Mi-Grid vs. the Powerwall

Mi-Grid vs. the Powerwall

We’ve had a lot of requests to layout the difference between a Mi-Grid system and a Powerwall. So, here goes!

First, let’s define a “Powerwall”. It is a Lithium-ion battery pack. It is not a complete power system. Implementing it requires a StorEdge inverter from Solar Edge. If you have solar, you also need a SolarEdge grid tied inverter and all of the required safety systems, breakers, disconnects, to properly implement. The “cost” most people associate with the Powerwall is only the price of the battery pack.

The SolarEdge+Powerwall system is a Grid-Tied solution. It cannot be used for off-grid. The Powerwall+SolarStor is designed to supply short term power from its battery pack for short (hours) service interruptions. If solar is present, it can store and disperse energy from the solar panels after sunset. However, the cost to store and retrieve the energy may be above the cost to sell to the network, even without net-metering.

http://www.solaredge.com/sites/default/files/se_storedge_inverter_datasheet_eng.pdf

Mi-Grid was originally designed as an Off-Grid system, specifically for the Off-Shore oil industry. It is designed to allow long term or permanent power with or without a utility connection. Mi-Grid’s Energy Management System (EMS) can take in multiple AC and DC sources, supply power and recharge batteries, all at the same time. It is also rugged and can be implemented outdoors.

Mi-Grid is “Agnostic” with respect to AC power, type of and manufacturer of solar panels, battery systems, as long as they meet the specified voltage ranges. Mi-Grid even has modules which can make use of “dirty” unstable utility power and turn it into “clean” pure sine-wave power.

Mi-Grid can be connected to a generator, allowing off-grid or utility down operation. The generator is only used off-grid or if the utility is down. The Generator recharges the batteries on cloudy or high power usage days, then shuts down. Even when operating with the generator, the solar array can assist recharging the batteries and supplying power. If the batteries become full, the EMS will modulate the array to match the power required,

The StorEdge-Powerwall system cannot implement a generator safely, unless the entire Solar/PowerWall/Stor-Edge system is bypassed. It uses a grid-tied inverter which cannot modulate the solar array output. Once the batteries are full, if the solar array output exceeds the user’s needs, it would send power to the generator, probably damaging it, potentially catastrophically.

Cost: It depends. Don’t you hate it when people say that? Mi-Grid comes with a generator and many more AC and DC inputs. If you eliminate the generator, you can compare the costs of the systems. The most fair comparison would be a Mi-Grid 1000 or Mi-Grid 2000 setup in essential circuits configuration. A Mi-Grid 1000 costs around $28,000 installed with 4.7kW solar and a 10kW generator. A Mi-Grid 2000 costs around $47,000 installed with 9.4kW solar and a 16kW Generator. Depending on location and codes, these prices can vary. For a “fair” comparison, you would need to implement 2 Powerwalls with any StorEdge System. You also need to include a SolarEdge 5 or 8kW grid-tied inverter and Optimizers at each panel.

Capability Comparison

Mi-Grid 1000 Mi-Grid 2000 SE5000+PW SE6000+PW
Max AC Power 4000 8000 5000 6000 Watts
Max AC Surge 8000 16000 7300 7300 Watts
Maximum Battery Output 4000 8000 1xPW=3300, 2xPW=6600 Watts
Energy Storage 19.2 38.4 1xPW=6.8, 2xPW=12.8 kWh
Energy Storage Usable 9.6-15.4 19.2-30.8 1xPW=6.8, 2xPW=12.8 kWh
Noise <30dB <30dB 1xPW=56dB, 2xPW=61dB  dB
Generator for contingencies Yes Yes No No
Grid-Tied Yes Yes Yes Yes
Off-Grid Yes Yes No No
Sell Excess Power Yes Yes Yes Yes
Run Whole House Air Conditioner No Yes No Maybe
Battery Life 3000 or 1800 Cycles,

50%/80% DOD respectively

1000@20% capacity loss

3000@60% capacity loss

Outdoor Rating NEMA 4/IP66 StorEdge IP65, PW IP10

 

Whole House vs. Essential Circuits

Whole House vs. Essential Circuits

Mi-Grid is a hybrid solar energy system, combining battery storage PV solar with a backup generator. It can provide for all of your power needs, on-grid or off-grid, stationary or mobile, on-shore or off-shore. It can provide your power in times of emergency.

Mi-Grid can provide power two ways. Standard Mi-Grid systems are primarily solar powered. The solar PV panels collect power during the day. What isn’t used is stored in the batteries for use later. The solar is designed to provide average power needs, year-round. The generator provides backup power, in cases of low sunlight or a day of very high energy use.

The generator is sized to recharge the batteries only if they become discharged, running long enough to recharge and providing power at the same time. Generator control is automatic and switching is so fast you may never notice. Even using Air Conditioning in the summer, an appropriately sizes Mi-Grid will use about 1 hour of generator time per day. Some days more and some days, none at all. These Mi-Grids are designed to provide all day power, even Air Conditioning, at all times.

The other way Mi-Grid can work is to provide a smaller Mi-Grid system but a larger generator. Sometimes it is not possible to provide a full size Mi-Grid. This could be due to available space for solar panels or even cost issues. A small Mi-Grid provides essential power at all times and the generator powers larger systems as needed.

The electrical system is split into essential and intermittent. The essentials are powered by Mi-Grid’s inverter output. They never lose power. Intermittent systems are only provided power when the generator is running.

Essential systems include small 110VAC air conditioners, microwave oven, toaster over, small appliances, TVs, lights and ceiling fans. Basically, anything that is 110VAC. Depending on the size of the Mi-Grid, care may be necessary with what is run together. But most day to day items work are fine. For a regular house, small mini-split or window A/C units can be run at night in the bedrooms.

Intermittent systems include large 220VAC air conditioners, 220VAC appliances, electric stoves, electric ovens electric dryers and electric hot water heaters. With a larger Mi-Grid system, some of these systems could be placed in the essentials area. A manual switch is provided to start and stop the generator when the intermittent systems are desired. Mi-Grid still can start the generator if the batteries become low. And the intermittent systems can be used anytime the generator is running.

The Mi-Grid 250 and 500 are 110VAC. You have to use to generator for 220VAC systems. With the Mi-grid 1000 and up, 220VAC appliances can be in the essentials.