I am a tree called Soulr...
If you're not sure where to begin, what size tree you need or have some gaps in understanding, well, you've come to the right spot. Let's jump right in.
I’ll use bold type in headings so you can jump around easily and just get the info you need. Control-F will search the page for a particular word – beats scrolling.
There's no particular order so feel free to jump around. Footnotes denoted by * are at the bottom.
What you need...2 factors
It's all about the sun: how many hours you get in a day in the different seasons of the year at your location. Does it go behind a mountain or disappear behind a barn at certain times of the day or year? Are the skies usually clear in morning but cloud up in the evening? Do you sometimes not see the sun for days or weeks in the winter? What time of the day or year does it go behind that big oak tree? If you've lived in your place for a while you probably know these things intrinsically and that's good because you'll need this information.
The next thing you'll need to know is yourself: Temet Nosce if you're fan of Latin or the Matrix. Many will say and indeed expect that living on solar can be exactly like living on the grid and I suppose if you're grid connected that could be true but it helps to be honest: it is different but probably in ways you don’t expect.
Types of systems: Grid-tied/grid-connected, Off-Grid or hybrid
First, when I use the term ‘grid’, I’m talking about the electrical grid – the electrical lines you see on poles all over the place. The ones going to your house connect you to the grid.
Grid-tied/grid-connected When your solar panels generate electricity, the electricity goes to the grid run by the local power company. With a grid-tied system, the power company buys electricity from you at wholesale prices (*think less than 5 cents a kwh) dictated by the rules of your state* or governing body. When you need energy, the power company sells to you at retail (*think 5 times the wholesale amount). Wait! I'm selling at wholesale but I still have to buy at retail? Yup, this rubs a lot of people the wrong way but power companies have lots of lawyers so they usually get their way. Grid-tied is the least expensive option because you are using the grid as your battery – many will say this justifies the wholesale/retail discord. One other thing, when the power goes out (as it has in Texas as I write this), it goes out for you just like your neighbor.
Off-grid is my favorite and I think you know why: self sufficiency, independence, control of one’s own destiny (and the feel good from sticking it to the man isn’t a bad feeling either). You are totally independent from the grid and thus the power company and any existing relationship with them will come to a grinding halt. But here’s the honesty part: an off-grid system requires extra effort, planning and diligence on your part because there’s no power company to save the day when things go wrong. But then again, when the power goes out for everyone else it doesn’t go out for you. In an increasingly unstable world this can be a life or death advantage. Off-grid systems are typically the most expensive because you need batteries and they’re expensive but if being prepared for the **Zombie apocalypse is your deal, then off-grid, is the way to go.
Hybrid systems are connected to the grid like a grid-tied system but they have small batteries as well so if the power goes out, an electrical device disconnects you from the grid and reconnects to your battery giving you a small amount of power autonomy – hours not days - but for a lot of people it’s a good compromise in cost and functionality. A hybrid system also allows you to offset peak prices the electrical company charges during high-use/peak times. It's the most complex of the arrangements discussed.
There's a lot going in this space. For example, VPPs or Virtual Power Plants would allow the power company to buy power from your system if the need arises during demand response scenarios (adding supply when demand is great). It's not here yet but is on the drawing boards.
EVs – Electric Vehicles
EVs will be the predominate means of mobility in the near future and they can re-write the rules regarding solar renewable energy systems meant to last many decades so it’s something you should consider now.
If you want to charge your future EV, plan on a bigger system because why wouldn’t you want to drive for free and never stop at a gas station again? Not to mention, you’ll get to stick it to man a second time (the man this time being the big oil companies and oil nation states).
EVs contain big batteries. It is not idle speculation that your car could in the very near future be the battery for your home and supply a portion of those needs and that changes the calculus of a purchase. The implications are considerable.
PV Panels – Photovoltaic Panels
PV panels, hereafter just ‘panels’ are the business end of a renewable solar energy system because they generate the electricity. They come in many shapes, sizes, prices and aesthetics but some characteristics remain constant across the field.
They all perform best when the sun is perpendicular to the plane of the panel. Think of a ‘T’ where the vertical part is a ray of sun and the top is the panel. The tilt of the panels matters big time. If the panel’s orientation is rigid and fixed like it is on a roof top system, you choose the latitude at your location as the tilt. For example, if your latitude is 35⁰ N then your panels are tilted 35⁰ from horizontal. If you want more electrical production in the summer then subtract 10-15⁰ of tilt or add 10-15⁰ of tilt if you want more in the winter.
It is undisputed and it just makes sense that you need fewer panels if you track the sun both seasonally and daily because the sun will always be perpendicular and will not ‘glance off’ the panel. You get about 20-40% more juice with a tracker. Think what your car would do with that much additional power. The bottom line is you need fewer panels and less space with a tracker.
A day in the summer's electrical
production. The pumpkin color is yield of
a fixed tilt array and the yellow is yield from a 2-axis tracker.
With our tree the tilt issue is a non-issue because the panels are always positioned to maximize efficiency. Our trees have 2-axis tracking as standard equipment.
A word about tilting and tracking with Soulr’s trees
North to south tilting is called seasonal tilting – this tilting allows the tree to track the sun as its position in the sky changes with the seasons. East to west tilting is called daily tilting – this tilting allows the tree to track the sun as it traverses the sky east to west on a daily basis.
In default configuration, our trees tilt a maximum of 70⁰ north to south and 140⁰ east to west. You may think 180⁰ east to west would be better but the amount of atmosphere the photons have to travel through early in the morning and late in the evening limits the yield.
The north to south tilt of 70⁰ mostly*** affects tilting on the shortest day of the year month which for the northern hemisphere is December (June in southern hemisphere). The farther north you go towards the north pole, the steeper the angle of tilt has to be in December to remain perpendicular to the sun. At latitudes whose winter tilt is greater than 70⁰, the tree will not be able to attain ‘perfect’ perpendicularity. Where are those latitudes? In the northern hemisphere that is roughly the latitude of Vancouver Canada. In the southern hemisphere it is roughly the latitude of Christchurch New Zealand. The deviation and slight inefficiency in December generally only affects December – all other months maintain perfect perpendicularity. However, as one travels further north the inefficiency starts to accrue.
This being said, optional linkages are able to give steeper tilt angles in excess of 70⁰.
Soulr's tree works every place on earth but some locales are better than others. In the green box the tree can always point the panels to be perpendicular to the sun leading to maximum yield. In the blue box the yield is still significant but slightly less so. Outside the blue box is still fair game but production will be less than that produced in the blue and green.
Power – How much and how many panels?
Calculators for computing your needs can be found on plenty of websites. Optionally, you can drop us a line and we’ll do it for you. For the DIYer (Do It Yourself-er), the best place to start is your monthly power bill. Pick the highest monthly bill with the most kWh used. This will be your base line. Figure out the daily usage by dividing the monthly by 30 or 31 (if they don’t give it to you directly). Let’s call this ‘U’ for usage.
Next determine hours of sun per day your location will receive. If you don’t know, search the internet using the terms like “solar irradiance in the usa” or “solar insolation map for mylocation”. The search will return maps and/or charts that give you a number in kWh/m2/day – that’s the hours per day to use for your calculation – let’s call it ‘H’. Some will give a month or seasonal break-down. You can optionally run different scenarios based on these break-downs. Next, search for PV panels according to what’s important to you: aesthetics, price, origin etc. Find the panel’s watt or power rating, we’ll call that ‘W’ and now you have all that you need to get a good feel for the size of your system.
(U * 1000)/(W x H) = number of panels ‘P’: round up. Let’s look at an example.
Say daily average use is 10 kWh. 10 x 1000 = 10,000; I like the 300 watt panels made by USAPV (fictitious). Looking at the irradiance map returned from the search engine, I see my hours/per day average for my location is 5. It follows then that 300W x 5= 1500W.
10000/1500 = 6.6 Round up to 7 and that’s a good starting point. Easy-peasy. Seven, 300 watt panels equates to 2,100 W or a 2.1 kW system and should equal current usage for this month of the year in said location with a 2-axis tracking (Soulr) tree.
The SMALL size tree has a 5 panel minimum configuration. Working backwards we know we need to get 2,100 watts from 5 panels so: 2,100 / 5 = 420 Watt per panel.
You can now look around for 420 Watt panels.
Determine how you might reduce your demand to coincide with panels producing less than 420 watts.
Go to a larger sized tree with more panels.
Add another tree.
Like we said up top, you can also drop a line and we’ll do the figuring for you.
Disclaimers and Exceptions and 'we told you so'
You may want to adjust the size of your system up or down depending on your situation. Maybe you’re going to get an EV which should increase the size of your system. Maybe you’re going to be empty nesters soon in which case you might lower it a tad. Maybe you winter someplace else so winter figures are irrelevant. You’ll have to make the call here depending on your life’s circumstances. Crunch the numbers, do the research, try other website calculators.
Secondly, these calculations are based on weather averages. We all know the climate is changing and weather extremes are part and parcel of that change so these irradiance averages may be subject to revision. I like a little cushion so I always go a little bigger.
Like any man-made system there will be inefficiencies in addition to site variations that skew the numbers. Obstructions from buildings, trees and so forth need to be considered. Take your personal knowledge of the area and turn it to your advantage; don’t hesitate to run different scenarios with different numbers.
And as always we here to help. Drop us a line if you have questions.
PV Panels on the roof – know the impacts!
If you’re considering a roof top system be aware of the real world impacts.
Having panels on your roof means they are going to be in an ‘average’ fixed position for their entire existence or at least as long as they’re on the roof. You will need more of them because they will almost never be efficiently positioned perpendicular to the sun. If you have more roof to spare then that’s fine but reality is a bit messier than that. You might have trees shading part of your roof or you might have a chimney and vents in the way. And then there are the National Electrical Code limitations not to mention, an array on your roof means holes will be needed to get the electric wires and hardware to your distribution panel and they might have to tear up the attic, roof and drywall a bit depending on your house. And what happens when you need to replace your shingles? That’s right, all the panels need to come off and then put back on and reconnected after the roof is replaced. (A neighbor of mine had to do that...it was not pretty.)
There’s also aesthetics. A lot of folks think panels look fine on the roof and others think they’re an abomination – that’s your call.
Snow on the roof means you may be up on the roof with a broom.
The take aways…
Here’s where you come in because you know your house and how the sun shines at your location and well, you know you. A roof top system may be initially cheaper and if up-front cost is the driving factor then go that route but as with many things in this life, the cheapest initially is not always the cheapest in the long run. Here’s a little mental list of questions that might help you rank other intangible characteristics.
Am I in an area that has hurricanes, tornadoes and generally nasty weather that could compromise my roof top PV system?
Am I going to need a new roof before the end-of-life expectancy of the solar system (ie 25-30 yrs)?
Is my roof big enough with enough unobstructed clear sky to generate the energy I need?
Do I mind roof penetrations and rework necessary to get a system on my roof?
Are the aesthetics of a roof PV system to my liking?
Am I in a location that may require getting up on the roof to remove snow and debris from my panels?
Am I going to be moving soon? Will a roof system increase or decrease the value of my house?
Do I mind a bit of hassle-factor? Dealing with a power company and state and local governments can be exasperating.
Other Influential Factors: Efficiency
Before you think about a renewable energy system you ought to take a good look at your appliances and power hungry devices and see if there’s room for reducing your energy footprint by replacing with more energy efficient models. Also, make a best guess at how your future purchases and living situation might alter your energy use and thus the size of your system. The examples below are not a comprehensive list but rather intended to get you thinking in the right frame of mind regarding energy use.
Got kids leaving the nest (finally)? Reducing people reduces energy usage.
Is an EV in your future? If yes, plan for a bigger system.
Going to put in or take out a pool? This will definitely increase or decrease (respectively) your energy consumption.
Many companies that sell solar will push a system designed to give you everything that you have today. Sounds fair but I don’t agree with that philosophy: that doesn’t get us closer to solving our problems. Just because you're getting on solar doesn't mean you should keep on being profligate.
Many will say you need a big system or a big battery bank for autonomy (days without sunshine) and comfort reasons or to handle extreme weather events but they rarely mention that simple changes in your daily routine and life style can obviate the need for and the cost of big systems. This is understandable – they want to sell you big systems because they make more money (kind of like the automakers selling huge SUVs – the margins are higher).
If I told you, you could decrease the size of your system by a big fraction simply by choosing to do little things like doing your laundry during the day or on weekends or delaying laundry until the weather improves, would you do it? Would you freak if you had to turn the fridge off once every few years because of an extreme weather event? If you have the capacity to think ahead, freezing a couple gallons of water can keep that fridge cold for days without power in even the warmest climates and this can significantly reduce the size of your system. Do you need to keep your house at 65 even though its 105 outside? Small changes can not only save you big money, they can also help humanity get back to real.
Going solar is a great opportunity to asses what is important in life. If you chose this route it will be the first step in many. It is contagious. The small changes required of you that some will inevitably perceive as sacrifice does not in any way mean one is entering the drudgery of an austere existence or that we're headed back to the dark neanderthal days of living in caves - that's just ignorant fear mongering. I can tell you with near certainty, you will be stoked to get all or a portion of your energy needs met by the sun, knowing that you were not the demand in supply and demand that is responsible for blasting the tops off mountains, drilling into the last wild areas on the planet or starting a war with an oil rich state. You'll be smiling when your energy costs stay the same year after year after year while everybody else gripes about the injustice of the system. An if the next step is towards e-mobility, I can guarantee driving for free and never having to refuel at the pump will be a life changing event.
*Some states are friendly and fair and others are downright hostile. Read-up on what your state offers. Wholesale and retail rates vary widely - almost all are a great deal for the power company.
** The Zombie apocalypse is a metaphor for more realistic, more likely and more unpleasant dystopian scenarios that we usually feel uncomfortable discussing – a euphemism couching unpleasantness in humor and film genre as it were.
***Latitudes between above 50-55⁰ N/S latitude will experience imperfect perpendicularity during 3 or more months.