 5 minutes is only a concern for sizing the inverter. But if you ran that microwave 12 hours straight each day then the size of the inverter is not relevant if the solar array and battery bank cannot keep up by putting in the same amp-hours that this load took out.
The same is true for your 1 HP pump example in an earlier email. I can easily size an inverter to handle the surge or start load from a 1 HP pump that cycles on a few minutes each day for showers and clothes washing, and add soft start if the surge is too high for the inverter. But if this pump ran continuously for 12 to 16 hours each day, which is what an air conditioner has to do on hot months, then the surge load on the inverter is the last thing you will be concerned with.
Powering an air conditioning system in an off-grid application should be avoided at all cost, unless the client has the money for all costs and buys a solar array that far exceeds their daily summer non-cooling energy needs. But a system sized for summer cooling will be over-sized during the winter months unless you would actually consider heating with solar electricity which will drain the battery bank faster than your air conditioner. Since there is no grid to sell back to, you have sold a solar system that has to waste a large part of its daily capacity for half of the year.
Sorry, but sometimes you do have to tell a client they are wrong, and I do not always have the Zen time to help them discover that realization on their own through a slow learning process.
Jeff Yago
Netscape. Just the Net You Need.
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