More Information About Powering A Tiny House With Solar Panels And Batteries
To begin, let's start with an overview of how an off-grid solar energy system works:
- Solar panels capture sunlight using photovoltaics or PV for short. Most solar panels absorb energy in direct current (DC) form, although recently manufacturers have begun introducing AC-modules which use alternating current.
- Connecting multiple solar panels together creates what is called a solar array, and using electrical wires the solar array sends energy into a battery bank where it is saved and stored until needed.
- Once energy is needed, like when a light switch is flipped on, energy is pulled from the battery bank and through a device called an inverter which changes it from DC to AC form. The inverter is connected to the load center which is usually an electric panel/breaker box. All of the electrical loads like lighting, refrigerator, fans, electronics, etc. are tied into the electric panel/breaker box using electrical wiring connected directly to the load.
Calculating Power Requirements For Your Tiny House
Ok, so now you have a pretty basic understanding of how an off-grid solar energy system works. The next thing to consider is how much energy your tiny house uses, so let's briefly discuss how power is measured:
- Power is measured in Watts (W) and kilowatts (kW). 1,000 watts is the same as 1 kilowatt (1,000W = 1kW). Imagine a 1,000 Watt light bulb burning for a period of 1 hour – This is equivalent to 1 kilowatt hour which can be expressed as 1 kWh.
So to understand how much solar with battery storage capacity a tiny house owner needs, one must first know what loads are to be supported by the off-grid solar energy system, and the approximate amount of power that will be burned by each of these loads. These vary by individual, but in our case we use a mixture of the following:
- Stove Hood (for ventilation when cooking)
- Interior LED Lights
- Ceiling Fan With LED Light
- Exterior LED Lights
- Small Electronic Appliances (Laptops, iPads, iPhone Chargers, etc.)
- Water Pump
- Small Heater/Air Conditioner*
Once you know which loads are used within the tiny house you can determine what the load profile will look like using ENERGY STAR electronics data or electrical information on the specific product (if a label available) and a little bit of math. For instance, here is an example off-grid load profile:
- Refrigerator/Freezer Combo @ 24 hour of use = 2.73 kWh
- Small Electric Range Burner @ 1 hour of use = 1.2 kWh
- 6 10W LED Lights @ 16 hours of use = 0.96 kWh
- Outdoor Security Light (2 10W LEDs) @ 12 hours of use = 0.24 kWh
- Electric Fan @ 8 hours of use = 1.6 kWh
- Coffee Maker @ 1 hour of use = 0.2 kWh
- Cell Phone Charger @ 8 hours of use = 0.30 kWh
- Total Daily Loads = 7.23 kWh
- Using a detailed load profile you can then determine what size battery bank and how many solar panels would be needed to provide a given amount of power.
Battery Backup For An Off-Grid Solar Energy System
Without getting too dense, below is the basic math to calculate battery backup storage for an off-grid solar powered tiny house. Note that we recommend you consult an electrician or NABCEP certified solar installer in your area:
(((Battery Amp Hours * # of Strings) * Appliance Operating Voltage) * 50%)/1000 Watts = Battery Bank kWh
Appliance Voltage/Battery Voltage = # Batteries/String
(# kWh * 1000)/Appliance Watt Hours = Hours of Use
For example, this is a basic calculation which doesn’t include derate factors or inverter/battery efficiency:
(((305aH * 1 String) * 48 Volts) * 50%)/1000 Watts = 7.32 kWh
48 Volts/6 Battery Volts = 8 Batteries per String
Light Bulb Example: (7.32kWh * 1000W)/100Wh Light bulb = 73.2 hours of light per charge.
A properly designed 1 kW (Kilowatt) array of solar panels, when situated to maximize sun exposure, will generate more than 1 MWh (Megawatt hour) per year.
To prevent confusion we will not get into the detailed calculation. Instead, for your own example calculations of how much power can be generated by solar panels at your location, do some calculations using the PV Watts tool designed by the National Renewable Energy Labs (NREL): http://pvwatts.nrel.gov/
Additional Solar Resources
You can order the same exact solar setup used by the Tiny Solar House! Click here to lean about our off-grid solar kit.
SolarWorld is the largest solar panel manufacturer in America, producing solar products for over the past 40 years. Click here to learn more about their high performance solar power systems.
NABCEP which stands for North American Board of Certified Energy Practitioners is the go-to certification program for energy professionals. Click here to find a NABCEP certified solar professional near you.
NREL which stands for the National Renewable Energy Labs develops clean energy and energy efficiency technologies and practices and provides knowledge and innovations to integrate energy systems at all scales. Click here to visit the NREL website.
DSIRE which stands for Database of State Incentives for Renewables & Efficiency is a website designed to offer information about incentives and rebates for residential and commercial energy upgrades including solar. If there's an opportunity for you to save money on the cost of going solar (and there likely is), the DSIRE website will include the relevant information. Click here to learn about policies & incentives available in your state.