How to Figure Loads for Solar Power & Water-Heating
Providing electrical and thermal energy to your home from renewable energy sources such as solar or wind power can be a smart move if it's done correctly. An important step in the process is to calculate how much electricity you are now using and which appliances use the most. Water heating can be a major part of your total energy consumption, so this load needs to be calculated. Remember that your house needs to use energy as efficiently as possible no matter what sources of energy you use. Does this Spark an idea?
Other People Are Reading
Instructions
-
-
1
Examine your utility bill from the power company. Your monthly bill will show you exactly what you are paying for. Find the number of kiloWatt hours (kWh) you were charged for during the period. Look for the number of days covered by the bill. Divide the energy consumed in kWh by the number of days. This gives you your average daily electricity consumption over the period in kWh per day. Check back over the last 12 months and do the same calculation for each month of the year. Make a list of your average daily electricity use for each month of the year. Note the month when the consumption was highest.
-
2
Determine how much current your electrical appliances are using. This is measured in amperes (often called "amps"), and is always shown on the back or side of large electrical appliances. For lighting, the power is given in watts and shown on the light bulb or on its base. Go to each room in the house in turn and write down the current in amps used by every electrical appliance in the room. Count the number of lights and write down the total number of watts. Don't forget the basement and the garage.
-
-
3
Add up the total current in amps of all the appliances and the total lighting load in watts. Convert the number of watts of lighting into amps by dividing the total watts by 110 volts. For example, 360 watts of lighting will consume 3.27 amps of current. Add the lighting current to the total current consumed by the appliances. This number is the maximum amount of current your electrical appliances, equipment and lights will consume if all the appliances and all the lights are turned on at the same time.
-
4
The calculation you have made gives you a figure for the maximum possible electrical load. But few families switch on all the appliances and turn on all the lights at the same time. Look again at the list of appliances and the lights. Which appliances might be running at the same time, perhaps in the evening when most of the lights are on? Add up this total in amps. This is a more realistic estimate of the maximum electrical load you need to plan for.
-
5
The calculation of the water heating load is much more technical. Although detailed calculations are possible, they are complex. For this reason the engineers that design and install solar water heaters rely on simple guidelines to estimate what you need. For example, the Florida Solar Energy Center recommends 10 square feet of solar collector area per person. Many contractors use a guideline of 20 square feet for each of the first two family members, with an additional 8 to 14 square feet needed for each additional family member depending on your location. In general, the further north you are, the larger the area of solar collectors required. The solar storage tank is sized in relation to the total area of the solar collectors. Contractors generally propose a tank size of between 1.5 and 2.0 gallons per square foot of collector area.
-
6
Calculate the area of solar collectors based on your family size. For example, if there are four people in the house, apply the guidelines above to show that you need between 56 and 68 square feet of solar collector area. Calculate the storage tank volume by applying the guidelines to show that you will need a tank holding between 84 and 136 gallons. Since water heaters come in standard sizes, you would want to buy a tank volume that fits somewhere in this range.
-
1
Tips & Warnings
Knowing the average daily energy consumption in kWh will let you correctly size the batteries needed for the photovoltaic system. The maximum electrical load in amps will be needed to size the inverter for a stand-alone system.
References
Resources
- Photo Credit photo Solar energy image by Aleksandar Radovanovic from Fotolia.com
