The design of purpose built off grid solar is one of the most complicated and frustrating facets of the renewable energy industry. It’s become a metaphor for the old adage “If you ask the wrong question, you are guaranteed the wrong answer”.
You will often see articles written by various luminaries espousing hybrid solar or off grid solar, where grid power is available, as not being financially viable. The problem with most of their modeling is that it selectively chooses only existing technologies so amortization is corrupted, ignores mitigation solutions, uses a presumptive hardware costing model and fails to recognize that the world of residential electricity is moving back to DC. We will be living in a residential world of battery driven appliances within 5 years. I could easily produce a financial model that could well prove that off grid is not only currently viable and fiscally attractive but also far more appealing than the standard grid offering. And this would suffer any scrutiny.
The electrical engineering mind is typically analytical and about as subtle as a falling rock.
Growing our highly specialised business out of a solar consultancy one of my early mentors strongly advised me against diversifying into the off grid arena pointing out that I was only likely to meet two types of clients: those who were on a tight budget and those who proved that a little knowledge is a dangerous thing.
And in very quick time he was proved, in large part, correct. We suddenly found ourselves back in the consultancy business spending most of our time in remediation of substandard systems and designs which had mostly been purchased as “kits” or sold by retailers who had little or no understanding of off grid hardware and systems software.
So, as a company, we radically changed our business model to literally create a new breed of client and to do this we asked a very different question.
Let’s start to dispel a few myths, take a wrecking ball to some accepted conventions and open the discussion beyond the standard stoic offering.
Until recently off grid solar has been the choice of “does the system design the lifestyle?” or “does the lifestyle design the system?”. Certainly budget is a precursor to the former but irrespective of which avenue is chosen the result is rarely satisfactory.
So why should this be?
Well, it’s a bit like building a house then asking where to put the plumbing. Traditionally off grid solar has been something of an after thought. It’s a call we usually get when the house is almost complete and all the appliances have been sourced and installed so every possible mistake that can be made has been made
and we are left with a very narrow solution envelop. And this typically comes down to budget and compromise.
OK then, how can we make this process simpler, more effective, less costly and almost purpose perfect?
The FIRST STEP is to engage the client at the very beginning of the design stage and bring in all of his consultants and advisors. You would be surprised how little most architects know about solar and just what products are out there in the mitigation of energy usage.
We were recently contracted to design a substantial off grid solar system for a large rural property where the house had already been designed. What was presented to us was a set of plans where there was little usable roof for panels, no provision for solar hot water and a large 3 phase ducted air conditioning unit. The property was also dependent on tank water yet the area had experienced no rain for more than four months and an attempt at drilling for water had been unsuccessful.
So, we apprised all parties of the available new and horizon technologies which would dramatically change the way they viewed interfacing with the home. Our recommendations included the following:
1. Replace the gas hot water system with evacuated gas solar on roof water heating. Evacuated gas is easily the most effective way to heat large volumes of water requiring little or no electricity boost. And, unlike conventional old technology thermal solar panels, has rapid recovery and can work in very cool climates.
2. Replace the three phase ducted air conditioning unit with a series of dc reverse cycle air conditioners in a hybrid scenario working off a central battery system. This technology is relatively new and does not work well in isolation as our own testing of these shows. The manufacturers are somewhat more enthusiastic about their performance than our testing reveals but, if they are “hybridized” they work far better. This recommendation extended to the use of dc fans throughout the house.
3. Replace the swimming pool pump with a dc to dc solar pump with panels.
4. Replace the pressure pumps with variants that had slow start motors.
5. Replace the irrigation pump with a dc to dc version with panels.
6. Recommend the addition of a low wattage 500 litre air to water machine with slow start condenser motor as a primary backup to ensure supply and drought proofing.
7. Recommend dc to dc refrigeration connected to the centralized battery bank.
Whilst the customer and architect resisted our calls to change the roof profiles the compromise was found in the addition of a large shed with a skillion roof facing in the desired direction which could host a significant panels system. And it involved a leap of faith to move away from the standard AC powered comforts of home into
solutions that better fitted the geographic and prevailing circumstances of energy and water supply.
The above simply demonstrates a more cohesive and productive approach to system design but most of this is in reducing the need for electricity from a central source.
But this is only the initial part of the conversation.
If you want to get half a dozen electrical engineers into a raging argument just bring up the subject of batteries.
Our company operates in an environment where the “take up” is usually several years behind the development of technology. This mindset permeates the industry via levels of bureaucracy and instills a distrust within the analytical mind. Battery technology has advanced in great leaps and bounds but there is a reluctance to embrace it.
As an example, in Australia, the greatest number of full off grid energy systems are still backed up with gel lead acid (AGM) batteries. Now, don’t get me wrong, AGM batteries are relatively inexpensive and, if configured correctly, can have an effective life of up to 15 years. However, they are bulky, not suitable for use near sea water, don’t like fast paced use and have a very limited depth of discharge (DOD) at 30%.
The current technology is lithium ion, manifesting mostly as lithium phosphate (LifePo4). Our company has tested a large number of LifePo4 batteries from many suppliers and our results show that not all batteries are the same. And, surprisingly, not all the “big brands” manufacture a product that we would consider suitable for off grid scenarios.
We have identified a fairly simple set of criteria for LifePo4 batteries to ensure their suitability for any battery storage system and, especially, off grid. These are:
1. Recognised cell manufacturer
2. Minimum 5 year manufacturer’s warranty
3. Minimum 3500 cycle life at 80% DOD
4. Infinitely stackable
5. Able to be configured in single, dual and three phase
6. Internal Battery Management System (BMS) and charger
7. Protocols to work with any hybrid or dedicated off grid inverter
8. Cells can be replaced (massive saving in cost of longevity)
9. Recognised communication protocols
A couple of these criteria are interesting and warrant a little more expansion.
Recognised cell manufacturer. The cell is probably the most important component of any battery. We all think of Tesla as a battery manufacturer but that couldn’t be further from the truth. Tesla makes an integrated battery system that uses other manufacturer’s cells and the quality of these cells is crucial to the quality of Tesla’s product. (We have enormous respect for what Tesla has done for the battery industry and I have been involved in a significant number of Tesla Powerwall and Powerpack sales. However, at present, these are not suitable for residential off grid use.
Infinitely stackable. This allows for the battery storage system to be easily expanded as needs dictate. Some of the big name brands have some serious issues with this.
Protocols to work with any hybrid or dedicated off grid inverter. There is a lot of misinformation and disinformation surrounding compatibility issues with certain inverters and batteries. The bottom line is that these “issues” are more about marketing alliances than they are about realities. Given the right caliber of engineering ANY dedicated off grid or hybrid inverter can talk to ANY Battery Management System and this typically defines the technology behind the battery and the quality of the product.
Cells can be replaced. Many LifePo4 batteries come as sealed units making them a limited life option. More contemporary LifePo4 batteries have the ability to be easily opened up and new cells replace old in the same way one would change batteries in a torch. Replacement cells cost less than half the cost of the battery dramatically improving the amortization of the system. In essence, if the battery housing and BMS is well maintained, the battery can last for a very long time.
Price. Depending on which country you are in PRICE is manipulated by the various margin levels applied as the product moves from manufacturer to distributer to retailer to customer.
Lesson here is to deal with companies who source most of their hardware directly from the manufacturer.
Now, if you want to elevate the argument between the electrical engineers, as you are not yet having enough fun, throw in lithium titanate (LTO), then duck.
We could talk for hours about all the possible battery technologies out there in either theoretical or experimental stages but, if you want to get the heart racing, start looking at Lithium Titanate.
These are high cycle lithium batteries (25,000 to 30,000) with a degradation curve (the rate at which a battery deteriorates over time and usage) that is almost flat for 10 years. And these are in production and use. So, for a cost of about 50% more, you
can install a battery that offers at least 5 times the life of LifePo4. So now the financial case dynamic changes dramatically.
We have tested a few of these and they are a new breed indeed. They are super fast to recharge and just love reactive power. Put one of these in your golf buggy and hang on….for almost forever.
Finally, let’s look at other hardware considerations.
There is now a great range of dedicated off grid inverters designed to work in black out mode. There is no need to have a pairing with an inverter and controllers as these units are an “all in one” package and superbly built at a price of about a quarter of what was normally expected.
And, of course, we need to look at solar panels.
This is a debate that can be confused when one factors in any form of Government subsidy. When a panel is subsidised or qualifies for a rebate the decision is confused. Remove the subsidy and the decision becomes simpler.
As an extreme example imagine the use of quality second hand panels. If we are considering an off grid scenario with enough roof real estate, then the use of second hand panels makes sense in a non subsidised scenario. Good quality 250W poly panels are coming onto the market at prices a tenth (or less) than new panels. These are likely to last at least 10 -15 more years as, at time of manufacture, the quality was excellent (7-8 years ago). If you have the space it doesn’t matter if the panels are second hand provided they have been cleaned properly, were previously Tier One and passed a thermal imaging audit.
And we haven’t even started on system CONFIGURATION. Do we go AC, or DC or Both?
But that is another discussion.
So, BOTTOM LINE, off grid solar energy works on so many levels. It can easily replace current on grid options or provide a robust alternative to expensive introduction of grid power in remote locations. If you understand how costing really works in these scenarios and remove all the pontificating rubbish about traditional system design and replace it with common sense and new technologies, then you have an excellent blueprint moving forward to create self sufficiency at Return on Investment (ROI) that makes better sense than you were ever told before.
And as for those arguing Electrical Engineers, they’re still at it, and, I suspect, for some time to come.
John Palmer is CEO of No Grid Solar Pty Ltd, a specialist designer of off grid and water production and remediation systems in Australia and the Pacific Islands.