Volts, Amps, Watts... Oh My!
Dan Diehl
So electricity isn't intuitive like water, but there are some similarities at least in explaining the relationship between volts, amps and watts. In solar we usually talk about Kilowatt Hours or kWhs. This is the unit of measurement that your electric bill is in and what the estimated output of a solar system is in. So I get the question from time to time how amps are related to kWh or something similar. Below is an explanation I wrote to one of my customers and I thought it might be useful to someone else out there in the ether.
The equation is Watts = Volts * Amps. If you enter in the time aspect it is Watts * Hours = Watt-hours (Wh) and when you get a thousand Wh’s you get a kilowatt hour (kWh) which is what your bill is based on.
So the common unit is kWh. You can sort of think of electricity like water. The pressure of the water in the pipe is volts and the diameter of the pipe is Amps. So both of them combined give you the max amount of water that can be delivered in a given amount of time like an hour. This is the Watt hours.
The volts you receive at your house will always be about 240 volts. That’s what your appliances, lights, etc. are expecting and that is what the solar inverter and LPEA deliver. The service to your house from LPEA is 200 Amps. So you can have about 200 Amps of stuff on at your house before the main breaker trips because you are drawing too much power. That being said, 200 Amps is a LOT of power.
For example, your 10kW electric heater uses about 42 amps maximum. Amps = Watts / Volts. 10 kW = 10,000 Watts so Amps = 10,000 Watts / 240 Volts = 41.67 Amps. That is probably the biggest draw in your house and it doesn’t even use a quarter of your available capacity.
I don’t know if this is answering your question, but these are the equations.
As an example of how the Watts (and therefore the Amps, but not the Volts; Volts are constantly 240) fluctuate from hour to hour and day to day, take a look at this write up I did on why a 5.2 kW system isn’t producing 5.2 kW. Maybe this page will help with your questions: http://www.flatrocksolar.com/durango-solar-faqs/2014/12/6/why-does-my-52-kw-system-not-produce-52-kw