Starting from the top down, the Sun rays hit the solar panel exciting electrons and protons to move in what they call direct current or "DC." This DC power then typically heads directly to an inverter which converts the DC power to a more usable AC power just like what your home or business uses. Now of course there are few other components involved to get this DC power to the inverter or microinverters, but once the power is being produced it then consumed by your house and any excess power will then flow back onto the utility grid.
When it passes through your utility meter the utility meter will record the power being sent back onto the utility lines. At the end of the billing cycle which for us in missouri is on a monthly basis you will be billed on the "net" or what’s left. If you produce exactly what you use then your net is Zero which is great and you are only left with a service charge which will never be offset by solar production. If you have produced more than you have used in a months time you will be left with a credit. Those credits will be applied towards next months utility bill at the "avoided cost" which can change up or down based on the current cost for the utility company to produce electricity. If you produce less than what you consumed that month then you will just pay the difference left over.
There are three main types of solar systems:
Grid Tie: Purely meant for investment purposes, designed to produce power that your house uses in order to reduce your utility bill. Typically this is looked at as though you are locking in your utility rates by going solar and avoiding rate hikes from the utility companies over the usable 25 year warranty period of the solar system. When the power from the utility goes out however you will not have any backup power, the solar system must cease to produce power due to the anti islanding rules. Today there is only one inverter on the market that is grid tie only that allows you to have a receptacle powered directly by the available solar production during a grid down scenario known as the Sunny Boy TL series, HOWEVER on the horizon Enphase microinverters are coming out with the Ensemble which will allow you to power your entire home with the same principal during a grid down scenario except it will prioritize your loads in your house so that is a hypothetical cloud passes over while you are using the pv direct power and there is not enough solar pv direct power to take care of the loads, your loads will begin to be shut off by priority of least to most important, and when paired with a small battery bank from enphase known as the encharge bank this will allow for those brief moments during the day to take care of the typical cloud scenario. I am super excited to see this come out and they say first will be the Encharge battery in 2019 and then late 2020 will be the ensemble portion which allows you the backup power during the day without the use of batteries.
Grid tie with battery backup: The best of both worlds, you get to reduce your utility bill while at the same time creating a renewable form of backup for your critical loads. Like anything else with batteries they will not last for ever and eventually need to be replaced, and if using a lithium solution you will typically get more life out of them and be able to keep them in a little bit more of a harsh temperature say in a garage where the temps vary throughout the year here in Missouri. To be honest if there is not a need for "renewable" backup power then it is always best to forgo the battery backup option and just go with a whole house backup generator like the Generac 22kw Air-cooled automatic backup power solution which we can typically turn key install for ball park $8-9k depending on a LOT of variables this is a good ballpark. When looking at batteries and especially like an AC coupled solution like Sonnen, or Tesla, Or Outback Power you could be looking at over $20-30k pretty quick depending on your specific backup needs. Everyone is different and has different needs which is why it’s important to go over you and your specific needs or desires when it comes to backup power in a grid tie with battery backup scenario
Off Grid: Simply having no connection to the Utility grid living as efficiently and conservatively as possible and most times the home is specifically designed to collect sun rays in the winter and block them in the summer with extended awnings or overhangs, along with the most efficient insulation, Solar thermal water heater system, passive cooling and of course the heart of the system being your solar systems power which is a combination of batteries, solar panels, inverters, backup generator, and a wind turbine or hydro if water source is available in all reality know that Off Grid really means the following:
"Lifestyle change!" unless you are Bill Gates or similar you have to look at going off grid as a lifestyle change. Most people have no clue how much power they consume on a daily basis and to give you an example think about just doing a simple load of laundry, your dryer can run for an hour on average and using somewhere close to 4500 watts if you were to convert that in to a battery bank required to do so you would take 4500 watt hours divided by nominal voltage of the battery typically being 48vdc that gives you the amp hours of storage being 93a/h now that you have this you can never get the full amount of power out of a battery, but let’s say we are working with Lithium, we will want to figure in a 10% efficiency loss of the battery, and then figure that our inverter will be another 10% loss and then lets say that we can only drain that battery to an 80% DOD or Depth of Discharge that would then take our 93a/h and turn into 144a/h and that’s just for one load, how many back to back loads does a family with many kids potentially do? Just for reference one lithium battery that is 137.5 a/h from Discover will msrp around $7,200 and that’s just the battery.
Point being that living your life as though nothing changed off grid would be a very large and expensive battery based system and remember that batteries do not last forever. So say you get 10,000 cycles out of them before you need to replace them and lets say that you only ended up with $50,000 battery bank. You can see where I am going with this.
Topics: Solar 101 Basics