One of the most common questions we get is "How much Solar do I need?"
Our goal is to estimate and design a solar system that meets your needs in the environment you'll be in. Not everyone can ditch a generator for solar panels, but they sure can help.
Offgrid & RV Solar System Estimation
Solar System Estimation
It can be daunting at first, how much Solar , Batteries and Inverting power will you need? Enough should be the answer, but how much is enough?
First thing you need to do is get an estimate, rounding up or down is fine here.
Here are some basic guidelines when estimating off grid power usage ,battery storage and inverting power.
We'll be using watt hours here, this is critical what we keep all figures in watt hours. Watt hours or watts can easily be computed by multiplying volts x amps . Using watts is critical because it's the same no matter what voltage we're working with. In offgrid energy systems there can be many different voltages.
- Residential Fridge - 1000 watt hours (more in the hot summer, less in winter)
- Modern Flat TV - 300 watt hours
- Laptop computer - 500 watt hours
- Coffee Pot - 400 watt hours ( A coffee pot will use 800 watts while running, but if it only runs 30 minutes, that's 1/2 of the watt hour rating)
- Inverter Overhead - 480 watt hours (This is power the inverter uses internally every day)
- Misc Other Loads - 500 watt hours ( Things like phone chargers, system monitors, LED lights, etc)
Total = around 3,180 watt hours
I'm sure we're missing some, but for your average Offgrid system, this will get you close. If you cook with electric, add more, if you want to run fridge off propane subtract some (but you might prefer electric in the end).
Measuring your current power usage
Something else you can try is a Kil-A-Watt device. This is something you can plug into the shore power connection or a generator to measure your current power needs. Run this for an entire day and you'll know exactly how many watt hours you use.
Keep in mind many high power draw appliances such as air conditioners, water heaters, coffee pots, microwaves, slow cookers, etc cycle on and off during operation. While a residential refrigerator may draw 250 watts while running, it may only run 15 minutes or less every hour.
RV & Offgrid Solar System Design
Solar System Design
Now that you know, how much energy you need, how do you capture it, store it and use it?
We recommend planning for 5000 watt hours or more of usage per day if you do not plan to run your AC from batteries. If you do want A/C from batteries you'll want to triple or quadruple that number, this is why many people still use a generator when it's very hot and cloudy.
Estimating Inverter Size
We recommend at least a 3000 watt or 3000 KVA Pure sine wave inverter charger. This will handle most people's needs just fine. If you need more there are larger inverters or they can be paralleled for more 120 VAC power. Our favorites are the Victron Mutplus and Multiplus II or Quattro. If you're looking to save some money the AIMS or SunGold Inverters are also a good pick. We do not recommend MOSFET style inverters, these are usually cheaper and lighter. They work fine for a while, but eventually over heat and burn up. The other ones mentioned here are heavy and using copper coils to transform the 12v or 24v DC power to 120 VAC power your house appliances can use.
Estimating Battery Capacity
This is most often the most expensive part of any solar system. We recommend 1.5 to 2 times your daily power usage for battery capacity. Example, 5000 watt hours would be 7,500 - 10,000 watt hours of energy storage. The reason for this it will give you greater run time when sunlight is not perfect and allow you to choose when to run a generator. Having this extra capacity also will allow you to run your batteries in more healthy way but not depleting them fully.
There is nothing to say you can not start with a smaller battery bank and build as you go. You'll eventually find what works and what doesn't.
Batteries are not listed in watt hours.
Most batteries are listed in amp hours. For Example a Battle Born Lithium Battery is 12v @ 100 ah Using the formula from above that would be 12 x 100 = 1200 watt hours. Meaning that one battery can power a 1200 watt load for 1 hour, a 600 watt load for 2 hours, a 300 watt load for 4 hours and so on. If you're looking at batteries online do this conversion to better understand how much energy is stored in each battery. Some are 130 ah, some are now 200 or more ah!
Estimating Solar Panels
This is where most people start and we're ending here on purpose. Generally, the answer is simple, as many as you can fit on your RV , roof or ground mount platform. The reason is simple, very rarely will you get ideal conditions where you will get full rated power. Clouds, Partial clouds, dirt, smoke / haze, leaves, etc can all reduce the amount of solar energy you capture by 50-90%!
If you want to do the math on it though, you'll want to plan to replenish your daily usage during the available sun hours. These are dependent on time of year and latitude, summer and further south is more, winter and further north is less. In the upper mid-west you can generally plan on a solid 5-6 sun hours in the warmer months and 3-4 in the colder months.
If you have 5000 watts of usage, and 5 sun hours, that means you need a minimum of 1000 watts of solar to not run a generator. However, that's in an ideal world that we've not found to exist outside of parts of Arizona (they have most sun hours in the US). A good rule of thumb would be to multiply by 1.5 to 2 times that figure, that brings us to 1500-2000 watts of PV solar panels that will capture enough energy to never run a generator.
What if you don't mind running a generator an hour or two a day or every other day? Then 1000 watts or less can work just fine.
This can all be very confusing and complicated. We're here to help. Contact us today and we can help design and estimate your solar system.