A boat's power supply is completely different from anybody on the grid. Unlike most people, we are disconnected from any outside power source except on very rare occasions. Also, we do not have a constant supply of power available. Even during the day, when the solar panels are producing at their best, there is a very finite and limited amount of power they are producing. In the short run, we can draw more power than our panels produce by taking the excess power from the batteries, but unless the batteries are allowed to recharge, we cannot do that for long. If we run the batteries flat, we have no electricity available except what we are producing, and at night the solar panels are useless. Although we have the engines as a backup, we do not like to use them, and do not carry a lot of fuel.
Basically, we need to be completely self sufficient. If we increase our power consumption, it is not merely a case of paying a higher electricity bill. If we need more production capabilities, we must realize that and acquire those capabilities before we run out. Also, electricity is more to us than it is to most people. On a boat, loss of electricity is more than an annoyance, it is a threat. Without electricity, many of the things that people on shore take for granted (such as gas stoves, pressurized water, and telephones) will not work. Important safety equipment, such as radios, depth sounders, watermakers, and GPSs also need power. Aside from determining how much electricity we gain and lose , another function of the energy budget is to determine what our minimal power needs are. Once we know them, we can divide that number by our stored battery power to determine how long our batteries would last if we lost the ability to generate electricity.
Although electricity is always essentially the same, boats usually measure it differently than shore. Several terms that are relevant are DC, AC, Watts, Amps, Amp-Hours, and Voltage. Most electricity on shore is AC (Alternating Current) of either 115 or 230 volts (V,) while yachts usually use 12V DC (Direct Current.) Although AC and DC are fairly different, and have different uses, it is not important to understand them to comprehend this project.
Volt and amps are the terms most often used in my energy budget. Volts can be thought of as the force that causes electricity, and if a battery's charge is increased, its voltage will go up (batteries use DC.) This allows us to use our battery voltage to get a rough idea of the status of our batteries. Amps (properly called amperes) are a unit of electrical current, the flowing of electrons. If something uses electricity, the current it uses is measured in amps. Some things, like a light bulb, may only use 0.5 amps, while a refrigerator may need 4 amps or so. Current from solar panels is also often measured in amps, although the panels themselves may be rated in watts. Amp-hours are how we measure charge. 1 Amp-hour of charge means a number of amps times a number of hours equals 1. For example, 3 amps for 20 minutes is one amp-hour, as is 1 amp for 1 hour, and 0.25 amps for 4 hours.
Watts (and watt-hours,) which are terms nearly always used on shore, refer to amps times volts. 1 kilowatt-hour could be 100 volts time 10 amps for 1 hour, or 200 volts times 5 amps for 2 hours. Watts are a unit of power, as apposed to just current (amps) or force (volts.) Although we could use watts instead of amps in most cases, we choose to use amps. If you wish to determine watts when amps are mentioned, multiply the number of amps by the voltage.
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