A renewable energy system: The load profile.

In this issue of the Solar Cowboy we start with planning a "load profile" and finding the most cost-effective renewable energy design through energy efficiency.

Users will often begin their load analysis with their current utility bill. The user's utility bill can be used for system design but it is a coarse tool for this purpose and should only be used when precision is not required. In this case building a somewhat oversized system can be the result. This is preferable to building undersized systems that do not perform adequately. This method, while reflecting the user's current usage, does not recognize the savings available through efficiency. This is why we use a very specific analysis of each electrical appliance (load) when we begin a design. We call this a "load profile" and we use it throughout the design process to allow us to create an effective system at the lowest cost to the user.

By drawing up a load profile the user gets a clear understanding of where their demand is greatest and where they can generate the greatest cost savings through load reduction. The load profile is also necessary for designing an appropriate back-up battery and knowing what size inverter will be adequate.

Loads, or the appliances, need to be as efficient as possible in order to keep system costs down. Conservation through use of super-efficient appliances will allow the user to run a system at the lowest cost with the greatest reliability. Efficient appliances are more readily available and a new group of appliances are available that are designed for super efficiency specifically for the renewable energy market.

Users often find that building their system in blocks, rather than all at once, is a more affordable option. Because this is often the case, system expansion should be a key design consideration. Planning for expansion can eliminate costly wiring upgrades and equipment changes. Understanding the goals of the user is key to planning.

Load expansion = capacity expansion. Once a system is working users often expand their load profile. It needs to be clear during the design process that expanding the load profile requires expansion of the capacity of the generation and storage system. Adding PV modules and battery capacity will accommodate greater load demand and can be planned for the same way that the system was originally planned. Failure to expand capacity when adding loads to the system will prematurely age the battery and can lead to system failure.

As with any sustainable project knowing your goals (or your client's goals) is the primary way of achieving success. By carefully outlining the project goals and expectations all involved can have their interests met and desires achieved.

The basic load profile chart has categories for AC and DC loads and columns that indicate the quantity of that type of load, its wattage, its on time and the number of days per week the appliance is used. This information is then calculated into an average watt-hour consumption per day figure. By totaling these numbers and correcting for inefficiencies a daily watt-hour consumption figure is arrived at. This number is the starting point for the system to be designed. To be effective the system will need to be able to create the daily watt-hour consumption each day (on the average). A sample chart is illustrated on page 86.

A load profile analysis shows the power requirements of each electrical
appliance and helps design an effective renewable energy system. The
total average watt-hours per day helps determine the size of the system
needed. The chart also pinpoints the greatest loads--and therefore the
greatest opportunity for conservation through limiting use or more
efficient appliances. (If an appliance is rated in amps--usually on a
metal plate in the back--convert that to watts: watts = amps x volts.)

(Multiply quantity X wattage X hours/day X days/week and then divide by
7 to determine, average watt-hours/day)

Qty/Appliance    Wattage   Hours/Day   Days/Week   Avg. Watt-Hrs/Day

2 lights           15        2             7            60
1 radio             4        1             6             3.4
Sewing machine    100         .25          1             3.6

Note: Stand-alone systems multiply by 1.35 (correct for battery and
system inefficiency)

Additional items to consider: What is the largest load, in watts, and
what is the largest combined load?

The accuracy with which you create a load profile greatly influences the effectiveness of future planning. A good load profile will allow the user to understand exactly what appliance is using the most electricity and which is not. This analysis can lead to choosing more efficient appliances and thereby reducing the cost of the renewable energy system by making it smaller. Failure to accurately portray the energy use at a planned site can lead to premature battery failure and failure of the system to operate properly. By calculating the loads accurately and designing a system robustly for the correct loads the user can be confident of a successful renewable energy installation.

Once we've got a good load profile we can start to look at the information we generated by the "Site Survey" (March-April 2001 Solar Cowboy) and shape the design of the system. This is exactly what we'll cover in the next installment of the Solar Cowboy.

Dear Mr. LaForge,

What about free energy? Tesla coils, rotational physics, vortex energy, the energy grid/harmonics, etc. Are you familiar with these theories? Is it real? Practical? Is it worth seriously looking into for a homesteader? I believe my husband and I could build anything if we had proper instructions.

Are these energy sources only for scientists or would it be worth our while to buy the books? I've seen ads for plans for tesla coils. Is this a scam? A joke? A pipedream? So many questions, I know. If you can't provide the answers could you tell me where to look for them? We live near Indiana State University. Could I start asking questions there? -- Kerra Fowler

Well Kerra, I think that there is no free lunch. While many of the ideas you list have merit and have been around a long time the photovoltaic effect is the closest thing to free energy that I have found and we know that PV panels are not cheap. The fuel is free and that is a lot better than most of our options but the panels do cost!

If I were to be hunting for a free energy source I would look into Tesla. That man was on to something.

If you have a question for the Solar Cowboy, send it to: COUNTRYSIDE, c/o Solar Cowboy, W11564 Hwy. 64, Withee, WI 54498.

CHRIS LA FORGE GREAT NORTHERN SOLAR 77450 EVERGREEN ROAD, SUITE #1 PORT WING, WI 54865 [phone]