How Many Days Storage Back Up Do You Require
The most expensive part of any solar power system is the batteries. Because you can only use a maximum of 50% of your battery per cycle to ensure you dont damage them and they last longer, you generally need a minimum of 2 x energy requirement in storage space.
For example, if you need 5kwhrs per day, and you want to be able to store 1-day backup in case there may be no sunlight for 24 hrs, you would need:
5kwh x 2 = 10 kwh x 2 = 20 kwh
20 kw hours in battery terms for a 12v battery that is a 250amph would be:
= 6.666 batteries required
Now that you have the totals, you know what size solar power system you need:
Max peak power: i.e. 2000w
Your Daily usage: i.e. 12kwh
Battery storage: i.e. 1 day back up
Ballparking A Solar System Size With Your Annual Usage
Based on your annual electricity and monthly consumption pattern, we can ballpark a general system size for you. To do this, we use a rule-of-thumb number for solar production in NC to estimate your needed system size. Based on our experience, our rule of thumb is that 1 kilowatt of solar installed in NC will produce 1,300 kilowatt hours per year. So if your home uses 12,000 kWh per year, wed estimate you need around a 9.2 kW solar system to meet 100% of your energy needs .
Remember, this is just an initial rough estimate. We always refine your system size with more accurate annual production estimates based on the exact solar potential of your site after we perform a full site evaluation of your home, discuss your goals of going solar, and work through any limitations if encountered. With that said, this graph shows how this rough estimation translates to solar kW and number of solar panels.
Roof space needed for a solar system
If a space meets all those criteria, then it is ready to shine. For a roof mounted solar system, each panel takes up an area of approximately 18 square feet. So for the 100% energy offset 9.2 kW solar system we have been using as an example, we would need 31 panels or 470 sq feet of eligible roof space .
Energy Usage = How Much You Need
We always start with energy usage when sizing a solar system. For existing homes we prefer to look at your previous 12 months of electric bills so we can establish a good sense of your energy usage patterns over the course of a year. If we arent able to get a full 12 month view of your bills, we can estimate your monthly usage based on your peak winter and peak summer usage while factoring in whether you use natural gas or electricity for heating.
For new construction homes, our building science team can create an energy model for your home that predicts your future energy usage .
Once we have a sense of your electricity consumption needs, well talk with you about any events on the horizon that might impact your usage. Are you thinking about getting an electric vehicle? Are your kids moving out soon? Are you going to get a pool with your end of year bonus? Are you contemplating mining Bitcoin or starting a hydroponic farm? Well take all of these changes into account to appropriately size your system up or down.
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Your rate of self-consumption will depend the amount of energy that you use on a daily basis, the pattern of your consumption throughout the day, and the size of the system that you install.You can increase your solar self-consumption ratio by running more of your devices during daylight hours possibly manually, on timers or using a home energy management system.
The table below contains very rough solar self-consumption ratio estimates for a range of popular solar system sizes and energy consumption levels. If the cell is red, the system is probably too large . If the cell is green, the system size is likely have a favourable payback period .
|Your daily energy consumption|
Remember: The table above is a highly generalised, indicative guide it does not take into account your location or the tilt & orientation of your roof not to consider system prices or financial details like payback period. If youd like to take a more detailed look, use our Solar PV System Payback Estimator or our Simple Solar System Sizing Estimator.
The Climate Of The Area And Peak Sunlight Hours Calculation
The sunlight hours available to your location will directly impact the watts generated from the solar set up.
The more hours of sunlight available the less number of panels required to generate a given output.
Inversely, with lesser sunlight hours, more solar panels will be required. By dividing this average hourly wattage requirement by the number of sunlight hours daily at the location, you calculate the watts your panels need to produce every hour. Using this figure you can select the panels required. The sunlight hours and sun angles vary by season. This will also be a factor for calculating the number of available sunlight hours and thus the panels required.
Lets look at a simple calculation to understand this concept better.
Lets say the summer season sunlight at the location is available for 6 hours and for mid winter it is 4 hours. Then in mid winter a 10w panel will provide 10w * 4h = 40watt-hours of DC power into your battery. In summer the amount would be 10w*6= 60watt-hours. There would be a little energy lost due to resistance through the regulators, cables, and batteries chosen. In calculating the solar power system you would built some assumption of loss into the final calculation.
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Choose The Right Solar Panels
If you have a small or odd-shaped roof, solar panel size is an important consideration when deciding on the size of a solar system. Take these factors into account:
- With a large usable roof area, you can buy more larger panels to get to your target energy output.
- If your usable roof area is limited or partially shaded, using fewer smaller high efficiency panels will ultimately be the most cost-effective, long-term solution. You can add more panels later on to accommodate increased energy needs.
Consider Whether Battery Storage Is A Worthwhile Option For You
Not all solar PV systems come with battery storage systems, which may actually be sold separately or fitted onto existing solar systems retroactively. If youre interested in battery storage for your solar system, there are a number of things you should consider before making a decision. What are your goals in installing batteries, for example do you want to go off the grid, or just want to save a bit of your solar energy for nighttime usage? We break down your options in our article, How much battery storage capacity do you need?
Want to explore battery size options & payback periods? Check out our Battery Storage Sizing & Payback Estimator!
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Solar System Sizing Table
If youre considering solar panels for your home, youll get the most value from them by directly self-consuming the energy that they produce during the daylight hours. The simple reason for this is that using the solar yourself allows you to avoid purchasing expensive energy from the grid instead of earning only a small credit for sending it into the grid. This is a crucial fact about going solar in Australia today.
Other Factors Influence Battery Sizing:
- Ambient Temperature – Heat or cold has a big impact on battery performance and capacity.
- Seasonal Factors – People use more power at different times of the year. The sun produces more power in the summer than in the winter.
- Budget – Battery bank size is often a compromise between what you want to spend on batteries and how often you’ll need to run your backup generator.
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Calculating The Size Of Your Solar Pv System
Now you know how much power you typically use and the times of day you use it. What capacity will your solar PV system need to be to cover your power usage?
First, we’re assuming you’ll have a grid-connected system. This is by far the most common type and it simply means you have solar panels generating electricity during the day, and a grid connection to supply electricity when the solar panels aren’t generating enough . See grid-connected vs off-grid for more.
How much electricity can you expect per kW of solar panels?
Solar PV systems are rated in watts or kilowatts . You’ll see systems described as 4kW, 5kW, 10kW and so on.
1kW of solar panels = 4kWh of electricity produced per day .
For each kW of solar panels, you can expect about 4kWh per day of electricity generation. So a 6.6kW solar system will generate about 26.4kWh on a good day .
It’s just a general rule the actual amount of electricity generated per kW of solar panels depends on your location, the time of year and the amount of sunlight you’re getting, the quality of the system, the orientation of the panels, how old they are, and so on. In southern regions such as Hobart it could be as low as 3.5kWh per day, while the same 1kW of panels in Darwin could generate 5kWh.
What Size Solar Panel Do I Need To Run A 12v Fridge
The size of the solar panel you need to run a 12v fridge depends on the daily energy needs of the fridge. It also depends on the average daily duration of sunshine in your region.
So, we know the fridge is 12v, but we do not know its wattage or amperage. So, we will assume the amperage is 4 amps. This will make the wattage of the 12v fridge = 12 x 4 = 48 watts.
Now, if you let this 12v fridge run for 6 hours a day, its daily energy consumption would be 48 x 6 = 288 Wh.
Then if the average daily duration of sunshine in your area is 8 hours, the size of the solar panel you need for the fridge would be:
288 ÷ 8 = 36 watts.
To run a refrigerator rated 12v, 4 amps for 6 hours a day with daily sunshine of 8 hours, you need a 36-watt solar panel.
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About Solar & Battery System Sizing
Battery storage system sizing is significantly more complicated than sizing a solar-only system. While solar panels generate energy, batteries only store it, so their usability is based first and foremost on the energy available to fill them up . The size of the solar system installed will usually be the primary dictator of the size range of the batteries which can be paired with it, followed by the homes energy consumption levels and usage patterns if a home uses a lot of energy during the day, there will be less solar available to go into the batteries.
In fact, the most important thing to look at is the relationship between the amount of energy that the household consumes on a daily basis and the amount of energy that the solar panel system produces day-to-day.
How Much Solar Power Will You Need
To determine your homes average energy requirements, look at past utility bills. You can calculate how many solar panels you need by multiplying your households hourly energy requirement by the peak sunlight hours for your area and dividing that by a panels wattage. Use a low-wattage and high-wattage example to establish a range . Note that the size of your roof and how much sunlight your roof gets are factors as well.
If you work with an experienced solar installer, they will handle all these calculations for you. If youre searching for a calculator to figure out how many solar panels do I need?, look no further. You can use SunPower Design Studio to estimate your own system size, monthly savings, and the actual appearance of a solar array on your own roof. This interactive tool provides a solar estimate in just a few seconds and can be done on your own or on a call with a SunPower 786-7693.
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How Much Roof Space Is Needed For Solar Panels
The average solar installation will require between 335 and 405 square feet of roof space. To find out how much roof space your solar system needs, just multiply the number of panels you need by 17.55 square feet, which is the area of most residential solar panels sold today.
If you have limited roof space, you may need to get high-efficiency panels, or panels with a higher power output so you can install fewer panels while still covering your energy needs.
What Roadblocks Are There To Filling Your Roof With Solar Panels
Besides the obvious , the other obstacle preventing you from maxing out your roof with panels are limitations set by your Distributed Network Service Provider, or DNSP.
You can see all of the DNSP rules for each state here.
But, to use an example, here in South Australia, SA Power Networks is our only DNSP.
They have set system size limits of:
- Single-phase homes: 10 kW inverter limit, 5 kW export limit.
- Three-phase homes: 30 kW inverter limit, 15 kW export limit.
Meaning if you have a single-phase home in SA, you could have up to 13.3 kW of solar panels on your roof with a 10 kW inverter. Remember you can oversize an inverter by 33%. But youd be export limited to 5 kW
Export limitations mean your inverter will intelligently ramp down solar power production to ensure a maximum of 5 kW is sent to the grid at any one time.
Some homeowners ask me If my energy needs are low-to-moderate, isnt it pointless to install a large system if Im export limited?
The answer, surprisingly, is no. You lose less generation than youd expect with export limitation due to a variety of factors.
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How Big Are Solar Cells
Lately, manufacturers started to experiment with different individual solar cells sizes in order to reach higher solar panel efficiencies and performance.
Nowadays, the market is dominated by two solar cell sizes:
- 5 W x 5 L
- 6 W x 6 L
The 5 are mostly used by Sun Power in their 96-cells panels, making that panel to look like a common 60-cells one.
What Size Solar System Do I Need The Definitive Solar Sizing Guide
When it comes to figuring out what size solar system you need, there are a couple simple calculations well want to keep in mind. This is a super basic example, however you can always substitute our numbers for yours.
The first thing youll want to figure out is how many watts per day youll be using and for how long. We have a handy load calculator you can use for this here, but first lets take a look at our example.
Lets say you want to power a 150 watt LCD TV for 5 hours per day.
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How Voltage Rating Affects The Power Needs Of Refrigerators
Refrigerators come with different voltage ratings, and these ratings define their power consumption. Generally, the higher the voltage rating, the more solar power you will need to run the refrigerator. Some of the common refrigerator ratings are 12 v, 24 v, 12/24 v, 48 v, 12/120 v, 110-120 v, and 220-240 v.
Determine Available Roof Space For Installing Panels
A standard RV today is 96 inches or 8 feet wide. There are some Class A motorhomes that are wider and some trailers and truck campers that are more narrow, so be sure to get your exact width.
Determine the total square footage of your RVâs roof.
The width should be calculated by finding the usable width of your RVâs roof.
The length of your RV should be the length of the roof, do not include any length that does not have a roof, like a trailer tongue or cargo rack.
This will give you an idea of the absolute maximum square footage on your roof. This square footage will not be all useable to mount solar panels. You will still need to remove square footage from areas with air conditioners, vent pipes, TV antennas, awnings, roof racks, skylights, and fan ports.
Draw a sample RV roof using your width and length. Note all items on the roof that will keep you from mounting a solar panel. Consider how roof-mounted items and penetrations will cause shading on your panels and remove these areas from potential layout areas.
You will now have a good sample of what your RV roof looks like and can create a sample layout for your solar panels. This will be a huge help in sizing your rv solar system because you cannot put more panels than your roof can handle.
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What Is Solar Energy
Simply put, solar is the most abundant source of energy on Earth. About 173,000 terawatts of solar energy strike the Earth at any given time – more than 10,000 times the world’s total energy needs.
By capturing the sun’s energy and turning it into electricity for your home or business, solar energy is a key solution in combating the current climate crisis and reducing our dependence on fossil fuels.