Bigger is not Necessarily Better
Sizing your power generation system for your applications is very important. In the event you oversize the power generation equipment you will over allocate funds for equipment and you will most likely not be operating in the efficient range of the equipment resulting in higher fuel consumption or back feeding power to the grid when applicable.
So how do you know how much power you are currently using?
You can look at your bill to find you total usage but the wont show you how much you are using at an instance and for how long which is what is required for sizing. You can take a guess or run a quick calculation regarding average consumption of appliances. With modern technology and automation we recommend taking an intelligent and calculated approach. Home power monitors are becoming more readily available and more efficient and user friendly. We recommend using a Shelly 3EM. The Shelly 3EM will work with 1, 2 or 3 phase power or measure independent power legs. The current transformers are good for up to 120 amps for each which will easily measure the standard 200 amp residential service. The Shelly 3EM have split clamps that can be installed on existing power feeds and can be installed in minutes. It is recommended to wire the voltage leads to a separate breaker to monitor the voltage of each leg without landing two wires on a single breaker. Once it is installed the power consumption can be monitored real time and trended to review the power usage over time.
Shelly 3EM for Power Monitoring
Once it was installed, I turned off all of the breakers (opened all breakers) and then proceeded to turn on each breaker (close each breaker independently) and ran the appliances on each circuit. The real power consumption can then be determined for each circuit. Then all breaker can be closed and the house power is returned to normal. Through watching the power consumption on a day to day basis you will begin seeing trends and understanding how much power you actually use and how much is required for different appliances. We noted that during day to day activities in the winter months we utilize around 3-5 KW on a fairly normal basis. For gasoline generators the optimum efficiency is between 50% & 70% of the capacity and you don’t want to run below 30% or above 70% for long periods as its hard on the generator. Therefore we looked for a generator in the 30% to 70% range with a KW output of 3-5KW and settled on a 7KW running watt generator.
| Generator Size (Running KW) | Recommended Min Capacity | Recommended Max Capacity |
| Running Capacity (Not Surge) | 30% | 70% |
| 1.5 | 0.45 | 1.05 |
| 2 | 0.6 | 1.4 |
| 2.5 | 0.75 | 1.75 |
| 3 | 0.9 | 2.1 |
| 3.5 | 1.05 | 2.45 |
| 4 | 1.2 | 2.8 |
| 4.5 | 1.35 | 3.15 |
| 5 | 1.5 | 3.5 |
| 5.5 | 1.65 | 3.85 |
| 6 | 1.8 | 4.2 |
| 6.5 | 1.95 | 4.55 |
| 7 | 2.1 | 4.9 |
| 7.5 | 2.25 | 5.25 |
| 8 | 2.4 | 5.6 |
| 8.5 | 2.55 | 5.95 |
| 9 | 2.7 | 6.3 |
| 9.5 | 2.85 | 6.65 |
| 10 | 3 | 7 |
| 10.5 | 3.15 | 7.35 |
| 11 | 3.3 | 7.7 |
| 11.5 | 3.45 | 8.05 |
| 12 | 3.6 | 8.4 |
| 12.5 | 3.75 | 8.75 |
| 13 | 3.9 | 9.1 |
| 13.5 | 4.05 | 9.45 |
| 14 | 4.2 | 9.8 |
| 14.5 | 4.35 | 10.15 |
| 15 | 4.5 | 10.5 |
Consider Your Seasons
Keep in mind the sizing between the winter and summer will be different but we recommend sizing the generator when you are expecting to use it. If you are more inclined to use it in the summer or as a off grid power source you need to monitor the power consumption during those instances to gather the most accurate information.
Choose Your Equipment
Now that we have a target generator size we needed to iron out which generator to purchase. We have a few options but we narrowed it down quickly to two specific types, a conventional generator or an inverter generator. Inverter generators are typically more quiet and provide a cleaner power for sensitive electronics. Inverters are typically more expensive and are on the smaller side power wattage but the have a unique capability of paralleling generators. The conventional type are not able to be paralleled, are more noisy but are reliable and generally more cost effective to purchase. After looking around for a good deal we located a Predator 8750/7000 watt generator with minimal runtime at a very appealing deal. It meets all of the basic requirements that I deemed as important and had the potential with a few adjustments to have remote start and monitoring. Stay tuned and as always reach out with any questions or request.