Running Monster Power Tools on Off-Grid Solar? Here are the Fine Prints (and how we solve it)

Right-sizing your solar solution is critical to providing the power you need without paying for the capacity you don’t use. That means understanding your power consumption and usage pattern to determine the accurate inverter and battery capacity.

While the total amount of power consumed daily (e.g., numbers from your power bills) gives us some idea of your needs, it doesn't provide enough information to determine the precise capacity. 

We measure usage in a 24-hour timeframe to calculate the battery capacity a client needs. Our chart also shows current measurements, which helps us determine how big an inverter is required to handle peak power draw.

Why is measuring current and peak power important?

A 9000W inverter is substantially more expensive than a 3000W or 6000W one. It also draws a much higher quiescent current and drains a battery noticeably faster, even if nothing is running. 

Of course, we can just sell everyone a 9000W inverter and call it a day, but we don’t want our clients to pay for the capacity they don’t need.

Most people draw a modest amount of current most of the time. But the charts may have spikes that last a few seconds to a few minutes. Those surges may push the system over the edge, requiring a more powerful inverter and more battery capacity (even when the sun is out, the system draws power from the battery temporarily to handle the surge).

So, what causes these surges?

The usual suspects include well pumps, power tools, and anything with a big motor. Think shop vacs, air compressors, shop fans, welding machines, etc.

(A note about well pumps: We have seen many clients in Caliente with well pumps that draw way more power than the amount stated on the label. That’s why we measure the current to get a complete and accurate picture to dimension the system correctly.)

How do we address high-surge power scenarios?

First, we discuss the current measurement charts with our clients to see what may have caused the spikes. Sometimes, we discover adjustments they can make to reduce these surges. Or, we may discuss the cost/benefit trade-off of supporting the surge current with more inverter and battery capacity vs. adapting their consumption patterns.

There’s no right or wrong answer. You can throw money at it if you don’t want to think about it. But if you don’t want to pay $30k+ for a grossly over-dimensioned off-grid solar system, then we can help.

If you’re our grid-as-backup customers

If you adopt our grid-as-backup approach, we dimension your off-grid system to handle your baseline, day-to-day load. Whenever you run that monster power tool and exceed the threshold, our proprietary system automatically draws power from the grid to handle the peak power. It switches back to solar when the surge subsides. 

Why is shifting the load to the grid a smart move? The cost would multiply if we dimension an off-grid system to handle the 0.1% scenarios. However, if we dimension it for your everyday load, every component will work as hard as possible, and your payback time will be much shorter. You’re paying SCE anyway, so let them do the heavy lifting ;)

If you’re completely off-grid

There are 2.5 ways to go about it if you’re fully off-grid.

Use a generator. While we build in more margin for our completely off-grid clients, it isn’t cost-effective to accommodate every permutation. If you have a generator sitting around anyway, plug that monster power tool you use once in a while into the generator instead of paying thousands for the surge capacity.

Invest in a big-ass inverter and a bigger-ass battery pack. If you don’t have a generator or use your monster power tools often enough to make the investment worthwhile, spend the money and build in the margins for a worry-free off-grid setup that can handle everything you want to do. 

If you only hit peak power a few seconds at a time, you may use an inverter with a high surge tolerance to keep the cost down (e.g., one rated to handle a consistent 6000W load but can do 12000W for a very short time). You will need extra battery capacity to act as a buffer when the appliance draws power from the system.

Pair a big-ass inverter with our surge-and-sustain battery pack. While there’s no way around getting a more powerful inverter, our custom battery technology can save you a pretty penny. Instead of buying a super big-ass pack just to accommodate the surge requirement, you buy a relatively smaller one for less and get the same surge capacity.

The science behind our surge-and-sustain battery pack

First, we want to introduce a couple of terms: Energy density is the total amount of electricity a cell can store per unit of weight or volume. Power density is the total amount of electricity a cell can squeeze out within a short period (e.g., from a few seconds to half an hour).

While all lithium-ion battery chemistries are intrinsically suitable for high-drain use cases (i.e., provide high surge power), the cells must be specially designed and manufactured to support the application. 

These cells have beefier electrodes to extract high power quickly to start appliances like agricultural water pumps, kinetic tools (e.g., impact drivers), winches, shop vacs, compressors, and heavy-duty power tools.

Yet, achieving higher surge power comes with a cost. When you put more electrode material into the cells, you have less room for energy-storing lithium chemistry, affecting the cell’s energy density (i.e., you need more cells to store the same amount of electricity). Moreover, the rapid discharging shortens the cells’ lifespan.

Meanwhile, cells for sustained power output typically have higher energy density and are more cost-efficient. The law of supply and demand favors these cells and lowers their costs. They also have a longer lifespan and, therefore, a lower total cost of ownership (TCO).

Determining surge vs. sustained power in an application and customizing cells with the appropriate capacity is extremely costly and time-consuming — not an option even for the average equipment manufacturer, let alone the typical consumer…

… unless you have a modular and flexible approach to combine the right number of cells with the right characteristics based on each use case. Well, that wasn’t possible until now (and most battery engineers still tell you, “No, can’t do.”)

Our proprietary battery technology allows us to mix cells of different characteristics to create battery packs that support peak power requirements without incurring unnecessary costs. The technique maximizes longevity while satisfying surge power needs with a much smaller battery pack. Additionally, you can switch out the “surge cells” when they deteriorate without tossing out the entire pack to minimize waste.