I have spoken about our battery bank, appliances, solar panels, and backup generator, but I haven’t put it altogether to explain the efficiency of our system.
When designing an off grid power system, the first thing to do is know your current use of power and cut it till it hurts either because you can no longer use that appliance anymore or you have to pay top dollar for a new energy efficient appliance.
In our case, I created a spreadsheet and calculated the battery costs as well as their storage capability. I also budgeted in the storage system because I would only be able to use 70% – 80% of my stored power to prolong battery life. In the case of lead-acid batteries, you can rapidly destroy a battery system’s ability to store power if you drain the batteries below 20% capacity. To charge the batteries, solar panels are our main source of power.
We decided to purchase at the time the once U.S. made, REC 235 watt solar panels. We maxed out our charge controller by purchasing 10 panels. Ten panels can produce almost 80 amps and our circuit breaker from the panels to the charge controller is 80 amps, which protects the charge controller from being cooked by the panels. We have yet to trip this breaker, but we have gotten close. Our panels produce around 7 amps a piece with a total of 70 amps of potential power on a sunny day for a 24 volt system. The panels can surge up to 7.8 amps, hence the need for the breaker. To calculate the watts, my panels produce 70 amps x 24 volts = 1,680 watts an hour or 1.6 kW. That is not a lot of power. To put this into perspective, most affordable off the shelf generators from a home improvement store produce 5,500 watts or 5.5 kW an hour. So, how does one produce enough electricity in an off grid home without needing the generator?
First, an energy efficient home and living consciously aware of the weather are the keys to successful power generation, usage, and storage. Here are some things to think about when planning an off grid home.
Lighting: Try to use as much natural light as possible. Have the majority of your home’s windows on the south side of the building. This will allow maximum light to enter the home even on cloudy days. Our kitchen is strategically placed in the front of the home to provide enough natural light during the day to not require using the electric lights in the kitchen. During the summers we have light in the early AM to the late PM, but we make enough power to not really worry about running lights. During the winter we need to use the electric lights more often, but we are conscious enough to turn them off when they are not in use. Plus, our home uses all LED light bulbs which take only .3 amps or 7 watts each per hour.
Appliances: Say goodbye to your electric oven and range. Say goodbye to an electric water heater. Say goodbye to your AC refrigerator & freezer. Say goodbye to your clothes dryer. Say hello to a propane oven and range. Say hello to a propane instant hot tankless water heater or using a wood cook stove. Say hello to an efficient DC refrigerator and freezer. Say hello to hang drying your clothes. To supplement during sunny days, consider purchasing a toaster oven and a great mixer. Say goodbye to your coffee maker that uses a hot plate and clock and find one that pours into a thermos craft or use a French press. Look for phantom loads mentioned in an earlier post and eliminate them by purchasing appliances without them. On those appliances like a DVD player or TV, purchase a six strip that can be shutoff when you are not using them. Purchase “dumb” products without “smart” computers that take electricity when you are not using them. Purchase a wood cook stove if you want to go the extra step of independence away from using propane all the time. Plus, the wood stove is a great heat source. I have mentioned the many uses of our wood cook stove in previous posts. However, plan on not using your wood cook stove during the summer months. Also, plan a home without carpet and sweep a lot, on sunny days use the vacuum.
Plan and Strategize: Wait for sunny days to do laundry. Purchase at least a two weeks supply of clothes to last you till the next sunny day in the winter to do laundry. If the next sunny day is a month away, which happened to us this past January, do laundry while charging the battery bank with the generator. Watch less television unless you have a super-efficient LED TV and yet, it would be best to watch less of it anyways. Power the inverter down at night and shut the home’s AC electricity completely off while you sleep and have a LED flashlight within easy grasp if you have to get up and it’s still dark. Power the inverter back on in the morning when your family is awake.
Celebrate: Keep records of your homes achievement on a calendar, celebrate sunny days, play the game to see if dropping your battery bank to 30% would reach the next sunny day and charge the system completely without firing up the gas generator.
Here is our typical power use in the winter…
- 5 LED Lights on total for the home and chicken coup at most times during the day = 5 lights x .3 amps = 1.5 amps per hour x 16 hours = 24 amps
- Television DVD player average 2 hours a night = 6 amps x 2 hours = 12 amps
- Fridge and Freezer roughly estimated at 1.4 amps per hour x 24 hours = 33.6 amps
- Computer with a dead battery and using the wireless Internet 6 amps x 1 hour = 6 amps
- The inverter to convert the batteries’ DC power to AC = 1.6 amps per hour x 16 hours = 25.6 amps
Lights = 24 amps
Entertainment TV, DVD, and Computer = 18 amps
Fridge & Freezer = 33.6 amps
Inverter = 25.6 amps
The grand total of power used on a typical day = 101.2 amps or 2,428.8 watts
Our battery bank stores 675 amps or 16.2 kW, so in one day typical day, we used 15% of our stored power. Now, that is if no electricity is produced from the solar panels. For that to happen, I would have to flip the breakers on the solar panels and turn them off completely because even on a cloudy day they still make a small amount of power. During the winter, I budget that our battery bank will drop 10% each socked in cloudy day. That means I have roughly 6-7 days, 8 if I conserve and push the battery banks’ limits, till the next sunny day which could bring our bank up another 30% or more depending on sunlight conditions. During the winter, despite having power in the battery bank or not, I will bring out the generator at least once a month to equalize the batteries, which helps maintain the system and life of the batteries.
During the summer, my wife and I use a lot of electricity because we have so much in plenty. We use our well pump regularly to deliver water to the orchard and gardens. We use an electric log splitter. We use power tools building new projects. I almost purchased an electric lawn mower, but decided to wait to see if the batteries for them would come down in price first. I even made ice cream using our Kitchen-aide this week. I am even hoping to build a ice chest air cooler sometime this weekend to use for those 100 degree days or spend the money to purchase an air conditioning unit for the house.
Hopefully, this gives you a decent perspective of what is necessary to create a home powered by the sun. By following our philosophy and guidelines mentioned above, we use our generator only 5-7 times a year. It could be less, but sometimes 3 gallons of gas for the generator is worth taking a break from energy conservation, especially in the dark months.