The long and short of it is that it wont. Join us today as we discuss how the momentum in the solar industry has already reached a point where it will continue to build. Solar Jobs were 2nd in the energy sector behind oil jobs, and demand is only going up as worn out coal fired plants come offline, utilities respond to the public sentiment, and people take advantage of federal, state,and utility level incentives. I discuss how I think China is competing with us on the R&D side and that we could lose our leadership on this front during the current administration. The reality is that coal jobs aren’t coming back. Storage and Natural Gas technologies will fill the off peak generation gap and as they become cheaper the switch becomes even easier.
Today we will discuss battery maintenance. It is one of the big differences between a grid tied and an off grid system. A grid tied system just sits there and generates electricity either for your home use or to be fed back onto the grid. The battery bank in an off grid system adds a whole new level of complexity. We have previously discussed the types of batteries but for the purpose of this conversation I am going to focus on lead acid batteries. Here are the primary topics for discussion:
- The Chemistry behind discharging and recharging batteries
- Standard Maintenance
- Charging Cycles
- How to measure Specific Gravity and Equalization(overcharging)
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Today we are going to discuss Inverters and the balance of system components. Inverters are the component that takes the DC(Direct Current) Provided by the solar array and stored in the battery bank, and converts it to AC(Alternating Current) for your home use. Alternating current means that the current alternates its direction over and over again(every 8 milliseconds) to create a nice wave pattern. It goes up, rounds off, goes down, rounds off, and repeats.
You want to match your inverter to your battery bank, so if you have a 24V battery bank you don’t want to buy a 12v solar inverter. Once you have cut out or reduced usage of all the devices that you can, you need to do an analysis of the devices you still have and how often they are used to understand what the demands of your inverter are going to be. You need to look at both the peak or startup loads as well as the running loads. For example a refrigerator compressor may draw 5 times its running amps for half a second while starting up. There are many tools on the internet that can help you with this as well, my favorite is over at the Alt-E Store. Once you have your total Watt-Hours per day and your peak loads you can decide on an inverter.
Here are a few things you need to consider while evaluating solar inverter choices.
- Pure Sine Wave vs. Modified Sine Wave – these are the two main classes of solar inverters you will be looking at. Sine waves are that nice up and down curve I spoke about before with rounded peaks and valleys. Pure or True Sine wave Inverters create AC electricity that is just like the grid power. Everything in your house was designed to run on true sine wave. But that doesnt mean that it can run on Modified Sine Wave. MSW is more blocky than TSW. MSW goes up to peak for a few milliseconds, goes to zero for a few milliseconds, and goes down for a fe milliseconds and then repeats. High tech and sensitive electronics may have problems with Modified Sine Wave. Personally, with the price difference not being that much anymore, I would go with the TSW to ensure that I wasnt going to have problems. ANother option would be to have a MSW inverter for normal loads and a seperate smaller TSW inverter for finisky loads.
- Inverter/Charger or not – An inverter/charger is a combination of an inverter, battery charger and transfer switch into one device. When a generator is on an hooked up, or you are hooked to the grid, the inverter recharges the battery bank. It also allows any surplus AC power to pass through and power houseAC loads, such as a television. When AC power is disconnected, the unit inverts DC battery power into AC electricity. I would advise using this because it makes adding a generator to the system plug and play.
- Future expand-ability – Some solar inverters play well with others and can be wired in parallel to expand the system and others cant. If you are building out your system slowly this may be a consideration you should make.
Balance of System – The balance of system is simply the other components you need to complete your system. These include wiring and combining the solar panels, fuses, safety switches, battery cables, disconnects, monitors and controllers or data displays, and mounting systems.
Batteries for Solar Off Grid or Hybrid System
OK everyone, we have covered solar panels, a solar array, and charge controllers, so the logical next step is for us to discuss batteries. Over the lifetime of your system, Batteries will be the most expensive part because the ones that are cost effective when starting a system don’t last very long and the ones that last a relatively long time are prohibitively expensive. Batteries are the center cog of any system because they store the excess energy produces by your source(solar array, generator, or even the grid) and then distribute that energy when generation falls below need.
Here are a few things to remember when considering a battery bank:
- How many days of autonomy do you want? So if your panels stop producing, how long do you want your battery bank to be able to provide energy to the house?
- What climate will the batteries be stored in? Batteries are rated for about 80 degrees, if they are stored at below freezing conditions, you may need 50% more capacity to meet your needs. A cruel fact is that when its cold you normally have less sunlight as well.
- What voltage will your battery bank be? 12v systems are easy but when you start drawing a lot of current it makes sense to step up to 24v or even 48v to reduce the wire size and reduce the number of parallel strings.
- How committed to maintenance will you be? If you want plug and play batteries that you rarely need to visit, expect to pay more than for minimalist flooded lead acid batteries that require regular measurement and maintenance.
We are going to discuss the main categories that batteries fall into and how to use them.
- Flooded Lead Acid Batteries for Solar such as golf cart batteries are the most common off grid battery bank component. They are the lowest cost option, last between 4 and 7 years depending on how well they are cared for and what depth of discharge you normally take them to, and will work pretty well even if you dont religiously equalize and fill them.
- Sealed Batteries for offer some advantages over Flooded Lead Acid because they are relatively maintenance free. They only require a regular full charge. They dont spill or leak fluid, they can be installed in any orientation because you dont need to get to the tops to fill the electrolyte. They are expected to last around 8 years when protected from overcharging.
- Lithium Ion Batteries are the wave of the future, offering 2x the average lifespan of a lead acid battery with higher Depth of Discharge, smaller space and about half as heavy per kWh of storage. The problem with them is that the current charge technology in the market hasn’t caught up with Lithium Ion and they are very picky when it comes to overcharging. Currently I would not recommend Lithium Ion batteries for solar until more research and development is done. The Powerwall may be a solution for grid connected hybrid systems but that’s a specific niche that would require its own article.
- Nickel Iron Batteries are the most expensive but also the most bulletproof batteries for solar systems on the market. They can take 11000 cycles at 80% depth of discharge, with a wide range of operating temperatures and resistance to both over and under-charge conditions. Unfortunately they are very expensive. If you are looking for a battery that will last as long as your solar array, with low maintenance and have the financial means to utilize Nickel Iron this is the battery choice for you.
Well i hope you learned something today, bear with me as I continue to convert the blog to a podcast. I am self teaching as I go and watching a ton of youtube videos and reading a bunch of articles, but implementation will be hit or miss.
Thanks for visiting the blog and check out our other articles if you liked this one or ask questions in the comment section!
Charge Controllers, what are they?
OK so we have covered what solar panels are, and how to design a solar array, but what happens once your panels are generating power? Well you obviously want to get them into your battery bank, but other than some very specific situations, you will charge your batteries through a charge controller. So what is a charge controller…in essence, it is the device that regulates the amount of energy, both in terms of voltage and amperage, that goes from your solar array to your battery bank.
Charge controllers come in two primary modes, Pulse width modulation(PWM) and Maximum Power Point Tracking(MPPT). Pulse Width Modulation Solar Charge Controllers reduce the amount of voltage applied to the batteries in an inverse relationship to the charge level of the batteries. So as the state of charge goes up, the voltage is reduced so as not to damage the batteries. MPPT Solar Charge Controllers match the incoming power from the PV array to the most efficient use of that power in terms of charging the battery. This allows the array and the battery bank to be vastly different voltages. The ability to step up the voltage and therefore reduce amps(because watts always equals amps x volts), especially if the array is sited a long distance from the charge controller, can allow a person to pay for the charge controller in wire savings. This is because higher voltage/low amp power can run through thinner wires from the PV array to the Charge Controller. To give you an example, using 6 gauge wire vs. using 2/0 gauge wire can save you nearly 70% in wiring costs.
We will dig into MPPT chargers in more depth at a later date. Feel free to ask questions in the comment section below.
Sizing a Solar Array
A Solar Array is just a fancy term for your solar panels, which themselves are combinations of solar cells, combined into a single system. Today we discuss “sizing a solar array.” The first step is determining what your needs are. It is always good to eliminate or reduce some parts of your usage before determining the size of your solar array. For example at our house we got rid of our drip coffee maker and began buying roasted beans, hand grinding them, heating water on a propane stove, and using a french press. The amount of electricity we need to make our morning coffee is now zero. Switching to LED lighting, putting appliances on surge protectors that we turn off when not using, and drying our clothes on the line rather than in an electric dryer were some other adjustments we made before going off grid.
If you are currently on grid, you have a very easy meter to determine your usage in your monthly electric bill. Depending on your climate, you may see higher usage during certain times of the year. For example in TN, we saw summer months where we were cooling with electricity as our major power need. One hard rule we have living off grid is that we don’t use electricity to generate heat. No electric furnaces, space heaters, microwaves, hot plates, crock pots, or electric water heaters for us. So my suggestion would be to reduce your consumption as much as possible, then review your bill to see how much electricity you are using. In the US, the average utility customer uses 901 kWh per month of electricity. Your bill will be denoted in kWh which means kilowatt-hour, Or 1000 watts for 60 minutes. For the sake of this example, lets assume that you have dropped your consumption to 450 kWh per month(half the average household). So on average you are using 15 kWh per day. Once we have this information we need to look at an insolation map, which will show you the average daily hours of sun you receive in your location. Here is a map of the us provided by the NREL.
Armed with the insolation data you have for your location, back to sizing a solar array. You need to divide your daily use by the number of hours you get. The NREL posts maps for each month so you could break this down month by month and use the worst case scenario if you like. Where I live in TN we average 4.5 sun hours per day. This means over the course of an average day, we get the equivalent of 4.5 hours of full sun. So using our above number of 15 kWh per day and 4.5 average hours of sun, the total array size that I need is 3333.33 watts. You will notice I went ahead and made the conversion from kWh to watts. Now you can figure how many panels you need in your array to meet your needs. You may decide you want to replace 50% of your needs, or you may go all out and decide to take out all 3333 1/3 watts. Lets take the latter and assume we are going to get a great deal on 10 or more 310 watt panels. We divide the wattage of the panels into the watts needed, so 3333.33/310, which gives us 10.75 panels. My suggestion is to increase this number by 25% to account for losses at different points in the system(which we will discuss later). Doing this gives us 13.44 Panels, which we will round up to 14. If you followed along, you now now exactly what your usage is, how much you want to replace with solar, and how many panels you need at a specified wattage to meet your needs. We hope this post on “Sizing a Solar Array” was helpful. Shot us an email on our Contact Page if you have any questions we would be happy to help!
How do Solar Panels work?
Solar, or Photovoltaic, Panels work by converting light energy from the sun, or photons, into electricity through the “Photovotaic effect.” Interestingly, a French physicist built the first ever photovoltaic cell at 19 years old, in 1839. The first practical photovoltaic cell was demonstrated by Bell Laboratories in 1954 and early on they were primarily used in space.
A Solar Panel is a collection of solar cells that are made up of semiconductors. Semiconductors absorb the photons–through a process I wont describe in detail–and cause electrons to be excited and break free to be converted into usable DC electricity. Solar cells are arrangements of silicon “sandwiches” where one layer is activated with boron and the other activated with phosphorus. This helps the charge to be created and directs the free electrons to the wiring that leads to your charge controller.
The key to remember here is that its the light energy that is converted to usable electricity, so when siting a group of solar panels, also known as an array, you should do an insolation analysis, which is a fancy phrase for looking at whether or not you are going to have full sun hitting the panels or if there will be shadows cast from structures or vegetation. A part of this analysis will also be determining how much full sun you get in your area and using that information to determine how many panels you need to charge your battery bank.
This post is about “how do solar panels work” but now that you have a basic understanding, here are a few things to remember that can reduce to the amount of energy your panels can produce: dust/pollen/leaves, temperature, and wire resistance. If you let your panels get dirty or accumulate leaves or snow, it should be quite obvious that the light cannot reach the covered up cells, which will logically result in less energy production. When your panels heat up, they also become less efficient. Remember above when I discussed the electron becoming excited and breaking free? Well the hotter the cell gets, the less potential there is between the different electrons because the ones that are at rest are already a little “excited” because they are hot. As a matter of fact when sunlight shines in through your window and heats the air in your house, this is specifically due to excited particles, and its no different with a solar panel. We will discuss wire sizing in more detail in another post, but remember that current is measured in amps, and wire resistance simply means that smaller wires cannot handle high amps. This is why we use ideas such as stepping up voltage the reduce the number of amps required to move the same amount of energy. Amps x Volts always equals Watts so increasing one number always decreases the other.
Types of solar installations
There are a variety of ways to harness the power of the sun. Today we are going to define the ways and discuss them:
- Grid Tied
- Off Grid
- PV Direct
- Solar Thermal
Energy vs. power
This short series is to help build some foundational knowledge that will help you understand the building blocks of Solar.
Energy is the capacity to do work. Measurements for energy include calories, BTUs, Joules, and Watt-Hours. We would use the term energy when discussing how much capacity you have in your battery bank. If you are on grid you will get a utility bill from the power company and that will normally provide you with the number of kWh or Kilowatt-Hours you used last month. A Kilowatt is 100 watts and a watt hour is one watt being used for one hour.