The load list provides the basis for your off-grid design. It is critical that this is correct, and reflects how you want to live and what you want to do.
Once your system is designed, you will need to live with the decisions you made preparing the list, unless you want to upgrade your system. Consider adding contingency to allow for addition of future appliances/usage, but adding too much can lead to over specifying and adding cost. Remember also, the system is not a continuum – it comes in blocks of batteries, inverters and panels.
Solar providers should provide you with a load list template to complete so that they can design your system. I’ve included ours below (my version), with some comments.
A couple of key things to note:
Many appliances are not “on” all the time, or have variable loads throughout their operation. For example a fridge turns on and off as required to maintain the temperature. If you just took the rated power of the fridge and multiplied in by 24 hours, you would be really overestimating the power usage.
For energy star rated appliances in Australia, its reasonably easy to get the kWhr, however these are based on specific tests, under specific conditions. You will need to adjust for your circumstances eg. We do not run our dishwasher everyday, so the energy usage quoted is an overestimate. We do run our clothes dryer more than once per week in winter, so the usage is an underestimate. Refer to https://www.energyrating.gov.au/calculator.
For other appliances, its really hard to work out. For our heating and air conditioning for example its depends on the energy rating of our house, what the ambient temperature is, and what temperature we’re trying to maintain. For a breadmaker, I’ve found random sites that quote values, not sure how valid it is. I’ve included some appliances with really small loads, just to demonstrate where you might need to focus, and where you don’t.
Many on line sites that tell you power usage just calculate hours x watts, as do some of the off-grid energy suppliers we’ve spoken to. This will lead to a potentially significant overestimate of your power usage.
As a check, I’ve done a load list for our current house, and compared it to our bill, using the same methodology for both. Our summer/shoulder average is 7.7 kWhr/day, and my load list predicts usage of 9.65, 25% higher than actual use, although for a couple of months we have averaged 9 kWhr, which is only 8% higher. This is well below the Australian average, but we have been buying energy efficient appliances for years, and have recently moved to a 6 star energy rated house.
The biggest variable appears to be in the oven – when I use it I can really see it. Our energy provider allows us to break down our electricity by half hour increments, and when I have big baking days I can easily add 5-8 kWhr.
For this reason, we have included 2 x 600mm ovens – one LPG, and one electric. In summer, I can use the electric, in winter LPG.
We also have an LPG cooktop. We had thought we would have an induction cooktop, but when talking to Rory at Off Grid Energy, we were advised, correctly I think, not to. Induction cookers (and motors) have very high starting currents and loads. These loads can dictate the sizing of your solar system, and inverter selection. They may be efficient when up and running, but getting them there can be hardware expensive. This may also be true for other equipment – induction motors, some power tools. etc Watch out for this.
Also, look at the actual power, kW, that you might want to use at the same time. The lower your inverter capacity, the less you can run at one time.
When we first got our quote, we included the nice to haves of an electric heated floor in the ensuite and using ducted reverse cycle heating for the odd hour in the design of the system and the house. This essentially was our contingency – we just wouldn’t use them if we struggled for power – and it would give us margin to change what electrical equipment we used.
Circumstances change unexpectedly, and your loads can too. It looks like for a little while at least, we may have 600+l tropical fish tank staying with us – a whopping 4.5 kWhr load for the heaters and filters. This has increased our actual winter power load to 15.3 kWhr, while our load list forecast is 6% higher.
Our offgrid load list below gives us much higher loads, because it has electric heating & cooling, water pumps, septic, mobile boosters, surround sound system currently in storage etc etc. It adds up quickly. It still retains our “nice to haves”, we’ll see if they last once we get the quote for purchase.
This is a really large load list – we were only using 7.7 kWhr/day in summer, before the fish, and the dryer. It’s a >18kW system. A nice to have list. We have a quote, including generator, for about $80k. This could be very easily reduced by removing the nice to haves and/or modifying our behaviour. Food for thought.
Note than in summer, the system should generate over twice the power that it does in winter – so I’m not so worried about the AC.